Version 4.0.4 User’s Guide June 2004 User’s Guide BOOST Version 4.0.4 Address comments concerning this document to: AVL LIST GmbH A-8020 Graz Hans-List-Platz 1 Phone: +43 316 787-1615 Telefax: +43 316 787-1922 E-Mail:
[email protected] Web Site: http://www.avl.com Revision Date Description Document No. A 01-Sep-1995 User’s Guide v2.0 01.0104.0425 B 01-Apr-1997 User’s Guide v3.1 01.0104.0426 C 01-Aug-1998 User’s Guide v3.2 01.0104.0427 D 01-Apr-2000 User’s Guide v3.3 01.0104.0428 E 12-Apr-2002 User’s Guide v4.0 01.0104.0429 F 03-Mar-2003 User’s Guide v4.0.1 01.0104.0434 G 18-Jul-2003 User’s Guide v4.0.3 01.0104.0439 H 23-Jun-2004 User’s Guide v4.0.4 01.0104.0449 Copyright © 2004, AVL All rights reserved. No part of this publication may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated into any language, or computer language in any form or by any means, electronic, mechanical, magnetic, optical, chemical, manual or otherwise, without prior written consent of AVL. This document describes how to run the BOOST software. It does not attempt to discuss all the concepts of 1D gas dynamics required to obtain successful solutions. It is the user’s responsibility to determine if he/she has sufficient knowledge and understanding of gas dynamics to apply this software appropriately. This software and document are distributed solely on an "as is" basis. The entire risk as to their quality and performance is with the user. Should either the software or this document prove defective, the user assumes the entire cost of all necessary servicing, repair or correction. AVL and its distributors will not be liable for direct, indirect, incidental or consequential damages resulting from any defect in the software or this document, even if they have been advised of the possibility of such damage. All mentioned trademarks and registered trademarks are owned by the corresponding owners. User’s Guide BOOST Version 4.0.4 AST.01.0104.0449 - 23-Jun-2004 i Table of Contents 1. Introduction_____________________________________________________1-1 1.1. Scope _______________________________________________________________________1-1 1.2. User Qualifications ___________________________________________________________1-1 1.3. Symbols _____________________________________________________________________1-2 1.4. Documentation_______________________________________________________________1-2 1.5. Platforms____________________________________________________________________1-3 1.6. BOOST_HOME Environment Variable _________________________________________1-3 2. Theoretical Basis ________________________________________________2-1 2.1. The Cylinder_________________________________________________________________2-1 2.1.1. High Pressure Cycle, Basic Equation________________________________________2-1 2.1.1.1. Combustion Models ___________________________________________________2-3 2.1.1.2. Heat Release Approach ________________________________________________2-4 2.1.1.3. Extended Heat Release Approach ______________________________________2-10 2.1.1.4. Quasi-dimensional Combustion Models _________________________________2-12 2.1.1.5. Theoretical Combustion Models________________________________________2-22 2.1.1.6. User Models _________________________________________________________2-23 2.1.2. Gas Exchange Process, Basic Equation _____________________________________2-23 2.1.2.1. Port Massflow Rates__________________________________________________2-24 2.1.2.2. Scavenging __________________________________________________________2-26 2.1.3. Piston Motion ___________________________________________________________2-28 2.1.4. Heat Transfer ___________________________________________________________2-29 2.1.4.1. In Cylinder Heat Transfer ____________________________________________2-29 2.1.4.2. Port Heat Transfer ___________________________________________________2-33 2.1.5. Dynamic In-Cylinder Swirl________________________________________________2-34 2.1.6. Blow-By Losses in the Cylinder____________________________________________2-34 2.1.7. Wall Temperature _______________________________________________________2-35 2.1.8. Direct Gasoline Injection _________________________________________________2-35 2.1.9. Divided Combustion Chamber_____________________________________________2-36 2.1.10. BURN Utility __________________________________________________________2-39 2.2. Plenum (Variable Plenum) ___________________________________________________2-39 2.3. Flow Restriction (Rotary Valve) _______________________________________________2-41 2.4. Check Valve ________________________________________________________________2-42 2.5. Junction____________________________________________________________________2-43 2.6. Turbocharger _______________________________________________________________2-44 2.7. Mechanically Driven Superchargers ___________________________________________2-46 2.8. Fuel Injector or Carburetor___________________________________________________2-47 2.9. Waste Gate _________________________________________________________________2-48 2.10. Pipe Flow _________________________________________________________________2-48 BOOST Version 4.0.4 User’s Guide ii AST.01.0104.0449 - 23-Jun-2004 2.10.1. Bends _________________________________________________________________2-52 2.10.2. Variable Wall Temperature ______________________________________________2-53 2.10.2.1. Forced Convection __________________________________________________2-53 2.10.2.2. Free Convection ____________________________________________________2-54 2.10.3. Forward / Backward Running Waves______________________________________2-54 2.10.4. Perforated Pipe ________________________________________________________2-55 2.10.4.1. Perforated Pipe contained in Pipe_____________________________________2-55 2.10.4.2. Perforated Pipe contained in Plenum__________________________________2-56 2.11. Pipe Attachment (System or Internal Boundary)_______________________________2-56 2.12. Assembled Elements________________________________________________________2-58 2.12.1. Catalyst _______________________________________________________________2-58 2.12.2. Particulate Filter _______________________________________________________2-58 2.13. Engine Control Unit and Wire _______________________________________________2-58 2.14. Gas Properties _____________________________________________________________2-60 2.15. Definition of Global Engine Data (SI-Units) ___________________________________2-61 2.15.1. Cylinder Data __________________________________________________________2-62 2.15.2. Gas Exchange Related Data______________________________________________2-65 2.16. Abbreviations ______________________________________________________________2-70 3. Graphical User Interface ________________________________________3-1 3.1. BOOST Specific Operations ___________________________________________________3-1 3.1.1. Menu Bar ________________________________________________________________3-2 3.1.2. BOOST Buttons __________________________________________________________3-4 3.1.3. Elements Tree____________________________________________________________3-4 3.1.4. Model Tree_______________________________________________________________3-8 3.1.5. Data Input Window_______________________________________________________3-9 3.1.5.1. Sub-group Icons______________________________________________________3-10 3.1.6. Table Window___________________________________________________________3-10 3.2. General Input Data__________________________________________________________3-12 3.2.1. Simulation Tasks ________________________________________________________3-12 3.2.1.1. Date, Project ID and Run ID __________________________________________3-13 3.2.1.2. Simulation Tasks ____________________________________________________3-13 3.2.2. General Control _________________________________________________________3-13 3.2.2.1. Engine Speed ________________________________________________________3-14 3.2.2.2. Steady State / Transient Simulation____________________________________3-14 3.2.2.2.1. Engine Only Transient Calculation ___________________________________3-14 3.2.2.2.2. Driver Transient Calculation ________________________________________3-15 3.2.2.3. Calculation Modes____________________________________________________3-21 3.2.2.4. Identical Cylinders ___________________________________________________3-21 3.2.2.5. User-Defined Concentrations __________________________________________3-21 3.2.2.6. Mixture Preparation__________________________________________________3-21 3.2.2.7. Fuel Data ___________________________________________________________3-21 3.2.2.8. Reference Conditions _________________________________________________3-22 3.2.2.9. Gas Properties _______________________________________________________3-22 User’s Guide BOOST Version 4.0.4 AST.01.0104.0449 - 23-Jun-2004 iii 3.2.3. Time Step Control _______________________________________________________3-23 3.2.4. FIRE Link Control_______________________________________________________3-25 3.2.5. BMEP Control __________________________________________________________3-25 3.2.6. Convergence Control _____________________________________________________3-26 3.2.7. Engine Friction__________________________________________________________3-27 3.2.8. Volumetric Efficiency ____________________________________________________3-27 3.3. Design a BOOST Calculation Model ___________________________________________3-28 3.3.1. Pipe Design _____________________________________________________________3-28 3.4. Specification of Input Data for Elements _______________________________________3-28 3.4.1. Pipe____________________________________________________________________3-28 3.4.1.1. Bending Radius ______________________________________________________3-29 3.4.1.2. Friction Coefficient___________________________________________________3-30 3.4.1.3. Heat Transfer Factor _________________________________________________3-30 3.4.1.4. Variable Wall Temperature____________________________________________3-30 3.4.2. Cylinder ________________________________________________________________3-31 3.4.2.1. Combustion Model ___________________________________________________3-33 3.4.2.2. Divided Combustion Chamber _________________________________________3-47 3.4.2.3. Heat Transfer _______________________________________________________3-48 3.4.2.4. Scavenging __________________________________________________________3-50 3.4.2.5. Valve / Port Data_____________________________________________________3-51 3.4.3. Measuring Point_________________________________________________________3-58 3.4.4. Boundaries______________________________________________________________3-58 3.4.4.1. System Boundary ____________________________________________________3-58 3.4.4.2. Aftertreatment Boundary _____________________________________________3-60 3.4.4.3. Internal Boundary ___________________________________________________3-61 3.4.5. Transfer Elements _______________________________________________________3-62 3.4.5.1. Flow Restriction _____________________________________________________3-62 3.4.5.2. Rotary Valve_________________________________________________________3-63 3.4.5.3. Check Valve _________________________________________________________3-64 3.4.5.4. Fuel Injector / Carburetor _____________________________________________3-64 3.4.5.5. Pipe Junction________________________________________________________3-65 3.4.6. Volume Elements ________________________________________________________3-67 3.4.6.1. Plenum _____________________________________________________________3-67 3.4.6.2. Variable Plenum_____________________________________________________3-70 3.4.6.3. Perforated Pipe in Pipe _______________________________________________3-71 3.4.7. Assembled Elements _____________________________________________________3-72 3.4.7.1. Air Cleaner __________________________________________________________3-72 3.4.7.2. Catalyst_____________________________________________________________3-73 3.4.7.3. Air Cooler ___________________________________________________________3-74 3.4.7.4. Diesel Particulate Filter (DPF) ________________________________________3-75 3.4.8. Charging Elements ______________________________________________________3-76 3.4.8.1. Turbocharger________________________________________________________3-76 3.4.8.2. Positive Displacement Compressors ____________________________________3-84 3.4.8.3. Turbo Compressor ___________________________________________________3-85 BOOST Version 4.0.4 User’s Guide iv AST.01.0104.0449 - 23-Jun-2004 3.4.8.4. Waste Gate __________________________________________________________3-85 3.4.9. External Links Elements _________________________________________________3-86 3.4.9.1. FIRE Link___________________________________________________________3-86 3.4.9.2. User Defined Element ________________________________________________3-86 3.4.10. Control Elements _______________________________________________________3-87 3.4.10.1. Wire _______________________________________________________________3-87 3.4.10.2. Engine Control Unit_________________________________________________3-88 3.4.10.3. MATLAB DLL Element______________________________________________3-92 3.4.10.4. MATLAB API Element ______________________________________________3-94 3.4.11. Acoustic Elements ______________________________________________________3-95 3.4.11.1. Microphone ________________________________________________________3-95 3.5. Case Series Calculation ______________________________________________________3-96 3.5.1. Parameters _____________________________________________________________3-96 3.5.1.1. Assign Parameters ___________________________________________________3-96 3.5.1.1.1. Assign a Model Parameter ___________________________________________3-96 3.5.1.1.2. Assign an Element Parameter _______________________________________3-97 3.5.1.1.3. Case Explorer ______________________________________________________3-98 3.6. Running a Simulation________________________________________________________3-99 3.7. Utilities ___________________________________________________________________3-102 3.7.1. BURN_________________________________________________________________3-102 3.7.1.1. Input Data Specification _____________________________________________3-102 3.7.1.2. Run the Calculation _________________________________________________3-105 3.7.1.3. Results_____________________________________________________________3-105 3.7.2. Search_________________________________________________________________3-105 3.7.3. License Manager _______________________________________________________3-106 3.7.4. Pack Model ____________________________________________________________3-107 4. External Links___________________________________________________4-1 4.1. MATLAB____________________________________________________________________4-1 4.1.1. Application Programming Interface (API) ___________________________________4-1 4.1.1.1. Running a MATLAB API Simulation ____________________________________4-2 4.1.2. Real Time Workshop ______________________________________________________4-4 4.1.3. Pure Code Generation_____________________________________________________4-8 4.1.4. System Function (s-function) ______________________________________________4-9 4.1.4.1. Running an s-function Simulation _____________________________________4-12 4.2. AVL FIRE__________________________________________________________________4-13 4.3. AVL CRUISE _______________________________________________________________4-13 5. BOOST Post-processing__________________________________________5-1 5.1. Analysis of Summary Results __________________________________________________5-1 5.2. Analysis of Cycle Dependent Results____________________________________________5-2 5.3. Analysis of Crank Angle Dependent Results _____________________________________5-9 5.4. Analysis of Composite Elements_______________________________________________5-14 5.5. Analysis of Frequency Dependent Results and Orifice Noise______________________5-15 User’s Guide BOOST Version 4.0.4 AST.01.0104.0449 - 23-Jun-2004 v 5.6. Analysis of Case Series Results________________________________________________5-16 5.7. Analysis of Animated Results _________________________________________________5-17 5.8. Message Analysis____________________________________________________________5-18 5.8.1. Message Description _____________________________________________________5-19 5.8.2. Message Examples _______________________________________________________5-20 5.8.3. Fatal Errors_____________________________________________________________5-21 5.8.3.1. MATLAB API _______________________________________________________5-21 5.9. Analysis of Aftertreatment Analysis Results ____________________________________5-22 6. The BOOST Files ________________________________________________6-1 6.1. The .bwf Files________________________________________________________________6-1 6.2. The .bst Files ________________________________________________________________6-1 6.3. The .atm Files _______________________________________________________________6-1 6.4. The .rs0 and .rs1 Files ________________________________________________________6-2 6.5. The .uit File _________________________________________________________________6-2 6.6. The .gpf File _________________________________________________________________6-2 6.7. The rvalf.cat File _____________________________________________________________6-2 7. Recommendations _______________________________________________7-1 7.1. Modeling ____________________________________________________________________7-1 7.2. Analysis of Results ___________________________________________________________7-5 7.3. Important Trends ____________________________________________________________7-6 7.4. Turbocharger Matching ______________________________________________________7-12 8. Literature _______________________________________________________8-1 9. Appendix ________________________________________________________9-1 9.1. Running The Executable ______________________________________________________9-1 9.1.1. Command Line ___________________________________________________________9-1 9.1.1.1. Options ______________________________________________________________9-1 9.1.1.2. File Search Paths _____________________________________________________9-4 9.1.2. Batch Mode ______________________________________________________________9-5 9.1.2.1. Create Model with GUI ________________________________________________9-5 9.1.2.2. Preparing the Batch File: ______________________________________________9-5 9.1.2.3. Start the Run_________________________________________________________9-5 9.2. Required Input Data__________________________________________________________9-6 9.2.1. Engine Data _____________________________________________________________9-6 9.2.2. Turbocharging System Data _______________________________________________9-6 9.2.3. Fuel Data ________________________________________________________________9-6 9.2.4. Boundary Conditions______________________________________________________9-6 9.2.5. Drawings ________________________________________________________________9-6 9.2.6. Measurements ___________________________________________________________9-7 9.2.7. For Transient Simulation__________________________________________________9-7 9.3. Available Channel Data _______________________________________________________9-8 BOOST Version 4.0.4 User’s Guide vi AST.01.0104.0449 - 23-Jun-2004 9.4. Compiling and Linking BOOST _______________________________________________9-10 9.4.1. NT Visual Studio ________________________________________________________9-10 9.4.2. UNIX __________________________________________________________________9-10 9.5. Using the BOOST Dynamic Link Library ______________________________________9-10 9.5.1.1. Loading Problems ____________________________________________________9-10 9.6. Flow Coefficients Directions __________________________________________________9-11 9.7. Variation Parameters from V3.3 to V4.0 _______________________________________9-12 User’s Guide BOOST Version 4.0.4 AST.01.0104.0449 - 23-Jun-2004 vii List of Figures Figure 2-1: Energy Balance of Cylinder (High Pressure Cycle) ........................................................................... 2-2 Figure 2-2: Influence of Excess Air Ratio on IMEP............................................................................................... 2-4 Figure 2-3: Approximation of a Measured Heat Release....................................................................................... 2-6 Figure 2-4: Influence of Shape Parameter 'm' ........................................................................................................ 2-6 Figure 2-5: Superposition of Two Vibe Functions ............................................................................................... 2-10 Figure 2-6: Schematic of the Spray/Package Structure........................................................................................ 2-16 Figure 2-7: Schematic of the Physical Processes taking place in the Package................................................... 2-16 Figure 2-8: Energy Balance of Cylinder (Gas Exchange Process) ...................................................................... 2-24 Figure 2-9: Inner Valve Seat Diameter................................................................................................................. 2-25 Figure 2-10: User-Defined Scavenging Model ...................................................................................................... 2-28 Figure 2-11: Standard Crank Train ...................................................................................................................... 2-29 Figure 2-12: The Pressure Function ψ.................................................................................................................. 2-41 Figure 2-13: Full Check Valve Model .................................................................................................................... 2-42 Figure 2-14: Flow Patterns in a Y-Junction......................................................................................................... 2-43 Figure 2-15: Waste Gate......................................................................................................................................... 2-48 Figure 2-16: Finite Volume Concept ..................................................................................................................... 2-50 Figure 2-17: Linear Reconstruction of the Flow Field ........................................................................................ 2-51 Figure 2-18: Pressure Waves from Discontinuities at Cell Borders................................................................... 2-51 Figure 2-19: Pipe Bend Parameters ...................................................................................................................... 2-52 Figure 2-20: Pipe Bend Loss Coefficient............................................................................................................... 2-52 Figure 2-21: Forward / Backward Running Waves.............................................................................................. 2-54 Figure 2-22: Perforated Pipes contained in Pipe ................................................................................................. 2-55 Figure 2-23: Two perforated Pipes contained in Plenum................................................................................... 2-56 Figure 2-24: Flow Chart of the ECU..................................................................................................................... 2-59 Figure 2-25: Considered Mass Fractions .............................................................................................................. 2-61 Figure 2-26: Relation of Gas Exchange Data........................................................................................................ 2-69 Figure 3-1: BOOST - Main Window........................................................................................................................ 3-1 Figure 3-2: Model Submenu..................................................................................................................................... 3-8 Figure 3-3: Data Input Window............................................................................................................................... 3-9 Figure 3-4: Element Sub-group Submenu............................................................................................................ 3-10 Figure 3-5: Table Window...................................................................................................................................... 3-11 Figure 3-6: Graph Context Menu .......................................................................................................................... 3-12 Figure 3-7: Simulation Control – Simulation Tasks Window............................................................................. 3-12 Figure 3-8: Simulation Control – Globals Window.............................................................................................. 3-13 Figure 3-9: Load Characteristic for Engine Only................................................................................................. 3-15 Figure 3-10: Driver Input Window........................................................................................................................ 3-17 Figure 3-11: Shifting Process................................................................................................................................. 3-18 Figure 3-12: Vehicle Input Window....................................................................................................................... 3-20 Figure 3-13: Simulation Control – Constant Gas Properties Window............................................................... 3-22 Figure 3-14: Simulation Control – Time Step Control Window......................................................................... 3-23 Figure 3-15: Simulation Control – BMEP Control Window................................................................................ 3-25 Figure 3-16: Simulation Control – Convergence Control Window..................................................................... 3-26 Figure 3-17: Example Table Input for Bending Radius ...................................................................................... 3-29 Figure 3-18: Standard Cranktrain......................................................................................................................... 3-31 Figure 3-19: Crank Angle related to Combustion Duration ............................................................................... 3-34 Figure 3-20: Flat Cylinder Head............................................................................................................................ 3-39 BOOST Version 4.0.4 User’s Guide viii AST.01.0104.0449 - 23-Jun-2004 Figure 3-21: Disc Chamber Cylinder Head........................................................................................................... 3-39 Figure 3-22: Spherical Cylinder Head................................................................................................................... 3-39 Figure 3-23: Backset Special Cylinder Head ........................................................................................................ 3-40 Figure 3-24: Pent Roof Cylinder Head.................................................................................................................. 3-40 Figure 3-25: Flat Piston Top.................................................................................................................................. 3-41 Figure 3-26: Heron Piston Top.............................................................................................................................. 3-41 Figure 3-27: Spherical Bowl Piston Top ............................................................................................................... 3-41 Figure 3-28: Spherical Piston Top......................................................................................................................... 3-42 Figure 3-29: Pent Roof Piston Top........................................................................................................................ 3-42 Figure 3-30: Definition of Angle between Spark Plug and Bowl/Top Center ................................................... 3-43 Figure 3-31: Definition of Spark Plug Position.................................................................................................... 3-43 Figure 3-32: AVL MCC Combustion Model Window........................................................................................... 3-47 Figure 3-33: Scavenging Models ............................................................................................................................ 3-50 Figure 3-34: Valve Port Specifications Window................................................................................................... 3-51 Figure 3-35: Calculation of Effective Valve Lift................................................................................................... 3-52 Figure 3-36: Modification of Valve Lift Timing ................................................................................................... 3-52 Figure 3-37: Positive intake valve opening and closing shift (same value) ........................................................ 3-53 Figure 3-38: Positive intake valve closing shift only ............................................................................................ 3-53 Figure 3-39: Positive intake valve opening shift only........................................................................................... 3-53 Figure 3-40: Positive exhaust closing shift and positive intake opening shift ................................................... 3-53 Figure 3-41: Positive exhaust opening and closing shift (same value) ............................................................... 3-54 Figure 3-42: Positive exhaust opening shift only.................................................................................................. 3-54 Figure 3-43: Positive exhaust valve closing shift only.......................................................................................... 3-54 Figure 3-44: Positive exhaust valve closing shift and negative intake opening shift ........................................ 3-54 Figure 3-45: Negative exhaust shifts (same value) and positive intake shifts (same value) ............................ 3-55 Figure 3-46: Interpolation of Flow Coefficients ................................................................................................... 3-55 Figure 3-47: Definition of Window Geometry ...................................................................................................... 3-57 Figure 3-48: Calculation of Minimum Duct Cross Section.................................................................................. 3-57 Figure 3-49: Mounting of a Pipe End.................................................................................................................... 3-59 Figure 3-50: Engine Cylinder Sub-model.............................................................................................................. 3-61 Figure 3-51: Sudden Diameter Change................................................................................................................. 3-62 Figure 3-52: Flow Coefficients of a Junction........................................................................................................ 3-66 Figure 3-53: Perforated Pipe in Plenum Window................................................................................................ 3-69 Figure 3-54: Perforated Pipes Contained in Plenum........................................................................................... 3-69 Figure 3-55: Perforated Pipe in Pipe Window...................................................................................................... 3-71 Figure 3-56: Steady State Air Cleaner Performance ........................................................................................... 3-73 Figure 3-57: Deterioration Factor of a Twin Entry- or Multiple Entry Turbine.............................................. 3-78 Figure 3-58: Compressor Map................................................................................................................................ 3-79 Figure 3-59: Turbine Map ...................................................................................................................................... 3-81 Figure 3-60: PD-Compressor Map......................................................................................................................... 3-84 Figure 3-61: UDE Input ......................................................................................................................................... 3-86 Figure 3-63: Interaction between BOOST and External-Link Element............................................................ 3-87 Figure 3-64: Selection of ECU Actuator Channels .............................................................................................. 3-89 Figure 3-65: ECU Map Specification..................................................................................................................... 3-90 Figure 3-66: Time Constants for Transient ECU Functions .............................................................................. 3-91 Figure 3-67: MATLAB DLL Element Input ......................................................................................................... 3-92 Figure 3-68: Sensor Channel Selection................................................................................................................. 3-93 Figure 3-69: Actuator Channel Selection.............................................................................................................. 3-93 Figure 3-70: MATLAB API Element Input .......................................................................................................... 3-94 User’s Guide BOOST Version 4.0.4 AST.01.0104.0449 - 23-Jun-2004 ix Figure 3-71: Microphone Position......................................................................................................................... 3-95 Figure 3-72: Assign Parameter Menu................................................................................................................... 3-96 Figure 3-73: Model Parameter Window................................................................................................................ 3-97 Figure 3-74: Case Explorer Window...................................................................................................................... 3-98 Figure 3-75: Run Simulation Window................................................................................................................... 3-99 Figure 3-76: Simulation Status Window............................................................................................................. 3-100 Figure 3-77: View Cycle Simulation Logfile Window........................................................................................ 3-101 Figure 3-78: View Aftertreatment Analysis Logfile Window............................................................................ 3-101 Figure 3-79: View Animation Logfile Window................................................................................................... 3-102 Figure 3-80: Burn Utility - Fitting Data Window.............................................................................................. 3-103 Figure 3-81: Search Utility Displaying Initialization Data for Pipes............................................................... 3-106 Figure 3-82: License Manager Window............................................................................................................... 3-106 Figure 4-1: Simulink Settings for the Integration Algorithm.............................................................................. 4-5 Figure 4-2: Simulink Settings for the MAT-Files .................................................................................................. 4-6 Figure 4-3: Simulink Settings for the Boost-DLL Creation.................................................................................. 4-7 Figure 4-4: The BOOST MATLAB/SIMULINK Library..................................................................................... 4-10 Figure 4-5: Mask Parameters Window.................................................................................................................. 4-11 Figure 5-1: Summary Analysis Window.................................................................................................................. 5-2 Figure 5-2: IMPRESS Chart Main Window............................................................................................................ 5-3 Figure 5-3: Show Elements Window..................................................................................................................... 5-15 Figure 5-4: Microphone position............................................................................................................................ 5-16 Figure 5-5: Create Series Results Window........................................................................................................... 5-17 Figure 5-6: PP3 Main Window............................................................................................................................... 5-18 Figure 5-7: Message Analysis Window.................................................................................................................. 5-18 Figure 5-8: MATLAB API Error - version mismatch .......................................................................................... 5-21 Figure 7-1: Modeling of Steep Cones....................................................................................................................... 7-1 Figure 7-2: Modeling of an Intake Receiver ........................................................................................................... 7-2 Figure 7-3: Modeling of an Intake Receiver with Pipes and Junctions ............................................................... 7-2 Figure 7-4: Intake Receiver Models......................................................................................................................... 7-3 Figure 7-5: Influence of Intake Receiver Modeling on Volumetric Efficiency and Air Distribution ................ 7-3 Figure 7-6: Exhaust Port Modeling......................................................................................................................... 7-4 Figure 7-7: Modeling Multi-Valve Engines............................................................................................................. 7-5 Figure 7-8: Influence of In-Cylinder Heat Transfer on Engine Performance..................................................... 7-7 Figure 7-9: Influence of Port Flow Coefficients on Engine Performance............................................................ 7-7 Figure 7-10: Influence of IVC on Engine Performance......................................................................................... 7-8 Figure 7-11: Influence of EVO on the Engine Performance................................................................................. 7-8 Figure 7-12: Air Feed to Intake Receiver................................................................................................................ 7-9 Figure 7-13: Influence of Air Feed Pipe Length on Engine Performance ......................................................... 7-10 Figure 7-14: Influence of Number of Cylinders on Engine Performance.......................................................... 7-10 Figure 7-15: Intake Running Length.................................................................................................................... 7-11 Figure 7-16: Influence of Intake Runner Length on Engine Performance ....................................................... 7-11 Figure 7-17: Engine Operating Line in the Compressor Map ............................................................................ 7-13 Figure 7-18: Engine Operating Line in the Compressor Map (compressor too small)..................................... 7-14 Figure 7-19: Engine Operating Line in the Compressor Map (compressor too large) ..................................... 7-14 Figure 7-20: Engine Operating Line in the Compressor Map (correct compressor) ........................................ 7-15 Figure 7-21: Engine Operating Point in the Turbine Map ................................................................................. 7-15 User’s Guide BOOST Version 4.0.4 23-Jun-2004 1-1 1. INTRODUCTION BOOST simulates a wide variety of engines, 4-stroke or 2-stroke, spark or auto-ignited. Applications range from small capacity engines for motorcycles or industrial purposes up to large engines for marine propulsion. BOOST can also be used to simulate the characteristics of pneumatic systems. The BOOST program package consists of an interactive pre-processor which assists with the preparation of the input data for the main calculation program. Results analysis is supported by an interactive post-processor. The new pre-processing tool of the AVL Workspace Graphical User Interface features a model editor and a guided input of the required data. The calculation model of the engine is designed by selecting the required elements from a displayed element tree by mouse- click and connecting them by pipe elements. In this manner even very complex engine configurations can be modelled easily, as a large variety of elements is available. The main program provides optimised simulation algorithms for all available elements. The flow in the pipes is treated as one-dimensional. This means that the pressures, temperatures and flow velocities obtained from the solution of the gas dynamic equations represent mean values over the cross-section of the pipes. Flow losses due to three- dimensional effects, at particular locations in the engine, are considered by appropriate flow coefficients. In cases where three-dimensional effects need to be considered in more detail, a link to AVL's three-dimensional flow simulation code FIRE is available. This means that a multi-dimensional simulation of the flow in critical engine parts can be combined with a fast one-dimensional simulation elsewhere. This feature could be of particular interest for the simulation of the charge motion in the cylinder, the scavenging process of a two-stroke engine or for the simulation of the flow in complicated muffler elements. The IMPRESS Chart and PP3 post-processing tools analyze the multitude of data resulting from a simulation. All results may be compared to results of measurements or previous calculations. Furthermore, an animated presentation of selected calculation results is available. This also contributes to developing the optimum solution to the user's problem. A report template facility assists with the preparation of reports. 1.1. Scope This document describes the basic concepts and methods for using the BOOST Version 4.0.1 program to perform engine cycle simulation. 1.2. User Qualifications Users of this manual: Must be qualified in basic UNIX and/or Microsoft Windows. Must be qualified in basic engine cycle simulation. BOOST Version 4.0.4 User’s Guide 1-2 23-Jun-2004 1.3. Symbols The following symbols are used throughout this manual. Safety warnings must be strictly observed during operation and service of the system or its components. ! Caution: Cautions describe conditions, practices or procedures which could result in damage to, or destruction of data if not strictly observed or remedied. Note: Notes provide important supplementary information. Convention Meaning Italics For emphasis, to introduce a new term or for manual titles. monospace To indicate a command, a program or a file name, messages, input / output on a screen, file contents or object names. SCREEN-KEYS A SCREEN font is used for the names of windows and keyboard keys, e.g. to indicate that you should type a command and press the ENTER key. MenuOpt A MenuOpt font is used for the names of menu options, submenus and screen buttons. 1.4. Documentation BOOST documentation is available in PDF format and consists of the following: Release Notes User's Guide Primer Examples Aftertreatment Aftertreatment Primer Linear Acoustics 1D – 3D Coupling Thermal Network Generator (TNG) User’s Guide Thermal Network Generator (TNG) Primer Validation AVL Workspace Installation Guide (Windows NT and UNIX) AVL Workspace GUI Introduction FLEXlm User's Guide User’s Guide BOOST Version 4.0.4 23-Jun-2004 1-3 1.5. Platforms BOOST has been compiled on the following platforms: Platform Operating System Version Bin directory Notes Windows 2000, XP ia32-unknown-winnt Silicon Graphics IRIX64 6.5 mips4-sgi-irix6.5 mips4 64bit Hewlett Packard HP-UX 11.00 pa-risc-hp-hpux11.00 PA-RISC 2.0 IBM AIX 5.1 rs6000-ibm-aix4.3 Linux Linux 2.4 ia32-unknown-linux 1.6. BOOST_HOME Environment Variable In order for BOOST to locate required files (e.g. gas property files) the environment variable BOOST_HOME must be set correctly. This should be done automatically during installation and should point to the bin directory for the appropriate platform. For example, an NT installation might have the following settings: Variable: BOOST_HOME Value: C:\AVL\BOOST\v4.0.4\bin\bin.ia32-unknown-winnt The value of this environment variable should be checked before running BOOST. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-1 2. THEORETICAL BASIS Theoretical background including the basic equations for all available elements is summarized in this chapter to give a better understanding of the AVL BOOST program. This chapter does not intend to be a thermodynamics textbook, nor does it claim to cover all aspects of engine cycle simulation. 2.1. The Cylinder 2.1.1. High Pressure Cycle, Basic Equation The calculation of the high pressure cycle of an internal combustion engine is based on the first law of thermodynamics: ( ) α α α α α d dm h d dQ d dQ d dV p d u m d BB BB w F c c ⋅ − − + ⋅ − = ⋅ ∑ (2.1.1) ( ) α d u m d c ⋅ change of the internal energy in the cylinder α d dV p c ⋅ − piston work α d dQ F fuel heat input ∑ α d dQ w wall heat losses α d dm h BB BB ⋅ enthalpy flow due to blow-by c m mass in the cylinder u specific internal energy c p cylinder pressure V cylinder volume F Q fuel energy w Q wall heat loss α crank angle BB h enthalpy of blow-by α d dm BB blow-by mass flow BOOST Version 4.0.4 User’s Guide 2-2 23-Jun-2004 Figure 2-1: Energy Balance of Cylinder (High Pressure Cycle) The first law of thermodynamics for high pressure cycle states that the change of the internal energy in the cylinder is equal to the sum of piston work, fuel heat input, wall heat losses and the enthalpy flow due to blow-by. Equation 2.1.1 is valid for engines with internal and external mixture preparation. However, the terms, which take into account the change of the gas composition due to combustion, are treated differently for internal and external mixture preparation. For internal mixture preparation it is assumed that • the fuel added to the cylinder charge is immediately combusted • the combustion products mix instantaneously with the rest of the cylinder charge and form a uniform mixture • as a consequence, the A/F ratio of the charge diminishes continuously from a high value at the start of combustion to the final value at the end of combustion. For external mixture preparation it is assumed that • the mixture is homogenous at the start of combustion • as a consequence, the A/F ratio is constant during the combustion • burned and unburned charge have the same pressure and temperature although the composition is different. In order to solve this equation, models for the combustion process and the wall heat transfer, as well as the gas properties as a function of pressure, temperature, and gas composition are required. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-3 Together with the gas equation c o c c T R m V p ⋅ ⋅ ⋅ = 1 (2.1.2) establishing the relation between pressure, temperature and density, equation 2.1.2 or 2.1.3 for the in-cylinder temperature can be solved using a Runge-Kutta method. Once the cylinder temperature is known, the cylinder pressure can be obtained from the gas equation. 2.1.1.1. Combustion Models The combustion of fuel in an engine is a chemical process influenced by many parameters. One of these is the ratio between air and fuel. If more air is available than required to burn the fuel completely the combustion is called lean. The opposite is called rich combustion. The ratio between air and fuel at which neither unburned fuel nor air remains after combustion is the stoichiometric air fuel ratio. The following equation for the stoichiometric air requirement specifies how much air is required for a complete combustion of 1 kg fuel: ( ¸ ( ¸ | . | \ | − + + ⋅ = Fuel kg Air kg o s h c L st 00 . 32 06 . 32 032 . 4 01 . 12 85 . 137 (2.1.3) For lean combustion, the total heat supplied during the cycle can be calculated from the amount of fuel in the cylinder and the lower heating value of the fuel. The lower heating value is a fuel property and can be calculated from the following formula: − ⋅ + ⋅ + ⋅ + ⋅ = s n h c H u 10465 6280 93870 34835 [ ] kg kJ w o / 2440 10800 ⋅ − ⋅ − (2.1.4) u H lower heating value c mass fraction of carbon in the fuel h mass fraction of hydrogen in the fuel o mass fraction of oxygen in the fuel s mass fraction of sulfur in the fuel n mass fraction of nitrogen in the fuel w mass fraction of water in the fuel In rich combustion, the total heat supplied during the cycle is limited by the amount of air in the cylinder. The fuel is totally converted to combustion products even if the amount of air available is less than the amount of stoichiometric air. However, the composition of the combustion products is different if fuel is burned under rich or lean conditions. The composition itself depends on the type of fuel used, the air fuel ratio, pressure and temperature. It is always the same if sufficient time is available to reach chemical equilibrium. BOOST Version 4.0.4 User’s Guide 2-4 23-Jun-2004 It is well known that under real engine conditions, complete combustion as assumed above can never be achieved. This is very important for excess air ratios close to 1.0 (the excess air ratio is defined as the ratio between the amount of air in the cylinder and the amount required for stoichiometric combustion). For this reason, a model for the fuel conversion factor, which considers the incomplete combustion for excess air ratios between 0.9 and 1.2, was included in the BOOST program. Figure 2-2: Influence of Excess Air Ratio on IMEP Figure 2-2 shows the Indicated Mean Effective Pressure (IMEP) of a gasoline engine with a fixed amount of air in the cylinder as a function of excess air ratio. 2.1.1.2. Heat Release Approach The simplest approach to model the combustion process is the direct specification of the rate of heat release. The rate of heat release of an engine at a specific operating point is determined from the measured cylinder pressure history. By means of a reversed high pressure cycle calculation, i.e. by solving equations 2.1.2 or 2.1.3 for α d dQ F instead for α d dT c , the heat release versus crank angle is obtained. To simplify this approach, only the dimensionless heat input characteristic must be specified over crank angle. From the total heat supplied to the cycle, which is determined by the amount of fuel in the cylinder and by the A/F ratio, BOOST calculates the actual heat input per degree crank angle. For the direct input of the rate of heat release curve the following options are available: 1. Table The heat release curve is approximated by specifying reference points versus crank angle. The y-values are scaled to obtain an area of one beneath the curve. Values between the points specified are obtained by linear interpolation. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-5 2. Vibe Function The Vibe function [C13] is often used to approximate the actual heat release characteristics of an engine: ( ) ( ) 1 1 + ⋅ − ⋅ ⋅ + ⋅ ∆ = m y a m c e y m a d dx α α (2.1.5) Q dQ dx = (2.1.6) c o y α α α ∆ − = (2.1.7) Q total fuel heat input α crank angle o α start of combustion c α ∆ combustion duration m shape parameter a Vibe parameter a = 6.9 for complete combustion The integral of the vibe function gives the fraction of the fuel mass which was burned since the start of combustion: ( ) ∫ + ⋅ − − = ⋅ = 1 1 m y a e d d dx x α α (2.1.8) x mass fraction burned Figure 2-3 shows the approximation of an actual heat release diagram of a DI Diesel engine by a vibe function. The start of combustion, combustion duration and shape parameter were obtained by a least square fit of the measured heat release curve. BOOST Version 4.0.4 User’s Guide 2-6 23-Jun-2004 Figure 2-3: Approximation of a Measured Heat Release In Figure 2-4 the influence of the vibe shape parameter 'm' on the shape of the vibe function is shown. Figure 2-4: Influence of Shape Parameter 'm' 3. Vibe Two Zone For engines with external mixture preparation, the selection of a two zone model is possible. The rate of heat release, and thus the mass fraction burned, is specified by a vibe function. However the assumption that burned and unburned charges have the same temperature is dropped. Instead the first law of thermodynamics is applied to the burned charge and unburned charge respectively [C10]. α α α α α α d dm h d dm h d dQ d dQ d dV p d u dm b BB b BB b u Wb F b c b b , , − + − + − = ∑ (2.1.9) User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-7 ∑ − − − − = α α α α α d dm h d dm h d dQ d dV p d u dm u BB u BB B u Wu u c u u , , (2.1.10) index b burned zone index u unburned zone The term α d dm h B u covers the enthalpy flow from the unburned to the burned zone due to the conversion of a fresh charge to combustion products. Heat flux between the two zones is neglected. In addition the sum of the volume changes must be equal to the cylinder volume change and the sum of the zone volumes must be equal to the cylinder volume. α α α d dV d dV d dV u b = + (2.1.11) V V V u b = + (2.1.12) Substituting into equation 2.1.11, together with some elementary algebra leads to an equation for the derivative of the burned zone temperature versus crankangle. ( ) ¦ ¦ ¹ ¦ ¦ ´ ¦ ( ( ( ¸ ( ¸ ∂ ∂ − − − − ∂ ∂ = α α α α α α d T u d T m u u d dm d dQ d dQ T u m d dT b b b u B b Wb F b b b b 1 ( ) ( ) ( ¸ ( ¸ − + − − − − α α α β α α β d dR T m V V d dR T m T R T R d dm d dV p u u u u b b b b u u b b b b b b ¦ ¦ ) ¦ ¦ ` ¹ | | | | . | \ | ∂ ∂ + − α α δ d T u d T m d dQ u u u Wu b (2.1.13) with: u b b u u b u b V V V V γ γ γ α + + = u b b u b u b V V V ß γ γ γ + = BOOST Version 4.0.4 User’s Guide 2-8 23-Jun-2004 u b b u b b u b V V V V γ γ δ + ∂ − = T u R T u b u b u b u b u ∂ ∂ + ∂ ∂ = , , , , γ A similar equation can be found for the temperature derivative of unburned zone: ( ) ¦ ¦ ¹ ¦ ¦ ´ ¦ ( ( ( ¸ ( ¸ ∂ ∂ − − − − ∂ ∂ = α α α α α α T u d T m u u d dm d dQ d dQ T u m d dT b b b u b b Wb F u u u u 1 ( ) ( ) − ( ¸ ( ¸ − + − − − − α α α α α d dR T m V V d dR T m T R T R d dm ß d dV p ß u u u u b b b b u u b b b u u u ¦ ¦ ) ¦ ¦ ` ¹ | | | | . | \ | ∂ ∂ ∂ + α α δ T u d T m d dQ u u u wu u (2.1.14) The amount of mixture burned at each time step is obtained from the Vibe function specified by the user. For all other terms, like wall heat losses etc., models similar to the single zone models with an appropriate distribution on the two zones are used. A knock model calculates the minimum octane number required for engine operation free of knock. The threshold for the onset of knock is exceeded if the integral ( ) dt t t o iD ∫ τ 1 (2.1.15) iD τ ignition delay at the unburned zone’s condition is larger than one before the end of combustion is reached. The ignition delay for the knock model depends on the octane number of the fuel and the gas condition according to T B n a iD e p ON A − ⋅ ⋅ = τ (2.1.16) User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-9 iD τ ignition delay [ms] ON octane number of the fuel p pressure [atm] T temperature [K] B n a A , , , model constants A= 17.68 ms a =3.402 n =1.7 B =3800 K 4. Double Vibe Function The superposition of two vibe functions (Double Vibe) is used to approximate the measured heat release characteristics of a compression ignition (CI) engine more accurately. In this case two vibe functions are specified, the first one is used to model the premixed burning peak and the second one to model the diffusion controlled combustion. If the fuel allotment to each of the vibe functions is known, the heat releases obtained from the two vibe functions can be added, thus giving a double vibe heat release, Figure 2-5. BOOST Version 4.0.4 User’s Guide 2-10 23-Jun-2004 Figure 2-5: Superposition of Two Vibe Functions 2.1.1.3. Extended Heat Release Approach For the simulation of engine transients, the above mentioned approaches are not sufficient because the heat release characteristics change with engine speed and load. As the speed and load profile for a transient is not known prior to a simulation run, a model predicting the rate of heat release dependent on the operating point is required. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-11 WOSCHNI / ANISITS Model For diesel engines the approach used is based on the model by Woschni and Anisits [C1]. The vibe function and the characteristic parameters of one operating point must be defined. The model predicts the change of the vibe parameters according to the actual operating conditions: 5 . 0 6 . 0 , | | . | \ | ⋅ | | . | \ | ⋅ ∆ = ∆ ref ref ref c c n n AF AF α α (2.1.17) 3 . 0 , , 6 . 0 | | . | \ | ⋅ | | . | \ | ⋅ | | . | \ | ⋅ | | . | \ | ⋅ = ref IVC ref IVC ref IVC IVC ref ref n n T T p p id id m m (2.1.18) c α ∆ combustion duration AF air fuel ratio n engine speed m Vibe shape parameter id ignition delay IVC p pressure at intake valve closes IVC T in-cylinder temperature at intake valve closes Index ref at reference operating point The ignition delay is calculated with the relations found by Andree and Pachernegg [C3] which assume that the ignition of the injected fuel droplets takes place if the integral of gas temperature versus time exceeds a threshold. HIRES ET AL Model For gasoline engines the change of the combustion duration and the ignition delay is calculated from the in-cylinder conditions at ignition timing [C2]. 3 / 2 3 / 1 , | | . | \ | ⋅ | | . | \ | ⋅ ⋅ ∆ = ∆ s s f f n n ref ref ref ref c c α α (2.1.19) 3 / 2 3 / 1 | | . | \ | ⋅ ⋅ | | . | \ | ⋅ = s s f f n n id id ref ref ref ref (2.1.20) s laminar flame speed f piston to head distance at ignition timing The laminar flame speed itself is a function of the in-cylinder conditions, the A/F ratio and the mole fraction of the residual gases [C4]. BOOST Version 4.0.4 User’s Guide 2-12 23-Jun-2004 2.1.1.4. Quasi-dimensional Combustion Models SI ENGINES The quasi-dimensional combustion model for SI engines implemented in BOOST predicts the rate of heat release in a homogeneous charge engine. Thereby the influence of the following parameters is considered [C10, C11, C12] • The combustion chamber shape • The spark plug location and spark timing • The composition of the cylinder charge (residuals, recirculated exhaust gas, air and fuel vapor) • The macroscopic charge motion and turbulence level The thermodynamics of the two zone combustion model is outlined in section 2.1.1.2 - Vibe Two Zone. The two zone vibe is used to calculate the gas conditions of the combustion products (i.e. the burned zone) and the remaining fresh charge (i.e. the unburned zone). However the rate of heat release is determined from Equation 2.1.21 rather than a user supplied vibe function b b e b m m dt dm τ − = (2.1.21) b m total mass burned e m mass entrained into flame b τ characteristic combustion time The mass entrained is calculated from the flame surface area, the density of the unburned zone, the laminar flame speed and the turbulence intensity: ( )( ) it t l f u e e S u A dt dm τ ρ / 1 − − + ′ = (2.1.22) u ρ density of unburned zone f A Flame surface area u′ turbulence intensity l S laminar flame speed it τ characteristic combustion time at ignition timing t time since ignition A spherical propagation of the flame from the spark plug through the combustion chamber is assumed. With this assumption the instantaneous flame radius, the flame area and the wetted piston, head and liner surface of the burned and unburned zone can be determined from purely geometrical considerations. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-13 However, experimental evidence shows that both entrainment and depletion of fuel do not strictly follow geometrical correlations. This is corrected by an approach by Bargende [C21], which improves the heat release versus crankangle. This approach is referred to as Empirically Based Combustion Model (EBCM). Therefore, the following correction is introduced into Equation 2.1.22. ( )( )( ) ) 1 ( 1 / B B m S t l f u e Y Y b b e S u A dt dm it − + − + ′ = • − τ ρ (2.1.23) with B Y denoting the volume of the burned gas. The parameters S b and m b are determined as follows: S b = 2.13 - 0.26 X m b = 2.9 - 5.5(λ - 0.9)² + 0.17ρ ZZP where X is the residual gas content. Since the above mentioned method relies on empirical correlations, a physically based approach takes into account the interaction between turbulence and combustion. This approach is referred to as Physically Based Combustion Model (PBCM). This leads to increased turbulence, which contributes to the entrainment of fresh charge as follows: ( )( ) ) ( ( )( ) X e S X u u A dt dm it t l B C f u e − − + − ′ + ′ = − 1 1 1 /τ ρ (2.1.24) where X B stands for the mass fraction burned. The turbulent velocities are weighted by the mass fraction of unburned gas to effect the fresh charge only. Furthermore, Equation 2.1.24 accounts for a decreasing combustion rate, when the mass of residual gas increases. The additional turbulent intensity due to combustion is estimated as follows: 3 1 | | . | \ | ′ = ′ ZZP B ZZP C u u ρ ρ (2.1.25) For the calculation of the turbulence intensity u′ , a simple ε − k model with the following assumptions is used: • The global turbulence is neither influenced by diffusion nor boundary layer flows • The turbulence is isotropic • No swirl is generated during the intake stroke • The turbulence is generated entirely during the intake stroke • The moment of momentum is conserved according to the rapid distortion theory • The overall flow pattern has just one component in the direction of the cylinder axis BOOST Version 4.0.4 User’s Guide 2-14 23-Jun-2004 The turbulent kinetic energy k is defined as: ( ) 2 2 2 2 2 3 5 . 0 u u u u k z y x ′ = ′ + ′ + ′ = (2.1.26) and ε is its rate of dissipation. The rate of change of the turbulent kinetic energy is described by ε − + = D P dt dk (2.1.27) dt d k P ρ ρ 3 2 = 2 / 3 k l C = ε P production D diffusion, this term is neglected i.e. it is set to zero C model constant l turbulent length scale For the prediction of the knocking characteristics, the two zone vibe model is used as described in section 2.1.1.2. CI ENGINES BOOST uses two models for the prediction of the combustion characteristics in direct injection compression ignition engines: the method proposed by Hiroyasu and the MCC model developed by AVL. HIROYASU et al. Model The formulation of Hiroyasu et al. [C14, C15, C16, C17] requires a minimum degree of user input based on the overall properties of the engine (geometrical parameters, injection rate diagram etc..) and then calculates the spreading of an evaporating spray, its ignition and subsequent high temperature combustion. Despite the complexity of spray combustion processes in high pressure environments, the formalism is particularly suited to cost-effective, parametric studies on engines with the aim of lowering levels of NOx and soot. This is partly because the governing equations draw on a considerable amount of experimental work relating to turbulent flows involving droplet combustion. In the following the main theoretical features of the model will be briefly described. More detailed information is available in the references cited above. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-15 An important feature of the model is the manner in which the spray enters the combustion chamber. Liquid fuel is introduced into the domain by means of annular packages, shown in Figure 2-6, which behave as self-contained fluid elements. Each individual package entrains air from and exchanges heat with its surroundings without regard for its neighboring packages. The liquid fuel is represented as droplets whose size distribution is determined by empirical equations. It is assumed that there is no heat, mass and momentum transfer between the various packages and that each annular section is subject to circumferential symmetry. The packages move forward so that they always remain in contact and cannot overtake one another, somewhat like a plug flow. The number of packages created is determined by the user through his choice of the radial resolution and the time step used for the calculation. At every time step of the calculation during the fuel injection period a new cross-sectional array of packages is brought into the computational domain. The evolution of the spray is defined by empirical equations stemming from detailed experimental investigations. These equations determine the axial location of the packages. The volume or deformation of the packages is controlled by the inter-coupled physical processes such as entrainment of the surrounding cylinder gas into the package, droplet evaporation within the package, heat loss to the walls and heat release resulting from the diffusion flame type combustion. The various physical processes are illustrated in Figure 2-7. BOOST Version 4.0.4 User’s Guide 2-16 23-Jun-2004 Figure 2-6: Schematic of the Spray/Package Structure Figure 2-7: Schematic of the Physical Processes taking place in the Package The droplet size distribution within a package, expressed in terms of the Sauter mean diameter (the Sauter mean diameter, 32 D , is the diameter of a droplet whose ratio of volume to surface area is equal to that of the entire spray) is given by the following empirical expressions: ( ¸ ( ¸ = D D D D MAX D D HS LS 32 32 32 , (2.1.28) 18 . 0 54 . 0 75 . 0 12 . 0 32 Re 12 . 4 | | . | \ | | | . | \ | = − a l a l LS We D D ρ ρ µ µ (2.1.29) User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-17 47 . 0 37 . 0 32 . 0 25 . 0 32 Re 38 . 0 − − | | . | \ | | | . | \ | = a l a l HS We D D ρ ρ µ µ (2.1.30) MAX larger of the two values appearing in the square brackets µ dynamic (absolute) viscosity ρ density subscript l liquid subscript a air Each individual package has its own Sauter mean diameter, which together with the mass of liquid fuel in the package provides a value for the number of droplets in it. Using an energy and mass balance for a single droplet in each package, ordinary differential equations can be set up for the rate of change of the droplet temperature and diameter which are subsequently solved using a fourth order Runge-Kutta-Gill method. The details can be found in [C14]. The solution of these equations yields values for the amount of gaseous fuel available in the package and the change in temperature which is experienced as a result of the heating up of the droplet by the surroundings and its subsequent evaporation. The spray tip is defined by the first set of packages which are injected into the combustion chamber. Experimental studies demonstrate that the spray tip penetration, S is directly proportional to the time elapsed after the start of injection up to a break-up time, b t , and that thereafter t Sα . The complete set of equations for the penetration length along the axis of symmetry of the nozzle is as follows: b t t < < 0 , 2 l P c v ρ ∆ = vt S = (2.1.31) , b t t ≥ , 2 2 1 25 . 0 t D P c v n a | | . | \ | ∆ = ρ α vt S 2 = (2.1.32) where: 2 2 1 | | . | \ | = ∆ c v P inj e ρ | | . | \ | = 4 6 n e D inj g e inj D N t Q N V π ρ 2 / 1 2 − | | . | \ | ∆ = a N l b P D C t ρ ρ α BOOST Version 4.0.4 User’s Guide 2-18 23-Jun-2004 α Constant = 15.8 C Constant = 0.39 p ∆ pressure drop across the nozzle inj V injection velocity e N engine speed inj t injection duration D N number of nozzle holes n D nozzle hole diameter g Q total fuel mass injected The above empirical equations are strictly speaking only valid for initially quiescent air flows. When the in-cylinder flow has a swirling motion, the following modification is proposed for the penetration length, designated as S c S S S S S = : where 1 30 1 − | | . | \ | + = S v N R c inj e S S π and S R is the swirl number. It is assumed that the injection pressure and swirl ratio remain constant during this period. For off-axis penetration lengths Hiroyasu et al. propose the following modification to account for the penetration of a package along the th L radial section when counting the axial one as L = 1: ( ) [ ] 2 3 1 10 557 . 8 exp − × − = − L S S L . The amount of air entrained into a package is treated using the principle of conservation of momentum. A simple 1-D analysis yields: ( ) ( ) | | . | \ | − − = t t v t v v m C m p p inj fu ov ov air δ δ 1 1 (2.1.33) ov C coefficient of overall air entrainment fu m fuel mass in the package ( ) t v p current package velocity The velocity can be obtained using the relations described in the previous section. It is to be expected that such a level of phenomenological analysis of what is a complicated process would incorporate constants of proportionality. Consequently Hiroyasu’s formulation modifies the air entrainment prescribed by Equation 2.1.34 when the following physical effects also become relevant: before ignition and wall impingement ov air big big air m C m δ δ = ; after ignition but before wall impingement ov air aig aig air m C m δ δ = ; User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-19 after wall impingement ov air aw aw air m C m δ δ = . The constants require calibration and should be adjusted to reproduce measurements of the pressure trace, for example, in an engine. Once they have been suitably calibrated they can be used as part of a parametric study. Ignition is modeled in terms of an ignition delay; in other words no explicit chemistry is employed to account for this. A global ignition criterion is not employed, which means that each package is considered individually. The ignition delay period comes to an end when the following condition has been satisfied in the package: ( ) ∫ = 1 0 1 , , τ φ τ p p T P t d (2.1.34) P cylinder pressure p T package temperature p φ package equivalence ratio i τ ignition delay (time) The integration begins at the start of injection. At every time step the additional contribution to the integral is added to the existing sum and when the cumulative value equals or just exceeds unity then i τ is taken as the ignition delay. The function ( ) p p T P φ τ , , is based on the following empirical relation: ( ) | | . | \ | = − − − p p p p T E p x T P * 04 . 1 5 . 2 3 exp 10 0 . 4 , , φ φ τ (2.1.35) * E ratio of activation energy to the universal gas constant (typically 5000) Generally the consumption of fuel is controlled by the local stoichiometry in the package. For this purpose upper and lower flammability limits are employed, r fu Y and l fu Y respectively. In addition the combustion can be either evaporation or entrainment rate controlled, depending on the value of the local fuel mass fraction ) ( fu Y in relation to its theoretical stoichiometric value ) ( st fu Y . The results are summarized in terms of ratio of fuel burned in the package, ( ) fu Y R : • if l fu fu Y Y < or r fu fu Y Y > then ( ) fu Y R = 0. If the mixture strength lies outside the flammability limits, there will be no combustion. • if r fu fu st fu Y Y Y ≤ ≤ , then ( ) fu Y R = -0.2683 + 0.008106 | | . | \ | − Y Y fu 1 . Here combustion proceeds as fast as entrainment of air into the package allows. The quantity of fuel consumed (referred to as entr fu m ∆ ) is limited by the local O 2 concentration in that package. Consequently ( ) fu entr st fu entr fu Y R m m × ∆ = ∆ , . BOOST Version 4.0.4 User’s Guide 2-20 23-Jun-2004 • if st fu fu l fu Y Y Y < < , then ( ) fu Y R = 1. In this combustion regime the evaporation of the droplet is rate limiting. Under these circumstances all gaseous fuel present are consumed by the local mixture rich in oxygen. For n-dodecane Yoshizaki et al. [C11] quote the following values: st fu Y = 0.06007, r fu Y = 0.232 and l fu Y = 0.04. The heat release due to chemical reaction is then taken to be the sum of all the heat releases in the various packages. The latter is evaluated by multiplying the mass of fuel consumed to the fuel’s calorific heating value. Although all packages are assumed to have the same pressure, their temperatures are different. This is an essential requirement if the NO x predictions are to be realistic. The temperature in each package is evaluated using an iterative procedure whereby the enthalpy of the mixture is expressed in terms of the composition and a polynomial expression involving the temperature. Eleven chemical species are taken into consideration, namely: CO, CO 2 , O 2 , H 2 , H 2 O, OH, H, O, N 2 , N and NO. Except for NO and N all other species are assumed to be in partial equilibrium. Consequently the calculation of their concentrations does not require a chemical mechanism. The minimization of the Gibb’s free energy is sufficient. For rich mixtures, where the equivalence ratio can be less than unity, the actual equivalence ratio used for the equilibrium calculation is arbitrarily set to unity, in order to avoid unrealistically high levels of intermediates from being predicted. However, NO formation is a non-equilibrium process. The well-known extended Zeldovich mechanism is employed, which therefore only predicts the thermal contribution to NO X . The details can be found in the aforementioned papers. The concentration of soot in the exhaust is governed by its formation and oxidation processes during the engine cycle. Based on the existing knowledge of soot chemistry, for example its sensitivity to pressure, temperature and equivalence ratio, the following suggestions for the soot formation and consumption rates are postulated: | | . | \ | − = RT E P m A dt dm sf f f sf g exp 5 . 0 (2.1.36) | | . | \ | − = RT E P P Po m A dt dm Sc s c sc exp 8 . 1 2 (2.1.37) S m soot mass fg m gaseous fuel mass sf m soot mass formed sc m soot mass oxidated sf E Activation energy formation | . | \ | × = kmol kcal 4 10 25 . 1 sc E Activation energy oxidation | . | \ | × = kmol kcal 4 10 4 . 1 User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-21 The actual soot formation rate is obtained by taking the difference between Equations (2.1.36) and (2.1.37). The constants f A and c A need to be calibrated for a specific test case where measurements are available so that they can be used as part of a sensitivity analysis for that particular engine. AVL MCC Model The Mixture Controlled Combustion (MCC) model [C18, C19] requires less input than the Hiroyasu model. By shortening the ignition delay due to developments in recent years, the causal and thus time related connection between injection and combustion have become very close. So the heat release is considered to be controlled by the fuel quantity available and the turbulent kinetic energy density: ( ) ( ) V k f Q M f C d dQ F Mod , , 2 1 ⋅ ⋅ = ϕ (2.1.38) with ( ) LCV Q M Q M f F F − = , 1 (2.1.39) ( ) | | . | \ | ⋅ = 3 2 exp , V k C V k f Rate (2.1.40) Mod C Model Constant [kJ/kg/deg CrA] C Rate Constant of mixing rate [s] k local density of turbulent kinetic energy [m2/s2] F M injected fuel mass [kg] LCV lower heating value [kJ/kg] Q cumulative heat release [kJ] V instantaneous cylinder volume [m3] ϕ Crank Angle [deg CrA] Since the distribution of squish and swirl to the kinetic energy are relatively small, only the kinetic energy input from the fuel spray is taken into account. The amount of kinetic energy imparted to the cylinder charge is determined by the injection rate using 3 2 , 18 F F F kin V A n d dE ⋅ | | . | \ | ⋅ = µ ρ ϕ (2.1.41) A µ effective nozzle hole area [m 2 ] F ρ fuel density [kg/m 3 ] F V injection rate [m 3 /s] BOOST Version 4.0.4 User’s Guide 2-22 23-Jun-2004 n engine speed [rpm] For the calculation of the instantaneous level of kinetic energy the dissipation should be taken into account also. The dissipation is considered as proportional to the kinetic energy giving: diss F kin Diss F kin diss F kin E n C d dE d dE , , , , , 6 − = ϕ ϕ (2.1.42) With oxidation the kinetic energy of the jet is transferred to the combustion gas. So for mixture preparation, only the kinetic energy of the unburned fuel can be utilized for mixture preparation. The local turbulent kinetic energy density k is then given by ( ) stoich Diff F Diss F kin Turb m M E C k λ + = 1 , , (2.1.43) The constant Turb C considers the efficiency of the transformation from kinetic energy to turbulent energy. Turb C constant for turbulence generation [-] F kin E , kinetic jet energy [J] Diss F kin E , , kinetic jet energy considering dissipation [J] stoich m stoichiometric mass of fresh charge [kg/kg] Diff λ Air Excess Ratio for diffusion burning [-] 2.1.1.5. Theoretical Combustion Models For theoretical investigations, BOOST allows the specification of the following theoretical combustion models: 1. Constant Volume The complete charge is burned instantaneously at the specified crankangle. 2. Constant Pressure Part of the charge is burned instantaneously at top dead center to achieve the desired peak firing pressure. The remaining charge is burned in such a way as to maintain the specified PFP. This combination of constant volume and constant pressure combustion is also called Seiliger process. If the pressure at the end of the compression stroke already exceeds the specified PFP, combustion starts when the pressure drops below this pressure during the expansion stroke. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-23 2.1.1.6. User Models USER MODEL By linking a user supplied subroutine (usrcmb.for) to BOOST, the user may define heat release characteristics using BOOST’s high pressure cycle simulation. USER DEFINED HIGH PRESSURE CYCLE The user-defined high pressure cycle (user supplied subroutine usrhpr.for) replaces the entire high pressure cycle simulation of BOOST. 2.1.2. Gas Exchange Process, Basic Equation The Equation for the simulation of the gas exchange process is also the first law of thermodynamics: ( ) e e i i w c c h d dm h d dm d dQ d dV p d u m d ⋅ − ⋅ + − ⋅ − = ⋅ ∑ ∑ ∑ α α α α α (2.1.44) c m mass in the cylinder u specific internal energy c p cylinder pressure V cylinder volume w Q wall heat loss α actual crank angle i dm mass element flowing into the cylinder e dm mass element flowing out of the cylinder i h enthalpy of the in-flowing mass e h enthalpy of the mass leaving the cylinder BOOST Version 4.0.4 User’s Guide 2-24 23-Jun-2004 Figure 2-8: Energy Balance of Cylinder (Gas Exchange Process) The variation of the mass in the cylinder can be calculated from the sum of the in-flowing and out-flowing masses: ∑ ∑ − = α α α d dm d dm d dm e i c (2.1.45) 2.1.2.1. Port Massflow Rates The mass flow rates at the intake and exhaust ports are calculated from the Equations for isentropic orifice flow under consideration of the flow efficiencies of the ports determined on the steady state flow test rig. From the energy Equation for steady state orifice flow, the Equation for the mass flow rates can be obtained: ψ ⋅ ⋅ ⋅ ⋅ = 1 1 2 o o o eff T R p A dt dm (2.1.46) dt dm mass flow rate eff A effective flow area 1 o p upstream stagnation pressure 1 o T upstream stagnation temperature o R gas constant User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-25 For subsonic flow, ( ( ( ¸ ( ¸ | | . | \ | − | | . | \ | ⋅ − = + κ κ κ κ κ ψ 1 1 2 2 1 2 1 o o p p p p , (2.1.47) 2 p downstream static pressure κ ratio of specific heats and for sonic flow, 1 1 2 1 1 max + ⋅ | . | \ | + = = − κ κ κ ψ ψ κ . (2.1.48) The actual effective flow area can be determined from measured flow coefficients µσ: 4 2 π µσ ⋅ ⋅ = vi eff d A (2.1.49) µσ flow coefficient of the port vi d inner valve seat diameter (reference diameter) The flow coefficient µσ varies with valve lift and is determined on a steady-state flow test rig. The flow coefficient, µσ, represents the ratio between the actual measured mass flow rate at a certain pressure difference and the theoretical isentropic mass flow rate for the same boundary conditions. The flow coefficient is related to the cross section area. of the attached pipe. The inner valve seat diameter used for the definition of the normalized valve lift can be seen in the following figure: Figure 2-9: Inner Valve Seat Diameter The composition of the gases leaving the cylinder via the exhaust port is determined by the scavenging model. BOOST Version 4.0.4 User’s Guide 2-26 23-Jun-2004 2.1.2.2. Scavenging A perfect mixing model is usually used for four-stroke engines. This means that the composition of the exhaust gases is the mean composition of the gases in the cylinder, and also that the energy content of the exhaust gases is equivalent to the mean energy content of the gases in the cylinder. In this case the change of the air purity over crank angle can be calculated from the following Formula: ( ) α α d dm R m d dR i c ⋅ − ⋅ = 1 1 (2.1.50) R air purity In the case of a two-stroke engine, the perfect mixing model is not sufficient for accurate simulations. For this reason BOOST also offers a perfect displacement scavenging model and a user-defined scavenging model. In the perfect displacement model no mixing between intake and residual gases takes place and pure residual gases leave the cylinder (so long as they are available). The User-defined scavenging model used in the BOOST code divides the cylinder into the displacement zone and the mixing zone. The mass balance is based on the following scavenging types: SCAVENGING TYPE A According to the (positive) Scavenging Quality SC Q the incoming gas delivers both the displacement and the mixing zone while pure mixing zone gas is leaving the cylinder 0 > = IZ ID SC m m Q ID m massflow into the displacement zone IZ m massflow into the cylinder SCAVENGING TYPE B According to the (negative) Scavenging Quality SC Q the incoming gas is flowing into the mixing zone and partially short-circuited to the exhaust port, while shortcut and mixing zone gas is leaving the cylinder. 0 < − = IZ IS SC m m Q IS m shortcut massflow IZ m massflow into the cylinder Taking these two scavenging types into account, the Scavenging Quality Function ) (SE Q SC is calculated from the user defined Scavenging Efficiency Function SE(SR). User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-27 ( ) ( ) ( ) Z AS const V const SREF AS V t V m t m t SR CY = = = = ρ AS m aspirated mass SREF m reference mass of cylinder charge AS V volume of aspirated charge Z V cylinder reference volume ( ) ( ) ( ) Z TAS const V const ZEVC TAS V t V m t m t SE CY = = = = ρ TAS m aspirated mass trapped ZEVC m total mass of cylinder charge at EVC (Exhaust Valve Closing) TAS V volume of aspirated charge trapped Z V cylinder reference volume To consider the different zone temperatures (and densities) during the scavenging process, the scavenging efficiency SE(t) (used for calculating the scavenging quality SC Q (t)= )) ( ( t SE Q SC ) is determined as follows: ( ) ( ) ( ) ( ) ( ) ( ) ( ) t t m d m m t SE Z Z t t EF EF IZ IZ ρ τ τ ρ τ τ ρ τ ∫ | | . | \ | − = 0 IZ m mass flow into the cylinder EF m fresh charge mass flow out of the cylinder Z m total mass of cylinder charge IZ ρ density of mass flow into the cylinder EF ρ density of fresh charge mass flow out of the cylinder Z ρ density of cylinder charge 0 t intake valve opening time BOOST Version 4.0.4 User’s Guide 2-28 23-Jun-2004 In order to specify the quality of the scavenging system of a two-stroke engine, scavenging efficiency is required as a function of scavenge ratio SE(SR). This can be obtained from scavenging tests or the literature. Figure 2-10: User-Defined Scavenging Model 2.1.3. Piston Motion Piston Motion applies to both the High Pressure Cycle (Section 2.1.1) and the Gas Exchange Process (Section 2.1.2). For a standard crank train the piston motion as a function of the crank angle α can be derived from Figure 2-11: User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-29 Figure 2-11: Standard Crank Train ( ) ( ) ( ) 2 sin 1 cos cos | . | \ | − + ⋅ − ⋅ − + ⋅ − ⋅ + = l e l r l r l r s α ψ α ψ ψ (2.1.51) | . | \ | + = l r e arcsin ψ (2.1.52) s piston distance from TDC r crank radius l con-rod length ψ crank angle between vertical crank position and piston TDC position e piston pin offset a crank angle relative to TDC 2.1.4. Heat Transfer 2.1.4.1. In Cylinder Heat Transfer The heat transfer to the walls of the combustion chamber, i.e. the cylinder head, the piston, and the cylinder liner, is calculated from: ( ) wi c w i wi T T A Q − ⋅ ⋅ = α (2.1.53) wi Q wall heat flow (cylinder head, piston, liner) i A surface area (cylinder head, piston, liner) w α heat transfer coefficient c T gas temperature in the cylinder wi T wall temperature (cylinder head, piston, liner) BOOST Version 4.0.4 User’s Guide 2-30 23-Jun-2004 In the case of the liner wall temperature, the axial temperature variation between the piston TDC and BDC position is taken into account: c x e T T x c TDC L L ⋅ − ⋅ = ⋅ − 1 , (2.1.54) | | . | \ | = BDC L TDC L T T c , , ln (2.1.55) L T liner temperature TDC L T , liner temperature at TDC position BDC L T , liner temperature at BDC position x relative stroke (actual piston position related to full stroke) For the calculation of the heat transfer coefficient, BOOST provides the following heat transfer models: • Woschni 1978 • Woschni 1990 • Hohenberg • Lorenz (for engines with divided combustion chamber only) • AVL 2000 Model WOSCHNI Model The Woschni model published in 1978 [C5] for the high pressure cycle is summarized as follows: ( ) 8 . 0 , 1 , 1 , 1 , 2 1 53 . 0 8 . 0 2 . 0 130 ( ( ¸ ( ¸ − ⋅ ⋅ ⋅ ⋅ + ⋅ ⋅ ⋅ ⋅ ⋅ = − − o c c c c c D m c c w p p V p T V C c C T p D α (2.1.56) 1 C = 2.28 + 0.308 ⋅ u c / m c 2 C = 0.00324 for DI engines 2 C = 0.00622 for IDI engines D cylinder bore m c mean piston speed u c circumferential velocity D V displacement per cylinder o c p , cylinder pressure of the motored engine [bar] 1 , c T temperature in the cylinder at intake valve closing (IVC) 1 , c p pressure in the cylinder at IVC [bar] User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-31 The modified Woschni heat transfer model published in 1990 [C6] aimed at a more accurate prediction of the heat transfer at part load operation: 8 . 0 2 . 0 2 1 53 . 0 8 . 0 2 . 0 2 1 130 ¦ ) ¦ ` ¹ ¦ ¹ ¦ ´ ¦ ( ( ¸ ( ¸ ⋅ | . | \ | + ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ = − − − IMEP V V c c T p D TDC m c c w α (2.1.57) TDC V TDC volume in the cylinder V actual cylinder volume IMEP indicated mean effective pressure In the case that ( ) 2 . 0 2 1 , 1 , 1 , 2 2 − ⋅ | . | \ | ⋅ ⋅ ⋅ ≥ − ⋅ ⋅ ⋅ ⋅ IMEP V V c C p p V p T V C TDC m o c c c c D , the heat transfer coefficient is calculated according to the formula published in 1978. For the gas exchange process, both Woschni models use the same Equation for the heat transfer coefficient: ( ) 8 . 0 3 53 . 0 8 . 0 2 . 0 130 m c c w c C T p D ⋅ ⋅ ⋅ ⋅ ⋅ = − − α (2.1.58) m u c c C / 417 . 0 18 . 6 3 ⋅ + = w α heat transfer coefficient D cylinder bore m c mean piston speed u c circumferential velocity HOHENBERG Model In the Hohenberg heat transfer model [C7] the following equation is used for the calculation of the heat transfer coefficient: ( ) 8 . 0 4 . 0 8 . 0 06 . 0 4 . 1 130 + ⋅ ⋅ ⋅ ⋅ = − − m c c w c T p V α (2.1.59) BOOST Version 4.0.4 User’s Guide 2-32 23-Jun-2004 LORENZ Model The Lorenz Heat Transfer Equation is valid for a cylinder with an attached combustion chamber. In Equation 2.1.56 and 2.1.57 the characteristic speed is: m C c C w ⋅ = 1 C w characteristic speed in the cylinder For the Lorenz equation the term C w is modified: m CP C C C x D dt dV w 1 . . 4 + ⋅ = π (2.1.60) dt dV CP volume flow from the connecting pipe to the cylinder x clearance between the cylinder head and the piston AVL 2000 Heat Transfer Model The heat transfer during gas exchange strongly influences the volumetric efficiencies of the engine, especially for low engine speeds. Based on AVL experience the Woschni heat transfer has been modified to take this effect into account. During the gas exchange the heat transfer coefficient is calculated from the following equation: ( ( ¸ ( ¸ | | . | \ | | . | \ | = − − 8 . 0 2 4 53 . 0 8 . 0 2 . 0 013 . 0 , in in Woschni v d d c T p d Max α α (2.1.61) α heat transfer coefficients [J/K/M2] 4 C = 14.0 d bore [m] p pressure [Pa] T temperature [K] in d pipe diameter connected to intake port [m] in v intake port velocity [m/s] The diameter of the intake port directly at the valve is of special significance for this model, therefore these diameters of the intake ports should be accurately specified over the whole port length. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-33 2.1.4.2. Port Heat Transfer During the gas exchange process it is essential also to consider the heat transfer in the intake and exhaust ports. This may be much higher than for a simple pipe flow because of the high heat transfer coefficients and temperatures in the region of the valves and valve seats. In the BOOST code, a modified Zapf heat transfer model is used: ( ) w c m A w u d T e T T T p p w + ⋅ − = | | . | \ | ⋅ ⋅ − α (2.1.62) The heat transfer coefficient, α p , depends on the direction of the flow (in or out of the cylinder): The formula [ ] ( ¸ ( ¸ ⋅ − ⋅ ⋅ ⋅ ⋅ ⋅ − ⋅ + = − vi v vi u u u p d h d m T T C T C C 797 . 0 1 5 . 1 5 . 0 44 . 0 2 6 5 4 α (2.1.63) is used for outflow and the formula [ ] ( ¸ ( ¸ ⋅ − ⋅ ⋅ ⋅ ⋅ ⋅ − ⋅ + = − vi v vi u u p d h d m T T C T C C 765 . 0 1 68 . 1 68 . 0 33 . 0 2 9 8 7 α (2.1.64) is used for inflow. p α heat transfer coefficient in the port d T downstream temperature u T upstream temperature T w port wall temperature A w port surface area m mass flow rate c p specific heat at constant pressure h v valve lift d vi inner valve seat diameter The following table contains the constants used in the formulas above. Exhaust Valve Intake Valve 4 C 1.2809 7 C 1.5132 5 C -4 10 0451 . 7 ⋅ 8 C -4 10 7.1625⋅ 6 C -7 10 4.8035⋅ 9 C -7 10 3719 . 5 ⋅ BOOST Version 4.0.4 User’s Guide 2-34 23-Jun-2004 2.1.5. Dynamic In-Cylinder Swirl BOOST allows the user to specify the swirl characteristics of an intake port versus valve lift. During the intake process, the moment of momentum of the mass entering the cylinder is calculated from the instantaneous mass flow rate and the swirl produced at the instantaneous valve lift. The in-cylinder swirl at the end of the time step is calculated from ( ) ( ) ( ) ( ) | | . | \ | ⋅ ⋅ + ⋅ ⋅ ∆ + = ∆ + swi piston piston i sw c c sw n v v dm t n t m t t m t t n 1 (2.1.65) sw n in-cylinder swirl c m in-cylinder mass i dm in-flowing mass swi n swirl of in-flowing mass piston v actual piston velocity piston v mean piston velocity 2.1.6. Blow-By Losses in the Cylinder BOOST considers blow-by losses in the cylinder using the specified effective blow-by gap and the mean crankcase pressure. The blow-by mass flow rates are calculated at any time step from the orifice flow Equations (2.1.46 - 2.1.48). The effective flow area is obtained from the cylinder bore and from the effective blow-by gap: δ π ⋅ ⋅ = D A eff (2.1.66) eff A effective flow area D cylinder bore δ blow-by gap If the cylinder pressure exceeds the mean crankcase pressure, the cylinder pressure and temperature are used as upstream stagnation pressure and temperature. The mean crankcase pressure represents the downstream static pressure. The gas properties are taken from the cylinder. The blow-by gas has the same energy content as the gases in the cylinder. If the cylinder pressure is lower than the mean crankcase pressure, the pressure in the crankcase is used as upstream stagnation pressure, and the cylinder pressure as the downstream static pressure. The upstream stagnation temperature is set equal to the piston wall temperature, and the gas composition is set equal to the composition of the gas which left the cylinder just before the reverse flow into the cylinder started. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-35 2.1.7. Wall Temperature The cycle averaged wall temperatures influence the wall heat losses during the high pressure cycle and thus the efficiency of the engine. During the gas exchange, the heat transfer from the cylinder walls heats the fresh charge and lowers the volumetric efficiency of the engine. The heat balance between the heat flux from the working gas in the cylinder to the cooling medium determines the wall temperatures. For transient simulations, this energy balance can be calculated for the cylinder head/fire deck, the liner, and the piston. In addition, the heat balance of the port walls may be considered. The 1D heat conduction equation is solved using the average heat flux over one cycle as boundary condition at the combustion chamber side and the heat transfer to the cooling medium on the outside. With these assumptions the heat conduction Equation 2 2 dx T d c dt dT ⋅ = ρ λ (2.1.67) T wall temperature λ conductivity of wall material ρ density of wall material c specific heat capacity of wall material can be solved. The mathematical formulation of the boundary conditions is: dx dT q in λ − = (2.1.68) in q average heat flux to the combustion chamber wall ( ) CM WO CM out T T q − ⋅ =α (2.1.69) out q heat flux to cooling medium CM α outer heat transfer coefficient WO T outer combustion chamber wall temperature CM T temperature of cooling medium For the piston, another term for the heat flux to the liner is taken into account. 2.1.8. Direct Gasoline Injection Depending on the operating point, direct gasoline injection engines are operated either with homogenous or stratified charges. The former operating strategy is applied near wide open throttle (WOT) operation. The fuel is injected into the cylinder early during the intake stroke. The charge is cooled by the evaporating fuel and thus the volumetric efficiency is increased. BOOST Version 4.0.4 User’s Guide 2-36 23-Jun-2004 In the stratified operation mode fuel is injected late during the compression stroke. A balance must be found between sufficient time for the mixture preparation avoiding a fuel cloud spread too wide. Insufficient mixture preparation or a too wide spread of the fuel cloud result in poor fuel consumption and high emissions. For part load operation the stratified operation strategy is preferred as it allows to control the engine load by the quantity of fuel injected at full or only slightly reduced air flow through the engine. The engine is less throttled and the reduction of pumping losses increases the fuel economy of the engine. The model for direct gasoline injection in BOOST relies on the specification of the rate of evaporation. It is assumed that the density of the liquid fuel is much higher compared to the fuel vapor density. Hence the presence of liquid fuel can be neglected. In the equation describing the conservation of mass in the cylinder, a term is added to account for the fuel evaporation. Similarly the energy conservation equation is extended by the term dt dm f q ev ev ⋅ ⋅ − ev q evaporation heat of the fuel f fraction of evaporation heat from the cylinder charge ev m evaporating fuel 2.1.9. Divided Combustion Chamber Indirect Injection (IDI)-Diesel engines or lean burn gas engines with ignition in a stoichiometric or even rich mixture in a pre-chamber may be modeled in BOOST with divided combustion chamber. The combustion chamber is connected to the cylinder. For modeling the fuel or air fuel mixture feed of gas engines to the combustion chamber, pipes may be attached also to the chamber. The energy Equation of the cylinder (2.1.1) must be modified by a term considering the energy flow associated with mass flow from the chamber to the cylinder or vice versa. Thus 2.1.1 becomes: ( ) α α α α α α d dm h d dm h d dQ d dQ d dV p d u m d cp cp BB BB w F C c ⋅ + ⋅ − − + ⋅ − = ⋅ ∑ (2.1.70) α d dm h cp cp ⋅ enthalpy flow from/to the connecting pipe User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-37 The concentration changes due to the flows from the chamber are: C CP CP c c m dm ci dci dci ⋅ − = + + , 1 , , 1 α α α 1 + α Ci Concentration at time step 1 + α in the Cylinder CP Ci / 1 + α Conc. at time step 1 + α in the connecting pipe Similar extensions must be made in the energy Equation for the gas exchange. CONNECTING PIPE MASS FLOW With a modification of the isentropic flow equation the wall heat flow and the inertia of the gas column in a pipe are taken into account. The downstream states are the same as the pipe states, because no storage effects are taken into account. ( ) ∫ − = + + − 2 1 2 2 2 1 2 1 w w dl t w q h h w ∂ ∂ (2.1.71) 2 2 360 1 W A n d dm ⋅ ⋅ ⋅ ⋅ = ρ µ α (2.1.72) 2 1 , h h specific enthalpies upstream/downstream 2 1 ,W W speed upstream/in the pipe ∫ L dl t w ∂ ∂ inertia of the gas column w q specific wall heat n engine speed [1/s] 2 ρ density in the pipe µ flow coefficient The mass flow is obtained from: l t w qw T T T cp A d dm n ⋅ + + | | . | \ | − ⋅ ⋅ ⋅ ⋅ = ∂ ∂ ρ µ α 2 2 1 2 360 1 1 2 1 2 (2.1.73) The wall heat is calculated from Equation 2.10.5. BOOST Version 4.0.4 User’s Guide 2-38 23-Jun-2004 COMBUSTION CHAMBER The combustion chamber is treated as a plenum. Heat release, wall heat losses, volume work and mass flows out of or into the plenum are accounted for (refer to Section 2.2). With the addition of a term for the heat released due to combustion, Equation 2.2.1 becomes: ( ) ∑ ∑ ∑ ⋅ − ⋅ + + − ⋅ − = ⋅ α α α α α α d h dme d hi dmi d dQ d dQw d dV p d u m d e B PL Pl (2.1.74) Q B ..... heat released due to combustion The Kamel-Watson equation for the wall heat flow is based on the Nußelt-Reynolds Analogon and takes into account the swirl in the chamber. ( ) 2 . 0 53 . 0 8 . 0 013 . 0 − − − ⋅ ⋅ ⋅ = PL PL PL PL W K r T w p L (2.1.75) PL w characteristic speed in the plenum PL T gas temperature PL r radius of the plenum 2 i PL PL r m T w ⋅ = (2.1.76) T torque i r inertia radius ( ) ∫ − = dt M M T FR ADD (2.1.77) ADD M added Momentum FR M friction Momentum cp cp cp ADD r w dt dm M ⋅ ⋅ = (2.1.78) dt dm cp mass flow from the connecting pipe to the chamber cp w speed in the connecting pipe cp r eccentricity of the connecting pipe to the center of the torque 5 3 2 Pl Pl Pl f FR r C M ⋅ ⋅ ⋅ = ϖ ρ (2.1.79) 2 , 0 1 . 0 Re 01 , 0 Pl Pl Pl f r s C ⋅ | | . | \ | = (2.1.80) User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-39 ν ϖ 2 Re Pl Pl Pl r ⋅ = (2.1.81) f C coefficient of the friction momentum Pl s swirl radius in the chamber Pl Re Reynolds Number in the chamber Pl ϖ angular speed in the chamber 2.1.10. BURN Utility The BURN utility can be used for combustion analysis. That is the rate of heat release (ROHR) can be obtained from measured cylinder pressure traces. With the BOOST one- zone model, pressure and temperature of the cylinder is calculated from the specified rate of heat release. The inverse procedure, the determination of the rate of heat release from measured pressure traces is called combustion analysis. The BOOST interface offers a tool based on the algorithms used in the BOOST cylinder to fulfil this task. The algorithm is based on the first law of thermodynamics shown in equation 2.1.1. The in-cylinder heat transfer is calculated using the models described in chapter 2.1.4. Piston motion and blow by losses are calculated using the approach of chapters 2.1.3 and 2.1.6. 2.2. Plenum (Variable Plenum) The calculation of the gas conditions in a plenum is very similar to the simulation of the gas exchange process of a cylinder, as described in Section 2.1.2: ( ) e e i i w Pl Pl h d dm h d dm d dQ d dV p d u m d ⋅ − ⋅ + − ⋅ − = ⋅ ∑ ∑ ∑ α α α α α (2.2.1) Pl m mass in the plenum u specific internal energy Pl p pressure in the plenum V plenum volume w Q wall heat loss α crank angle i dm mass element flowing into the plenum e dm mass element flowing out of the plenum i h enthalpy of the in-flowing mass e h enthalpy of the mass leaving the plenum For plenums with constant volume, the term of equation 2.2.1 which covers the variation of the volume is equal to zero. BOOST Version 4.0.4 User’s Guide 2-40 23-Jun-2004 In the case of a variable plenum, the change of the plenum volume over crank angle is calculated from the input specified by the user (user-defined), or from the motion of the piston (crankcase or scavenging pump). No detailed models for the heat transfer coefficient in a plenum are available. This means that the heat transfer coefficient must be specified by the user, depending on the actual shape of the plenum. As an alternative, BOOST offers a very simple heat transfer model for the plenum which may be used if only limited information is available: ( ) 4 2 . 0 8 . 0 10 3 . 1 127 . 0 2 . 0 1 018 . 0 − − ⋅ ⋅ + ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ − ⋅ = T L u R ch ch o ρ κ κ α (2.2.2) 3 V L ch = 2 1 ch pipe n pipe ch L A u n u ∑ = L ch characteristic length V plenum volume u ch characteristic velocity n number of pipe attachments pipe u velocity at the pipe attachment A pipe cross-section at the pipe attachment T temperature in the plenum ρ density in the plenum o R gas constant κ ratio of specific heats If a variable wall temperature of the plenum must be considered for transient simulations, a similar model is used as for the cylinder (refer to Section 2.1.7). User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-41 2.3. Flow Restriction (Rotary Valve) The simulation of the flow through a restriction is based on the energy equation, the continuity equation, and the formulae for the isentropic change of state: ψ α ⋅ ⋅ ⋅ ⋅ ⋅ = 1 1 2 o o o geo T R p A m (2.3.1) m mass flow rate α flow coefficient geo A geometrical flow area 1 o p upstream stagnation pressure 1 o T upstream stagnation temperature o R gas constant The pressure function ψ depends on the gas properties and on the pressure ratio: ( ( ( ¸ ( ¸ | | . | \ | − | | . | \ | ⋅ − = + k o k o p p p p 1 1 2 2 1 2 1 κ κ κ ψ (2.3.2) 2 p downstream static pressure κ ratio of specific heats Figure 2-12 shows the shape of the pressure function ψ over pressure ratio. Figure 2-12: The Pressure Function ψ ψψ ψ In the case of subcritical flow, the pressure ratio, which is defined as the downstream static pressure divided by the upstream stagnation pressure, is higher than the critical pressure ratio and less than or equal to 1.0. The pressure function ψ follows the trend shown in the figure for this range of pressure ratios. BOOST Version 4.0.4 User’s Guide 2-42 23-Jun-2004 If the pressure ratio drops to the critical pressure ratio 1 1 1 2 − | . | \ | + = κ κ κ o crit p p , (2.3.3) the flow in the orifice reaches a Mach number of 1.0. The pressure function ψ reaches its maximum at the critical pressure ratio. The actual value of ψ max is dependent on the pressure ratio: 1 1 2 1 1 max + ⋅ | . | \ | + = = − κ κ κ ψ ψ κ , (2.3.4) The values of the pressure function ψ shown in Figure 2-12 for pressure ratios less than the critical pressure ratio are valid only for supersonic flow in the orifice. However, it should be pointed out that supersonic flow can never be achieved just by lowering the backpressure, but always requires a special shape of the pipe upstream of the orifice (Laval-Nozzle). 2.4. Check Valve The calculation of the flow in a check valve is very similar to the procedure discussed in Section 2.3 for the flow restriction. Two types of models are available. The simple model considers flow coefficients which depend on the difference of the static pressures at the two pipe attachments. This model does not consider the inertia of the valve body. If this inertia is to be taken into account, in addition to the mass flow rates, also the valve lift must be calculated over time. For this purpose a spring-damper-mass model as shown in Figure 2-13 is used. Figure 2-13: Full Check Valve Model The motion of the valve can be calculated from the following Formula: ( ) v d x c F p p A a m o ⋅ − ⋅ − − − ⋅ = ⋅ 2 1 (2.4.1) m mass of the valve a acceleration of the valve A cross-section of the valve 2 1 , p p static pressure User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-43 o F spring pre-load c spring stiffness x valve lift d damping constant v valve velocity Equation 2.4.1 describes the motion of a pressure actuated valve under consideration of its inertia, the spring pre-load, the spring stiffness, and the viscous damping. The flow coefficient of the check valve is determined as a function of valve lift and is then used to calculate the mass flow rate as a function of upstream and downstream pressure. 2.5. Junction The BOOST program features three models for junctions. The constant pressure model and the constant static pressure model can be used for all junctions. In the former case the junction is treated like a plenum without any volume. As for a plenum, the flow coefficients for flow into the junction and flow out of the junction must be defined for each pipe attachment. From the gas conditions in the pipe, the static pressure and the temperature at the center of each junction is calculated. The constant static pressure model enforces the same static pressure in all pipe cross sections attached to the junction. The flow coefficients are set to 1. For three pipe junctions a more refined junction model is available. In this case the BOOST code distinguishes between six possible flow patterns in the junction, as shown in the following figure. Figure 2-14: Flow Patterns in a Y-Junction For each of the flow paths indicated in Figure 2-14, the equation for the orifice flow (2.3.2) is solved. The flow coefficients depend on the geometry of the junction, i.e. the area ratio between the pipes and the angles between the centerlines of the pipes, and for a specific junction on the flow pattern and on the mass flow ratio between one branch and the common branch. BOOST Version 4.0.4 User’s Guide 2-44 23-Jun-2004 As the equations for orifice flow are applied to both separating or joining flows, two sets of flow coefficients are required, (i.e. two times six flow coefficients must be supplied to the program). In order to facilitate the application of this model, a database is provided with the BOOST program. The flow coefficients contained in this database were obtained from steady-state flow tests of junctions with different pipe diameters and different branching angles. The mass flow ratios in the junction as well as the Mach numbers were also varied during these tests. The program interpolates a suitable set of flow coefficients from this database. 2.6. Turbocharger For steady state engine operation the performance of the turbocharger is determined by the energy balance or the first law of thermodynamics. The mean power consumption of the compressor must be equal to the mean power provided by the turbine: T c P P = (2.6.1) The power consumption of the turbo compressor depends on the mass flow rates in the compressor and the enthalpy difference over the compressor. The latter is influenced by the pressure ratio, the inlet air temperature, and the isentropic efficiency of the compressor. ( ) 1 2 h h m P c c − ⋅ = (2.6.2) c P compressor power consumption c m mass flow rate in the compressor 2 h enthalpy at the outlet of the compressor 1 h enthalpy at the inlet to the compressor ( ( ( ¸ ( ¸ − | | . | \ | ⋅ ⋅ ⋅ = − − 1 p p T c 1 h h 1 1 2 1 p c , s 1 2 κ κ η (2.6.3) c s, η isentropic efficiency of the compressor p c mean value of the specific heat at constant pressure between compressor inlet and outlet 1 T compressor inlet temperature 1 2 , p p compressor pressure ratio User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-45 The power provided by the turbocharger turbine is determined by the turbine mass flow rate and the enthalpy difference over the turbine. Furthermore, it is conventional to allocate all mechanical losses of the turbocharger to the turbine side: ( ) 4 3 , h h m P TC m T T − ⋅ ⋅ = η (2.6.4) T P turbine power T m turbine mass flow 3 h enthalpy at the turbine inlet 4 h enthalpy at the turbine outlet TC m, η mechanical efficiency of the turbocharger ( ( ( ¸ ( ¸ | | . | \ | − ⋅ ⋅ ⋅ = − − κ κ η 1 3 4 3 , 4 3 1 p p T c h h p T s (2.6.5) ⋅ T s, η isentropic turbine efficiency ⋅ p c mean specific heat at constant pressure between turbine inlet and outlet 3 T turbine inlet temperature 3 4 , p p turbine expansion ratio The overall turbocharger efficiency is defined as follows: c s T s TC m TC , , , η η η η ⋅ ⋅ = (2.6.6) TC η overall turbocharger efficiency For steady state engine performance a simplified turbocharger model may be used for the simulation. Within this model the dynamics of the turbocharger (i.e. the variation of the turbocharger speed) are not considered. Furthermore, the turbocharger efficiency is kept constant during the engine cycle. As many test calculations have proven, this model provides good accuracy for steady state engine calculations. It is very convenient to work with this model, as only the mean values for the compressor efficiency, the turbine efficiency, and the mechanical efficiency of the turbocharger must be specified. This reduces the required input dramatically in comparison to the full turbocharger model where entire compressor and turbine maps must be defined. Since turbine performance maps cannot be provided by turbocharger manufacturers very often, this simplified solution is usually the only alternative. In BOOST, three calculation modes for the simplified model are available: 1. In the turbine layout calculation, the desired pressure ratio at the turbo compressor is specified as input to the calculation. The program adjusts the flow resistance of the turbine automatically, until the energy balance over the turbocharger is satisfied. BOOST Version 4.0.4 User’s Guide 2-46 23-Jun-2004 2. For the boost pressure calculation, the actual turbine size is specified in the input. By solving the energy balance over the turbocharger, the actual boost pressure is calculated. 3. For the waste gate calculation, both the turbine size as well as the desired pressure ratio at the turbo compressor are specified in the input. The program bypasses a certain percentage of the exhaust gases in order to achieve the energy balance over the turbocharger. If the desired compressor pressure ratio cannot be achieved with the specified turbine size, the program switches over to the boost pressure calculation mode. For unsteady engine operation the rotor dynamics of the turbocharger must be considered because the wheel speed of the charger changes. From the balance of momentum at the turbocharger wheel the change of wheel speed is obtained: TC c T TC TC P P I dt d ω ω − ⋅ = 1 (2.6.7) TC ω turbocharger wheel speed TC I turbocharger wheel inertia The turbocharger full model requires the input of the compressor and turbine map. The speed of the turbocharger wheel is calculated using Equation 2.6.7. With the instantaneous wheel speed and the mass flow rate through the compressor, the compressor's isentropic efficiency and the pressure ratio are interpolated from the compressor map. The efficiency and the swallowing capacity of the turbine are interpolated from the turbine map using the wheel speed and the pressure ratio across the turbine. If a variable geometry turbine (VGT) is used, the vane position or some equivalent information is also required. In this case the turbine data is obtained from interpolation in the two maps valid for vane positions nearest to the instantaneous one and from linear interpolation afterwards. 2.7. Mechanically Driven Superchargers For the simulation of mechanically driven superchargers, the performance characteristics along a line of constant supercharger speed proportional to the steady state engine speed or the complete supercharger map for transient simulations are required. The maps are provided by the supercharger manufacturer. In the course of the calculations the pressure ratio over the compressor is adjusted depending on the actual mass flow rate (and supercharger speed if the full model is used). From the pressure ratio and the isentropic efficiency of the compressor, the compressor outlet temperature can be obtained: ¦ ) ¦ ` ¹ ¦ ¹ ¦ ´ ¦ ( ( ( ¸ ( ¸ − | | . | \ | ⋅ + ⋅ = − 1 1 1 1 1 2 1 2 κ κ η p p T T s (2.7.1) User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-47 2 T compressor outlet temperature 1 T air inlet temperature s η isentropic efficiency of the compressor 2 p compressor outlet pressure 1 p compressor inlet pressure κ ratio of specific heats The power consumption of the mechanically driven compressor can be calculated from the following formula: ( ( ( ¸ ( ¸ − | | . | \ | ⋅ ⋅ ⋅ ⋅ = − 1 1 1 1 2 1 κ κ η p p T c m P tot p (2.7.2) P compressor power consumption m mass flow rate p c specific heat at constant pressure tot η total efficiency of the compressor = s m η η ⋅ m η mechanical efficiency of the compressor 2.8. Fuel Injector or Carburetor The fuel injector model in BOOST is based on the calculation algorithm of the flow restriction (refer to Section 2.3). This means that the air flow rate in the fuel injector depends on the pressure difference across the injector and is calculated using the specified flow coefficients. In addition, the amount of fuel specified is fed into the air flow. In the case of the carburetor model, the fuel flow is set to a specified percentage of the instantaneous mass flow. For the fuel injector model, a measuring point must be specified at the location of the air flow meter. In this case the mean air flow at the air flow meter location during the last complete cycle is used to determine the amount of fuel. As is the case for continuous fuel injection, the fuelling rate is constant over crank angle. The fuel is added in gaseous form to the pipe flow. No evaporation is considered. BOOST Version 4.0.4 User’s Guide 2-48 23-Jun-2004 2.9. Waste Gate The waste gate models a valve actuated by the pressure difference on a diaphragm (Figure 2-15). The flow through the valve is treated in the same way as for the flow restriction (refer to Section 2.3). The flow coefficients required are specified versus the lift of the valve. The instantaneous valve lift is calculated from the solution of the motion equation of the valve body (refer to Section 2.4). A defined leakage between the high pressure and the low pressure of the actuation diaphragm may be taken into account. Figure 2-15: Waste Gate This type of valve is used mostly to control the boost pressure of a turbocharged engine. The boost pressure is fed to the high pressure side of the actuation diaphragm. The low pressure side is connected to the ambient. If the pressure difference exceeds a certain value, set by the spring pre-load, the valve opens and a part of the exhaust gases is bypassed around the turbine thus diminishing the energy available at the turbine and preventing a further increase of the boost pressure. 2.10. Pipe Flow The one dimensional gas dynamics in a pipe are described by the continuity Equation ( ) dx dA A u x u t ⋅ ⋅ ⋅ − ⋅ − = 1 ρ ∂ ρ ∂ ∂ ∂ρ , (2.10.1) the equation for the conservation of the momentum ( ) ( ) V F x A A u x p u t u R − ⋅ ⋅ ⋅ − + ⋅ − = ⋅ ∂ ∂ ρ ∂ ρ ∂ ∂ ρ ∂ 1 2 2 , (2.10.2) and by the energy Equation ( ) [ ] ( ) V q dx dA A p E u x p E u t E w + ⋅ ⋅ + ⋅ − + ⋅ − = 1 ∂ ∂ ∂ ∂ . (2.10.3) User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-49 ρ density u flow velocity x coordinate along the pipe axis A pipe cross-section t time p static pressure R F wall friction force V cell volume ( ) dx A⋅ = E energy content of the gas | . | \ | ⋅ ⋅ + ⋅ ⋅ = 2 2 1 u T c V ρ ρ V c specific heat at constant volume T temperature w q wall heat flow The wall friction force can be determined from the wall friction factor λ f : u u D V F f R ⋅ ⋅ ⋅ ⋅ = ρ λ 2 (2.10.4) f λ wall friction coefficient D pipe diameter Using the Reynold's analogy, the wall heat flow in the pipe can be calculated from the friction force and the difference between wall temperature and gas temperature: ( ) T T c u D V q w p f w − ⋅ ⋅ ⋅ ⋅ ⋅ = ρ λ 2 (2.10.5) p c specific heat at constant pressure w T pipe wall temperature During the course of the numerical integration of the conservation laws defined in the Equations 2.10.1 to 2.10.3, special attention should be focused on the control of the time step. In order to achieve a stable solution, the CFL criterion (stability criterion defined by Courant, Friedrichs and Lewy) must be met: a u x t + ∆ ≤ ∆ (2.10.6) t ∆ time step x ∆ cell length u flow velocity a speed of sound BOOST Version 4.0.4 User’s Guide 2-50 23-Jun-2004 This means that a certain relation between the time step and the lengths of the cells must be met. The BOOST program determines the time step to cell size relation at the beginning of the calculation on the basis of the specified initial conditions in the pipes. However, the CFL criterion is checked every time step during the calculation. If the criterion is not met because of significantly changed flow conditions in the pipes, the time step is reduced automatically. An ENO scheme [P1, P2] is used for the solution of the set of non-linear differential equations discussed above. The ENO scheme is based on a finite volume approach. This means that the solution at the end of the time step is obtained from the value at the beginning of the time step and from the fluxes over the cell borders: Figure 2-16: Finite Volume Concept For the approach shown in Figure 2-16, the calculation of the mass, momentum and energy fluxes over the cell borders at the middle of the time step is required. This can be done using the basic conservation equations, which give a direct relation between a gradient in the x-direction and the gradient over time. The gradient in the x-direction is obtained by a linear reconstruction of the flow field at the beginning of the time step. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-51 Figure 2-17: Linear Reconstruction of the Flow Field From this information, the mass, momentum and energy fluxes at the cell borders of each cell can be calculated. Normally the flux at the right cell border will not be equal to the flux at the left cell border of the adjacent cell, which is a necessary condition to meet continuity requirements. To overcome this problem, a Riemann-Solver is used to calculate the correct mean value from the two different fluxes at the cell border, as shown in the following figure. Figure 2-18: Pressure Waves from Discontinuities at Cell Borders The main advantage of an ENO scheme is that it allows the same accuracy to be achieved as can be obtained with second order accurate finite difference schemes, but has the same stability as first order accurate finite difference schemes. BOOST Version 4.0.4 User’s Guide 2-52 23-Jun-2004 2.10.1. Bends BOOST features a simple model which considers the influence of the bend of a pipe on the flow losses. The bend model in the BOOST program increases the wall friction losses dependent on a loss coefficient, ζ. 2 2 v p ρ ζ = ∆ (2.10.7) This loss coefficient is a function of the bend angle and the ratio between the bend radius and the pipe diameter. For this reason the variation of bend radius over pipe length must be specified. The bend radius is defined as the bend radius of the pipe centerline. r D θ Figure 2-19: Pipe Bend Parameters Figure 2-20: Pipe Bend Loss Coefficient This model is only valid as long as no significant flow separations occur in the pipe. In the case of a distinct flow separation, it is recommended to place a flow restriction at that location and to specify appropriate flow coefficients. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-53 2.10.2. Variable Wall Temperature BOOST can also model variable pipe wall temperatures. This takes account of the effect of the heat transfer between the gas in the pipe and the heat transfer from the outer surface of the pipe to the surrounding ambient. The latter is modeled using convective heat transfer (heat transfer between a moving fluid and a solid surface). The rate of convective heat is given by Newton’s Law of Cooling written as: ) ( ∞ − = ′ ′ T T h q s q ′ ′ convective heat flux (W/m2) h local convective heat transfer coefficient T s surface temperature T ∝ fluid temperature The convection coefficient (average or local) is expressed in a non-dimensional form called the Nusselt Number, the expression for which is given below: f k L h Nu = k f thermal conductivity of the fluid L characteristic dimension (outer diameter of the pipe). There are two main classifications of convective heat transfer, forced convection and free convection. Forced convection occurs when the fluid flow is being driven over the surface by external means, such as a pump or a fan or atmospheric wind (non-zero characteristic velocity). Free convection occurs in buoyancy driven flows, i.e. temperature gradients in the fluid lead to density gradients causing a ‘free’ convective current to be established. Models for both types of convective heat transfer are available in BOOST and are described below. 2.10.2.1. Forced Convection For forced convection the non-dimensional convective heat transfer coefficient, the Nusselt number is given by the following: n m L C Nu Pr Re = Re is the Reynolds Number given µ ρVL = Re Pr is the Prandtl Number given by α ν = Pr . The other properties are as follows: ρ density of the fluid. µ dynamic viscosity of the fluid. α thermal diffusivity of the fluid. ν kinematic viscosity of the fluid and ν = µ/ρ L characteristic dimension of the model. For air, Pr = 0.7, under standard conditions. The values of C, m and n are functions of the geometry and the Reynolds number range. BOOST Version 4.0.4 User’s Guide 2-54 23-Jun-2004 2.10.2.2. Free Convection In free convection correlations, another non-dimensional parameter called the Grashoff number is used. The Grashoff number, Gr, is defined as: 2 3 ) ( ν β L T T g Gr s L ∞ − ≡ β volumetric thermal expansion coefficient of the fluid, a thermodynamic property. The volumetric thermal expansion coefficient brings in the effects of buoyancy in free convection flows; for an ideal gas, β = 1/T, where T is the absolute temperature of the gas. The Grashoff number plays the same role in free convection that the Reynolds number plays in forced convection in that it is the ratio of buoyancy forces to viscous forces on the fluid n m L CGr Nu Pr = 2.10.3. Forward / Backward Running Waves The flow conditions at each location in a pipe is the result of a superposition of forward and backward running waves. Shock capturing schemes, as used in BOOST, do not provide this information as they solve the set of partial differential equations directly. Therefore, this information must be constructed from the solution afterwards. Figure 2-21: Forward / Backward Running Waves An outline of the procedure is shown in the above figure. The reference state is determined as the time average of gas velocity and sound speed. At each instant those conditions are calculated, by which it is possible to come from the reference state to the instantaneous calculated state by two simple waves only. The two simple waves are the forward running wave or λ - characteristic, and the backward running wave or β - characteristic. The conditions between the reference state, the state behind the waves and the calculated states are linked by the compatibility equations along the respective characteristics. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-55 The path from the reference state to the state behind the forwards running wave (λ - characteristic) is along a β - characteristic. Thus, the following equation is valid. const c u = − + 1 2 κ Similarly the path from the state behind the forward running wave and the calculated state is along an λ - characteristic. The compatibility equation along an λ - characteristic is const c u = − − 1 2 κ The two equations are solved for the gas velocity and sound speed of the state behind the forward running wave. The pressure is calculated from the isentropic equation from the calculated state. The state behind the backward running wave is calculated analogously with the role of λ - and β - characteristics exchanged. 2.10.4. Perforated Pipe This element is specially suited for the refined modeling of, for example, silencing elements in an exhaust system. 2.10.4.1. Perforated Pipe contained in Pipe The model consists of two pipes of identical length who are connected via perforations along this length. Because of the pipes are the same length, the spatial discretization of the outer and inner pipes is the same, so that each individual inner pipe cell is connected to one cell of the outer pipe. Figure 2-22: Perforated Pipes contained in Pipe The calculation of the mass flow per unit of pipe length between these cells is based on the following formula: l t w T R p p p p p p T R p d m ∂ ∂ ⋅ | | . | \ | − ( ( ( ¸ ( ¸ | | . | \ | − | | . | \ | ⋅ − ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ = + 0 2 0 1 0 2 0 0 0 1 1 2 κ κ κ κ κ κ α π (2.10.8) BOOST Version 4.0.4 User’s Guide 2-56 23-Jun-2004 m mass flow through perforation per unit of pipe-length d pipe diameter α ratio of effective flow area to total (porosity*flowcoefficient) p static pressure downstream of the perforation holes 0 0 , T p stagnation pressure and temperature upstream of the perforation holes κ , R gas constant and ratio of specific heats l characteristic flow length (function of perforation hole diameter and wall thickness) t w ∂ ∂ acceleration of gas column through perforation holes 2.10.4.2. Perforated Pipe contained in Plenum Due to the nature of the plenum model (no spatial discretization and velocity state) all cells of contained perforated pipes are connected to the same single cell of the plenum. The flow through the perforations is calculated using the same formula (2.10.8) as for the perforated pipe in pipe. Figure 2-23: Two perforated Pipes contained in Plenum 2.11. Pipe Attachment (System or Internal Boundary) The flow at the end of a pipe is calculated from the pressure in the pipe, the ambient pressure and the effective flow area at the pipe end. The flow direction is determined from the calculated pressure if the pipe end was closed. If this pressure exceeds the ambient pressure, flow out of the pipe will result. If this pressure is lower than the ambient pressure, flow into the pipe will occur. Depending on the ratio between the static pressure downstream and the stagnation pressure upstream of the orifice, subsonic, sonic, or even supersonic flow may result. Zero mass flow may also be obtained at the pipe end, either as a result of zero effective flow area, or as a result of zero pressure difference. User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-57 Based on the quasi steady-state equation for orifice flow the flow conditions at the end of the pipe can be calculated: ( ( ( ¸ ( ¸ | | . | \ | − | | . | \ | ⋅ − ⋅ ⋅ ⋅ ⋅ = + κ κ κ κ κ α 1 0 2 0 0 0 1 2 p p p p T R p m (2.11.1) m specific mass flow rate α flow coefficient p static pressure downstream of the orifice 0 0 , T p stagnation pressure and temperature upstream of the orifice κ , R gas constant and ratio of specific heats If the actual pressure ratio is lower than the critical pressure ratio 1 0 1 2 − | . | \ | + = κ κ κ p p k , (2.11.2) k p critical pressure but supersonic flow is not feasible, the mass flow is dependent on the actual pressure ratio: 1 1 2 2 1 1 0 0 + ⋅ | . | \ | + ⋅ ⋅ ⋅ ⋅ = − κ κ κ α κ T R p m . (2.11.3) From the instantaneous mass flow rates at a system boundary, the orifice noise can be determined. By means of a Fourier analysis the amplitudes of the mass flow rates over frequency can be obtained. They are considered sources of the noise generation and allow the instantaneous sound pressure at a certain microphone position to be calculated using a directivity function. Ground reflections can also be considered by assuming an image source region [A1, A2, A3]. BOOST Version 4.0.4 User’s Guide 2-58 23-Jun-2004 2.12. Assembled Elements 2.12.1. Catalyst In the BOOST cycle simulation the catalyst is purely considered as flow element, where no chemical reaction behavior is calculated. The gas dynamics of a catalyst is modeled using the same model equations as given for the pipe flow (see Section 2.10). The model additionally takes into account that a honeycomb-type catalytic converter consists of a huge number of small and individual channels. These small channels are the reason for very small Reynolds numbers and therefore for a flow in the laminar regime. In this case the friction coefficient is evaluated applying the Hagen-Poisseuille law, whereas in the turbulent region (if reached at all) a turbulent friction coefficient used. The possibility of different channel shapes is taken into account by Fanning friction factors that are applied in both, the laminar and turbulent region. If the catalyst is simulated in the aftertreatment analysis mode, a simplified fluid mechanical approach (compared to the full Riemann Problem described in Section 2.10) is used. More detailed information about this approach can be found in the BOOST Aftertreatment Manual. 2.12.2. Particulate Filter The diesel particulate filter as a flow device is treated, similar to the catalytic converter, as an assembled element. It consists of a regular pipe, to which two plenums at each end are attached. The open cross-sectional areas of the individual channels are replaced by a pipe of an equivalent cross-sectional area. Thus, the flow through a particulate filter is represented by a flow through a pipe described in the section for pipe flows. The specification of the cellular filter structure is made similar to the catalytic converter model as described in Section 2.12.1. In a simplifying way the model of filter friction and pressure drop is also similar to the one of the catalytic converter. If the particulate filter is simulated in the aftertreatment analysis mode, a simplified fluid mechanical approach (compared to the full Riemann Problem described in Section 2.10) is used. More detailed information about this approach can be found in the BOOST Aftertreatment Manual. 2.13. Engine Control Unit and Wire In most modern engine concepts some functions of the engine are controlled by an electronic engine management system. It is necessary to model such a control device especially for the simulation of transients. Usually engine control units are state machines. This means that the same input to the unit produces different output depending on the state of the unit. The engine control model in BOOST features three states: • Steady state • Engine acceleration • Engine deceleration User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-59 The transition from steady state to the state of engine acceleration is triggered if the gradient of the load signal versus time exceeds a threshold specified by the user. The transition to engine deceleration is triggered the same way when the negative gradient of the load signal exceeds the user specified threshold. Maps up to two dimensions are used to link the output (Actuators) of the control unit to the input (Sensors). Figure 2-24 shows the principle of the calculation of an output value: Figure 2-24: Flow Chart of the ECU In the diagram x, y values = Sensor channels output value = Actuator channel A baseline steady state value is taken from the baseline map. This value may be subjected to corrections by adding values from correction maps or by multiplying it by factors from correction maps. In the case of acceleration or deceleration, other corrections may be applied to the steady state value. Then it is checked whether the output is within predefined bounds which themselves may be defined as maps. Either the load signal or a desired engine speed can be selected as the guiding input signal of the control. For the full range of input (Sensor-Channels) and output (Actuator-Channels) please refer to the table in Chapter 9.3. BOOST Version 4.0.4 User’s Guide 2-60 23-Jun-2004 2.14. Gas Properties The gas properties like the gas constant or the heat capacities of a gas depend on temperature, pressure and gas composition. BOOST calculates the gas properties in each cell at each time step with the instantaneous composition. Thus BOOST can simulate exhaust gas recirculation without the need for a special treatment. For the calculation of the gas properties of exhaust gases the air fuel ratio is used as a measure for the gas composition. Air fuel ratio in this context means the air fuel ratio at which the combustion took place from which the exhaust gases under consideration originate. The composition of the combustion gases is obtained from the chemical equilibrium considering dissociation at the high temperatures in the cylinder. For engines with internal mixture preparation the average air fuel ratio of the gas is used for the calculation of the gas properties. Pure air is considered as a gas with infinite air fuel ratio. If air and exhaust gases mix the average (higher) air fuel ratio is determined. This approach is valid as long as the excess air ratio of the exhaust gases is higher than approximately 1.1. For engines with external mixture preparation, typically operated with rich mixtures at full load, combustion gases and air must be kept apart. Therefore conservation equations for combustion products (together with the air fuel ratio characteristic for them) and fuel vapor are solved. The mass fraction of air is calculated from CP FV air µ µ µ − − =1 (2.14.1) air µ mass fraction of air FV µ mass fraction of fuel vapor CP µ mass fraction of combustion products The air fuel ratio characteristic for the combustion products is calculated from FB FB CP CP AF µ µ µ − = (2.14.2) CP AF air fuel ratio of combustion products FB µ mass fraction of burned fuel User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-61 Figure 2-25 shows the relations of the mass fractions to each other. Figure 2-25: Considered Mass Fractions 2.15. Definition of Global Engine Data (SI-Units) Note: Some definitions have been refined since Version 3.3. Average (mean) values over the cycle duration CD: ( ) α α d y CD y CD ⋅ ⋅ = ∫ 1 ( ) α y variable depending on α α crank angle y average value of y CD cycle duration Mass flow weighted temperature: ( ) ( ) ( ) α α α α α d m d m T T CD CD MS ⋅ ⋅ ⋅ = ∫ ∫ MS T mass flow weighted temperature ( ) α T temperature depending on α ( ) α m mass flow rate depending on α BOOST Version 4.0.4 User’s Guide 2-62 23-Jun-2004 2.15.1. Cylinder Data Compression ratio: C D C V V V + = ε D C V V + maximum cylinder volume C V minimum cylinder volume (combustion chamber volume) D V displacement Note: The same definition is used for two and four stroke engines. Indicated mean effective pressure: dV p V IMEP CD c D ⋅ ⋅ = ∫ 1 c p cylinder pressure V cylinder displacement Indicated torque: π cycle D k V IMEP IT ⋅ = IT indicated torque cycle k cycle parameter: 2 for two-stroke engines 4 for four-stroke engines Number of cycles per second: n n cycle = for two-stroke engines 2 n n cycle = for four-stroke engines n crankshaft-revolutions per second Indicated specific torque: D s V IT IT = User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-63 Indicated power: cycle D i n V IMEP P ⋅ ⋅ = Indicated specific power: D i is V P P = Inj. Fuelmass: FV inj m , total mass of fuel directly injected Asp. Fuelmass: FV inj FV c FV astr m m m , , , − = FV astr m , mass of fuel aspirated trapped Fuelmass (tot.): FV c m , total mass of fuel trapped in the cylinder Trapping Efficiency Fuel: FV t FV c F tr m m , , , = η FV t m , total mass of fuel added Indicated fuel consumption (trapped fuel mass): i cycle FV c tr P n m ISFC ⋅ = , Indicated fuel consumption (total fuel mass): i cycle FV t tt P n m ISFC ⋅ = , BOOST Version 4.0.4 User’s Guide 2-64 23-Jun-2004 Friction mean effective pressure: cycle D fr n V P FMEP ⋅ = fr P friction power Note: FMEP does not contain the Work caused by Scavenging Pumps, Crankcase Scavenging or mechanically driven Supercharging Devices Scavenging mean effective pressure (individual cylinder): cycle D S n V P SMEP ⋅ = S P required power of related Scavenging Pump or Crankcase Scavenging Auxiliary Drives mean effective pressure (overall engine): cycle DE MC CS SP n V P P P AMEP ⋅ + + = CS P required power of Scavenging Pumps CS P required power of Crankcase Scavenging CS P required power of mechanically driven Supercharging Devices DE V Engine Displacement Brake mean effective pressure (individual cylinder): SMEP FMEP IMEP BMEP C − − = Brake mean effective pressure (overall engine): AMEP FMEP IMEP BMEP E − − = Mechanical efficiency: IMEP FMEP FMEP BMEP BMEP IMEP BMEP m − = + = = 1 η User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-65 Brake specific fuel consumption: m ISFC BSFC η = Indicated efficiency: u FV c CD c T H m dV p ⋅ ⋅ = ∫ , η u H lower heating value 2.15.2. Gas Exchange Related Data IMEP exhaust stroke (only four-stroke): ∫ = ⋅ ⋅ = 360 180 1 α dV p V IMEP c D ex IMEP intake stroke (only four-stroke): ∫ = ⋅ ⋅ = 540 360 1 α dV p V IMEP c D in IMEP gas exchange (= pumping mean effective pressure PMEP; only four- stroke): ∫ = ⋅ ⋅ = 540 180 1 α dV p V PMEP c D Air fuel ratio of Combustion: FV c t A c Cmb m m AF , , = t A c m , total mass of air in the cylinder BOOST Version 4.0.4 User’s Guide 2-66 23-Jun-2004 Excess air ratio: Stc Cmb AF AF = λ λ Excess air coefficient Stc AF Stoichiometric A/F-ratio Total mass at Start of High Pressure Cycle (SHP, all ports closed): SHP c m , total in-cylinder mass at SHP Airmass at SHP: t A c m , total mass of air in the cylinder at SHP Airpurity: SHP c t A c m m AP , , = Residual gas content: SHP c CP c m m RG , , = CP c m , mass of combustion products in the cylinder at SHP Note: Recirculated exhaust gas is added to the residuals. Air delivered: A as m , mass of air aspirated Air delivery ratio related to ambient conditions: a DR A as cycle D a A as a D m m n V m , , , , = ⋅ ⋅ = ρ λ A as m , mass flow of air aspirated a DR m , reference mass (ambient conditions) a ρ ambient air density User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-67 Air delivery ratio related to intake manifold conditions: m DR A as cycle D m A as m D m m n V m , , , , = ⋅ ⋅ = ρ λ m DR m , reference mass (manifold conditions) m ρ air density in the intake manifold (specified measuring point or plenum) Mass delivered: as m mass of fresh charge aspirated Airmass trapped: A tr m , mass of air trapped Trapping efficiency air: A as A tr tr m m , , = η Volumetric efficiency related to ambient conditions: a DR A tr cycle D a A tr a V m m n V m , , , , = ⋅ ⋅ = ρ η A tr m , mass flow of air trapped Volumetric efficiency related to intake manifold conditions: m DR A tr cycle D m A tr m V m m n V m , , , , = ⋅ ⋅ = ρ η Scavenge ratio: ( ) SR as cycle C D ref as m m n V V m SR = ⋅ + ⋅ = ρ as m aspirated mass flow SR m reference mass for scavenge ratio BOOST Version 4.0.4 User’s Guide 2-68 23-Jun-2004 Scavenge Loss: as sl as sl m m m m SL = = sl m mass flow lost during scavenging sl m mass lost during scavenging Scavenging efficiency: C tr SC m m = η tr m total mass trapped C m total mass of cylinder content Mean wall heat transfer coefficient in the cylinder ( M. Eff. HTC ): ( ) ∫ ⋅ ⋅ = CD w w d h CD h α α 1 ( ) α w h wall heat transfer coefficient depending on crank angle w h mean wall heat transfer coefficient Effective mean gas temperature for wall heat transfer in the cylinder (M. Eff. Temp.): ( ) ( ) α α α d h T h CD T CD G w eff g ⋅ ⋅ ⋅ ⋅ = ∫ 1 , G T gas temperature Air fuel ratio ( Reference value at EO ): EVO FB c EVO FB c EVO CP c EO m m m AF , , , , , , − = EVO CP c m , , mass of combustion products in the cylinder at Exhaust Valve Opening EVO FB c m , , mass of burned fuel in the cylinder at EVO Note: Gas Exchange data is defined in accordance with SAE standard J604 [G8]. The relation between the different data characterizing the gas exchange can be seen in the following figure: User’s Guide BOOST Version 4.0.4 23-Jun-2004 2-69 m SR reference mass for scavenge ratio m DR reference mass for delivery ratio m as mass of fresh charge aspirated m as, A mass of air aspirated m as, CP mass of combustion products aspirated (= m as, CPst for IMP) m tr mass of fresh charge trapped m sl mass lost during scavenging m tr,CP mass of combustion products trapped (= m tr, CPst for IMP) m tr, CPA mass of air included in trapped combustion products (= 0 for IMP) m tr, A mass of air trapped m tr,FV mass of fuel trapped (= 0 IMP) m inj,FV total mass of fuel directly injected m inj,ge,FV mass of fuel injected during gas exchange m inj,tr,FV mass of injected fuel trapped during gas exchange (= 0 for IMP) m inj,sl,FV mass of injected fuel lost during gas exchange (= 0 for IMP) m rg,CP mass of residual gas m rg, CPA mass of air included in residual gas m c total in-cylinder mass m c,A mass of air in the cylinder (= m c, At for IMP) m c,At total mass of air in the cylinder m c,CP mass of combustion products in the cylinder at SHP (=m c,CPst for IMP) m c,CPA mass of air included in combustion products,cylinder (= 0 for IMP) m c,CPst mass of stoichiometric combustion products, cylinder m c,FV total mass of fuel trapped in the cylinder (= m inj,FV for IMP) m SR m sl m DR m tr,CP m as m tr,CPA m tr m tr,A m tr,FV SHP m inj,ge,FV m inj,FV m inj,tr,FV m inj,sl,FV m c , F V m c , A t m c , C P A m c , C P s t m c m r g , C P m r g , C P A m c , A m c , C P Figure 2-26: Relation of Gas Exchange Data BOOST Version 4.0.4 User’s Guide 2-70 23-Jun-2004 2.16. Abbreviations The following abbreviations are used in this manual: µσ Flow coefficients of the ports BDC Bottom dead center BMEP Brake mean effective pressure BSFC Brake specific fuel consumption CRA Crank angle DPF Diesel Particulate Filter EVC Exhaust valve closing EVO Exhaust valve opening FIE Fuel injection equipment FMEP Friction mean effective pressure IMEP Indicated mean effective pressure ISFC Indicated specific fuel consumption IVC Intake valve closing IVO Intake valve opening PFP Peak firing pressure PMEP Pumping mean effective pressure TDC Top dead center VGT Variable geometry turbine VNT Variable nozzle turbine User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-1 3. GRAPHICAL USER INTERFACE Based on the AVL Workspace Graphical User Interface (AWS GUI), the pre-processing tool assists the user in creating an engine model for a BOOST simulation. For the general handling of the AWS GUI please refer to the AVL Workspace Graphical User Interface Manual. The BOOST specific operations are described as follows: 3.1. BOOST Specific Operations BOOST Menu Bar Icon Bar Element/Model Working Area Button Bar Tree Area Figure 3-1: BOOST - Main Window BOOST Version 4.0.4 User’s Guide 3-2 23-Jun-2004 3.1.1. Menu Bar Element Parameters Displays the parameters for the selected element. Parameters can be added or deleted. Alternatively click on an element with the right mouse button and select Parameters from the submenu. Refer to Section 3.5.1 or the AWS GUI Manual, Section 2.4 for further information. Properties Displays the dialog box for defining the values for the selected element. Alternatively click on an element with the right mouse button and select Properties from the submenu. Copy Data First select the source element type in the working area or model tree, then data can be copied from the selected source element to the selected target(s). Model Parameters Defines values for the model. Refer to Section 3.5.1 or the AWS GUI Manual, Section 2.4 for further information. Case Explorer Displays the case explorer for the current model. Simluation Run Displays the run dialog box. This displays both the cases for the current model and the tasks to be performed. The calculation can be started from this point. Status Displays the simulation status dialog box. Control Defines parameters used to control the simulation and define the global values used in the simulation. Refer to Section 3.2 for further information. Volumetric Efficiency Displays and sets the reference element to be used for volumetric efficiency calculations. This can be either a measuring point or a plenum. Refer to Section 3.2.8 for further information. Create Series Results Prepares the procedure for the Case Series results. Refer to Section 3.5 for further information. Create Animation Results Prepares the Animation for PP3. Refer to Section 5.6 for further information. Show Summary Cycle Simulation Aftertreatment Opens the ASCII browser and displays the summary values from either the cycle simulation or aftertreatment analysis. Show Results Opens the IMPRESS Chart post-processor which can be used to examine and plot the simulation results. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-3 Show Messages Cycle Simulation Aftertreatment Opens the Message browser and displays the messages generated by the solver during the cycle simulation or aftertreatment analysis. Show Elements Cycle Simulation Opens a browser to display more detailed information on compound perforated elements. Show Animation Opens the PP3 post-processor. Import Results Prepares results of a BOOSTFILENAME.bst file run outside the graphical user interface. View Logfile Displays the screen output of the calculation kernel during the simulation or model creation. Optimization Refer to the Optimization of Multi-body System using AVL Workspace and iSIGHT manual. Options Job Submission Parallel processing (currently not available). Lock Properties Locks Property dialogs (currently not available). Frame Set of graphical elements used for page layout, e.g. rectangle (frame), logo and text elements. None: Removes the frame from the page. AVL Report: The standard AVL frame. Frame Definitions Customized settings of the current frame. Specify text and the customer logo for the frame. Units Used to display and set the units used. Refer to the AWS GUI Manual, Section 2.4.2. Utilities BURN Tool for Combustion Analysis. Refer to Section 3.7.1 for further information. Search Displays tables of the input data used in the model. These can be saved in HTML format. Refer to Section 3.7.2 for further information. License Manager Controls availability and usage of licenses. Refer to Section 3.7.3 for further information. Pack Model Creates a compressed tape archive of all relevant model information. Refer to Section 3.7.4 for further information. Help Contents Opens the HTML help system. Search Searches the HTML help system for information. About Displays version information. BOOST Version 4.0.4 User’s Guide 3-4 23-Jun-2004 3.1.2. BOOST Buttons If selected the mouse can be used to connect a pipe between two elements. Refer to Section 3.4.1 for further information. If selected the mouse can be used to connect a wire between two elements. Refer to Section 3.4.10.1 for further information. If selected the mouse can be used to insert a perforated pipe into a plenum. Refer to Section 3.4.6.1 for further information. If selected the mouse can be used to connect aftertreatment boundaries to aftertreatment elements (catalyst, dpf) for running simulations in analysis mode. Refer to the Aftertreatment Manual. Reverses the positive flow direction of the selected pipe. Refer to the AWS GUI Manual, Section 2.2. Changes the attachments of a selected pipe or a wire. Refer to the AWS GUI Manual, Section 2.2. Rotates the selected object counter-clockwise (90 degrees steps) Rotates the selected object clockwise (90 degrees steps) Opens the input window for general simulation control (globals) data, equivalent to Simulation|Control. Runs the Simulation, equivalent to Simulation|Run. Search Tool – Refer to Section 3.7.2 for further information. 3.1.3. Elements Tree Cylinder Engine cylinder element. Refer to Section 3.4.2 for further information. Measuring Point Access to flow data and gas conditions over crank angle at a certain location in a pipe. Refer to Section 3.4.3 for further information. Boundaries System Boundary Provides the connection of the calculation model to a user-definable ambient. Refer to Section 3.4.4.1 for further information. Aftertreatment Boundary Provides the connection of the aftertreatment analysis model to a user- definable ambient. Internal Boundary Allows boundary conditions for the calculation model to be specified directly in the last cross section of a pipe where a model ends. Refer to Section 3.4.4.3 for further information. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-5 Transfer Restriction Considers a distinct pressure loss at a certain location in the piping system. Refer to Section 3.4.5 for further information. Rotary Valve Controls the air flow in a pipe as a function of crank angle or time. Refer to Section 3.4.5.2 for further information. Check Valve A pressure actuated valve used to prevent reverse flow. Refer to Section 3.4.5.3 for further information. Injector Used for engines with external mixture preparation to add the fuel to the air in the intake system. Refer to Section 3.4.5.4 for further information. Junction Used to connect three or more pipes. In the case of three pipes, a refined junction model may be used. This considers geometric information such as the area ratio of the connected pipes and the angles between the pipes. In other cases a simple constant pressure model is available. Refer to Section 3.4.5.5 for further information. Volumes Plenum An element in which spatial pressure and temperature differences are not considered. Refer to Section for 3.4.6.1 further information. Variable Plenum Considers the change of the volume and surface area of the plenum over time. Refer to Section 3.4.6.2 for further information. Perforated Pipe in Pipe Single element representing two pipes. An inner perforated pipe and an outer pipe. Refer to Section 3.4.6.3 for further information. Assembled Air Cleaner The instantaneous pressure loss is determined from the pressure loss specified in a reference point at steady state conditions. Refer to Section 3.4.7.1 for further information. BOOST Version 4.0.4 User’s Guide 3-6 23-Jun-2004 Catalyst The pressure loss in the catalyst must be defined for a reference mass flow. Its characteristics are determined from this input and additional geometrical information. It is important to note that chemical reactions in the catalyst are not considered by the cycle simulation model. Refer to Section 3.4.7.2 for further information. Using the aftertreatment analysis mode, chemical reactions can be simulated. Refer to the Aftertreatment Manual. Cooler The treatment of the Air Cooler is similar to the Air Cleaner. The pressure loss, cooling performance and the corresponding steady state mass flow must be defined as reference values. Refer to Section 3.4.7.3 for further information. Diesel Particulate Filter Pressure drop, loading, regeneration of particulate filters can be simulated using the aftertreatment analysis mode. Refer to the Aftertreatment Manual. Charging Turbocharger Turbocharger element. Both simple and full models are available. Refer to Section 3.4.8.1 for further information. Positive Displacement Compressor Either a constant mass flow and a constant compressor efficiency, an iso-speed line or a full map may be specified. The iso-speed line of the positive displacement compressor is defined by mass flow and efficiency versus the pressure ratio across the compressor. Refer to Section 3.4.8.2 for further information. Turbo Compressor Either a constant pressure ratio and a constant compressor efficiency, an iso- speed line or a full map may be specified. If an iso-speed line or a compressor map is defined, the pressure ratio and the efficiency are determined according to the instantaneous mass flow rate and the actual compressor speed. Refer to Section 3.4.8.3 for further information. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-7 Waste Gate A valve actuated by the pressure difference on the valve body plus the pressure difference on a diaphragm mechanically linked to the valve body. Refer to Section 3.4.8.4 for further information. External Fire Link Simulation of three dimensional (3D) flow patterns. Refer to Section 3.4.9.1 for further information. User Defined Element Allows the user to implement algorithms. For maximum support, the UDE handles the data of the pipe attachments. Empty subroutines are shipped with the BOOST installation as a guide for the User to incorporate into his model. Furthermore results obtained from the UDE may be analysed in the post-processor. Refer to Section 3.4.9.2 for further information. Control Engine Control Unit Models all the important functions of an electronic engine control. The output of the ECU, such as ignition timing, start of injection or the setting of a control valve is calculated from maps dependent on specified input parameters. Possible input parameters are engine speed or ambient conditions and data from measuring points and plenums. The parameters specified in the baseline maps may be modified by a number of corrections for ambient conditions, acceleration or deceleration of the engine. Refer to Section 3.4.10.2 for further information. MATLAB DLL The Dynamic Link Library element can be used to include control algorithms or complete engine control models created with a commercial control algorithm design software (e.g. MATLAB/SIMULINK). Information channels are passed between elements and this junction using wires. The information channels include both sensor and actuator channels. The DLL may be written in any programming language provided the compiler supports mixed language programming. This junction is also used to link with the MATLAB s- function. Refer to Chapter 4 for further information. BOOST Version 4.0.4 User’s Guide 3-8 23-Jun-2004 MATLAB API Passes information to and from MATLAB. Information channels are passed between elements and this junction using wires. The information channels include both sensor and actuator channels. Refer to Section 3.4.10.3 for further information. Acoustic Microphone A microphone element can be added to any BOOST model in order to extract acoustic data such as overall dB(A) levels or order plots. The microphone is not attached to any pipes but linked in the input for the microphone to one or more system boundaries. Refer to Section 3.4.11.1 for further information. 3.1.4. Model Tree A list of elements and connections used in the model is displayed. Click on the required item with the left mouse button, then click the right mouse button and select the required option from the following submenu. Figure 3-2: Model Submenu Properties opens the selected element's properties window as shown in Figure 3-3. Parameters opens the selected element's parameters window as shown in Figure 3-72. Group Elements links all selected elements together. Sort Elements by Id organizes elements according to their Id. Sort Elements by Name organizes elements according to their name. Expand or expands the model tree. Collapse or closes the tree. Data can be copied from a selected element type in the model tree or working area by selecting Element|Copy Data. A window opens where the source element can be selected and copied to the target element. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-9 3.1.5. Data Input Window Double click the required element in the Element tree to display it in the working area. Select the displayed element with the right mouse button and select Properties from the submenu to open the relevant data input window. The following window relates to the general data of the pipe. Figure 3-3: Data Input Window Data input windows are available for sub-groups displayed in the tree shown in the above figure by clicking on the required sub-group with the left mouse button. New or existing parameters can be inserted in the input fields by clicking on the label to the left of the field with the right mouse button and selecting the required option from the submenu. Refer to section 3.5.1 for further information. While inputting data, the following options are available: Apply: The specified data is saved when the error check is valid. The sub-group icon turns green. Accept: The specified data is saved but no error check is executed and/or insufficient data is accepted by the user after a warning dialog. The sub- group icon turns yellow. Reset: Returns to the previous applied settings. Revert: Returns to the default settings. Help: Online help is available. OK: Confirms data input completion and exits the element. Cancel: Modified data input is not saved. This also exits the element. BOOST Version 4.0.4 User’s Guide 3-10 23-Jun-2004 If all required data for the element is applied and/or accepted, the red exclamation point disappears, indicating that the input process for that element is completed. If any input data is missing after selecting apply or accept, a window appears with a list of the missing data and a red exclamation point is displayed on the element. However, the user should be aware that incomplete or incorrect data usually renders a calculation of the data set impossible. After confirming the element input data, the calculation model must be stored in a file with the extension .BWF by selecting File Save as. 3.1.5.1. Sub-group Icons The Sub-group icons inform the user as to their status as follows: Green Sub-group Icon: Valid data has been specified. White Sub-group Icon: Data has not yet been specified. Grey Sub-group Icon: Disabled. Red Sub-group Icon: Insufficient data. Yellow Sub-group Icon: Insufficient data has been accepted by the user. Select a Sub-group icon with the right mouse button to open the following submenu. Figure 3-4: Element Sub-group Submenu Expand or displays all available items in a folder. Collapse or closes a folder. Show All displays the complete list of items in the tree. Show Enabled Only displays the available green and white sub-group icons. Show Invalid Only displays the gray sub-group icons. 3.1.6. Table Window Depending on the selected sub-group, the user can enter a constant value or a list of values where the Table icon is displayed. The Table window represents a standard window used throughout the program to specify values dependent on a certain parameter. As shown in Figure 3-5, select the Table icon and select Table from the submenu. Then select the Table button which appears on the input field to open the following window. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-11 Figure 3-5: Table Window Select Insert Row to add a line and enter the relevant values. Select Remove Row to delete a selected line. New or existing parameters can be inserted in the table by clicking on the active field with the right mouse button and selecting the required option from the submenu. Refer to section 3.5.1 for further information. Large data arrays can be read from an external file by selecting Load. If the data has been specified in the pre-processor, it may be saved in an external file by selecting Store. These files have the default extension .dat. It is ASCII format with one pair of data in each record. The values are separated by one or more blanks. No heading lines are allowed. If data is defined versus time, the total time interval for which the values are specified may be less than, equal to or greater than the cycle duration. If the time interval is shorter than the specified maximum calculation period, BOOST treats the specified function as a periodic function. Note: A data point at 0 degrees and 360 degrees or 720 degrees is needed to obtain a period of 360 or 720 degrees for the specified function. 0 degree crank angle corresponds to the Firing Top Dead Center (TDC) of cylinder 1 (or the selected cylinder at the cylinder input). The data entered in the table is plotted in the graph as shown in Figure 3-5. The axes and legend of the graph can be manipulated as desired. Click with the left mouse button, then click the right mouse button and select the required option from the following context menu. BOOST Version 4.0.4 User’s Guide 3-12 23-Jun-2004 Figure 3-6: Graph Context Menu 3.2. General Input Data Since the general input data is used to control the input process for each element, BOOST requires the specification of the general input data prior to the input of any element. The Global input data must be defined first. Select Simulation Control to open the following window. This data is used to prepare the input process for each element. 3.2.1. Simulation Tasks Figure 3-7: Simulation Control – Simulation Tasks Window User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-13 3.2.1.1. Date, Project ID and Run ID The date is when the BOOST data set was last changed. It is automatically inserted by the pre-processor. Project-ID and Run-ID are comment lines which may be specified to identify the calculation. Both may have a length of up to 50 characters. 3.2.1.2. Simulation Tasks Depending on the new tasks before starting with the model at least one of the following should be selected: Cycle Simulation: Gas exchange and combustion BOOST calculation Aftertreatment Analysis: Simulation of chemical and physical processes for aftertreatment devices Linear Acoustics: Frequency domain solver to predict the acoustic performance of components 3.2.2. General Control Select General Control to open the following window: Figure 3-8: Simulation Control – Globals Window BOOST Version 4.0.4 User’s Guide 3-14 23-Jun-2004 3.2.2.1. Engine Speed The engine speed is the revolution speed of the crankshaft. For steady state simulations, it is kept constant. For transient simulations it is the starting value and is kept constant for the first three cycles to dampen excessive gas dynamics due to the initialization. Afterwards, the instantaneous engine speed is calculated from solving the moment of momentum equation applied to the crankshaft at each time step. 3.2.2.2. Steady State / Transient Simulation Steady state simulations are default. BOOST can also simulate engine and vehicle acceleration or deceleration processes by selecting Transient Calculation. Additional input must be defined for Engine Only or Driver sub-groups as described below. The relevant inertia data must also be defined. 3.2.2.2.1. Engine Only Transient Calculation In the Globals window, select Engine Only for the Transient Calculation. The inertia input field is activated. Input the average inertia of the cranktrain plus all auxiliary drives and the inertia of the load reduced to engine speed. The inertia and the coefficients may depend on time or crank angle, therefore input the values in the Table . For converting the mass of a vehicle to a rotational inertia related to engine speed, the following formula may be used: 2 2 i r m I T V ⋅ = (3.2.1) I rotational inertia of the vehicle T r (dynamic) tire radius i total gear ratio between engine and drive wheels, given: w e n n i = (3.2.2) e n engine speed w n wheel speed User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-15 The following input fields are also activated when the Engine Only sub-group is selected in the tree. Figure 3-9: Load Characteristic for Engine Only The load torque is calculated from the formula: 2 s s s dn cn b n a M + + + = (3.2.3) M load torque d c b a , , , coefficients Coefficients a, b, c and d should be selected in such a way that for example, the road load is approximated in the speed range of interest. It should be noted that the torque, like the inertia, is related to engine speed. Thus the load torque can be calculated from: i r D M T ⋅ = (3.2.4) D drag and rolling resistance of the vehicle 3.2.2.2.2. Driver Transient Calculation The Driver transient calculation allows the user to simulate the dynamic behavior of the two-body system vehicle and engine which can be decoupled by a gear shift. The ECU (Section 3.4.10), which has to be present when executing the driver model, tries to follow a specified speed course by calculating the load signal depending on the deviation of the actual vehicle speed from the desired one. Select Desired Engine Speed for the ECU guiding input (the value or table of the Desired Engine Speed is not taken into account). BOOST Version 4.0.4 User’s Guide 3-16 23-Jun-2004 The following combustion models are available for the Driver Transient Calculation: • Single Vibe function • Double Vibe function • Single Zone Table • Woschni/Anisits • Hires et al. • Constant Volume Combustion • Constant Pressure Combustion • Motored In the Globals window, select Driver for the Transient Calculation. The inertia input field is activated. Input the inertia of the engine plus all auxiliary drives (not including mechanically driven supercharging devices, inertia of drivetrain and inertia of vehicle). Input can be a constant value or a Table of time or crank angle dependent values. The crank angle dependent inertia caused by the translatory moved masses of a standard crank train (no piston pin offset considered) can be calculated from: | | | | | . | \ | − | . | \ | + = ) ( sin 2 2 ) 2 sin( ) sin( 4 2 2 2 α α α s l s m I t (3.2.5) t I inertia of translatory moved masses [kgm 2 ] m translatory moved masses [kg] s stroke [m] l con-rod length [m] User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-17 The following input fields are also activated when the Driver sub-group is selected in the tree. Figure 3-10: Driver Input Window 1. Clutch The transferred torque of the implemented model of the clutch has the following states: a. The clutch does not slip (transferred torque is smaller than the maximum transferable torque) b. The clutch slips (transferred torque is equal to the maximum transferable torque) The maximum transferable torque is given by the formula cc cm tm p t t = (3.2.6) tm t maximum transferable torque [Nm] cm t maximum clutch torque [Nm] cc p clutch-control position [ 1] Specify the maximum clutch torque cm t [Nm]. BOOST Version 4.0.4 User’s Guide 3-18 23-Jun-2004 2. Driver During the Shifting process the load signal and clutch-control position are determined according to the following figure. The input parameters for the shifting process are: Shifting Time: Period of shifting process s t [s] Clutch Pedal On: End of decoupling period s d t t [1] Acceleration Pedal Off: End of the load-signal decreasing period s ld t t [1] Acceleration Pedal On: Start of the load-signal increasing period s lc t t [1] Clutch Pedal Off: Start of coupling period s c t t [1] Figure 3-11: Shifting Process User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-19 ls Load signal [1] 0 ls Load signal at start of shifting process [1] cc p Clutch-control position [1] s t Period of shifting process [s] s d t t End of decoupling period [1] s c t t Start of coupling period [1] s ld t t End of the load signal decreasing period [1] s lc t t Start of the load signal increasing period [1] 3. Gear Shifting Minimum Engine Speed: A gear shift downwards is initiated if the engine speed falls below the minimum engine speed [rpm]. Maximum Engine Speed: A gear shift upwards appears by exceeding the maximum engine speed [rpm]. 4. Vehicle Velocity Based on the deviation of the actual vehicle speed from the specified value(s), the ECU calculates the load signal according to the formula ( ) ( ) ( ) ∫ − + − + − = t des des des n n d n n i n n p ls 0 dt d dt ls load signal [1] p proportional control gain [1/rpm] i integral control gain [1/rpms] d differential control gain [s/rpm] des n desired vehicle speed reduced to crank shaft speed[rpm] n engine speed [rpm] The desired vehicle speed is interpolated from a specified constant value or a Table of time dependent values. 5. Gearbox To initialize the gearbox, input the gear step which will calculate the vehicle speed at the start of the calculation (the corresponding engine speed is specified in Simulation|Control|Globals). BOOST Version 4.0.4 User’s Guide 3-20 23-Jun-2004 Input a table of corresponding gear ratios in ascending order [1]. Definition of the total gear ratio: w e n n i = (3.2.7) i gear ratio [1] e n engine speed [rpm] w n driving wheel speed [rpm] Vehicle Characteristics When Driver is selected for the Transient Calculation, the following input fields of the Vehicle sub-group are activated. Figure 3-12: Vehicle Input Window Specify Inertia of Drivetrain, Vehicle Mass and Rolling Radius. The vehicle load is calculated from the formula: 2 v d v c b v a F + + + = (3.2.8) F vehicle load [N] v vehicle speed d c b a , , , vehicle load coefficients ( in general determined by : b ... rolling resistance, uphill gradient; c ... friction caused by laminar flow; d ... air resistance ) Input a constant value for Coefficient a or a Table of time dependent values. Coefficients b, c, d are treated analogous. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-21 3.2.2.3. Calculation Modes Two calculation modes are available: • Single calculation: Calculation of a single operating point of one engine configuration; full output is available for a detailed analysis of the flow in the engine. • Animation: Special output for the animated display of the results with the BOOST post-processor is provided for last calculated cycle. 3.2.2.4. Identical Cylinders BOOST features individual cylinders which means that each cylinder can have its own specifications. If this feature is not required, it is recommended to select identical cylinders in order to simplify the input process. In this case, only the specifications for cylinder 1, the firing order and the firing intervals must be specified. Provided that the cylinders feature identical data, the ROHR transfer option to other cylinders may be activated. In this case, the Quasi-dimensional combustion model is only applied to Cylinder 1 to calculate the rate of heat release curve. The obtained curve is transferred to the remaining cylinders. For these cylinders, the high pressure cycle will be simulated with a single zone model. This also applies to the Hiroysau and AVL MCC combustion models. 3.2.2.5. User-Defined Concentrations BOOST calculates the distribution of an arbitrary number of tracer gases (gases which do not influence engine performance). The required number of tracer gases is specified by the number of user-defined concentrations. 3.2.2.6. Mixture Preparation Two types of mixture preparation are available: • Internal: The fuel is added to the cylinder during the high pressure cycle. • External: The fuel is fed to the intake system by a carburetor or a fuel injector or is aspirated together with the air from the ambient. DGI engines have to be defined as External. 3.2.2.7. Fuel Data BOOST provides accurate gas properties for the following fuels: • Gasoline • Diesel • Methane • Methanol • Ethanol • Hydrogen • Butane • Pentane • Propane BOOST Version 4.0.4 User’s Guide 3-22 23-Jun-2004 For each fuel, default values for the lower heating value and for the stoichiometric air/fuel ratio are also available. If more accurate data is available, the default values may be overwritten. 3.2.2.8. Reference Conditions The reference conditions (pressure and temperature) are required in order to calculate specific engine performance data such as delivery ratio, volumetric efficiency etc. related to ambient conditions. It is the user's responsibility to ensure that these conditions match the conditions at the system boundary from which the engine aspirates its air. Otherwise, the results might be misleading. 3.2.2.9. Gas Properties In general, BOOST uses variable gas properties, which means that at any location in the system the gas properties are determined from the actual gas composition, actual pressure and actual temperature. If there is no cylinder in the calculation model, constant gas properties may be used in order to simplify the calculation. For the calculation of constant gas properties used through out the model, reference conditions and a reference gas composition must be defined. Select Constant Gas Properties and then select the Gas Properties sub-group in the tree to open the following window. Figure 3-13: Simulation Control – Constant Gas Properties Window User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-23 3.2.3. Time Step Control Select the Time Step Control sub-group in the tree to open the following window. Figure 3-14: Simulation Control – Time Step Control Window 1. Cycle Select 2-Stroke or 4-Stroke. 2. Maximum Calculation Period The maximum calculation period sets the crank angle interval after which the simulation stops and the results will be written to the .bst file. For steady state simulations it must be sufficiently long in order to achieve stable calculation results. It is recommended to use a multiple of the cycle duration. The required calculation period until stable conditions are achieved depends upon the engine configuration. With an increasing number of cylinders, the calculation period may become shorter. 4-stroke engines need shorter calculation periods than 2-stroke engines. For turbocharged (TC) engines, especially if the BOOST pressure is calculated from the turbine size, significantly longer calculation periods are required than for naturally aspirated (NA) engines. For an initial estimate, the following data may be used: • Single cylinder NA 4-stroke engine: 7200 degrees CRA • Multi cylinder NA 4-stroke engine: 4320 degrees CRA • Multi cylinder TC 4-stroke engine: 14400 degrees CRA • Single cylinder 2-stroke engine: 7200 degrees CRA • Multi cylinder 2-stroke engine: 4320 degrees CRA BOOST Version 4.0.4 User’s Guide 3-24 23-Jun-2004 It is recommended to check whether stable conditions have been achieved using the transient analysis feature of the BOOST post-processor. 3. Pipes BOOST allows the user to specify either the calculation time step in degree crankangles or a target cell size in mm. From the stability criterion for the pipe flow, (refer to Chapter 2.11) and from the input time step or target cell size, BOOST will calculate the required cell size or the required time step respectively. The time step for the calculation determines the accuracy (especially the frequency resolution) of the calculation result. However, the number of cells in the pipe system increases dramatically with decreasing time step, which increases the required CPU time. To avoid unnecessary large output files, a separate time step for saving the results (time step for traces and animation output) must be specified. Note: CFL Multiplier is for advanced users and is currently under development. 4. Restart and Time Reset Restart allows a calculation to be continued from a previously saved point. Deselect Restart to start the new calculation with the initial values specified in the data set. A data saving interval may be specified in order to save restart data at regular crank angle intervals. With a data saving interval of 0 degrees crankangle, no restart data will be written to the hard disk. The restart files have same name as the model with the extension .rs0 and .rs1. The first restart file is written to .rs0 and the second to .rs1. The third restart file is written to .rs0, thus only the penultimate and last restart files exist. In the case of a restart, the program checks for the most recent file and takes the stored conditions for the initialization. The same directory as the input file is checked first and then the parent directory of the input file (one level up) for each restart file. This allows individual cases to be restarted from other cases provided it cannot find both restart files in its own case directory. Note that the restart file for a case is copied to the parent directory on completion of that case. If neither .rs0 nor.rs1 exist, the program run will be interrupted with an error message. Select Restart to start the new calculation with initial conditions taken from a restart file. For a single calculation the maximum calculation period is the sum of the calculation period of the initial calculation and that of the restart calculation. To avoid long transient output, select Time Reset. In a restart, this causes only the transient results from the restart on to be written to the .bst-file. The transient results will be lost from the calculation where the restart file was obtained. If Time Reset is deselected, the complete history will be stored on the .bst-file and can be analyzed using the transient analysis feature of the BOOST post-processor. Refer to Section 3.2.6 for Convergence Control. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-25 3.2.4. FIRE Link Control Please refer to the BOOST-FIRE 1D-3D Coupling Manual for further information. 3.2.5. BMEP Control The BMEP Control offers a convenient way to reach a target BMEP value without the need of using an ECU element. According to the following formula (3.2.9) either the injected fuel mass (DI, GDI) of selected cylinders or the flow-coefficient of selected restrictions (throttle, turbine waste- gate) is controlled. ( ) ( ) ∫ ⋅ − − + = t des CDUR lower upper guess dt BMEP BMEP t i vc vc vc vc 0 (3.2.9) vc controlled value (injected fuel mass [kg] or flow coefficient [1] ) guess vc initial value for controlled value ([kg] or [1] ) upper vc , lower vc upper and lower limit for controlled value ([kg] or [1] ) i integral control gain [1/Pa] CDUR t cycle duration [s] des BMEP target BMEP [Pa] BMEP current BMEP[Pa] Select BMEP Control in the Simulation Control / Globals window (Figure 3-8). Then select the BMEP Control sub-group in the tree to open the following window. Figure 3-15: Simulation Control – BMEP Control Window Specify the controlled elements and required parameters. BOOST Version 4.0.4 User’s Guide 3-26 23-Jun-2004 3.2.6. Convergence Control A convergence control can be performed, where either a convergence flag is set or the calculation stops, if a prescribed convergence criterion is fulfilled. Select Convergence Control in the Time Step Control window (Figure 3-14), then select the Convergence Control sub-group in the tree to open the following window. Figure 3-16: Simulation Control – Convergence Control Window The controlled elements, parameters and the corresponding threshold values can be specified. Also Finish or Flag should be specified. The convergence criterion is that the variation of the cycle averaged values (transients) of some parameters in BOOST elements over the last three consecutive cycles is less than a prescribed threshold. The following elements and variables can be used for convergence control: 1. Cylinder: • IMEP 2. Measuring point: • Convergence (combination of pressure, velocity and temperature) 3. Turbocharger: • Rotational speed • Turbine discharge coefficient • Turbine-to-total massflow • Turbine work • Compressor work User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-27 • Compressor pressure ratio • Boost pressure 4. Turbo Compressor: • Compressor work • Compressor pressure ratio • Boost pressure 5. Positive Displacement Compressor: • Compressor work • Compressor pressure ratio • Boost pressure 6. Plenum: • Pressure • Temperature • Mass For each selected variable the threshold value has to be specified. 3.2.7. Engine Friction For the calculation of the brake mean effective pressure (BMEP) and the brake specific fuel consumption (BSFC), the specification of friction mean effective pressure (FMEP) over engine speed and engine load is required. Select the Engine Friction sub-group with the right mouse button and then select Add. If the Engine Friction list is already available, click on it with the left mouse button to show the input window. Select it with the right mouse button to access Edit, Remove and Add. The engine friction may be defined versus engine speed for several loads expressed by BMEP. If only one friction curve is input, this curve will be used irrespective of the actual engine load. Values which are not specified explicitly in the table are obtained by interpolation. 3.2.8. Volumetric Efficiency The BOOST pre-processor allows a plenum or a measuring point to be specified as a reference location for the calculation of the air delivery ratio and the volumetric efficiency related to intake manifold conditions. Select Simulation Volumetric Efficiency and then select the desired element with the left mouse button to display the relevant information. Select OK to complete the selection process. BOOST Version 4.0.4 User’s Guide 3-28 23-Jun-2004 3.3. Design a BOOST Calculation Model To create a calculation model, double-click the required element in the Element tree with the left mouse button. In the working area move the displayed element to the desired location with the left mouse button. The positioning of the elements in the working area is assisted by a grid. The spacing of the grid points and the total size of the working area may be adjusted by selecting File|Page Setup. If a symbol must be positioned between grid points, snapping to the grid can be suppressed by pressing the shift key together with the left mouse button. It is recommended to locate all required elements in the working area and then connect them with the pipes. Finally the measuring points should be located in the pipes. The elements are numbered automatically in the order which they were inserted. 3.3.1. Pipe Design Select to insert a pipe. All possible points for a pipe attachment are indicated by small circles. Triangles are displayed for cylinders, air cleaners, catalysts and coolers to represent intake and exhaust connections. Select the desired circle (or triangle) with the left mouse button to attach the pipe to the element. Define the shape of the pipe by placing as many reference points in the working area as required with the left mouse button. The last of the series of points must be located at a possible pipe attachment and then click the right mouse button to complete the connection. The appearance of a pipe may be modified by selecting it with the mouse and then selecting . The pipe defined points become visible and can be moved with the left mouse button. Additional points may be inserted by clicking the line between two reference points with the left mouse button. The modification is finished by clicking the right mouse button. Attachment points of pipes at a plenum, a variable plenum, an air cleaner, catalyst or air cooler may be relocated by dragging the attachment point with the left mouse button. The direction in which the pipe was designed is suggested as the direction of positive flow (indicated by an arrow). The direction can be reversed by selecting . 3.4. Specification of Input Data for Elements Once the engine model is designed, the input data for each element must be specified. 3.4.1. Pipe For thermodynamic engine simulation programs which consider the gas dynamics of the intake and exhaust systems, the pipe element is one of the most important elements in the engine model. One dimensional flow is calculated in the pipes by solving the appropriate equations. This means that the pipe is the only element where the time lag caused by the propagation of pressure waves or the flow itself is considered. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-29 BOOST allows the pipe diameter (given the same cross-sectional area), bend radius, friction coefficient, wall heat transfer factor, wall temperature, as well as the initial values for pressure, gas temperature, A/F ratio, concentration of fuel vapor and concentration of combustion products to be specified depending on the location in the pipe by selecting Table . If this feature is used, the pipe length must be specified first. 3.4.1.1. Bending Radius For table input of the pipe bend radius, the pipe radius for a whole section is taken as the value at the highest (or furthest) point defined. That is, the first value defined for table input of bend radius will effectively be ignored. For example, in the following table the bending radius is, 120mm from 0 - 105mm (along the length of the pipe) 60mm from 105mm to 210mm 10000mm from 210mm to 315mm Figure 3-17: Example Table Input for Bending Radius The bend angle for a pipe section is then calculated from the length of the defined section divided by the bending radius. Using the same example as before, between 105mm and 210mm: degrees 100 radians 75 . 1 60 105 - 210 angle bend = = = BOOST Version 4.0.4 User’s Guide 3-30 23-Jun-2004 3.4.1.2. Friction Coefficient The pipe wall friction coefficient depends on the surface roughness of the pipe, pipe diameter and the Reynolds number of the flow in the pipe. For fully turbulent flow, the standard values for the friction coefficient may be taken from the following table: Pipe Diameter [mm] Material (Roughness [mm]) 30 60 100 150 Plastics (0.0015) 0.011 0.01 0.01 0.01 Steel new (0.05) 0.023 0.019 0.017 0.016 Steel old (0.17) 0.032 0.027 0.023 0.021 Cast Iron (min. 0.25) 0.037 0.029 0.026 0.023 Cast Iron (max. 0.5) 0.044 0.037 0.031 0.028 Values between the specified diameters may be obtained by linear interpolation. If the shape of the pipe cross-section is not circular, the friction coefficient must be increased by the ratio of the geometric diameter and the hydraulic diameter. The hydraulic diameter is defined as C A d h 4 = (3.4.1) A cross-sectional area C circumference of the cross-section 3.4.1.3. Heat Transfer Factor The heat transfer coefficient for the calculation of the heat flux from or to the pipe walls is calculated from the Reynolds’ analogy. The heat transfer factor allows the user to increase or to reduce the heat transfer as the calculated heat transfer coefficient is multiplied by this factor. 3.4.1.4. Variable Wall Temperature BOOST can model the variation of the pipe wall temperature. This takes into account the heat transfer from the outer pipe wall to a surrounding ambient and heat flux from the gas flow to the pipe wall. Additional input required for the variable wall temperature model is as follows, • wall thickness of the pipe. • specific heat capacity of the pipe material. • temperature in the ambient of the pipe. • cooling medium (air or water). • characteristic velocity. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-31 The outer heat transfer coefficient is calculated using the cooling medium (air or water) and a characteristic velocity of the coolant. For a characteristic velocity of zero, a formula for free convection is used for the calculation of the heat transfer coefficient. A forced convection formula is used for a non-zero characteristic velocity. The following table gives some property values of materials used typically for engine manifolds: Density Specific Heat Specific Heat Material [kg/m 3 ] [kJ/kgK] Capacity [kJ/m 3 K] Cast Iron 7200 0.545 3900 Steel 7840 0.46 3600 Aluminum 2700 0.91 2460 PVC (Plastics) 1390 0.98 1360 Ceramics 3500 0.84 2940 3.4.2. Cylinder The specifications for the cylinders cover the basic dimensions of the cylinder and the cranktrain (bore, stroke, compression ratio, conrod length, piston pin offset, firing order), plus information on the combustion characteristics, heat transfer, scavenging process and the valve/port specifications for the attached pipes. Furthermore, initial conditions for the calculation in the cylinder must be specified. If a standard cranktrain is used, the piston motion is calculated from the stroke, conrod length and piston pin offset. The direction of positive piston pin offset is defined as the direction of the rotation of the crankshaft at Top Dead Center (TDC). Figure 3-18: Standard Cranktrain BOOST Version 4.0.4 User’s Guide 3-32 23-Jun-2004 Alternatively, BOOST allows a user-defined piston motion to be specified. This gives the user freedom to simulate an unconventional powertrain. For a user-defined piston motion the relative piston position should be specified over crank angle. The relative piston position is defined as the distance of the piston from the TDC position relative to the full stroke. Zero degree crank angle corresponds to the Firing TDC of the selected cylinder. Considering blow-by from the cylinder, an equivalent effective blow-by gap must be specified as well as the average crankcase pressure. The actual blow-by mass flow is calculated from the conditions in the cylinder and the pressure in the crankcase, and from an effective flow area which is calculated from the circumference of the cylinder and the effective blow-by gap. The blow-by mass flow is lost. No recirculation to the intake may be considered. For the specification of the combustion characteristics, either a heat release approach, a theoretical combustion cycle, a user-written subroutine or a truly predictive model can be selected from the pull down menu. Thereby the total heat released during the combustion is calculated from the amount of fuel which is burned in the cylinder and the lower heating value of the fuel. For engines with internal mixture preparation the fuel is injected directly into the cylinder and the fueling is therefore part of the cylinder specification. For convenience, the fueling may be specified as the fuel mass which is injected into the cylinder or as a target A/F ratio, where the actual fueling is calculated every cycle from the mass of air in the cylinder and the specified target air/fuel ratio. In the case of external mixture preparation, the fuel is fed to the intake system and the total heat supply is calculated from the amount of fuel in the cylinder at intake valve closing. For modeling of gasoline direct injection engines, fuel may be added to the cylinder charge directly. In this case Cylinder Evaporation must be On and the normalized rate of evaporation must be specified. As for engines with internal mixture preparation, the evaporating fuel mass or the target A/F-ratio can be set by the user. If the target A/F-ratio is selected, the injected fuel mass will be determined as the fuel mass required in addition to the aspirated fuel mass to achieve the desired A/F-ratio. If the A/F-ratio is already lower than the target A/F-ratio, no fuel will be added. The evaporation heat is used to calculate the cooling of the cylinder charge due to the evaporation of the fuel. The following table may be used to determine the evaporation heat of different fuels: Fuel Evaporation Heat [kJ/kg] Methanol 1109 Ethanol 904 Gasoline 377-502 Gasoline (Premium) 419 Diesel 544-795 By specifying Heat from Wall greater than 0, the amount of evaporation heat covered from the combustion chamber walls can be input. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-33 For the definition of the heat release characteristics over crank angle, the following options are available: • Single VIBE function • Double VIBE function • Single Zone Table • Two Zone Table • Woschni/Anisits (internal mixture preparation only) • Hires et al. (external mixture preparation only) • User Defined Model • User Defined High Pressure Cycle • Constant Volume Combustion • Constant Pressure Combustion • Motored • Vibe 2 Zone • Quasi-dimensional (external mixture preparation only in conjunction with either a Physically Based or Empirically Based Combustion Model) • Hiroyasu (internal mixture preparation only) 3.4.2.1. Combustion Model Single Vibe Function The Vibe function is a very convenient method for describing the heat release characteristics. It is defined by the start and duration of combustion, a shape parameter 'm' and the parameter 'a'. These values can be specified either as constant values or dependant on engine speed (in rpm) and engine load (expressed as BMEP in bar). Select Map to specify these values. The heat release characteristic of gasoline engines, with essentially homogeneous mixture distribution in the cylinder, is mainly determined by the flame propagation speed and the shape of the combustion chamber. A high flame propagation speed can be achieved with high compression ratio and high turbulence levels in the cylinder. In diesel engines on the other hand, the combustion characteristic depends strongly on the capabilities of the fuel injection system, compression ratio and the charge air temperature. For accurate engine simulations the actual heat release characteristic of the engine, (which can be obtained by an analysis of the measured cylinder pressure history), should be matched as accurately as possible. To obtain an estimate on the required combustion duration to achieve a certain crank angle interval between 10% and 90% mass fraction burned, the following chart may be used. BOOST Version 4.0.4 User’s Guide 3-34 23-Jun-2004 Figure 3-19: Crank Angle related to Combustion Duration For example: A shape parameter of 1.5 is selected and the duration between 10% and 90% MFB is 30 degrees CRA. The crankangle interval between 10% and 90% MFB related to the combustion duration is 0.46. (read from the graph). Hence the combustion duration is 30/0.46 = 65 degrees CRA. The point of 50% MFB is at 10 degrees CRA ATDC. According to the graph the location of 50 % MFB after combustion start related to the combustion duration is 0.4. Thus the combustion start is calculated from 10 – 65 * 0.4 = -16 = 16 degrees BTDC. If measured heat release data is not available, the following standard values may be used to complete the engine model. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-35 Operating Point Comb. Duration Par. m Gasoline Engine Standard Combustion System (2-Valve Engine) 1500 rpm WOT 60 degrees CRA 2.3 5000 rpm WOT 65 degrees CRA 1.9 Standard Combustion System (4-Valve Engine) 1500 rpm WOT 50 degrees CRA 2.5 5000 rpm WOT 55 degrees CRA 2.1 Fast Burn Concepts 1500 rpm WOT 45 degrees CRA 2.6 5000 rpm WOT 50 degrees CRA 2.6 Passenger Car Naturally Aspirated (Full Load) Diesel Engine (IDI) Rated Speed 90 degrees CRA 0.5 30% Rated Speed 65 degrees CRA 0.5 Turbocharged (Full Load) Rated Speed 90 degrees CRA 1.0 30% Rated Speed 65 degrees CRA 0.8 Turbocharged Intercooled (Full Load) Rated Speed 90 degrees CRA 1.1 30% Rated Speed 65 degrees CRA 0.8 Passenger Car Naturally Aspirated (Full Load) Diesel Engine (DI) Rated Speed 80 degrees CRA 0.4 30% Rated Speed 55 degrees CRA 0.4 Turbocharged (Full Load) Rated Speed 75 degrees CRA 0.9 30% Rated Speed 55 degrees CRA 0.7 Turbocharged Intercooled (Full Load) Rated Speed 75 degrees CRA 1.0 30% Rated Speed 55 degrees CRA 0.7 BOOST Version 4.0.4 User’s Guide 3-36 23-Jun-2004 Heavy Duty Naturally Aspirated (Full Load) Truck Engine (DI) Rated Speed 70 degrees CRA 0.5 50% Rated Speed 55 degrees CRA 0.6 Turbocharged (Full Load) Rated Speed 70 degrees CRA 1.1 50% Rated Speed 55 degrees CRA 0.8 Turbocharged Intercooled (Full Load) Rated Speed 75 degrees CRA 0.9 50% Rated Speed 60 degrees CRA 1.0 Medium Speed Engines (DI, TCI) Rated Output 65 degrees CRA 1.0 The start of combustion must be defined considering fuel consumption, peak cylinder pressure limitation, or knocking characteristics for gasoline engines. The Vibe parameter 'a' characterizes the completeness of the combustion. For complete combustion, a value of 6.9 is required. Double Vibe Function For a good approximation of the double peak heat release characteristics of DI diesel engines (first peak due to premixed burning, second peak due to diffusion burning), BOOST allows two Vibe functions to be specified. These are superimposed during the calculation process. Besides the start of combustion, the fuel allotment must be specified. The fuel allotment is defined as the fraction of fuel burnt with the characteristics of Vibe 1. For each Vibe function, the combustion duration and the shape parameter 'm' must also be specified. Single Zone Table For an optimum approximation of the actual heat release characteristics of an engine, BOOST allows reference points for the rate of heat release over crank angle to be specified. As the specified heat release characteristics will be normalized by the BOOST code (i.e. converted to percent of the total heat input per degree CRA), the dimension of the heat release values is of no importance. Woschni/Anisits Model The Woschni/Anisits Model predicts the Vibe parameter for engines with internal mixture preparation if the parameters for one operating point are known. This model should be used for transient simulations as the heat release characteristics will change with different operating conditions. In addition to the Vibe parameters, the following data must be specified to characterize the baseline operating point: a) Engine speed b) Dynamic injection nozzle opening c) Ignition delay d) A/F ratio e) Cylinder conditions at intake valve closes User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-37 Hires et al. Model For gasoline engines the Hires et al. Model may be used for transient simulations. Similarly to the Woschni/Anisits model, the heat release characteristic is calculated from the Vibe parameters and some characteristic data of a baseline operating point. User Model If the heat release characteristics are set to User Defined Model, the subroutine usrcmb is called for the calculation of the rate of heat release. The source code of this subroutine is available for the user and any model may be implemented provided it is translated into valid FORTRAN 90, compiled and linked to the rest of the code. User-Defined High Pressure Cycle If the User-Defined High Pressure Cycle is selected, the complete high pressure cycle is replaced by the subroutine usrhpr. Note: Only experienced users should add user-defined subroutines. Constant Volume Combustion If Constant Volume Combustion is selected, the entire combustion takes place at the crankangle specified by the user. In theory, constant volume combustion yields maximum efficiency at a certain compression ratio if no peak firing pressure limits have to be considered and the combustion timing is set to firing TDC. Constant Pressure Combustion If the combustion characteristics are set to Constant Pressure Combustion, BOOST determines the rate of heat release with the following strategy from the specified peak cylinder pressure: • If the maximum cylinder pressure at the end of compression is lower than the specified peak cylinder pressure, the cylinder pressure is raised to the specified value by a constant volume combustion and the remaining fuel is burned in such a way that this pressure is kept constant. This combination of constant volume/constant pressure combustion is called the Seiliger process. • If the maximum cylinder pressure at the end of compression exceeds the specified value, constant pressure combustion is initiated when the cylinder pressure drops below the specified value during the expansion stroke. In theory constant pressure combustion yields maximum efficiency for a certain peak firing pressure if the compression ratio is selected to achieve the maximum sustainable peak firing pressure at the end of the compression stroke. The Seiliger process yields maximum efficiency for a certain combination of peak firing pressure and compression ratio. Motored If the heat release characteristics are set to Motored, no combustion will take place irrespective of the amount of fuel aspirated or injected. BOOST Version 4.0.4 User’s Guide 3-38 23-Jun-2004 Vibe 2 Zone Combustion Model For the Vibe 2 zone combustion model, the same input as for the single Vibe function is required. However, instead of one mass averaged temperature, two temperatures (burnt and unburned zone) are calculated. This model also predicts the knocking characteristics of the engine, provided the actual rate of heat release is described properly by the Vibe function specified. Quasi-Dimensional Combustion Model The quasi-dimensional approach, as the physically or empirically based combustion model (PBCM or EBCM), in BOOST predicts the rate of heat release for homogenous charge spark ignition engines. The combustion simulation is triggered at ignition timing. A simple turbulence model is used for the determination of the entrainment rate of fresh charge into the flame. The input required by this model are model constants for the calculation of the turbulent kinetic energy and turbulent length scale at intake valve closes. If the design of the combustion chamber features a small piston to head clearance, aiming to produce squish flow at the end of the compression stroke, a modified turbulence model can be used. In this case a Flow Constant for the turbulence generation by squish flow must be specified by the user. Provided that the cylinders feature identical data, the ROHR transfer option to other cylinders may be activated. In this case, the quasi-dimensional combustion model is only applied to Cylinder 1 to calculate the rate of heat release curve. The obtained curve is transferred to the remaining cylinders. For these cylinders, the high pressure cycle will be simulated with a single zone model. In addition to the model constants, the quasi-dimensional combustion model requires a table specifying the contact areas between burned zone and head, liner, piston and unburned zone (i.e. the free flame area) and the burned zone volume versus flame radius and crankangle (piston position). For simple geometries, the table can be generated by BOOST. Select the Chamber Geometry Calculation subgroup to input the main dimensions of the combustion chamber. For the cylinder head, the following shapes can be considered (required input as shown in the sketches): User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-39 Figure 3-20: Flat Cylinder Head Figure 3-21: Disc Chamber Cylinder Head Figure 3-22: Spherical Cylinder Head BOOST Version 4.0.4 User’s Guide 3-40 23-Jun-2004 Figure 3-23: Backset Special Cylinder Head Figure 3-24: Pent Roof Cylinder Head In addition, the user must select the shape of the piston top from the following list (required input as shown in the sketches): User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-41 Figure 3-25: Flat Piston Top Figure 3-26: Heron Piston Top Figure 3-27: Spherical Bowl Piston Top BOOST Version 4.0.4 User’s Guide 3-42 23-Jun-2004 Figure 3-28: Spherical Piston Top Figure 3-29: Pent Roof Piston Top If there is an offset between spark plug location and the cylinder axis as well as an offset between the center of the piston bowl or top, the angle between spark plug and bowl or top center must be input according to the definition shown in the following sketch. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-43 Figure 3-30: Definition of Angle between Spark Plug and Bowl/Top Center For a pent roof head or a pent roof piston, the spark plug position must be defined by two rectangular coordinates as shown in Figure 3-30. Alternatively, the table can be generated externally and the name of the file can be specified by the user. The file must be a sequential formatted ASCII file and may contain comment lines marked with a “#” in the first column. Note: The geometry file format has changed from version 3.2. Figure 3-31: Definition of Spark Plug Position BOOST Version 4.0.4 User’s Guide 3-44 23-Jun-2004 The file format can be seen in the following example. TYPE 2 # # Bore = 84.0mm, Stroke = 90.0mm, Compression Ratio = 9.0 # Headtype: flat # Spark Plug Position: x = 0.0mm, y = 0.0mm, z = 0.0mm # (Position x=0, y=0, z=0 means center of bore at head bottom) # Pistontype: flat # Number of flame radii NUMFLARAD 101 # Number of piston positions NUMPISPOS 101 # total head area [mm2] TOTHEADAREA 5541.77 # minimal liner area [mm2] MINLINAREA 2968.81 # total piston area [mm2] TOTPISAREA 5541.77 # volume in head [mm3] HEADVOL 0.00 # volume in piston [mm3] PISVOL 0.00 # minimum piston position [-] PISPMIN 0.00 # maximum piston position [-] PISPMAX 90.00 # increment of piston position [-] PISPINC 0.03 # minimum flame radius [mm] FRADMIN 0.00 # maximum flame radius [mm] FRADMAX 99.32 # increment of flame radius [mm] FRADINC 0.99 # minimum burned zone volume[mm3] BVMIN 0.00 # maximum burned zone volume[mm3] BVMAX 525001.01 # flame front radii: FLAMERADII 0.000000E+00 0.993177 ... # contact area burned zone - cylinder head versus flame front radius [mm2] HEADAREA 0.000000E+00 3.09887 ... # depending on piston position: # contact area burned zone - liner versus flame front radius [mm2] # contact area burned zone - piston versus flame front radius [mm2] # contact area burned zone - unburned zone versus flame front radius [mm2] # burned zone volume versus flame front radius [mm3] # data for piston position: PISPOS 0.000000 LINERAREA User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-45 0.000000E+00 0.000000E+00 ... PISTONAREA 0.000000E+00 0.000000E+00 ... FREEFLAMES 0.000000E+00 6.19773 ... BURNEDVOL 0.000000E+00 2.05182 ... # data for piston position: PISPOS 0.027930 LINERAREA 0.000000E+00 0.000000E+00 ... PISTONAREA 0.000000E+00 0.000000E+00 ... FREEFLAMES 0.000000E+00 6.19773 ... BURNEDVOL 0.000000E+00 2.05182 ... . Hiroyasu Combustion Model The combustion model developed by Professor Hiroyasu predicts the rate of heat release of DI Diesel engines. The model requires the swirl ratio as input for the in-cylinder charge motion. In addition, the combustion bowl diameter, limiting the free spray length, should be specified. The density and temperature at which the fuel is injected is required for the properties of the liquid fuel. The fuel’s activation energy influences the ignition delay. If the diameter of a fuel droplet gets smaller than the minimum droplet size specified, immediate evaporation is assumed. For calculating the spray behavior, the number of nozzle holes, their diameter and discharge coefficient must be specified. The number of packages in radial direction defines the number of subdivisions in radial direction of the spray. The rate of injection defining the amount of fuel injected per degree crankangle must be specified. The specified curve is normalized, so that the area beneath the curve is equal to one. The actual amount of fuel injected is obtained from multiplying the normalized rate of injection with the total fuel mass. For each radial subdivision of the spray, define a Sauter mean diameter and a relative mass content in the Package Data subgroup. The relative mass content influences the radial fuel mass distribution in the spray. The model constants for calibrating the model for a particular engine comprise of constants for the calculation of the ignition delay, the air entrainment into the spray (overall, before ignition and wall impingement and after wall impingement) the thickness of the spray at the wall after impingement, the entrainment of burnt gases into the spray and a constant for the amplification of turbulence intensity. Constants for the soot model influencing soot formation and its consumption (oxidation) complete the input for the Hiroyasu combustion model for the cylinder under consideration. BOOST Version 4.0.4 User’s Guide 3-46 23-Jun-2004 Provided that the cylinders feature identical data the ROHR transfer option to other cylinders may be activated. In this case Hiroyasu’s model will only be applied to cylinder one to calculate the rate of heat release curve. The obtained curve is transferred to the remaining cylinders. For these cylinders, the high pressure cycle will be simulated with a single zone model. AVL MCC Model The AVL MCC model requires the number of injector holes, the hole diameter, the discharge coefficient of the injector holes and the rail pressure to calculate with the effective hole area, the velocity and thus the kinetic energy of the fuel jet. The table containing the rate of injection determines injection rate. The input is normalized and used with the fuel specified in the general cylinder box to determine the fuel injected each time step. The ignition delay is calculated using the modified ignition delay model developed by Andree and Pachernegg. To fit the delay to measured data it can be influenced by the ignition delay calibration factor. The model parameters are normalised, therefore with a value of 1 good results should be obtained. The following parameters control the rate of heat release and the NOx production. 1. The ignition delay calibration factor influences the ignition delay, higher values result in longer ignition delays. 2. The combustion parameter has the greatest influence on the ROHR shape. A higher value results in a faster combustion. 3. The turbulence parameter controls the influence of the kinetic energy density while the dissipation parameter influences the dissipation of the kinetic energy. 4. Dissipation parameter controls the turbulence dissipation. 5. The NOx production parameter has influence on the NOx result. 6. The EGR influence parameter controls the influence of EGR on combustion. 7. The premixed combustion parameter determines the fraction of fuel injected during ignition delay burned during premixed combustion, a value of 0.7 should be used as default. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-47 Figure 3-32: AVL MCC Combustion Model Window 3.4.2.2. Divided Combustion Chamber If an engine with divided combustion chamber is to be simulated, the user may specify the pre chamber data after selecting Chamber Attachment in the General folder of the Cylinder element. The basic input of the pre chamber is its volume and the initial conditions (pressure, temperature and gas composition) at exhaust value opens. The geometry of the connecting pipe is described by its length and diameter. In addition the turbulent wall friction coefficient, the wall temperature and a heat transfer amplification factor must be input. In order to consider particular pressure losses resulting from multi dimensional flow phenomena at the connecting pipe orifice, BOOST requires the specification of flow coefficients for in-flow and out-flow at the connecting pipe. The flow coefficients are defined as the ratio between the actual mass flow and the loss-free isentropic mass flow for the same stagnation pressure and the same pressure ratio. The flow coefficients may be specified either as constant values or in a Table as functions of time in seconds, time in degrees crank angle or pressure difference between cylinder and chamber. For in-flow (flow into the chamber) the pressure difference is defined as the static pressure in the connecting pipe minus the pressure in the chamber. For out-flow it is defined as the pressure in the chamber minus the static pressure in the connecting pipe. The flow coefficients for flow from the chamber into a pipe depend mainly on the protrusion of the pipe end through the wall in which it is installed and on its bellmouth characteristics. BOOST Version 4.0.4 User’s Guide 3-48 23-Jun-2004 The following table may be used to determine flow coefficients for well manufactured pipe attachments. Values between the specified points can be obtained by linear interpolation. Relative Inlet Radius Relative Edge Distance 0.0 .02 .06 .12 .20 0.0 .815 .855 .910 .950 .985 0.025 .770 .840 .910 .950 .985 0.075 .750 .830 .910 .950 .985 0.20 .730 .825 .910 .950 .985 >0.50 .710 .820 .910 .950 .985 The relative inlet radius is defined as the inlet radius divided by the (hydraulic) pipe diameter. The relative edge distance is defined as the protrusion of the pipe end through the wall in which it is mounted divided by the (hydraulic) pipe diameter. A relative edge distance equal to zero represents a pipe mounted flush with the wall. To specify the heat release characteristics in the chamber, the user may use a Vibe- function, a double Vibe function or a single zone table. If the wall heat transfer in the chamber is turned on, the box for the input of the required data is accessed. The data comprise the chamber geometry (spherical or user-defined), the friction coefficient for the calculation of the friction torque, the connecting pipe eccentricity, the chamber wall temperature and a calibration factor. For a user defined chamber geometry the surface area, the characteristic radius for the calculation of the heat transfer coefficient by the Nußelt equation, and the inertia radius of the chamber are to be defined by the user. If a variable wall temperature is to be considered, the wall thickness of the pre chamber, the conductivity of the material and its heat capacity as well as the coolant temperature and the outer heat transfer coefficient must be input. 3.4.2.3. Heat Transfer The following heat transfer models are available for the cylinder: • Woschni 1978 and 1990 • Hohenberg • Lorenz 1978 and 1990 (Cylinders with attached chamber only) • AVL 2000 Alternatively, None can be selected. In addition to the heat transfer coefficient provided by the heat transfer model, the surface areas and wall temperatures of the piston, cylinder head and liner must be specified. The wall temperatures are defined as the mean temperature over the surface. A calibration factor for each surface may be used to increase or to reduce the heat transfer. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-49 For the surface areas the following guidelines may be used: Piston: DI diesel engines with a bowl: Surface area is approximately 1.3 to 1.5 times the bore area. SI engines: Surface area is approximately equal to the bore area. Cylinder Head: DI diesel engines: Surface area is approximately equal to the bore area. SI engines: Surface area is approximately 1.1 times the bore area. Liner with Piston at TDC: The area may be calculated from an estimated piston to head clearance times the circumference of the cylinder. Wall temperature must be specified at the piston TDC and BDC positions. Between those positions a special temperature profile is assumed (refer to Section 2.1.1). Refined Liner Layer Discretization: If detailed information about the liner wall temperature distribution along the liner is available, the option “Layer Discretization” allows the User to input the wall temperature dependent on the distance from cylinder head. This discretization can also be used in combination with an external link element (Liner Layer Wall Temperature Actuator, Liner Layer Wall Heat Flow Sensor). For both Woschni formulae, the user must specify whether the engine features a divided combustion chamber. Select IDI for IDI diesel engines (swirl chamber or pre-chamber combustion system). Select DI for DI diesel engines and gasoline engines. In order to consider the influence of the in-cylinder charge motion on the heat transfer coefficient, the in-cylinder swirl ratio (defined as the speed of the charge rotation relative to engine speed) must be specified. Select Variable Wall Temperature to calculate the heat balance of the combustion chamber walls. For each wall (head, piston and liner) an effective wall thickness together with material data must be specified. Conductivity and heat capacity are required and the following list provides some typical materials: Heat Capacity Conductivity Material [kJ/m 3 K] [W/mK] Cast Iron 3900 53 Steel 3600 48 Aluminum 2460 221 Ceramics 2940 5.5 For the heat transfer to the coolant (head and liner) and engine oil (piston), an average heat transfer coefficient and the temperature of the medium must be specified. For the heat transfer in the ports, a modified Zapf-model is used (refer to Section 2.1.2). BOOST Version 4.0.4 User’s Guide 3-50 23-Jun-2004 3.4.2.4. Scavenging Three scavenging models are available in the General window: • Perfect mixing: The gas flowing into the cylinder is mixed immediately with the cylinder contents. The gas leaving the cylinder has the same composition as the mixture in the cylinder. The perfect mixing model is the standard scavenging model for the simulation of 4-stroke engines. • Perfect displacement: A pipeline model is used to determine the exhaust gas composition. This means that all residual gases in the cylinder are exhausted first. Only when no more residual gases are left in the cylinder, is fresh charge lost to the exhaust. • User-defined scavenging model: For the simulation of 2-stroke engines, the specification of the scavenging efficiency over scavenge ratio is required to define the quality of the port arrangement with respect to scavenging flow. This data are usually taken from literature or from the results of scavenging tests. The scavenging efficiency is defined as the volume of fresh air in the cylinder related to the total cylinder volume. The scavenge ratio is defined as the total volume of air which entered the cylinder related to the total cylinder volume. Figure 3-33 shows a comparison of the scavenging efficiency curves of the perfect displacement and the perfect mixing models. Figure 3-33: Scavenging Models User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-51 3.4.2.5. Valve / Port Data For each pipe attached to a cylinder, the user must specify whether this port is controlled by a valve or by the piston (piston control is only feasible for 2-stroke engines). If the cylinder features a combustion chamber, the pipe may be also declared to be attached to the chamber. In this case, the port may be either controlled by a valve or with the standard definition of flow coefficients. Click on the input field with the left mouse button to open the submenu shown in the following window. Figure 3-34: Valve Port Specifications Window If the heat transfer in the intake and exhaust ports must be considered, the specification of the port surface area and the mean port wall temperature is required (valve controlled port only). For the calculation of the heat balance of the port wall, similar data as for the combustion chamber walls (i.e. the average thickness, the heat capacity and the conductivity of the material) is required. For the calculation of the summed up intake and exhaust mass flow characteristics, the user must specify whether the considered port is an intake or exhaust port. A pipe attached to the combustion chamber is considered as an intake. For valve controlled ports the inner valve seat diameter is required for the calculation of the port wall heat transfer coefficient, as well as for the conversion of normalized valve lift to effective valve lift. The valve lift is defined by the valve lift curve and by the valve clearance. By specifying the crank angle of the first valve lift value and the cam length, the crank angle range in the table is defined. The number of reference points for the valve lift curve can be specified directly or by inputting a constant crank angle interval between two valve lift points. After completing the input of reference points, the input is presented in the graphics window for immediate control purposes. If a valve lift curve is already specified in the table, a new specification of the timing of the first valve lift shifts the entire valve lift curve. BOOST Version 4.0.4 User’s Guide 3-52 23-Jun-2004 If the cam length is changed, a shorter or longer valve lift curve will be calculated from the baseline valve lift curve under the assumption of similar valve velocities. The actual valve lift at a certain crank angle is calculated from the valve lift, specified in the valve lift curve, minus the valve clearance, as shown in the figure below: Figure 3-35: Calculation of Effective Valve Lift For Valve Controlled valves a modification of the baseline valve lift curve can be specified in the Modification of Valve Lift Timing. This is possible for each individual valve connected to a cylinder so that different modifications can be applied to different intake (or exhaust) valves of a multiple valve model. Figure 3-36: Modification of Valve Lift Timing User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-53 The possible modifications using these options is shown in the following figures (dashed lines are the baseline valve lift curves before modification). Figure 3-37: Positive intake valve opening and closing shift (same value) Figure 3-38: Positive intake valve closing shift only Figure 3-39: Positive intake valve opening shift only Figure 3-40: Positive exhaust closing shift and positive intake opening shift BOOST Version 4.0.4 User’s Guide 3-54 23-Jun-2004 Figure 3-41: Positive exhaust opening and closing shift (same value) Figure 3-42: Positive exhaust opening shift only Figure 3-43: Positive exhaust valve closing shift only Figure 3-44: Positive exhaust valve closing shift and negative intake opening shift User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-55 Figure 3-45: Negative exhaust shifts (same value) and positive intake shifts (same value) To consider particular pressure losses resulting from multi dimensional flow phenomena which cannot be directly predicted by the program, BOOST requires the specification of flow coefficients of the ports. The flow coefficients are defined as the ratio between the actual mass flow and the loss-free isentropic mass flow for the same stagnation pressure and the same pressure ratio. BOOST allows the specification of the flow coefficients of ports as a function of the pressure ratio at the port. For the flow into the cylinder, the pressure ratio is defined as the pressure in the cylinder divided by the stagnation pressure in the port (pressure ratio <1). For flow out of the cylinder, the pressure ratio is defined as the cylinder pressure divided by the static pressure in the port (pressure ratio > 1). BOOST interpolates linearly the flow coefficients of pressure ratios which are less than and greater than one. It does not interpolate between the largest pressure ratio smaller than one and the smallest pressure ratio larger than one. Outside the defined range the value for the smallest/largest pressure ratio is taken. Figure 3-46 illustrates this procedure: Figure 3-46: Interpolation of Flow Coefficients The program interprets the specified flow coefficients of the ports are related to the cross- section of the pipe attached to the cylinder. If the measured flow coefficients of the ports are related to a different cross-section, the scaling factor for the effective flow area may be used to overcome this and achieve the correct effective flow areas. Usually, the flow coefficients are related to the inner valve seat area. In this case, the scaling factor may be calculated easily from the following formula: BOOST Version 4.0.4 User’s Guide 3-56 23-Jun-2004 2 2 pi vi v sc d d n f ⋅ = (3.4.2) sc f scaling factor v n number of valves modeled with the port under consideration vi d inner valve seat (= reference) diameter pi d attached pipe diameter The flow coefficients of the ports must be specified over valve lift. This can be done either by specifying the flow coefficients directly over valve lift or over the normalized valve lift. The latter is defined as valve lift related to the inner valve seat diameter (AVL definition). The advantage of using the normalized valve lift as a parameter is that the flow coefficients of similar ports can be used without modification. For intake ports, the swirl characteristics versus valve lift may also be specified by the user. With this input, a dynamic in-cylinder swirl is calculated. In addition, a static swirl with AVL's standard lift curve and the engines actual lift curve will be calculated for each port. The following options are available to specify the flow characteristics and the opening characteristics of the ports of 2-stroke engines: • Specification of the effective flow area: The user may specify the effective flow area over piston position or over crank angle. If, in addition to the effective flow area, the port geometry is specified, the pre-processor calculates the flow coefficients for the port automatically. They may be used to determine effective flow areas for slightly modified ports (e.g. modified timing). • Specification of port geometry and flow coefficients: Instead of specifying the effective flow area directly, the user may specify the port geometry over piston position or crank angle, and the flow coefficients of the port depending on the port opening. The port geometry, i.e. the port width over piston position or crank angle must be specified for each port opening. In a BOOST model one port may feature more than one opening so the number of openings must be specified. Similar to the valve controlled ports, BOOST allows the effective flow areas of the ports as a function of pressure ratio at the port to be specified. The definition of pressure ratio is the same as described for valve controlled ports. The scaling factor may be used to increase or to decrease the specified flow areas by a constant factor. The effective flow areas of the ports may be specified either as a function of the distance between the actual position of the piston and its TDC position, or on crank angle. If the effective flow area is specified over crank angle, the full crank angle range between port opening and port closing must be covered. It is the user’s responsibility to ensure that the timing relative to BDC is symmetrical. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-57 The flow coefficients are defined as the actual mass flow related to the specific mass flow rates calculated from the isentropic flow equations for the same stagnation pressure and temperature and for the same pressure ratio. The definition of the port geometry consists of the specification of the port openings, the port width (either as chord or as developed length) over the distance from the upper port edge, and the minimum duct cross-section. The port opening timing may be specified either in degrees crank angle after TDC or as the distance between the upper port edge and the TDC position of the piston top (location of upper port edge below TDC), Figure 3-47. Figure 3-47: Definition of Window Geometry The minimum duct cross-section is required to determine the upper limit for the geometric cross-section of the port. It may be specified directly or calculated from the port opening dimensions and the port angles (angles between the port centerline and the horizontal and radial planes), Figure 3-48. Figure 3-48: Calculation of Minimum Duct Cross Section BOOST Version 4.0.4 User’s Guide 3-58 23-Jun-2004 The flow coefficients of the ports of two-stroke engines are related to the actual port opening area which varies with piston position. They must be specified as a function of distance from the upper port edge. 3.4.3. Measuring Point Using measuring points, the user can access flow data and gas conditions over crank angle at a certain location in a pipe. The location of the measuring point must be specified as its distance from the upstream pipe end. The user may select the output for a measuring point. Standard : pressure, flow velocity, temperature, Mach number and mass flow rates. Extended : Additional output of stagnation pressure, stagnation temperature, enthalpy flow, fuel concentration, combustion products concentration, fuel flow, combustion products flow, forward and backward pressure and velocity waves. Additional acoustic data is also written to the acoustic folder for measuring points with extended output selected. 3.4.4. Boundaries 3.4.4.1. System Boundary The system boundary element provides the connection of the calculation model to a user- definable ambient. General Select Saving of Energy and Mass for Backflow to determine the temperature condition for Inflow by the accumulated Outflow. Boundary Type: Standard is the default setting for a system boundary. No special features are used. Anechoic Termination suppress backward pressure waves. This can be used for the termination of an acoustic model. Acoustic Source generates a varying pressure in the ambient. Used for generating source conditions for acoustic models. Boundary Conditions Both local or global boundary conditions can be set. In the later case one of the predefined global sets can be used to specify the boundary conditions. The ambient conditions (pressure, temperature, air/fuel ratio, fuel vapor and combustion products) must be specified either as constant values or in a Table as functions of time or crank angle. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-59 If internal mixture preparation is considered, the input of fuel vapor and combustion products is disabled. In this case the A/F ratio represents the A/F ratio of the mixture of air and combustion products in the ambient and no unburned fuel in the ambient is allowed. If external mixture preparation is considered, the A/F ratio represents the A/F ratio of the combustion gases in the ambient. In addition, the mass fractions of the combustion products and the fuel vapor must be specified. The input of user-defined concentrations is disabled if the number of user-defined concentrations was set to zero. Flow Coefficients The flow coefficients for flow from the ambient into a pipe depend mainly on the protrusion of the pipe end through the wall in which it is installed and on its bellmouth characteristics. The following table may be used to determine flow coefficients for well manufactured pipe attachments. Values between the specified points can be obtained by linear interpolation. Relative Inlet Radius Relative Edge Distance 0.0 .02 .06 .12 .20 0.0 .815 .855 .910 .950 .985 0.025 .770 .840 .910 .950 .985 0.075 .750 .830 .910 .950 .985 0.20 .730 .825 .910 .950 .985 >0.50 .710 .820 .910 .950 .985 The relative inlet radius is defined as the inlet radius divided by the (hydraulic) pipe diameter r/D h . The relative edge distance is defined as the protrusion of the pipe end through the wall in which it is mounted, divided by the (hydraulic) pipe diameter L/D h . A relative edge distance equal to zero represents a pipe mounted flush with the wall, refer to Figure 3-49. Figure 3-49: Mounting of a Pipe End BOOST Version 4.0.4 User’s Guide 3-60 23-Jun-2004 For flow out of a pipe into the ambient, a flow coefficient of 1.0 is normally used if there is no geometrical restriction in the orifice. Acoustic Source The numerical generation of an acoustic periodic signal (white noise) is carried out as the sum of N sinusoidal pressure oscillations with a fixed amplitude, ∆p, and frequency multiple of the fundamental frequency, f. ( ) ∑ = + ∆ + = N n n o ft p p t p 1 2 sin ) ( ϕ π p o is a constant value representing the mean ambient pressure. A random phase is used for each sinusoidal component of the sum. Minimum frequency: This is also the fundamental frequency for the pressure calculation. Maximum frequency: Frequency is incremented from the minimum frequency in steps of the fundamental frequency (also the minimum frequency) until the maximum frequency is reached. Mean Pressure, p o : Base pressure about which the pressure is varied. This can be used to control the mean flow during the simulation depending on the termination conditions. Delta Pressure, ∆p: The acoustic pressure of the source. 3.4.4.2. Aftertreatment Boundary The aftertreatment boundary element provides the connection of the aftertreatment analysis model to a user-definable ambient. Two aftertreatment boundaries (one inlet and one outlet) can be connected to one catalytic converter model or one diesel particulate filter. The application of this type of boundary can only be used for aftertreatment analysis simulations. More detailed information can be found in the BOOST Aftertreatment Manual. Note: Input values for an aftertreatment boundary are considered to be periodic. This means the defined period is repeated until the end of the simulation. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-61 3.4.4.3. Internal Boundary The internal boundary element allows boundary conditions for the calculation model to be specified directly in the last cross section of a pipe where a model ends. It is extremely helpful if measured boundary conditions in the intake and exhaust pipe of a cylinder are available. In this case a simplified sub-model of the engine between the two measuring points is made. An internal boundary is placed at the location of the measuring point, and the measured pressure and temperature over crank angle are specified. Figure 3-50: Engine Cylinder Sub-model General Select Save Energy and Mass for Backflow to determine the temperature boundary condition when flow is into the pipe from the accumulated flow out of the pipe into the boundary. Boundary Conditions Both local or global boundary conditions can be set. In the later case one of the predefined global sets can be used to specify the boundary conditions. The gas conditions in the pipe (pressure, temperature, air/fuel ratio, fuel vapor and combustion products) must be specified either as constant values or in a Table as a function of time or crank angle. If internal mixture preparation is selected, the input of fuel vapor and combustion products is disabled. In this case the A/F Ratio represents the A/F Ratio of the mixture of air and combustion products in the pipe, and no unburned fuel in the pipe is allowed. If external mixture preparation is considered, the A/F ratio represents the A/F ratio of the combustion products in the pipe. In addition, the mass fractions of the combustion products and of the fuel vapor in the pipe must be specified. The input of user-defined concentrations is disabled if the number of user-defined concentrations has been set to zero. BOOST Version 4.0.4 User’s Guide 3-62 23-Jun-2004 3.4.5. Transfer Elements 3.4.5.1. Flow Restriction The flow restriction element is used to consider a distinct pressure loss at a certain location in the piping system. This pressure loss may be caused by a geometrical restriction of the pipe cross-section (e.g. a butterfly valve, an orifice plate, etc.), or by a flow separation at that location caused by a step in the diameter of the piping or by a narrow elbow. For a flow restriction, flow coefficients must be specified for both possible flow directions. The flow coefficients are defined as the ratio between the actual mass flow and the loss- free isentropic mass flow for the same stagnation pressure and the same pressure ratio. The flow coefficients of restrictions depend very much on the design details of the restriction (control valve, orifice, flow separation, sudden change of diameter etc.). Standard values for the flow coefficients can only be given for a sudden change of the diameter. For a sudden expansion of the flow (flow direction from a smaller to a larger diameter pipe), the flow coefficients depend mainly on the cross-sectional area ratio. This influence is considered automatically by the BOOST program. The values specified in the input cover only the deterioration over the ideal geometry. Therefore, a value of 1.0 is recommended for a well manufactured diameter step. For a sudden contraction of the flow (flow from a larger to a smaller diameter pipe), the flow coefficients depend again mainly on the cross-sectional area ratio and on the relative radius at the inlet to the smaller pipe. This is defined as the actual radius divided by the (hydraulic) diameter of the smaller pipe (refer to Figure 3-51). Figure 3-51: Sudden Diameter Change User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-63 Area Ratio (d/D)² Relative Radius (r/d) 0.0 .4 .7 .9 1.0 0.0 .815 .865 .915 .960 1.0 0.02 .855 .895 .935 .970 1.0 0.06 .910 .935 .960 .980 1.0 0.12 .955 .970 .980 .990 1.0 >0.20 .985 .990 .995 .998 1.0 Values between the specified points can be obtained by linear interpolation. For all other types of restriction, the flow coefficients must be determined by steady state flow tests or estimated from the geometrical restriction of the pipe cross-section. Note: In BOOST the flow coefficients of restrictions are always related to the minimum attached pipe cross-section. BOOST allows the values for the user-defined concentrations to be defined at each flow restriction by selecting the respective switch. If this option is selected, the specified values for the user-defined concentrations will be permanently attributed to the mass flow at this location. 3.4.5.2. Rotary Valve Rotary valves are used to control the air flow in a pipe as a function of crank angle or time. A typical application is the control of the intake process of a two-stroke engine. In the BOOST system the rotary valve is treated in a similar way to the flow restriction For the rotary valve the flow coefficients must be specified for both possible flow directions depending on the time in seconds or on crank angle. The flow coefficients are defined as the ratio between the actual mass flow in the loss-free isentropic mass flow for the same stagnation pressure and the same pressure ratio. Note: For the rotary valve, the flow coefficients are related to the minimum pipe cross-section attached. BOOST allows the values for the user-defined concentrations to be defined at each rotary valve by selecting the respective switch. If this option is selected the specified values for the user-defined concentrations will be attributed to the mass flow at this location. BOOST Version 4.0.4 User’s Guide 3-64 23-Jun-2004 3.4.5.3. Check Valve A check valve is a pressure actuated valve used to prevent reverse flow. Two models are available: 1. Simplified Check Valve Model The flow resistance of the valve only depends on the pressure difference over the check valve. No inertia effects of the valve are considered. In this case BOOST requires the specification of flow coefficients for both possible flow directions as a function of the pressure difference over the check valve. 2. Full Check Valve Model The dynamic valve lift is calculated using an equivalent spring-damper-mass system. The flow coefficients must be specified as a function of the valve lift. The moving masses, damping coefficient, valve spring pre-load and valve spring rate must be defined. Furthermore, the specification of reference areas is required in order to calculate the forces acting on the valve resulting from the pressure difference over the valve. BOOST allows different reference areas for the closed valve and opened valve to be specified. The maximum valve lift may be limited as is often the case in real check valve configurations. Flow coefficients as a function of valve lift must be specified for both possible flow directions. BOOST allows the values for the user-defined concentrations to be defined for each check valve by selecting the respective switch. If this option is selected, the specified values for the user-defined concentrations will be permanently attributed to the mass flow at this location. 3.4.5.4. Fuel Injector / Carburetor The injector element is used for engines with external mixture preparation to add the fuel to the air in the intake system. Note: Wall film transport and evaporation model for the fuel are currently not available. Only completely vaporized fuel is added. To consider the particular pressure losses resulting from multi-dimensional flow phenomena which cannot be predicted by the program, BOOST requires the specification of flow coefficients at the fuel injector. The flow coefficients are defined as the ratio between the actual mass flow and a loss-free isentropic mass flow for the same stagnation pressure and the same pressure ratio. The fuel supply is specified by the A/F ratio. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-65 If the carburetor model is used, the instantaneous mass flow at the carburetor position is used together with the specified A/F ratio to calculate the amount of fuel supplied. Due to oscillating flow at the carburetor location a considerable enrichment of the mixture may occur. Note: It is necessary to check the actual A/F ratio in the cylinder and to correct the A/F ratio at the carburetor if the values are different to those desired. For the fuel injector model, a measuring point at the position of the air flow meter must be specified. In this case the fueling is calculated from the mass flow at the air flow meter position and the specified A/F ratio. As the air flow meter usually serves more than one injector, the percentage of the total air flow served by each injector must be specified. 3.4.5.5. Pipe Junction For the junction of pipes three sub-models are available: 1. Constant Pressure Model Flow coefficients for flow to the junction and flow out of the junction must be specified explicitly by the user for each pipe attachment. The flow coefficients for the pipe attachments may be specified either as constant values or as functions of time in seconds, time in degrees crank angle or on the pressure difference at the pipe attachment. For in-flow (flow into the junction), the pressure difference is defined as the static pressure in the pipe minus the pressure at the junction, and for out-flow as the pressure at the junction minus the static pressure in the pipe. Note: This model corresponds to a plenum with zero volume. The momentum of flow into the constant pressure junction is lost. 2. Constant Static Pressure Model This junction model enforces the same static pressure in all pipe cross sections attached to the junction. 3. Refined Model (Three-way Pipe Junctions) An accurate calculation model based on the equations for orifice flow is available. This model requires flow coefficients for each flow path in each possible flow pattern, which adds up to two times six flow coefficients. Figure 3-52 shows the qualitative trend of these flow coefficients versus the ratio of the mass flow in a single branch to the mass flow in the common branch for a joining flow pattern. BOOST Version 4.0.4 User’s Guide 3-66 23-Jun-2004 Figure 3-52: Flow Coefficients of a Junction The actual values depend on the geometry of the junction, i.e. the area ratio and the angle between the pipes. BOOST interpolates suitable flow coefficients for the considered junction from a database (RVALF.CAT) delivered with the program. The database contains the flow coefficients of six junctions, covering a wide range of area ratios and angles. The data was obtained from measurements on a steady state flow test rig. The file RVALF.CAT is a formatted ASCII file. The user may add measured flow coefficients for special junctions or for an extension of the catalogue. The structure of the file is as follows: MEASURED 0 30 1.3158 1.6900 11 0 0.7600 0.0000 0.2332 0.4385 0.6072 0.7400 0.8380 0.9032 0.9381 0.9462 0.9314 0.9029 12 30 0.5917 0.0000 0.1732 0.3530 0.5208 0.6624 0.7691 0.8375 0.8696 0.8727 0.8595 0.8490 21 30 1.6900 0.0000 0.0785 0.1517 0.2205 0.2859 0.3486 0.4087 0.4661 0.5202 0.5702 0.6192 22 150 1.2844 0.0000 0.0740 0.1430 0.2077 0.2690 0.3268 0.3807 0.4294 0.4712 0.5036 0.5418 31 0 1.3157 0.0000 0.1311 0.2565 0.3696 0.4696 0.5567 0.6315 0.6954 0.7507 0.8001 0.8241 33 150 0.7785 0.0000 0.1212 0.2297 0.3249 0.4061 0.4735 0.5271 0.5680 0.5972 0.6163 0.6351 41 0 1.3157 0.0000 0.1498 0.2997 0.4495 0.5133 0.5964 0.6811 0.7619 0.8453 0.9498 1.0800 42 30 1.6900 0.0000 0.1710 0.3420 0.5130 0.6099 0.7049 0.7894 0.8606 0.9216 0.9812 1.0400 51 30 0.5917 0.0000 0.0410 0.0831 0.1266 0.1720 0.2196 0.2698 0.3231 0.3795 0.4394 0.5023 52 150 0.7785 0.0000 0.0672 0.1290 0.1862 0.2394 0.2894 0.3366 0.3812 0.4234 0.4632 0.4944 61 0 0.7600 0.0000 0.0489 0.1006 0.1552 0.2135 0.2761 0.3439 0.4180 0.4995 0.5896 0.6862 62 150 1.2844 0.0000 0.1275 0.2319 0.3197 0.3952 0.4620 0.5226 0.5785 0.6304 0.6678 0.6959 S1 0 1.3157 0.6192 0.6892 0.7526 0.8059 0.8452 0.8687 0.8767 0.8720 0.8593 0.8456 0.8241 S2 30 1.6900 0.8241 0.8456 0.8593 0.8720 0.8767 0.8687 0.8452 0.8059 0.7526 0.6892 0.6192 CATALOGUE 0 90 1.6900 1.3158 11 0 0.5917 0.0000 0.2751 0.5096 0.6916 0.8227 0.9069 0.9510 0.9644 0.9643 0.9603 0.9496 12 90 0.7600 0.0000 0.1051 0.2158 0.3242 0.4236 0.5095 0.5796 0.6337 0.6739 0.7042 0.7380 21 90 1.3157 0.0000 0.0858 0.1615 0.2304 0.2943 0.3540 0.4098 0.4608 0.5055 0.5417 0.5715 22 90 0.7785 0.0000 0.1377 0.2595 0.3673 0.4626 0.5465 0.6196 0.6818 0.7328 0.7715 0.7985 31 0 1.3157 0.0000 0.0828 0.1701 0.2610 0.3545 0.4486 0.5403 0.6259 0.7006 0.7490 0.7705 32 90 0.7785 0.0000 0.0863 0.1697 0.2491 0.3241 0.3942 0.4589 0.5175 0.5691 0.6128 0.6575 41 0 1.6900 0.0000 0.1103 0.2298 0.3531 0.4760 0.5969 0.7167 0.8389 0.9698 1.1182 1.3000 42 90 1.3157 0.0000 0.1391 0.2488 0.3375 0.4121 0.4778 0.5385 0.5966 0.6532 0.7080 0.7520 51 90 0.7600 0.0000 0.0611 0.1255 0.1904 0.2538 0.3142 0.3708 0.4236 0.4730 0.5200 0.5609 52 90 1.2844 0.0000 0.1019 0.2085 0.3155 0.4192 0.5166 0.6054 0.6842 0.7523 0.8098 0.8446 61 0 0.5917 0.0000 0.0529 0.1057 0.1583 0.2112 0.2646 0.3193 0.3757 0.4349 0.4975 0.5619 62 90 0.7785 0.0000 0.0829 0.1565 0.2240 0.2874 0.3482 0.4075 0.4653 0.5213 0.5745 0.6217 S1 0 1.6900 0.5715 0.6028 0.6318 0.6617 0.6901 0.7149 0.7350 0.7501 0.7602 0.7665 0.7705 S2 90 1.3157 0.7705 0.7665 0.7602 0.7501 0.7350 0.7149 0.6901 0.6617 0.6318 0.6028 0.5715 User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-67 The lines are described as follows: 1 st line: • Measured: The flow coefficients are used for a junction with the same area ratio and the same angle between the pipes. • Catalogue: The flow coefficients are used for the interpolation of flow coefficients if no suitable measured flow coefficients are found. They are not used even if the specified junction in the data set exactly matches the junction from which the catalogue data was obtained. • Deflection angle for flow path 1 (a → c), flow pattern 1 • Deflection angle for flow path 2 (a → b), flow pattern 1 • Area ratio between pipe a and c • Area ratio between pipe b and c 2 nd to 13 th line: • The first two characters indicate the flow pattern and the flow path. • Deflection angle of the specific flow path • Area ratio between the pipe attachments upstream and downstream of the specific flow path • Flow coefficients for the mass flow ratio 0, 0.1, 0.2, 0.9, 1.0 between the flow in the specific flow path and the total mass flow through the junction. 14 th and 15 th line: Additional flow coefficients for the special treatment of injector effects in flow pattern 4 (joining flow). These lines must be omitted if there is no flow against a pressure gradient. 3.4.6. Volume Elements 3.4.6.1. Plenum A plenum is defined as an element in which spatial pressure and temperature differences are not considered. This means that the momentum of the flow in the plenum is neglected. General Specify the volume of the plenum. In case of contained perforated pipes the effective volume is calculated by subtracting the volume of the contained pipes from the specified one. Wall Heat Transfer may be selected or deselected. If selected, input fields in the Wall Heat Transfer sub-group are activated. The specification of the plenum surface, the wall temperature, and the heat transfer coefficient are required. The user may specify the heat transfer coefficient directly or use a simplified heat transfer model for plenums incorporated in BOOST. In this case, the calculated heat transfer coefficient may be increased or decreased by means of an amplification factor. In order to determine the transient wall temperature, the wall thickness of the plenums, its material properties and data describing the ambient of the plenum are required. BOOST Version 4.0.4 User’s Guide 3-68 23-Jun-2004 Initialization The initial conditions (pressure, temperature, gas composition and user-defined concentrations) must be specified for a plenum, as well as flow coefficients for each pipe attachment. Flow Coefficients In order to consider particular pressure losses resulting from multi-dimensional flow phenomena which cannot be directly predicted by the program, BOOST requires the specification of flow coefficients for in-flow and out-flow at each pipe attachment. The flow coefficients are defined as the ratio between the actual mass flow and the loss-free isentropic mass flow for the same stagnation pressure and the same pressure ratio. The flow coefficients for each pipe attachment may be specified either as constant values or in a Table as functions of time in seconds, time in degrees crank angle or pressure difference at the pipe attachment. For in-flow (flow into the plenum) the pressure difference is defined as the static pressure in the pipe minus the pressure in the plenum and for out-flow as the pressure in the plenum minus the static pressure in the pipe. The flow coefficients for flow from the plenum into a pipe depend mainly on the protrusion of the pipe end through the wall in which it is installed, and on its bellmouth characteristics. The following table may be used to determine flow coefficients for well manufactured pipe attachments. Values between the specified points can be obtained by linear interpolation. Relative Inlet Radius Relative Edge Distance 0.0 .02 .06 .12 .20 0.0 .815 .855 .910 .950 .985 0.025 .770 .840 .910 .950 .985 0.075 .750 .830 .910 .950 .985 0.20 .730 .825 .910 .950 .985 >0.50 .710 .820 .910 .950 .985 The relative inlet radius is defined as the inlet radius divided by the (hydraulic) pipe diameter. The relative edge distance is defined as the protrusion of the pipe end through the wall in which it is mounted divided by the (hydraulic) pipe diameter. A relative edge distance equal to zero represents a pipe mounted flush with the wall. For flow out of a pipe into the plenum, a flow coefficient of 1.0 is normally used if there is no geometrical restriction in the orifice. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-69 Perforated Pipe Select to insert a perforated pipe in the plenum. Specify the following perforation data: Porosity and Porosity Discharge Coefficient for both flow directions, which determine the effective perforation flow area. Perforation Hole Diameter and Perforation Wall Thickness which have influence on the inertia of the flow across the perforation (Porosity, Perforation Hole Diameter and Perforation Wall Thickness can be specified pipe location dependent). Figure 3-53: Perforated Pipe in Plenum Window In addition to the specification of standard pipe and perforation data, input for the pipe ends is necessary. Four types of connection for a perforated pipe end are available as shown in the following figure: Figure 3-54: Perforated Pipes Contained in Plenum BOOST Version 4.0.4 User’s Guide 3-70 23-Jun-2004 1. If the pipe end is attached to the plenum boundary and there is no outside pipe connected to the same anchor: this results in the pipe end being connected to a system boundary. This system boundary will be automatically generated but not shown on the screen. Additional data for this system boundary has to be specified. The data for this system boundary can be input in the data window for the appropriate perforated pipe. 2. If the pipe end is attached to a plenum boundary and an outside pipe connects to the same anchor: This results in a connection via a restriction element between these two pipes. The restriction will be automatically generated but not shown on the screen. Additional data for this restriction has to be specified. The data for this restriction can be input in the data window for the appropriate perforated pipe. 3. If a single pipe end is attached to an anchor point inside the plenum: This results in a connection between the pipe end and the plenum. The flow coefficients for the inflow and outflow from this pipe have to be specified in the data window for the plenum. 4. If two pipe ends are attached to the same anchor point inside the plenum: This results in a connection via a restriction element between these two pipes. The restriction will be automatically generated but not shown. Additional data for this restriction has to be specified. 3.4.6.2. Variable Plenum The variable plenum is similar to a standard plenum and in addition considers the change of the volume and surface area of the plenum over time. The user may specify the volume over time explicitly by selecting one of the following: 1. User-Defined BOOST allows the volume and the surface area to be specified depending on time in seconds or on time in degrees crank angle. Zero volume is not allowed as input. 2. Crankcase The user must specify the number of the cylinder to which the defined crankcase is related. By specifying the geometrical crankcase compression ratio, which is defined as the volume of the crankcase with the piston at TDC divided by the volume of the crankcase with the piston at BDC, the geometrical definition of the crankcase is completed. For consideration of the wall heat transfer in a crankcase BOOST requires the specification of the minimum plenum surface area (piston at BDC), the wall temperature, and the heat transfer coefficient. Similar to the plenum data for the calculation of the heat balance of the variable plenum wall can be specified by the user. The heat transfer coefficient may be specified directly or a simplified heat transfer model for plenums incorporated in BOOST can be used. 3. Scavenging Pump A scavenging pump is defined as a pumping cylinder which is directly actuated by the crankshaft. This means that the speed of the scavenging pump is equal to engine speed. For consideration of the power consumption of the scavenging pump the user must specify to which cylinder the scavenging pump is attached. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-71 The geometrical specifications of a scavenging pump cover the TDC delay relative to the attached cylinder, the bore and the stroke of the pumping cylinder as well as the con-rod length and the piston pin offset. The definition of the volume of the scavenging pump over crank angle is completed by the specification of the scavenging pump compression ratio, which is defined as the BDC volume divided by the TDC volume. 3.4.6.3. Perforated Pipe in Pipe In addition to the standard pipe data for inner and outer pipe, the following perforation data should be specified in the following window: Figure 3-55: Perforated Pipe in Pipe Window Porosity and Porosity Discharge Coefficient for both flow directions, which determine the effective perforation flow area. Perforation Hole Diameter and Perforation Wall Thickness which have influence on the inertia of the flow across the perforation (Porosity, Perforation Hole Diameter and Perforation Wall Thickness can be specified pipe location dependent). Heat transfer between the two pipes is not considered and the wall heat transfer dialog for the inner pipe is disabled. Note: The geometric outer pipe diameter should be input (not the diameter) to give the effective flow area in the outer pipe. This is because the effective flow area of the outer pipe is calculated from its cross sectional area less the cross sectional area of the inner pipe. BOOST Version 4.0.4 User’s Guide 3-72 23-Jun-2004 3.4.7. Assembled Elements 3.4.7.1. Air Cleaner For the air cleaner, the performance characteristics at the design point must be specified in addition to the geometrical data. BOOST automatically creates a more refined calculation model of a plenum-pipe-plenum type for the air cleaner. This is used to model the gas dynamic performance of the air cleaner as well as the pressure drop over the air cleaner depending on the actual flow conditions. Geometrical Properties The input of the total air cleaner volume, the inlet and outlet collector volumes and the length of the filter element is required. In addition, the user must specify what pipes are connected to the inlet and outlet of the air cleaner. It is important to note that the length of the filter element is also used to model the time a pressure wave needs to travel through the cleaner. Flow Coefficients Particular flow resistances at the inlet to and at the outlet from the air cleaner can be considered. The flow coefficients for the pipe attachments may be specified as a function of time in seconds, time in degrees crank angle or pressure difference at the pipe attachment. For in-flow (flow into the air cleaner) the pressure difference is defined as the static pressure in the pipe minus the pressure in the air cleaner collector, and for out-flow as the pressure in the air cleaner collector minus the static pressure in the pipe. Gas Properties The air cleaner performance is specified by means of a reference mass flow, the target pressure drop (defined as the static pressure difference at the inlet and the outlet pipe attachment) at the reference mass flow and the inlet air conditions (temperature and pressure), Figure 3-56. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-73 Figure 3-56: Steady State Air Cleaner Performance On the basis of this information, the wall friction loss of the model is adjusted by the program. 3.4.7.2. Catalyst For the catalyst, the performance characteristics at the design point must be specified in addition to the geometrical data. As for the air cleaner (refer to 3.4.7.1) BOOST automatically creates a more refined calculation model of the catalyst. This is used to model the gas dynamic performance of the catalyst as well as the pressure drop over the catalyst depending on the actual flow conditions. Note: The catalyst model in the BOOST cycle simulation is a purely gas dynamic model and does not include chemical reactions. Chemical reactions can be simulated using the aftertreatment analysis mode (refer to the Aftertreatment Manual). BOOST Version 4.0.4 User’s Guide 3-74 23-Jun-2004 Geometrical Properties The input of the total catalyst volume (i.e. the monolith volume consisting of the gas and also the solid structure), the inlet and outlet collector volumes and the length of the monolith is required. For the specification of the honeycomb cell structure the user can choose between the input of a square cell or general catalyst. In the first case the cell structure can be defined via CPSI values and wall thickness, in the latter the user can directly input the catalysts open frontal area (OFA), the channel hydraulic unit (diameter or area) the geometric surface area (GSA). The friction of the catalyst either can be specified by reference conditions and a target pressure drop(refer to 3.4.7.1) or by using a friction coefficient and a friction multiplier. This friction coefficient is applied for turbulent flows, whereas for laminar flow the Hagen-Poisseuille law is evaluated. The input of the friction multiplier can be used for taking different channel shapes into account in both the laminar and turbulent flow region (refer to the Aftertreatment Manual). In addition, the user must specify what pipes are connected to the inlet and outlet of the catalyst. Flow Coefficients Particular flow resistances at the inlet to and at the outlet from the catalyst can be considered. The flow coefficients for the pipe attachments may be specified as a function of time in seconds, time in degrees crank angle, or on the pressure difference at the pipe attachment. For in-flow (flow into the catalyst) the pressure difference is defined as the static pressure in the pipe minus the pressure in the catalyst collector, and for out-flow as the pressure in the catalyst collector minus the static pressure in the pipe. Gas Properties The catalyst performance is specified by means of a reference mass flow, the target pressure drop at the reference mass flow, and the inlet air conditions (temperature and pressure). On the basis of this information, the wall friction loss of the model is adjusted by the program. 3.4.7.3. Air Cooler For the air cooler the performance characteristics at the design point must be specified in addition to the geometrical data. BOOST automatically creates a more refined calculation model of the air cooler (plenum-pipe-plenum). This is used to model the gas dynamic performance of the air cooler as well as the pressure drop over the air cooler depending on the actual flow conditions. In addition, a model for the cooling performance of the air cooler is created based on the layout data. Geometrical Properties The input of the total air cooler volume, the inlet and outlet collector volumes, and the length of the cooling core is required. In addition, the user must specify what pipes are connected to the inlet and outlet of the air cooler. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-75 Flow Coefficients Particular flow resistances at the inlet to and at the outlet from the air cooler can be considered. The flow coefficients for the pipe attachments may be specified as a function of time in seconds, time in degrees crank angle, or on the pressure difference at the pipe attachment. For in-flow (flow into the air cooler), the pressure difference is defined as the static pressure in the pipe minus the pressure in the air cooler collector, and for out-flow as the pressure in the air cooler collector minus the static pressure in the pipe. Gas Properties The gas dynamic performance is specified by means of a reference mass flow, the target pressure drop at the reference mass flow, and the inlet air conditions (temperature and pressure). The cooling performance is specified by the coolant temperature and the target outlet temperature or the target efficiency. The cooler efficiency is the achieved temperature difference related to the maximum possible temperature difference: cool in out in c T T T T − − = η (3.4.3) c η cooler efficiency in T inlet temperature out T outlet temperature cool T coolant temperature On the basis of this information, the wall friction loss and the heat transfer in the pipe modeling the cooling core are adjusted by the program. 3.4.7.4. Diesel Particulate Filter (DPF) For the DPF, the performance characteristics at the design point must be specified in addition to the geometrical data. As for the air cleaner (refer to 3.4.7.1) BOOST automatically creates a more refined calculation model of the DPF. This is used to model the gas dynamic performance of the DPF as well as the pressure drop over the DPF depending on the actual flow conditions. Note: The DPF model in the BOOST cycle simulation is a purely gas dynamic model and does not include chemical reactions. Chemical reactions can be simulated using the aftertreatment analysis mode (refer to the Aftertreatment Manual). Geometrical Properties The input of the total DPF volume consisting of the gas and the solid volume fraction, the inlet and outlet collector volumes in conjunction with the length of the monolith is required. For the specification of the honeycomb cell structure the user can choose between a square cell or general DPF. For the former, the cell structure may be defined via CPSI values and wall thickness, in the latter the user can directly input the DPF open frontal area (OFA), the channel hydraulic unit (diameter or area) the geometric surface area (GSA). BOOST Version 4.0.4 User’s Guide 3-76 23-Jun-2004 The friction of the DPF either can be specified by reference conditions and a target pressure drop (refer to 3.4.7.1), or by using a friction coefficient and a friction multiplier. This friction coefficient is applied for turbulent flows, whereas for laminar flow the Hagen- Poisseuille law is evaluated. The input of the friction multiplier can be used for taking different channel shapes into account in both the laminar and turbulent flow region (refer to the Aftertreatment Manual). Flow Coefficients Particular flow resistances at the inlet to and at the outlet from the DPF can be considered. The flow coefficients for the pipe attachments may be specified as a function of time in seconds, time in degrees crank angle, or on the pressure difference at the pipe attachment. For in-flow (flow into the DPF) the pressure difference is defined as the static pressure in the pipe minus the pressure in the DPF collector, and for out-flow as the pressure in the DPF collector minus the static pressure in the pipe. Gas Properties The DPF performance is specified by means of a reference mass flow, the target pressure drop at the reference mass flow, and the inlet air conditions (temperature and pressure). On the basis of this information, the wall friction loss of the model is adjusted by the program. 3.4.8. Charging Elements 3.4.8.1. Turbocharger Two types of turbocharger models are available: 1. Simplified Model This model is only suitable for steady state simulations. BOOST considers the mean compressor and turbine efficiencies over the cycle in order to calculate the turbocharger energy balance. The advantage of this model is that it only requires limited data to describe the turbocharger performance characteristics. Furthermore, this model provides three modes for the turbocharger simulation: • Boost pressure calculation: The boost pressure is calculated from the specified turbine size and turbocharger efficiency. • Turbine layout calculation: The required turbine size is calculated from the target pressure ratio across the compressor and the turbocharger efficiency. • Waste-gate calculation: The waste-gate mass flow is calculated from the target pressure ratio across the compressor, the turbocharger efficiency and the specified turbine size. If the target pressure ratio cannot be achieved even with the waste- gate closed, the boost pressure which can be achieved will be calculated from the specified turbine size. Input data and calculation result relative to the turbocharger mode are shown in the following table: User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-77 Boost Pressure Turbine Layout Waste Gate Turbine size input result input Compressor pressure ratio result input input Turbine to total mass flow rate 1 1 result The turbine size is specified by the equivalent discharge coefficient of the turbine. The effective flow area of the turbine is calculated from the equivalent discharge coefficient and the cross-section of the pipe representing the turbine outlet. The conversion of the swallowing capacity taken from the turbine map at a certain pressure ratio to an effective flow area is done with Equation 3.4.4: 1 2 − • ⋅ | | | . | \ | = ψ R po To m A eff (3.4.4) eff A effective flow area po To m • swallowing capacity R gas constant ψ pressure function The pressure function ψ is evaluated at the pressure ratio at which the effective flow area is to be determined. Typical values for the gas constant R and the ratio of specific heats of combustion gases are 287 J/kgK and 1.36 respectively. When evaluating the pressure function ψ it must be observed whether the pressure ratio is supercritical. In this case, max ψ must be used instead of ψ . To determine the swallowing capacity from an effective turbine flow area obtained by a turbine layout calculation, Equation 3.4.4 must be solved for po To m . . The equivalent turbine discharge coefficient may be specified as a function of the turbine expansion ratio (Table ). The compressor efficiency can be taken from the compressor performance map using the expected pressure ratio and compressor mass flow data. The turbine efficiency can be taken either from a full turbine operating map (if available), or from any equivalent information provided by the turbocharger supplier. The turbocharger overall efficiency is the product of compressor efficiency, turbine efficiency and mechanical efficiency of the turbocharger. BOOST Version 4.0.4 User’s Guide 3-78 23-Jun-2004 For twin entry turbines and multiple entry turbines, the reduction of the turbine efficiency due to the unequal flow distribution at unequal pressure ratios across the flows is taken into account by a reduction of the turbine efficiency. Figure 3-57 shows the factor by which the turbine efficiency is multiplied depending on the pressure ratio between the flows. Figure 3-57: Deterioration Factor of a Twin Entry- or Multiple Entry Turbine Note: The turbine efficiency output in the global results or in the transients is the mass flow weighted average of the calculated efficiency over one cycle. For the BOOST pressure calculation the pressure ratio at the compressor only represents an initial value for the start of the calculation. Similarly, the equivalent discharge coefficient of the turbine only represents an initial value for the turbine layout calculation. In the case of a twin entry turbine or a multiple entry turbine, an inlet flow coefficient must be specified in order to describe the interference between the attached pipes. The inlet interference flow coefficient is related to the cross-section of the pipe representing the turbine inlet. For radial type turbines, an inlet interference flow coefficient of 0.2 is recommended and for axial type turbines a value of 0.05 is recommended. In the case of a waste-gate calculation, an initial value for the ratio between the mass flow through the turbine and the total exhaust mass flow (through turbine and waste- gate) also must be specified. The attachment type of each pipe (compressor inlet/outlet, turbine inlet/outlet) is known from the sketch of the model and can be checked in the Pipe Attachments sub- group. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-79 2. Full Model This model requires the input of the entire compressor and the entire turbine map. Compressor In the compressor map, iso speed lines (pressure ratio versus mass or volume flow) and lines of constant isentropic efficiency are plotted. The map is limited to the left side by the surge line. Beyond this line the mass flow through the compressor becomes unstable and the compressor will be destroyed if operated too often in this area. On the right side the map is limited by choked flow either through the compressor wheel or the diffuser. This is indicated by the steep gradient of the iso speed lines, see the following figure. Figure 3-58: Compressor Map Before the map can be input, the unit of the wheel speed and the x-axis of the map must be set. They may be related to a reference condition defined in the box. The suitable units may be selected from the list. For the specification of the compressor map points defined by the mass or volume flow, the pressure ratio, the wheel speed and the isentropic efficiency must be input by the user. In addition the x-axis of the compressor map can be scaled with the mass flow scaling factor and the efficiencies modified additively by the efficiency offset. Turbine The following turbine types are available for defining the turbine performance map: • Single entry • Single entry - Variable Turbine Geometry (VTG): For each vane position a map must be defined. • Twin entry - simplified model: Only one map is specified. The map is measured with the same pressure ratio across both flows of the turbine. The interaction between the flows can be modeled by the definition of a suitable inlet interference coefficient. BOOST Version 4.0.4 User’s Guide 3-80 23-Jun-2004 • Twin entry - full model: For each ratio of the total pressures at the turbine entry, a map containing the swallowing capacity of the two flows must be specified. • Twin entry – VTG - simplified model: For a twin entry VTG only the simplified model is available. • Multiple entry - simplified model: Only one map is specified. The map is measured with the same pressure ratio across all flows of the turbine. The interaction between the flows can be modeled by the definition of a suitable inlet interference coefficient. • Multiple entry – VTG - simplified model The vane position must be set for VTG’s. In a turbine map (Figure 3-59) the swallowing capacity is plotted versus the pressure ratio across the turbine with the wheel speed as parameter. The isentropic efficiency can be plotted in the same way or it can be plotted versus the blade speed ratio. BOOST supports the input of both map types. The suitable units for the definition of the swallowing capacity and the reference conditions can be selected from predefined lists. Similar to the compressor map, the data for the definition of each point in the map must be input by the user. For each map a mass flow scaling factor allows the user to scale the swallowing capacities specified and an efficiency offset to modify the efficiencies additively. For steady state simulations, an internal boost pressure control may be activated. For fixed geometry turbines an internal waste-gate is simulated, similar to the simplified model. For turbines with variable geometry, the vane position is determined. Select Internal Wastegate Simulation / Determination of vane position to activate the boost pressure control. The user must specify the target compressor pressure ratio and the initial value for the turbine to total massflow ratio (fixed geometry turbine only) in this case. Note: It is assumed that vane position 0 is the fully closed position and vane position 1 is the fully open position. In addition to the maps, the total inertia of the turbocharger wheel together with the setting of the unit and the mechanical efficiency of the turbocharger must be defined. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-81 Figure 3-59: Turbine Map The BOOST pre-processor features an import filter for digital compressor and turbine maps as ASCII-files according to SAE standard J1826 [T2]. The format of the files is: Compressor: Line 1: Description (supplier, model name, compressor nomenclature, reference test number) A15, A10, A20, A10 Line 2: Inlet diameter (mm), outlet diameter (mm), inlet type, outlet type, impeller inertia (N-m-s²) F10, F10, A15, A15, F10) Line 3, 4, 5: Additional comments (can be left blank) A80 Line 6 – N: Corrected speed (r/min), corrected mass flow (kg/s), pressure ratio (T-S), efficiency (decimal) F10, F10, F10, F10 Note: Corrected mass flow rates and speeds are listed in ascending order. BOOST Version 4.0.4 User’s Guide 3-82 23-Jun-2004 The following table shows an example supplier model compressor name ref. # 30.000 40.000 inlet type outlet type 0.0011 comment 1 comment 2 comment 3 20000 0.006 1.075 0.4 20000 0.025 1.05 0.42 40000 0.009 1.12 0.3 40000 0.05 1.02 0.5 80000 0.0368 1.3 0.65 80000 0.0515 1.26 0.7 80000 0.0632 1.233 0.7 80000 0.0794 1.15 0.65 100000 0.0368 1.5 0.65 100000 0.05 1.475 0.7 100000 0.1 1.26 0.65 120000 0.0441 1.74 0.65 120000 0.1 1.577 0.77 120000 0.125 1.38 0.65 140000 0.0574 2.04 0.65 140000 0.0735 2.01 0.7 Turbine: Line 1: Description (supplier, model name, turbine nomenclature, reference test number) A15, A10, A20, A10 Line 2: Test compressor, housing type, discharge connection description A20, A20, A20 Line 3: Inlet gas temperature (°C) or turbine inlet-to- compressor discharge temperature ratio (K/K), oil type, oil temperature (°C), rotor/shaft inertia (N-m-s²) F10, A10, F10, F10 Line 4: Cooling liquid description (if any), inlet temperature (°C), inlet pressure (kPa) A20, F10, F10 Line 5, 6, 7: Additional comments (can be blank) A80 Line 8 – N: Speed parameter (r/min – K), mass flow parameter (kg – K/s-kPa), expansion ratio (T-S), turbine x mechanical efficiency (decimal) F10, F10, F10, F10 Note: Expansion ratios and speeds are listed in ascending order. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-83 The following table shows an example supplier model turbine name ref. # test compressor housing type discharge connect. 800.00 oiltype 100.000 0.0011 cooling liquid 120.000 1500.00 comment 1 comment 2 comment 3 44000 4.33 1.5 0.52 44000 4.47 1.54 0.53 44000 4.53 1.58 0.53 55000 4.8 1.71 0.52 55000 5 1.8 0.54 55000 5.07 1.88 0.53 66000 5.2 2.02 0.52 66000 5.4 2.15 0.54 66000 5.53 2.28 0.55 The following table gives an overview about the usage of the different models and their modes together with the external waste gate element for steady state and transient simulations: simplified model Full model boost pressure turbine layout waste gate With internal boost pressure control Without internal boost pressure control calculation mode Steady state Without waste gate element Yes Yes Yes Yes Yes With waste gate element No Yes Yes No No Transient Without waste gate element No Yes No No No With waste gate element No Yes No No No BOOST Version 4.0.4 User’s Guide 3-84 23-Jun-2004 3.4.8.2. Positive Displacement Compressors For a mechanically driven positive displacement compressor, BOOST requires the specification of the performance characteristics along a line of constant compressor speed (Simplified Model) or the full performance map (Full Model). The full set of performance characteristics consists of the mass flow or volume flow characteristics, the temperature increase or isentropic efficiency and the power consumption or total efficiency as a function of pressure ratio. Figure 3-60: PD-Compressor Map The flow characteristics of the compressor may be specified either as the corrected mass flow over pressure ratio (defined as the actual mass flow multiplied by the ratio between inlet air temperature and reference air temperature, and the ratio between reference inlet pressure and air inlet pressure), or by the volume flow over pressure ratio. If the corrected mass flow is selected, the reference inlet pressure and the reference inlet temperature must be specified also. For the specification of the internal efficiency of the compressor, either the temperature increase over pressure ratio for reference inlet conditions or the isentropic efficiency may be specified. The information on the mechanical losses of the blower is obtained from the specification of the power consumption over pressure ratio at reference conditions or from the specification of the total efficiency. Using the Simplified Model all performance characteristics may be specified in a Table as a function of pressure ratio at the compressor (iso-speed line) or in a simplified way as a constant value. Applying the Full Model all performance characteristics have to be specified in the compressor operating map. In order to facilitate the input of operating maps provided by various hardware suppliers, BOOST allows the selection of the most suitable dimensions. The attachment type of each pipe (inlet/outlet) is known from the sketch of the model. They can be checked by clicking pipe attachments. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-85 3.4.8.3. Turbo Compressor For the simulation of a mechanically driven turbo-compressor, BOOST requires the specification of the mechanical efficiency, the specification of the performance characteristics of the turbocompressor along a line of constant compressor speed (Simplified Model) or the full map similar to the map of the compressor of a turbocharger (Full Model) refer to Figure 3-58. Using the Simplified Model the pressure ratio and the isentropic efficiency may be specified over the corrected mass flow or over the corrected volume flow for a line of constant turbo-compressor speed (Table ). For a simplified approach, constant values of pressure ratio and isentropic efficiency may also be specified. The corrected volume flow is defined as the actual volume flow multiplied by the square root of the ratio between reference and actual air inlet temperature. The corrected mass flow is defined as the actual mass flow multiplied by the square root of the ratio between inlet and reference inlet air temperature, and the ratio between reference and actual air inlet pressure. To match the actual calculated flow characteristics to the corrected volume or mass flow data, BOOST requires the specification of the reference temperature and reference pressure related to the correct flow data. They must be taken from the performance maps provided by the supplier. In order to facilitate the input of operating maps provided by various hardware suppliers, BOOST allows the selection of the most suitable dimensions. The attachment type of each pipe (inlet/outlet) is known from the sketch of the model and can be checked in the Pipe Attachments sub-group. 3.4.8.4. Waste Gate A waste gate is a valve actuated by the pressure difference on the valve body plus the pressure difference on a diaphragm mechanically linked to the valve body. The instantaneous valve lift is calculated using an equivalent spring-damper-mass system. The flow coefficients must be specified as a function of valve lift. General The area on the high and low pressure side of the diaphragm are required in order to calculate the forces acting on the valve resulting from the respective pressures. The maximum lift of the valve may be limited. Flow coefficients for flow must be specified. A leakage through the control diaphragm can be modeled by the input of a suitable flow coefficient for flow from the high to the low pressure side and vice versa. This flow is treated in the same way as the flow through a flow restriction. Valves The area of the valve body exposed to the high pressure with the valve closed and opened and the area of the valve body exposed to the low pressure are required. The moving masses, damping coefficient, valve spring pre-load and valve spring rate must be defined. BOOST Version 4.0.4 User’s Guide 3-86 23-Jun-2004 Flow Coefficients Flow coefficients as a function of valve lift must be specified in both possible flow directions. If an electronically controlled waste gate is modeled, a flow restriction influenced by the engine control unit should be used. 3.4.9. External Links Elements 3.4.9.1. FIRE Link Please refer to the FIRE–BOOST 1D-3D Coupling Manual for further information. 3.4.9.2. User Defined Element The User-Defined-Element (UDE) allows the user to include user-defined elements in the calculation model. The UDE is supported in both the pre and post-processor. Special subroutines allow user written code to simulate the element. The user written routines must be compiled and linked to create a new BOOST executable to run the model. The Appendix includes the options for compiling and linking a new BOOST executable. Data handling for all the pipe attachments is done by the UDE. The output generated by the user’s algorithm may be analyzed with the BOOST post-processor provided that the BOOST interface routines are used. For this purpose, the Number of Output Values must be input in the UDE General window. This defines the size of the vector for the output values. For each value a time average will be output in the TRANSIENT section and crank angle resolved data in the TRACES section. In addition to the number of output values, the flow coefficients at each pipe attachment must be defined. Similar to the system boundary or the plenum, different flow coefficients may be defined for in- and outflow of the UDE. The flow coefficients may also depend on time in degree crank angles or seconds or on the pressure difference between the UDE and the attached pipe cross section. Figure 3-61: UDE Input Please request the user written source code from
[email protected]. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-87 3.4.10. Control Elements There are two main types of engine control element available in BOOST: Internal Control Element: ECU External Link Elements: MATLAB API and MATLAB DLL The link to an External Control Element Library is a complementary element to the Engine Control Unit (ECU) element. It may be used to incorporate complex models of engine control and management systems developed with MATLAB/SIMULINK (MATLAB- API Element, MATLAB-DLL Element) or any commercial software featuring C-code generation (MATLAB-DLL Element). All the important functions of an electronic engine control device can be simulated. Figure 3-62 shows a flowchart giving an overview of the interaction between BOOST and the External Link. Figure 3-62: Interaction between BOOST and External-Link Element 3.4.10.1. Wire The wire element is a visual representation of a connection (information channel) between an engine control element (Engine Control Unit, MATLAB DLL, MATLAB API) and the elements. No specific input is required for the wire. The wire can represent both an actuator channel and a sensor channel. Elements providing sensor data to an External Link Element (or ECU) and elements controlled by actuators need to be connected to the External Link Element (or ECU) by a wire (exception: global engine data). The sensor channel and actuator channel selections are made in the control elements connected to the wires. BOOST Version 4.0.4 User’s Guide 3-88 23-Jun-2004 3.4.10.2. Engine Control Unit In order to facilitate the input of the Engine Control Unit specifications, the input is organized in several layers. In the first box the guiding input of the ECU is selected. Possible guiding inputs are: • Load signal: The load signal is a fictive input to the ECU. It can be understood as the drivers' command in a drive-by-wire arrangement. • Desired Engine Speed: The engine control calculates the load signal using the control gains proportional, integral and differential together with the deviation of the actual engine speed from the desired engine speed: ( ) ( ) ( ) ∫ − ⋅ ⋅ + ⋅ − + − ⋅ = t des des des dt n n d d dt n n i n n p ls 0 (3.4.5) ls load signal p proportional control gain i integral control gain d differential control gain n engine speed des n desired engine speed Both guiding inputs may be specified in the Table dependent on time. Note: The user must ensure that the available load signal is used correctly to control the engine load, i.e. to influence the flow restriction(s) modeling the throttle(s) for mixture aspirating engines or to influence the fueling for engines with internal mixture preparation. For the activation of dynamic functions thresholds for the maximum and minimum load gradient allowed must be defined. Then the Control Interaction Timestep (Cyclic / Every Calculation Timestep / Specified Timestep) must be selected. The selection of parameters to be controlled by the ECU is done inside the Map specification sub-group (elements connected by Wire and their possible actuator channels). User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-89 Figure 3-63: Selection of ECU Actuator Channels If the cylinders have identical specifications, only cylinder one is listed and the data is transferred to all other cylinders. The user must input maps for each actuator channel. First it must be determined whether a baseline map value or the last actual value should be used as starting value for the correction procedure. In the first case, the baseline map must be defined. The value in a map can depend on up to two sensor channels which are selected in the pull down menu for the element (global or wire connected) and the respective sensor channel. If only a table is defined either x- or y-value keeps it’s default setting none. If no dependency is specified this is equivalent to the specification of a constant value. Please refer to Chapter 9.3 for a list of available Actuator and Sensor Channels. BOOST Version 4.0.4 User’s Guide 3-90 23-Jun-2004 Figure 3-64: ECU Map Specification Before inputting map values, the size should be customized using Insert Row/Remove Row and Insert Col./Remove Col. Maps can be written to a separate file using Store or they can be read in from an external file using Load. Minimum and maximum maps are defined in the same way. If the baseline value is to be corrected depending on other parameters (e.g. ambient temperature or pressure) correction maps can be added by pressing the left mouse button on the tree item. In addition to the specification of the map the type of correction (multiplication or addition) must be defined. Note: Corrections are done in the same sequence as they are specified, i.e. a correction value added to the baseline value followed by a multiplicative correction will produce a different output than the same corrections done in the reverse order. If the positive gradient of the load signal exceeds the threshold specified in the first box, the corrections for acceleration become active. Their number, the maps themselves and the type of correction are specified in the same way as for the steady state corrections. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-91 A time lag for the activation and deactivation of the correction and the respective time constant (the time between 0 % and 99 % correction or 100 % and 1 % correction) complete the input of the acceleration corrections. Figure 3-65 shows the definition of the time intervals: Figure 3-65: Time Constants for Transient ECU Functions The procedure for the definition of the deceleration corrections is the same as for the acceleration corrections. BOOST Version 4.0.4 User’s Guide 3-92 23-Jun-2004 3.4.10.3. MATLAB DLL Element The MATLAB DLL junction can be used to exchange information between elements in a BOOST model and MATLAB/Simulink from Mathworks. This can be done by connecting wires between the MATLAB DLL junction and the appropriate element. The wire is used to pass both sensor (BOOST to MATLAB) and actuator (MATLAB to BOOST) data. Figure 3-66: MATLAB DLL Element Input There are two ways of using this element: MATLAB DLL BOOST can be run from the graphical user interface and dynamically loads a shared object created by MATLAB/Simulink. The full name and absolute path of this shared object must be given in the DLL Name input box (if the shared object isn’t located in the *.bst input-file directory the name has to contain the absolute path). • Feature supported for MATLAB V.5.3, V.6.0 and later versions. • Simulation should be run using the GUI (Simulation|Run) • The shared object must be created on the same operating system/platform on which BOOST is being run. • The MATLAB s-function link should not be selected. MATLAB s-function The BOOST model is run from MATLAB/Simulink via a system function. • Feature supported for MATLAB V.6.0 and later versions only. • The BOOST model should be created but not run by the BOOST GUI. The BOOST input file (*.bst) created should be specified as the BOOST input file name in the s- function mask. • Select the MATLAB s-function link. No DLL Name is required and will be grayed out when the check box is selected. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-93 CHANNEL SPECIFICATIONS Sensor Channels Figure 3-67: Sensor Channel Selection For the definition of the index of a Sensor value in the vector the channel numbers must be specified. This vector is passed to the External Link Element as input. If a type value is set to external (the External Link Element only), the user must supply its value either as a constant or in a Table as a function of time in seconds. Possible applications of an external input are gain coefficients of a control or a guiding input. Actuator Channels After selecting Actuator Specification, a box appears listing all elements connected to the DLL element which can have at least one parameter controlled by the DLL element. An example of this input is shown in the following figure: Figure 3-68: Actuator Channel Selection BOOST Version 4.0.4 User’s Guide 3-94 23-Jun-2004 If the cylinders have identical specifications, only cylinder one is listed and the data is transferred to all other cylinders. Similar to the sensor channels, the channel number defines the index of the Actuator value in the Actuator vector. Please refer to Chapter 9.3 for a list of currently available Actuator and Sensor Channels. 3.4.10.4. MATLAB API Element This element should be used when the model is to be run using the link to MATLAB using the API. Figure 3-69: MATLAB API Element Input In addition to the input of the Simulink-model (or m-Function) name, which performs the control algorithm, the name of the Sensor-channel and Actuator-channel vector must be specified (if the model isn’t located in the *.bst input-file directory the model name has to contain the absolute path). These vectors are introduced as members of the MATLAB Workspace and the Simulink-model (or m-Function). Then the Control Interaction Timestep (Cyclic / Every Calculation Timestep / Specified Timestep) must be specified. The Channel Specifications are done analogous to the MATLAB-DLL Element. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-95 3.4.11. Acoustic Elements 3.4.11.1. Microphone A microphone element can be added to any BOOST model in order to extract acoustic data such as overall dB(A) levels or order plots. The microphone is not attached to any pipes but linked in the input for the microphone to one or more system boundaries. Axis, x Vertical, z Lateral, y 0 Ground (optional) Height (optional) MICROPHONE ORIFICE Figure 3-70: Microphone Position The position of each system boundary relative to the microphone is defined as shown in the figure above. Results from each microphone in a model can be found in the Acoustics folder and the Transients folder. BOOST Version 4.0.4 User’s Guide 3-96 23-Jun-2004 3.5. Case Series Calculation Starting from a single case model, it is possible to create a case series calculation. This allows parameters to be assigned for a set of cases so that a series of operating points or engine variants can be calculated at one time. 3.5.1. Parameters Parameters can be assigned to input fields and are defined in Model|Parameters or Element properties windows. There are two types of parameters: 1. Global Parameters : These can be used for any element. 2. Local Parameters These can only used for individual elements and are used for: • Creating simplified and protected model views • Overriding commonly defined values by element-specific, local values. 3.5.1.1. Assign Parameters To assign a new or existing parameter in the properties dialog of an element, click the label to the left of the input value with the right mouse button to open the following submenu. Figure 3-71: Assign Parameter Menu Select Assign new parameter (global) or Assign new parameter (local), then enter a name for the new parameter, e.g. Speed. Select OK and it will replace the original input value. Select Assign existing parameter, then locate the predefined parameter in the dialog box. Note: Parameter names should not have any spaces. 3.5.1.1.1. Assign a Model Parameter Select Model|Parameters to show parameters for all elements used in the model (as shown in the following figure). User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-97 Figure 3-72: Model Parameter Window The parameter tree on the left shows all existing parameters for all elements of the model. Global parameters can be found at the top of the tree (e.g. Speed). On the right, the values of the parameters can be edited. Constant values or expressions can be used to define a value. Select Model and then select New Parameter to add new global parameter values. A default parameter name is automatically entered and this can be typed over as required. Select the required element and then select New Parameter to add new local parameter values. A default parameter name is automatically entered and this can be typed over as required. Enter the relevant value in the Value input field and select the relevant unit from the pull-down menu by clicking on the Unit input field. Select Delete to remove the selected parameter. 3.5.1.1.2. Assign an Element Parameter Select Element|Parameters to show the parameters of the selected element. Only the parameters in the element's domain can be edited in the table. To edit parameters for one element only, select the element in the working area and then select Parameters from the Element menu, or click the element with the right mouse button and select Parameters from the submenu. BOOST Version 4.0.4 User’s Guide 3-98 23-Jun-2004 3.5.1.1.3. Case Explorer The Case Explorer defines parameter variations for the model. Select Model|Case Explorer to open the following window. Figure 3-73: Case Explorer Window In this window 5000rpm is the active case as it has a red circle. To make a case active, double click on it with the left mouse button in the tree and it turns red. The assigned global parameters of the active case are displayed by selecting Model|Parameters. New case parameters, i.e. parameters that will be subject to variation, can be added by clicking Parameters. Then double click on the toggle switch with the left mouse button to add the required parameter. Enter the relevant values for each case. In this window Engine Speed is the main parameter as it follows State. To define it as a main parameter, select it first in the Add/Remove Parameters window. Note: Only global parameters can be subject to variation with the Case Explorer. When a parameter is defined in the case table, the parameter value is disabled in the MODEL|PARAMETERS dialog. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-99 3.6. Running a Simulation Select Simulation Run to open the following window. Figure 3-74: Run Simulation Window Cases: Select the required case(s) to be run. Select All allows all the cases to be activated. Tasks: Select Model Creation to create a calculation kernel input file (.bst file) in the case sub-directory. Select Cycle Simulation to run the standard cycle simulation. This passes the input file (.bst file) to the calculation kernel. Select Aftertreatment Analysis to run the aftertreatment analysis mode. This passes the input file (.atm file) to the calculation kernel. Select Animation to create animation results suitable for loading into PP3. This will be done after completion of the simulation run. Deselect All and Select All allows all the available tasks to be either deactivated or activated, respectively. Note: Animation task is only active if the Calculation Mode is set to animation in Simulation|Control Globals. Note: Aftertreatment Analysis task is only active if there is valid aftertreatment model. Then select Run to start the simulation. The following window then opens which provides an overview of the status of the simulation. BOOST Version 4.0.4 User’s Guide 3-100 23-Jun-2004 Figure 3-75: Simulation Status Window Simulation states are listed below: new No job has been submitted for that model case yet. queued A simulation job for that particular model case was submitted using a queuing system but that job is not running yet. submitted A simulation job was submitted as a background process and the simulation kernel is about to start. running Simulation kernel is processing simulation task(s). completed Simulation job processed successfully. error Simulation job processed with errors. Check the output from the calculation kernel for more information. This can be done by selecting View Logfile then Task Cycle Simulation or Aftertreatment Analysis. stopped process The current simulation kernel process has been stopped along with all parent job submission scripts. killed process The simulation kernel process was killed by the user with the Kill Process button. missing process Simulation kernel process terminated unexpectedly. Select View Logfile to view more detailed information on the different simulation tasks. • Select Model Creation to show messages generated by the GUI as to whether the model was created successfully. • Select Cycle Simulation task to show the information from the calculation kernel during the cycle simulation. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-101 Figure 3-76: View Cycle Simulation Logfile Window • Select Aftertreatment Analysis task to show the information from the calculation kernel during the aftertreatment simulation. Figure 3-77: View Aftertreatment Analysis Logfile Window BOOST Version 4.0.4 User’s Guide 3-102 23-Jun-2004 • Select Animation task to show the information about the creation of animation results. Figure 3-78: View Animation Logfile Window 3.7. Utilities 3.7.1. BURN The BURN utility can be used for combustion analysis. That is, the rate of heat release (ROHR) can be obtained from measured cylinder pressure traces. The resulting ROHR can be used to specify the combustion characteristics of a single zone model. 3.7.1.1. Input Data Specification Select BURN from the Utilities menu to open the following figure. In this example two operation points are loaded and Fitting Data is displayed. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-103 Figure 3-79: Burn Utility - Fitting Data Window Alternatively while inputting the cylinder data for a BOOST model, select Table under the Combustion sub-group. In this case the resulting ROHR can be accepted immediately after calculation. It is possible to perform the analysis for more than one operating point with a single procedure. Therefore two types of input data are available: • Data independent of the operating point, e.g. cylinder geometry, mixture preparation and fuel type. • Data describing the operating point, e.g. engine speed, wall temperatures, valve timing and mass flows. 1. Global and Cylinder Data This data is independent of the operating point. If a BOOST model is loaded or the BURN tool is applied while specifying the combustion data for a BOOST model, this data can be copied from a BOOST model by selecting a cylinder from the pull-down menu and then selecting Copy. Additional operating point data can be loaded for the first operating point to be calculated. The necessary global and cylinder data corresponds to the data required for the preparation of a BOOST model. 2. Operating Point Data Select the Operation Point sub-group folder to add or remove operating points by using Insert Row and Operating Point and Remove Row and Operating Point. The values for engine speed and load cannot be specified directly in the table but after specifying data each operating point, the table can be used to examine these values. BOOST Version 4.0.4 User’s Guide 3-104 23-Jun-2004 Select the required Operating Point, e.g. OP(1) and specify the following: • Engine Speed. • Load as BMEP. The load does not influence the results and is used only to describe the operating point. • The valve timing is specified to determine the range in which the analysis should be performed. For a standard four-stroke engine Start of High Pressure corresponds to intake valve closing (IVC) and • End of High Pressure to exhaust valve opening (EVO). • Ignition Time/Start of Injection is used to determine the compression phase of the high pressure cycle. This range is used to perform the fitting of the pressure curve. • Air Massflow and Fuel Massflow should be specified for the whole cylinder. The value for a single cylinder is determined from the number of cylinders in the engine assuming an even distribution to the cylinders. • If the assumption is not valid Trapping Efficiency Air and Trapping Efficiency Fuel also can be used to consider such an effect. • Wall Temperature must be defined for piston head and liner in the same way as it is done for BOOST. Select the Pressure Trace sub-group and specify the required data or read it in as a table. The pressure traces are required over a whole cycle. Select the Fitting sub-group to determine the absolute pressure level, top dead center (TDC) and compression ratio as required. From the pull-down menus, the user can select Manual to specify a value or Automatic to perform the fitting process automatically for Fixed Pressure Offset, Fixed TDC Offset and Fixed Compression Ratio. The None option turns off the process. The fitting procedures are based on the compression phase of the high pressure. By comparing the shape of the calculated compression curve and the measured one the offsets and the compression ratio are determined. Note: Choosing all three types of fitting may increase calculation time for one operating point. Distortions of the pressure traces can be improved by using the Cut Off Frequency Filter. The user can select Manual from the pull-down menu to specify a value or select Automatic. If Automatic is selected the cut off frequency is calculated from the engine speed using: ] [ 2 3 ] [ rpm n Hz f engine cutoff ⋅ = User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-105 3.7.1.2. Run the Calculation After specifying the data select Save Data and save it as an input file. This can be used for later examination by selecting Load Data. Select Calculate to start the calculation. A window appears in which the customer can check the operating points. Then select Run Calculation(s) to perform the calculation of all operating points. 3.7.1.3. Results The results for each operating point can be examined under the Results sub-group. The results of the fitting procedures are shown and the energy balance confirms the validity of the analysis. Energy Balance is defined as the ratio between the energy set free through combustion and lost to the exhaust divided by the energy brought in by the caught fuel. A valid analysis should show an energy balance value less than but close to 1. In the ROHR sub-group, the resulting rate of heat release is shown. In addition to the heat release, the net heat release (net ROHR) is also shown, which does not consider the wall heat transfer. In the Calculated Pressure Trace sub-group, the pressure traces after fitting and filtering are shown. If the analysis is started from modeling an engine with BOOST, the user is asked to accept the resulting ROHR for one of the operating points and the resulting ROHR is used as input data for the table. 3.7.2. Search The Search utility can be used to displays tables of the input data used in the model. These can be saved in HTML format. The current search options are: • Initialization data =ALL= • Initialization data =PIPES= • Geometry of and initial conditions in the Pipes • Volumes • Flow coefficients =RESTRICTIONS= • Vibe BOOST Version 4.0.4 User’s Guide 3-106 23-Jun-2004 Figure 3-80: Search Utility Displaying Initialization Data for Pipes 3.7.3. License Manager Select Utilities|License Manager to open the following window: Figure 3-81: License Manager Window The active configuration is shown on the left with the different license options: License is available and not checked out. License is available and checked out. License is not available. For a new configuration, turn on the toggle switch for the required license and then restart BOOST. User’s Guide BOOST Version 4.0.4 23-Jun-2004 3-107 3.7.4. Pack Model This creates a compressed tape archive of all files related to the current active model. These include input data, results, model layout, simulation messages and system information. On success, a message box will be displayed showing the path and name of the created file. The base name of the created file will match the current active model and will have the extension .tar.gz. This utility can be used for passing models to the BOOST support team to check problems or errors. User’s Guide BOOST Version 4.0.4 23-Jun-2004 4-1 4. EXTERNAL LINKS 4.1. MATLAB 4.1.1. Application Programming Interface (API) By running a BOOST model containing the MATLAB-API Element, the MATLAB/SIMULINK workspace is dynamically linked to the BOOST Executable. The user has runtime access to all control-related data. This allows parallel post-processing by using the full capability of the MATLAB Workspace. There are three options for viewing the data in MATLAB/Simulink: 1. Scopes can be used inside the SIMULINK model. 2. Based on the names assigned to the vectors these names can be used to generate plots from the MATLAB command window. 3. Plots can be generated automatically by using m-functions. Further details on plotting in MATLAB/Simulink can be found in the documentation from The Mathworks. A Restart Calculation with a saved Control-Unit State in the MATLAB-Workspace (according to the BOOST Restart procedure) is possible. Note: To use the restart option it is mandatory that the related BOOSTMODELNAME doesn’t start with a number (analogous to the restriction for a SIMULINK model or an m-function file name) . Additional MATLAB-API Element Specification In addition to the input of the Simulink-model (or m-Function) name, which performs the control algorithm, the name of the Sensor-channel and Actuator-channel vector must be specified. These vectors are introduced as members of the MATLAB Workspace and the Simulink-model (or m-Function). At every interaction step the values of the Sensor-channel are evaluated by BOOST, submitted to the MATLAB Workspace, the Simulink-model (or m-Function) performs a control algorithm step and returns the values of the Actuator-channel back to BOOST. The following settings are available for the interaction step size: • every BOOST cycle • every BOOST calculation timestep • specified timestep BOOST Version 4.0.4 User’s Guide 4-2 23-Jun-2004 Required MATLAB API Libraries For each platform two MATLAB libraries are required by BOOST to dynamically load the required functions. These libraries should be located in the following directory: <matlab>/extern/lib/$Arch where <matlab> is the MATLAB root directory and $Arch is your system architecture. This subdirectory and the platform dependent name of these libraries are listed in the following table. Platform Subdirectory Required Libraries Windows win32 libeng.dll libmx.dll Hewlett Packard hpux libeng.sl libmx.sl Compaq alpha libeng.so libmx.so IBM Ibm_rs libeng.a libmx.a Linux glnx86 libeng.so libmx.so 4.1.1.1. Running a MATLAB API Simulation There are several key steps to running a MATLAB API simulation with BOOST dependent on the platform being used. These are listed below: Windows NT/95/98/2000 1. Check the required libraries have been installed. 2. The required library paths should have been set during installation (check with your system administrator if the required libraries cannot be loaded). 3. Check that there is a valid MATLAB license available. UNIX 1. Check the required libraries have been installed for the current platform. 2. Set the library path environment variable LD_LIBRARY_PATH. In C shell, the command to set the library path is setenv LD_LIBRARY_PATH <matlab>/extern/lib/$Arch:$LD_LIBRARY_PATH User’s Guide BOOST Version 4.0.4 23-Jun-2004 4-3 In Bourne shell, the commands to set the library path are LD_LIBRARY_PATH=<matlab>/extern/lib/$Arch:$LD_LIBRARY_PATH export LD_LIBRARY_PATH where <matlab> is the MATLAB root directory and $Arch is your system architecture. The environment variable (LD_LIBRARY_PATH in this example) varies on several platforms. The following table lists the different environment variable names to be used on these systems. Platform Library Path Variable HP700 SHLIB_PATH IBM RS/6000 LIBPATH SGI 64 LD_LIBRARY64_PATH It is convenient to place these commands in a startup script such as ~/.cshrc for C shell or ~/.profile for Bourne shell. 3. Add the path to the MATLAB script/executable (matlab) so that it can be started by BOOST. In C shell, the command to set the path is setenv PATH <matlab>:$PATH In Bourne shell, the commands to set the library path are PATH=<matlab>:$PATH export PATH where <matlab> is the MATLAB root directory. 4. Check that there is a valid MATLAB License available. 5. If running on a remote host, set the DISPLAY environment variable to the current host. setenv DISPLAY <hostname>:0.0 BOOST Version 4.0.4 User’s Guide 4-4 23-Jun-2004 Restart If data of the MATLAB workspace must be saved in addition to the Simulink model, it should be stored on the Structure variable RestartState using the MATLAB-Callback Routine StopFcn. Modification of the MATLAB Workspace variable FinalState during the simulation will lead to erroneous results (it is reserved to save the State at the end of every simulation timestep). The MATLAB dialog that ordinarily appears on the MATLAB Command Window is redirected to the file SIMULINKMODELNAME_buffer.dat. If a script-file SIMULINKMODELNAME_startup.m is present in the MATLAB working directory (containing the performed Simulink-model or m-Function) it is executed at the start of the co-simulation, while SIMULINKMODELNAME_close.m is carried out at the end. 4.1.2. Real Time Workshop The following procedure may be used for the program development of the DLL. This procedure works with MATLAB v5.3, v6.0, v6.1, v6.5 and higher. By typing mex –setup on the MATLAB command line a menu appears were the c++ compiler for the DLL generation has to be selected. Depending on the MATLAB version, the following path must be added to the MATLAB/Simulink path: MATLAB V.5.3: BOOST_HOME..\..\matlab\version5.3 executing the MATLAB command addpath(‘path_to_add’) MATLAB V.6.0 (V.6.1and higher): BOOST_HOME..\..\matlab\version6.0 (BOOST_HOME..\..\matlab\version6.1) via the MATLAB GUI (File ⇒ Set Path… ⇒ Add Folder.. and then SAVE) (BOOST_HOME is defined as an environmental variable of the operating system) User’s Guide BOOST Version 4.0.4 23-Jun-2004 4-5 The following figures show the Real-Time Workshop options for the generation of the DLL in the SIMULINK Tools menu: 1. Solver Figure 4-1: Simulink Settings for the Integration Algorithm In the Solver window shown above, the integration algorithms and the incrementation must be selected. The incrementation must be constant (Fixed-step) and adapted to the selected incrementation of BOOST. It is recommended to use approximately a tenth of the BOOST incrementation. The entries for start time and stop time are not relevant. Select Fixed-step for the Type of Solver Options and ode1 (Euler) for the integration algorithm. Select 0.01 for the Fixed step size. Select Single Tasking for the mode. Note: If no integrators, memory blocks, etc were used in the model, the value for the Fixed step size incrementation is ignored and is automatically set to the BOOST time step. BOOST Version 4.0.4 User’s Guide 4-6 23-Jun-2004 2. Workspace I/O Figure 4-2: Simulink Settings for the MAT-Files In the Workspace I/O window shown above, certain data of the SIMULINK block diagram can be output to a MATLAB readable file which is characterized by the file extension MAT. After running the simulation this MAT file can be loaded into the Workspace from MATLAB. This file has the same name as the model. The actual time Time, the state variables States or the output values outputs, etc. can be selected for storing. The Output vector contains all output values. If a ' Scope'-block or 'To Workspace'-block was used, then this data will also be written to the MAT file. If none of the possible items were selected and in the block diagram no blocks for storing were used, no MAT file will be produced. Format determines whether the values will be recorded in a simple matrix or structured (with or without time). User’s Guide BOOST Version 4.0.4 23-Jun-2004 4-7 3. Real-Time Workshop Figure 4-3: Simulink Settings for the Boost-DLL Creation In the Real-Time Workshop window shown above, the settings for the DLL generation are input. System target file defines the type of the code which can be produced. Enter grt.tlc (general real-time). Template makefile defines the name of the template file from which the new Make file is generated. For the generation of the desired DLL file using the VC++ V6.0 compiler, enter the template file avl_grt_dll_nt.tmf (UNIX: avl_grt_dll_unix.tmf). This file must be in the directory %MATLABROOT%\rtw\c\grt or in the current work directory otherwise the complete path name must be entered. Enter make_rtw for Make command. Enter PROGRAM=new_name to define the file name of the DLL. Alternatively the model name is used and an underscore is placed in front. If the DLL file name should be equal to the MDL file name, an underscore must be placed in front (refer to the following table), otherwise no valid C-MEX DLL will be generated, as the MDL file in MATLAB could be not opened any longer, because it is always checked first whether there is DLL file with same name available. Make command Simulink-Model Created DLL make_rtw example.mdl _example.dll make_rtw PROGRAM=example example.mdl _example.dll make_rtw PROGRAM=test example.mdl test.dll Select Build to generate a c-code. Then the Makefile will be produced, nmake.exe will be called with this Makefile and the object files will be linked to the DLL. BOOST Version 4.0.4 User’s Guide 4-8 23-Jun-2004 4.1.3. Pure Code Generation The engine control model can also be compiled to a DLL from user written code so that the following entry points are defined and exported: _mdlInterfaceInitialize _mdlInterfaceStep _mdlInterfaceTerminate The definition of each routine is: void _mdlInterfaceInitialize ( double*stepSize, double**u, int*nu, double**y, int* ny); This routine initializes the DLL and is called once at the beginning of a simulation. The passed parameter list is as follows, • stepSize = defined interaction step size in seconds. • u = sensor vector u with one value per channel • nu = number of sensor channels • y = actuator vector with one value per channel • ny = number of actuator channels The stepSize can be used to set the frequency (in seconds) of the interaction between the DLL and BOOST. If set to zero they will interact every BOOST time step. Both channel vectors ( u and y ) must be allocated memory in the DLL code. The number of both the sensors (nu) and the actuators (ny) must also be set in the user code. void _mdlInterfaceStep (void) This routine controls the calculation of a time step in the DLL. BOOST passes copies of the sensor channels to the DLL. The DLL should set new values for the actuator channels y. Note that this routine is only called after an initial settling period of three BOOST cycles and then once every stepSize or every BOOST time step is stepSize is set to zero. void _mdlInterfaceTerminate (void) This routine terminates the Dynamic Link and is called once at the end of the simulation. User’s Guide BOOST Version 4.0.4 23-Jun-2004 4-9 4.1.4. System Function (s-function) BOOST can be run from MATLAB/SIMULINK using a masked subsystem block. This contains a C-MEX s-function that dynamically loads the BOOST calculation kernel from a shared object (dynamic link library). A BOOST model can pass information to the s-function using wires representing both sensors and actuators connected to the MATLAB-DLL Element. 1. MATLAB-DLL Element Specifications for BOOST Model To enable the BOOST model to pass information to MATLAB, select MATLAB s- function link in the main window of the MATLAB-DLL Element Specification Box. This will be displayed if the MATLAB DLL element in the BOOST model is double clicked. Required Files File Description Installation Location boost.mdl The MATLAB library file for the s-function ../boost/v4.0.3/matlab/v6.x MATLAB path BOOST_model.dll* The MATLAB s-function dll for BOOST ../boost/v4.0.3/matlab/v6.x MATLAB path. boost.dll The dynamic link library of the BOOST solver. ../boost/v4.0.3/bin/platform BOOST_HOME Note: On UNIX, the MATLAB s-function dll has the mexplatform extension. Time Control The time stepping of the simulation is controlled by BOOST and the simulation duration is controlled by MATLAB. BOOST constantly stores data during a MATLAB/Simulink run so when the simulation has finished, the last complete cycle of data will be available in the BOOST output. The BOOST model cannot run longer than the Max.Calc.Period [degCRA] specified in the Globals section. If this value is exceeded by BOOST during a simulation using the s-function then the MATLAB/Simulink model will stop at this point and an error message will be issued. To avoid this problem the max. crank angle for the BOOST model should be set to a higher crank angle than will be reached during the simulation. BOOST Version 4.0.4 User’s Guide 4-10 23-Jun-2004 2. Specifications for MATLAB/Simulink Model The s-function has been written for MATLAB Version 6.x only (earlier versions are not supported) on the following platforms. Platform Operating System Version Windows NT 4.0 Compaq OSF1 5.10 IBM AIX 4.3.3.0 Linux Linux 2.2.16 The BOOST block is supplied as a MATLAB/Simulink library called BOOST. Figure 4-4: The BOOST MATLAB/SIMULINK Library This can be displayed by typing boost at the MATLAB command prompt and the icon can be dragged into the model in the same way as any other MATLAB/Simulink block. User’s Guide BOOST Version 4.0.4 23-Jun-2004 4-11 Mask Parameters Double click the block to open the following window: Figure 4-5: Mask Parameters Window Input the following data to run a BOOST model via the s-function: BOOST input file name is the name of the file for the BOOST input. This will typically have the bst extension and can be generated by the GUI by selecting Model Creation in the Simulation|Run dialog box. Number of actuator channels is an integer value defining the number of inputs to the BOOST model (actuators). This must match the number used in the BOOST model. Number of sensor channels is an integer value defining the number of outputs from the BOOST model (sensors). This must match the number used in the BOOST model. Interaction allows the user to select how often BOOST and MATLAB/Simulink exchange information. The options available are, • BOOST time step : information exchange every BOOST time step. • Cyclic : information exchange every set number of BOOST cycles as given in the Defined input section (see below). • SIMULINK : information exchange every SIMULINK time step. • Defined : information exchange every set number of seconds as given in the Defined input section (see below). Defined is only used if Interaction is set to Cyclic or Defined, otherwise it is ignored. BOOST Version 4.0.4 User’s Guide 4-12 23-Jun-2004 • Cyclic : number of cycles between information exchange. • Defined : seconds between information exchange Pre-Converge is an optional check box that causes the model to run for a number of cycles before interacting with MATLAB/Simulink. This allows the model to pre converge. Synchronise is an optional check box that synchronises the BOOST time and the MATLAB/Simulink time. Verbose/debug is an optional check box that writes additional information to the screen in case of errors or difficulties. Path Settings The path to the BOOST library model (boost.mdl) and the BOOST s-function (BOOST_model.dll on Windows) must be added to the MATLAB/Simulink path so that the necessary files can be accessed. This can be done via the MATLAB GUI (File ⇒ Set Path… ⇒ Add Folder.. and then SAVE). If this is not done, the files are missing or the path is incorrect then a bad link error as shown below will be given by MATLAB/SIMULINK. The BOOST_HOME environment variable also needs to be set correctly as the BOOST dynamic link library is loaded from this directory. Note: BOOST_HOME should be set in the User Variables and not the System Variables. 4.1.4.1. Running an s-function Simulation The stages in building, running and analyzing a BOOST/MATLAB simulation are as follows: 1. Open/Create a BOOST model in the graphical user interface (GUI). 2. The BOOST model must include a MATLAB DLL element with MATLAB s- function link selected in the General input for this element. Wires should be connected between elements in the BOOST model and the MATLAB DLL junction. The sensor and actuator channels should also be selected. 3. Create a BOOST solver input file (.bst file). In the GUI, select Simulation|Run, select Model Creation only for Tasks and then select Run. A message box will inform the user of the name and location of the file that has been created. 4. Open/Create a model in MATLAB (.mdl file). User’s Guide BOOST Version 4.0.4 23-Jun-2004 4-13 5. The model should include the MATLAB BOOST library element (boost.mdl). If the paths have been set correctly this can be displayed by typing boost at the MATLAB prompt. 6. The mask parameters for the BOOST element should be set. This includes the 'BOOST input file name' created at stage 3. 7. Run the model in MATLAB by selecting Simulation|Start. 8. After completing the simulation the results from the BOOST model can be examined in the GUI. With the BOOST model still active in the GUI select Simulation|Import Results and select the BOOST input file created in 3 and used at stage 6. 9. The Simulation|Show Summary, Show Results, Show Messages and Show Animation should now work as for a standard BOOST simulation run through the GUI. 4.2. AVL FIRE Please refer to the 1D-3D Coupling Manual for further information. 4.3. AVL CRUISE The BOOST dynamic link library (DLL) can be called by AVL CRUISE. During a CRUISE-BOOST co-simulation the engine model is controlled by CRUISE via the Load Signal, thus the presence of an ECU Element is mandatory. Time Step Control The BOOST model cannot run longer than the Max.Calc.Period [degCRA] specified in the Globals. If this value is exceeded during the CRUISE-BOOST co-simulation an error will appear. To avoid this problem the Max.Calc.Period for the BOOST model should be set to a higher crank angle than will be reached during the simulation. Transient Calculation in Simulation Control / Globals of the boost model has to be disabled because the transient behavior of the engine is calculated by Cruise. User’s Guide BOOST Version 4.0.4 23-Jun-2004 5-1 5. BOOST POST-PROCESSING The IMPRESS Chart post-processing tool is used to display Traces, Transients, Acoustic and Series results and the PP3 post-processing tool is used for Animation results. For the general handling of the IMPRESS Chart and PP3 post-processing tools please refer to Chapter 3 of the AVL Workspace Graphical User Interface Manual. To accelerate the analysis process and to support the understanding of the complex flow phenomena in an internal combustion engine, the following analysis of the calculation results are available: • SUMMARY – Analysis of global engine performance data • TRANSIENTS – Analysis of global calculation results over the cycles calculated • TRACES – Analysis of calculation results over crank angle • ACOUSTIC – Analysis of orifice noise • CASE-SERIES – Analysis of the results of a case-series calculation • ANIMATION – Analysis of animated results • MESSAGES – Analysis of messages from the main calculation program Before starting a detailed analysis of the calculation run (Traces, Acoustic, Series, Animation, Summary), it is recommended to check MESSAGES for convergence failure and TRANSIENTS for achieved steady-state conditions. 5.1. Analysis of Summary Results Select Simulation|Show Summary to display the summary results of the calculation together with detailed information of the calculation model and the important boundary conditions for the calculation. An example of summary results displayed in the Ascii File Browser window is shown in the following figure: BOOST Version 4.0.4 User’s Guide 5-2 23-Jun-2004 Figure 5-1: Summary Analysis Window To access additional features for manipulating files select File from the menu bar of the Ascii File Browser. 5.2. Analysis of Cycle Dependent Results TRANSIENTS: The analysis of transients (the development of the solution over the cycles calculated) provides valuable information for the engineer. In a steady-state engine simulation, the transients should be checked to ensure that steady-state operating conditions have been achieved. If the reaction of the engine to modified settings of control elements was simulated, transients become the most important part when analyzing the calculation results. Select Simulation|Show Results to open the IMPRESS Chart main window and then select the Results tab to display the results as shown in the following figure: User’s Guide BOOST Version 4.0.4 23-Jun-2004 5-3 Figure 5-2: IMPRESS Chart Main Window The result tree is shown in the window area. Double-click Results.ppd to load the results data. Click the right mouse button in the window area to display the submenu as shown above. Select Model View to display the model and select the required element to display the relevant results in the working window. Performance data for the entire engine can be analyzed. In the Engine 1 subfolder average values of all cylinders or the sum of all cylinders are shown. Further values of each cylinder according to the firing order with an offset matching the firing interval are displayed in Engine 1|Cylinders. BOOST Version 4.0.4 User’s Guide 5-4 23-Jun-2004 Transients plot the variable versus the cycle number and Traces plot the variable versus the crankangle for the last complete cycle. The following data is available for each element in the Transients subfolder: Element Data Unit Comment PIPE: WALLHEAT J/cycle integral wall heat losses ENGINE: END OF CYCLE TIME sec time of Cylinder 1 FTDC CYCLE AVERAGED SPEED rpm CYCLE FREQUENCY Hz CYCLE PERIOD s IMEP bar indicated mean eff. pressure ISFC1 g/kWh ind. fuel cons. excl. scav. losses ISFC2 g/kWh ind. fuel cons. incl. scav. losses TORQUE Nm eff. engine torque POWER kW eff. engine power IMEP_EX bar exhaust work IMEP_IN bar intake work IMEP_GE bar gas exchange work DELIVERYRATIO_AMB - tot. mass at IC rel. to amb. cond. AIRDELIVERYRATIO_AMB - air del. ratio rel. to amb. cond. TOTAL FUEL MASS kg aspirated and injected fuel mass PISTONWALLHEATFLOW J/cycle HEADWALLHEATFLOW J/cycle LINERWALLHEATFLOW J/cycle PEAKCYLINDERPRESSURE Pa SWIRL BLOWBY kg/cycle AMEP bar Auxiliary Drives mean effective pressure BMEP bar brake mean eff. pressure FMEP bar friction mean eff. pressure BSFC g/kWh brake specific fuel consumption AIRDELIVERYRATIO_INT - air del. ratio rel. to intake mean cond. VOLUMETRICEFFICIENCY_AMB - vol. eff. rel. to amb. cond. VOLUMETRICEFFICIENCY_INT - vol. eff. rel. to intake man. cond. ACCUMULATED NOX g/kWh for two and multi zone models ACCUMULATED SOOT g/kWh for two and multi zone models SYSTEMBOUNDARY: for the ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - INTERNALBOUNDARY: for the ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - set equal to one (w/o meaning) User’s Guide BOOST Version 4.0.4 23-Jun-2004 5-5 MEASURINGPOINT: PRESSURE Pa VELOCITY m/s TEMPERATURE K MASSFLOWAVERAGED TEMP K MACHNUMBER - MASSFLOW kg/cycle ENTHALPYFLOW J/cycle WALLTEMPERATURE K A/F_RATIO - − total for internal mixture preparation − of the combustion products for external mixture preparation FUELCONCENTRATION - COMBUSTIONPRODUCTCONCENTRA TION - CONVERGENCE - sum of pressure temperature and velocity deviation between cycles PLENUM: PRESSURE Pa TEMPERATURE K MASS kg WALLHEATFLOW J/cycle WALLTEMPERATURE K for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - VARPLENUM: PRESSURE Pa TEMPERATURE K MASS kg VOLUME m3 VOLUMEWORK J/cycle WALLHEATFLOW J/cycle WALLTEMPERATURE K for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - CYLINDER: additional x-axis IMEP bar indicated mean eff. pressure ISFC1 g/kWh ind. fuel cons. excl. scav. losses ISFC2 g/kWh ind. fuel cons. incl. scav. losses IMEP_EX bar exhaust work IMEP_IN bar intake work IMEP_GE bar gas exchange work MASS kg total mass at IC DELIVERYRATIO_AMB - tot. mass at IC rel. to amb. cond. AIRDELIVERYRATIO_AMB - air del. ratio rel. to amb. cond. BOOST Version 4.0.4 User’s Guide 5-6 23-Jun-2004 A/F_RATIO - air fuel ratio for the combustion FUELMASS kg aspirated or injected fuel mass PISTONWALLHEATFLOW J/cycle HEADWALLHEATFLOW J/cycle LINERWALLHEATFLOW J/cycle PEAKCYLINDERPRESSURE Pa Peak Cylinder Pressure PEAKCYLINDERPRESSURE CRA degCRA Peak Cylinder Pressure Crankangle PEAKCYLINDERTEMPERATURE K Peak Cylinder Temperature PEAKCYLINDERTEMPERATURE CRA degCRA Peak Cylinder Temperature Crankangle PEAKPRESSURERISE Pa/degCrA Peak Pressure Rise PEAKPRESSURERISE CRA degCRA Peak Pressure Rise Crankangle BLOWBY kg/cycle SWIRL - dynamic swirl at IVC BMEP bar brake mean eff. pressure FMEP bar friction mean eff. pressure BSFC g/kWh brake specific fuel consumption AIRDELIVERYRATIO_INT - air del. ratio rel. to intake mean cond. VOLUMETRICEFFICIENCY_AMB - vol. eff. rel. to amb. cond. VOLUMETRICEFFICIENCY_INT - vol. eff. rel. to intake man. cond. LOAD bar ENGINESPEED rpm av. engine speed over last cycle PISTONTEMPERATURE K HEADTEMPERATURE K LINERTDCTEMPERATURE K LINERBDCTEMPERATURE K IGNITIONTIMING degCRA INJECTIONSTART degCRA dynamic injection nozzle opening IGNITIONDELAY degCRA COMBUSTIONSTART degCRA COMBUSTIONDURATION degCRA MASSFRACTION BURNED 02 CRA degCRA 2% Mass Fraction Burned Crankangle MASSFRACTION BURNED 05 CRA degCRA 5% Mass Fraction Burned Crankangle MASSFRACTION BURNED 10 CRA degCRA 10% Mass Fraction Burned Crankangle MASSFRACTION BURNED 50 CRA degCRA 50% Mass Fraction Burned Crankangle MASSFRACTION BURNED 90 CRA degCRA 90% Mass Fraction Burned Crankangle MASSFRACTION BURNED 95 CRA degCRA 95% Mass Fraction Burned Crankangle VIBEPARAMETER_M - COMBUSTION_NOISE db(A) PEAK TEMP BURNED ZONE K for two and multi zone models ACCUMULATED NOX g/kWh for two and multi zone models ACCUMULATED SOOT g/kWh for two and multi zone models COMCHAM_MASS kg total mass in the chamber at IC User’s Guide BOOST Version 4.0.4 23-Jun-2004 5-7 COMCHAM_WALLHEATFLOW J/cycle chamber wallheatflow COMCHAM_FUELMASS kg fuel mass in the chamber, aspirated or injected COMCHAM_AIRMASSFLOW kg/s COMCHAM_PEAKPRESSURE Pa COMCHAM_PEAKTEMP K COMCHAM_A/F_RATIO - COMCHAM_FUELVAPOUR - COMCHAM_COMBPROD - COMCHAM_FUELFRACTION - CYL_CHAM_A/F_RATIO - COMCHAM_PARAMETERM - Vibe parameter m for the chamber COMCHAM_COMBDUR degCRA chamber comb. duration COMCHAM_SOC degCRA chamber start of combustion COMCHAM_WALLTEMP K CONNPIPE_MASSFLOW kg/cycle mean massflow conn.pipe CONNPIPEWALLHEATFLOW J/cycle for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - VALVE PORT OPENING CRA Valve Port Opening Crank Angle VALVE PORT CLOSING CRA Valve Port Closing Crank Angle PORTWALLHEAT J/cycle PORTWALLTEMPERATURE K RESTRICTION: for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - ROTARYVALVE: for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - CHECKVALVE: for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - FUELINJECTOR: ADDEDFUEL kg/cycle for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - WASTEGATE: for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - AIRCOOLER: INLETPRESSURE Pa INLETTEMPERATURE K INLETMASS kg BOOST Version 4.0.4 User’s Guide 5-8 23-Jun-2004 OUTLETPRESSURE Pa OUTLETTEMPERATURE K OUTLETMASS kg REJECTEDHEAT J/cycle for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - AIRCLEANER: INLETPRESSURE Pa INLETTEMPERATURE K INLETMASS kg OUTLETPRESSURE Pa OUTLETTEMPERATURE K OUTLETMASS kg for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - CATALYST: INLETPRESSURE Pa INLETTEMPERATURE K INLETMASS kg OUTLETPRESSURE Pa OUTLETTEMPERATURE K OUTLETMASS kg for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - TURBOCHARGER: COMPRESSORWORK J/cycle COMPRESSORRATIO - mass flow averaged TURBINEWORK J/cycle TURBINERATIO - mass flow averaged BOOST PRESSURE Pa DISCHARGECOEFFICIENT - TURBINETOTOTAL - ROTATIONALSPEED rpm COMPRESSOREFFICIENCY - TURBINEEFFICIENCY - VANEPOSITION - for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - PD-COMPRESSOR: COMPRESSORWORK J/cycle COMPRESSORRATIO - mass flow averaged ROTATIONALSPEED rpm COMPRESSOREFFICIENCY - for each ATTACHEDPIPE User’s Guide BOOST Version 4.0.4 23-Jun-2004 5-9 MASSFLOW kg/cycle FLOWCOEFFICIENT - TURBOCOMPRESSOR: COMPRESSORWORK J/cycle COMPRESSORRATIO - mass flow averaged BOOST PRESSURE Pa ROTATIONALSPEED rpm COMPRESSOREFFICIENCY - for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - JUNCTION: for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - FIRE: for each ATTACHEDPIPE MASSFLOW kg/cycle FLOWCOEFFICIENT - ECU: LOAD SIGNAL - 5.3. Analysis of Crank Angle Dependent Results TRACES: The detailed analysis of the results from the last cycle calculated is recommended. The comparison of results (e.g. pressure, temperature, flow velocity) obtained at different locations in the engine model or the analysis of physically related results may help to locate problem areas in an engine, or to create new ideas on how to make improvement. Select Simulation|Show Results to open the IMPRESS Chart main window (refer to Figure 5-2). Double-click Results.ppd to load the results data. The following data is available for each element in the Traces subfolder: Element Data Unit Comment ENGINE: TIME s time ENGINESPEED rpm instantaneous revolution speed of the crank shaft TORQUE Nm instantaneous torque at the crank shaft SYSTEMBOUNDARY: for the ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - INTERNALBOUNDARY: for the ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - set equal to one (w/o meaning) BOOST Version 4.0.4 User’s Guide 5-10 23-Jun-2004 MEASURINGPOINT: PRESSURE Pa VELOCITY m/s FORWARDPRESSURE Pa forward moving wave BACKWARDPRESSURE Pa backward moving wave FORWARDVELOCITY m/s forward moving wave BACKWARDVELOCITY m/s backward moving wave TEMPERATURE K MACHNUMBER - STAGNATIONPRESSURE Pa STAGNATIONTEMPERATURE K MASSFLOW kg/s ENTHALPYFLOW J/s A/F_RATIO - − total for internal mixture preparation − of the combustion products for external mixture preparation FUELCONCENTRATION - COMBUSTIONPRODUCTCONCENTRA TION - FUELFLOW kg/s COMBUSTIONPRODUCTFLOW kg/s SPECIESCONCENTRATION - user defined concentration SPECIESFLOW kg/s PLENUM: PRESSURE Pa TEMPERATURE K MASS kg WALLHEATFLOW J/s A/F_RATIO - see measuring point FUELCONCENTRATION - COMBUSTIONPRODUCTCONCENTRA TION - SPECIESCONCENTRATION - for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - VARPLENUM: PRESSURE Pa TEMPERATURE K MASS kg VOLUME m3 VOLUMEWORK Nm WALLHEATFLOW J/s A/F_RATIO - FUELCONCENTRATION - COMBUSTIONPRODUCTCONCENTRA TION - User’s Guide BOOST Version 4.0.4 23-Jun-2004 5-11 SPECIESCONCENTRATION - for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - CYLINDER: PRESSURE Pa TEMPERATURE K MASS Kg VOLUME m3 VOLUMEWORK J/degCrA HEATTRANSFERCOEFFICIENT W/m2/K PISTONWALLHEATFLOW J/degCrA HEADWALLHEATFLOW J/degCrA LINERWALLHEATFLOW J/degCrA RATEOFHEATRELEASE J/degCrA BLOWBY kg/s SWIRL - dynamic in-cylinder swirl INTAKEMASSFLOW kg/s EXHAUSTMASSFLOW kg/s PRESSURERISE Pa/degCrA TEMPERATURERISE K/degCrA A/F_RATIO - FUELCONCENTRATION - COMBUSTIONPRODUCTCONCENTRA TION - SPECIESCONCENTRATION - BURNED ZONE MASS K for two and multi zone models BURNED ZONE TEMPERATURE K for two and multi zone models UNBURNED ZONE TEMPERATURE K for two and multi zone models ACCUMULATED NOX kg for two and multi zone models NOX FORMATION kg/s for two and multi zone models SOOT FORMATION kg/s for two and multi zone models for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - EFFECTIVE FLOW AREA m2 PORTWALLHEATFLOW J/s COMCHAM_PRESSURE Pa Data of att. chamber COMCHAM_TEMPERATURE K COMCHAM_MASS kg COMCHAM_WALLHEATFLOW J/s COMCHAM_HEATTRANSFCOEFF W/m2/K COMCHAM_A/F_RATIO - COMCHAM_COMBPROD - COMCHAM_FUELVAPOUR - CONNPIPEMASSFLOW kg/s Data of conn. pipe CP_ENTHALPYFLOW J/s CONNPIPEVELOCITY m/s CONNPIPEWALLHEATFLOW J/s BOOST Version 4.0.4 User’s Guide 5-12 23-Jun-2004 RESTRICTION: for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - ROTARYVALVE: for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - CHECKVALVE: VALVELIFT m for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - FUELINJECTOR: ADDEDFUEL kg/s for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - WASTEGATE: VALVELIFT m for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - AIRCOOLER: INLETPRESSURE Pa INLETTEMPERATURE K INLETMASS kg INLET_A/F_RATIO - INLETFUELCONCENTRATION - INLETCOMBUSTIONPRODUCTCONC ENTRATION - INLETSPECIESCONCENTRATION - OUTLETPRESSURE Pa OUTLETTEMPERATURE K OUTLETMASS kg OUTLET_A/F_RATIO - OUTLETFUELCONCENTRATION - OUTLETCOMBUSTIONPRODUCTCON CENTRATION - OUTLETSPECIESCONCENTRATION - for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - AIRCLEANER: INLETPRESSURE Pa INLETTEMPERATURE K INLETMASS kg INLET_A/F_RATIO - User’s Guide BOOST Version 4.0.4 23-Jun-2004 5-13 INLETFUELCONCENTRATION - INLETCOMBUSTIONPRODUCTCONC ENTRATION - INLETSPECIESCONCENTRATION - OUTLETPRESSURE Pa OUTLETTEMPERATURE K OUTLETMASS kg OUTLET_A/F_RATIO - OUTLETFUELCONCENTRATION - OUTLETCOMBUSTIONPRODUCTCON CENTRATION - OUTLETSPECIESCONCENTRATION - for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - CATALYST: INLETPRESSURE Pa INLETTEMPERATURE K INLETMASS kg INLET_A/F_RATIO - INLETFUELCONCENTRATION - INLETCOMBUSTIONPRODUCTCONC ENTRATION - INLETSPECIESCONCENTRATION - OUTLETPRESSURE Pa OUTLETTEMPERATURE K OUTLETMASS kg OUTLET_A/F_RATIO - OUTLETFUELCONCENTRATION - OUTLETCOMBUSTIONPRODUCTCON CENTRATION - OUTLETSPECIESCONCENTRATION - for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - TURBOCHARGER: COMPRESSORPOWER J/s TURBINEPOWER J/s ROTATIONALSPEED rpm COMPRESSOREFFICIENCY - TURBINEEFFICIENCY - COMPRESSORPRESSURERATIO - TURBINEPRESSURERATIO - for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - BOOST Version 4.0.4 User’s Guide 5-14 23-Jun-2004 PD-COMPRESSOR: COMPRESSORPOWER J/s MECHPOWER J/s ROTATIONALSPEED rpm COMPRESSOREFFICIENCY - for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - TURBOCOMPRESSOR: COMPRESSORPOWER J/s MECHPOWER J/s ROTATIONALSPEED rpm COMPRESSOREFFICIENCY - COMPRESSORPRESSURERATIO - for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - JUNCTION: PRESSURE Pa TEMPERATURE K FLOWPATTERN - for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - FIRE: for each ATTACHEDPIPE MASSFLOW kg/s FLOWCOEFFICIENTS - 5.4. Analysis of Composite Elements Some elements are displayed on the screen as composite elements but consist of more fundamental components in the actual input file. Examples of such elements are: • Perforated pipe in pipe • Perforated pipe in plenum. Some junctions are also not displayed on the screen and the perforated pipes use the same numbering scheme as the standard pipes although this is not shown. This effects: • Perforated pipe numbers • Pipe end junctions for perforated pipes in plenum (restriction or system boundary). • Pipe end junctions for pipes of perforated pipe in pipe elements (restriction or system boundary). User’s Guide BOOST Version 4.0.4 23-Jun-2004 5-15 To assist in post-processing data from such hidden elements, the fundamental contents of composite elements can be displayed by selecting Simulation|Show Elements to open the elements window. This information can then be used to post-process the data from the required location of composite elements. Note: This is only possible after completing a successful simulation. Figure 5-3: Show Elements Window 5.5. Analysis of Frequency Dependent Results and Orifice Noise ACOUSTIC: The acoustic folder contains the simulation results against frequency. Element Data Unit Comment ENGINE: EngineOrder - Engine order versus frequency. Can be used as the x-axis to generate plots versus engine order SYSTEMBOUNDARY: SpecificMassflow kg/s/m2 For use with the orifice noise post processing operation described below MEASURING POINT: PhaseAngle Deg RealPressure Pa ImagPressure Pa Linear : SoundPressure dB In duct sound pressure level MICROPHONE: PhaseAngle Deg Pressure Pa A-weighted : SoundPressure dB(A) A-weighted sound pressure level Linear : SoundPressure dB Linear sound pressure level BOOST Version 4.0.4 User’s Guide 5-16 23-Jun-2004 The microphone element described in Chapter 3 is recommended for determining orifice noise although the post processing operation described here is still supported. However, note that the post processing operation only supports single source data to a microphone whereas the microphone element can handle multiple sources. The orifice noise is determined from the calculated mass flow characteristics at the system boundaries. Select Simulation|Show Results to open the IMPRESS Chart main window. Click on the Operations tab and the acoustic operations are available in the Data Analysis folder. Click on the Results tab and select the Acoustic folder in Results.ppd to plot the Amplitude curve at the required system boundary. Additional input of the microphone position relative to the location of the orifice in Cartesian coordinates is required. Axis, x Vertical, z Lateral, y 0 Ground (optional) Height (optional) MICROPHONE ORIFICE Figure 5-4: Microphone position From this information the sound pressure levels in dB are calculated and displayed over frequency in a graphics window. In addition, the orifice noise in dB(A) is calculated and displayed in the acoustics window. 5.6. Analysis of Case Series Results For the Analysis of case series applications the full range of Transients result types (listed in 5.2) are available Select Simulation | Create Series Results. A one step solution for creating series results for all case sets is available. For each case set the main variation parameter can be freely chosen. User’s Guide BOOST Version 4.0.4 23-Jun-2004 5-17 Figure 5-5: Create Series Results Window • First column: defines if the results should be created • Second column: shows all available case sets • Third column: allows the definition of the main parameter for the results creation, this will be x-axis in IMPRESS Chart. • Last column: shows the state of the creation process Select Run Creation to start the processes of result creation. Then select Simulation | Show Results to open the IMPRESS Chart main window which shows one folder for each case set (name.case_set.case_no) and an additional folder containing the series related results (name.case_set). 5.7. Analysis of Animated Results ANIMATION: The display of animated results helps the user to comprehend the interaction of flow phenomena within the pipe system of an engine. Spatial Plots Depending on the specified output interval of Traces results, spatial plots for each pipe and time step can be accessed by selecting Simulation|Show Results (working_directory/bwf_file_name.Case_Set_X.CaseY/simulation.dir/Results.ppd). Animated Results An animated view on the whole system can be performed by selecting Simulation|Show Animation to open the PP3 main window. BOOST Version 4.0.4 User’s Guide 5-18 23-Jun-2004 Figure 5-6: PP3 Main Window The available animation data is: • Pressure • Gas velocity • Gas Temperature • A/F ratio of the combustion products • Fuel vapour • Combustion products 5.8. Message Analysis MESSAGES: Displaying messages after the calculation process allows the user to check for information, warnings and errors generated by the solver. Select Simulation|Show Messages to open the Message Browser as shown in the following window: Figure 5-7: Message Analysis Window User’s Guide BOOST Version 4.0.4 23-Jun-2004 5-19 From the Sorted by pull down menu, select Message Type, Message ID, Element Name or Position for the desired display. Select the respective values in the Start from and End at pull down menus to display messages occurring within a certain crank angle interval. The global information is shown and more detailed information can be shown by clicking <RUNINFO> with the mouse. Click the expand button + to show the detailed information in the folder. In a steady-state engine simulation it is strongly recommended to check the messages from the main calculation program displayed during the last calculated cycle. If major irregularities have occurred, it is essential to check whether the calculation results are plausible. 5.8.1. Message Description Messages generated by the BOOST solver consist of a message header followed by text giving more detailed information. The format and components of the message header are described as follows: <TYPE> <CODE> <ELEMENT> <NUMBER> <ROUTINE> <CRANK ANGLE> DEGCRA 1. Type The first part of the message header is the basic type of the message. The possible types and a brief description are given in the following table. Message Type Description FATALERROR A fatal error that causes the simulation to stop. READERROR An error occurred reading a value. This usually causes the simulation to stop. INVALIDINPUT The value has been read correctly but the value or string is invalid in this context. This also causes the simulation to stop. CONVERGENCEFAIL An iteration loop has reached the maximum number of iterations without converging. The loop will be exited and the simulation will continue. This message is not fatal. RUNINFO Contains useful information about the simulation. This includes the names and paths of loaded files and changes in default values. WARNING A warning about values or conditions in the current simulation. The simulation will continue to run. OUTOFRANGE A value is out of the permitted range. The accepted range is typically given in the body of the text. This is usually not fatal. FILEERROR An error occurred in reading or writing to files used by BOOST. This is a fatal error. MEMORYERROR A memory allocation error has occurred. Typically caused by insufficient memory available on the current host. This is a fatal error. BOOST Version 4.0.4 User’s Guide 5-20 23-Jun-2004 2. Code A number associated with the message which is useful for tracking the exact location in the code that generated the message. 3. Element If the message is generated by a specific BOOST element such as a cylinder or junction, this will be displayed at this location. Otherwise, a character string describing the current process, such as ‘INPUT’ or ‘CONTROL’, will be displayed. 4. Number The element number that generated the message. If the message is not associated with a particular element number then a zero will be displayed. 5. Routine The BOOST routine which generated the message. 6. Crank Angle The simulation crank angle when the message was generated. This will be in degrees. 5.8.2. Message Examples RUNINFO 0 CONTROL 0 STWINP 0.00 DEGCRA Opened file : C:/Program Files/avl/BOOST/v4.0/files/BENZIN.GPF The message states the name and path of a file that has been loaded by BOOST during the simulation. In this case it is the gas property file (.gpf) for benzin. The message was issued at 0.00 degrees crank angle by the routine STWINP (i.e. at the beginning of the simulation). WARNING 183658 TURBOCHARGER 1 TLVOLL 2880.22 DEGCRA The operating point of the compressor crossed the surge line of the performance map. Massflow: 0.036kg/s, Pressure ratio: 1.60 Warning number 183658 concerning the compressor operating point was issued by turbocharger number 1 at 2880.22 degrees crank angle in the routine TLVOLL. CONVERGENCEFAIL 143302 JUNCTION 3 PSTP0 6336.58 DEGCRA The iteration of the junction massflow failed to converge at flowpattern 6. calculated values: type 1 type 2 difference in % of total massflow attached pipe 1: 0.000609 0.000609 0.000000 attached pipe 2: 0.007190 0.007366 2.206129 attached pipe 3: 0.007970 0.007800 2.133474 User’s Guide BOOST Version 4.0.4 23-Jun-2004 5-21 5.8.3. Fatal Errors 5.8.3.1. MATLAB API FATALERROR 121901 DLL 1 INIDLL 106.00 DEGCRA MATLAB-ENGINE run error - Check that matlab executable directory is in PATH. - Check that a valid license is available. The calculation has been stopped. This message is generated when running with the MATLAB API option. There are several reasons this message is generated. MATLAB is not found in the directories listed in the PATH environment variable, a valid license is not available or there is a clash of MATLAB versions. For the last case this can happen when the version of the MATLAB mdl file does not match the version of MATLAB that BOOST is attempting to load. This can happen when there is more than one MATLAB version is installed on the computer. The following dialog box will be generated in such a case. Figure 5-8: MATLAB API Error - version mismatch The solution is to make sure the version of the MATLAB model (mdl file) matches the MATLAB version listed first in the PATH. BOOST Version 4.0.4 User’s Guide 5-22 23-Jun-2004 5.9. Analysis of Aftertreatment Analysis Results All data from the aftertreatment analysis simulations is given as transient values at different spatial positions of the element. The spatial position (can be defined by the user) is part of the folder and curve name respectively. The following data is available in Catalyst Analysis and Particle Filter Analysis subfolder: Element Data Unit Comment CATALYST: SOLID TEMPERATURE K Temperature of the solid substrate. This temperature is used for all conversion reactions. GAS TEMPERATURE K Temperature of the gas phase. PRESSURE Pa The pressure data are relative values related to the pressure at the catalyst. VELOCITY m/s The velocity is a interstitial velocity inside the catalyst channels. For the evaluation of the superficial velocity the open frontal area of the catalyst has to be applied. MASS FRACTION <<XX>> kg/kg <<XX>> represents any species defined in Globals/Aftertreatment Analysis, e.g. CO, CO2, C3H6, NO2,... PARTICULATE FILTER : SOLID TEMPERATURE K Temperature of the solid substrate. This temperature is used for all regeneration reactions. GAS TEMPERATURE K Temperature of the gas phase. PRESSURE Pa The pressure is given as relative value. A pressure difference is calculated between the pressure at the end of the filter outlet channel and the pressure at the corresponding axial position in the filter inlet channel. VELOCITY m/s The velocity is an interstitial velocity inside an ‘theoretically’ combined channel, where the inlet and outlet channel are put together. MASS FRACTION <<XX>> kg/kg <<XX>> represents any species defined in Globals/Aftertreatment Analysis, e.g. CO, CO2, C3H6, NO2,... This gas composition can be understood as part of the outlet channel. User’s Guide BOOST Version 4.0.4 23-Jun-2004 5-23 SOOT MASS kg/m 3 Filter The soot mass is given as volume specific value, where the overall volume of the filter is used as reference. SOOT HEIGHT m The soot height is evaluated assuming that soot is equally distributed over the entire inlet channel cross section. WALL VELOCITY - The wall velocity is given by normalized values. INLET CHANNEL VELOCITY m/s Th inlet channel velocity is the interstitial velocity inside the filter inlet channel. OUTLET CHANNEL VELOCITY m/s The outlet channel velocity is the interstitial velocity inside the filter outlet channel. INLET CHANNEL PRESSURE Pa Absolute pressure in the inlet channel. OULLET CHANNEL PRESSUER Pa Absolute pressure in the outlet channel. User’s Guide BOOST Version 4.0.4 23-Jun-2004 6-1 6. THE BOOST FILES 6.1. The .bwf Files The BOOSTFILENAME.bwf files contains all graphics and input data of the BOOST model. 6.2. The .bst Files The BOOSTFILENAME.bst file is the input file of the calculation kernel. It is generated by selecting Simulation|Run|Model Creation and is written into the subfolder BOOSTFILENAME.Case_X (X...Index of the Case Set). As it is an ASCII formatted file, it can be transferred to and executed on every platform or computer where a BOOST calculation kernel is available. The BOOSTFILENAME.bst file consists of the following sections: • SECTION HEADER: Contains the total number of elements for each type in a calculation model. • SECTION INPUT: Contains all input data. • SECTION MESSAGES: Summary of the messages from the main calculation program. • SECTION TRANSIENTS: Average results of each element over each cycle calculated (GIDAS format). • SECTION TRACES: Covers the crank angle dependent calculation results from the last calculated cycle (GIDAS format). In an animation calculation this section is not available. • SECTION ANIMATION: Summary of the results of an animation calculation (GIDAS format). In a single calculation this section is not available. • SECTION SUMMARY: Contains the global calculation results. In a series calculation, this section is available for each of the calculated operating points or engine variants. 6.3. The .atm Files The BOOSTFILENAME.atm is similar to the BOOSTFILENAME.bst but it is used to run the BOOST calculation kernel in aftertreatment analysis mode. The BOOSTFILENAME.atm file consists of the following sections: • SECTION HEADER: Contains the total number of elements for each type in a calculation model. • SECTION INPUT: Contains all input data. • SECTION MESSAGES: Summary of the messages from the main calculation program. • SECTION CAT_ANALYSIS: Transient results of catalyst analysis simulations (GIDAS format). BOOST Version 4.0.4 User’s Guide 6-2 23-Jun-2004 • SECTION DPF_ANALYSIS: Transient results of diesel particulate filter analysis simulations (GIDAS format). • SECTION SUMMARY: Contains the global calculation results and additional simulation data. 6.4. The .rs0 and .rs1 Files The BOOSTFILENAME.rs0 and BOOSTFILENAME.rs1 files are restart files. As they are ASCII formatted files, a data set can be transferred together with the restart files to a different platform and the calculation continued with a restart. 6.5. The .uit File This file is written by the main calculation program. It is used for writing debug information during the development of the code and can be deleted after a simulation run without any consequence. 6.6. The .gpf File These files contain the tables of gas properties in dependence on pressure, temperature and excess air ratio (located in $BOOST_HOME\..\..\files). 6.7. The rvalf.cat File This file contains the catalogue of flow coefficients for three-way junctions. It should be located in the directory $BOOST_HOME\..\..\files. User’s Guide BOOST Version 4.0.4 23-Jun-2004 7-1 7. RECOMMENDATIONS 7.1. Modeling In principle, the following requirements must be met by the engine model: 1. The lengths in the piping system must be considered correctly. 2. The total volumes of the intake and exhaust systems must be correct. As experience shows, major problems may occur when specifying the dimensions of pipes. The length of a pipe is determined along the centerline and may be difficult to measure. Also, the engine model should meet the requirement that both the lengths of the single pipes and the total length (e.g. the distance between inlet orifice and intake valves of the cylinder) are considered properly. The modeling of steep cones or even steps in the diameter of a pipe by specifying a variable diameter versus pipe length should be avoided. A flow restriction should be used instead. Figure 7-1: Modeling of Steep Cones If the modeling of steep cones is necessary, the mass balance (i.e. the difference of the in- flowing at out-flowing mass) of this pipe should be checked carefully by the user. In this context it is important to mention that the plenum elements do not feature a length in the sense of a distance which must be passed by a pressure wave. For this reason it is sometimes difficult to decide on a correct modeling of a receiver; on one hand a plenum could represent a convenient modeling approach while on the other a more detailed modeling with several pipes and junctions could be required. The decision must be made on the basis of the crank angle interval which pressure waves need to propagate throughout the receiver. This means that for high engine speeds a detailed pipe junction model is required, whereas for low engine speeds a plenum model may produce excellent results. The following figure illustrates both options for the example of the intake receiver of a four cylinder engine with frontal air feed. BOOST Version 4.0.4 User’s Guide 7-2 23-Jun-2004 Figure 7-2: Modeling of an Intake Receiver The plenum model may predict equal air distribution whereas in reality this is often a critical issue especially for long receivers with small cross sectional areas. For the latter, the pipe junction model is preferred. The step in the cross sectional area at the inlet to the intake receiver is modeled with a flow restriction. Ensure correct modeling of the length of the intake runners (refer to Figure 7-15). Figure 7-3: Modeling of an Intake Receiver with Pipes and Junctions User’s Guide BOOST Version 4.0.4 23-Jun-2004 7-3 The following figure shows three different models for an intake receiver of a four cylinder engine: Figure 7-4: Intake Receiver Models The first model is a simple plenum model. The second is a pipe and junction model with lateral inlet, and the third is a pipe and junction model with central inlet. The total volume of the receiver was kept constant. Figure 7-5 shows the predicted volumetric efficiency and air distribution for the three models. The air distribution is expressed as the difference between the maximum and minimum volumetric efficiency of an individual cylinder related to the average volumetric efficiency. Figure 7-5: Influence of Intake Receiver Modeling on Volumetric Efficiency and Air Distribution BOOST Version 4.0.4 User’s Guide 7-4 23-Jun-2004 The predicted overall volumetric efficiency is similar for all three models, except for shifts in the resonance speeds. As the plenum model does not account for pressure waves in the intake receiver, equal volumetric efficiencies are calculated for all cylinders. The lateral air feed proves to be most critical with respect to air distribution especially at higher engine speeds. Modeling of the ports deserves special attention, especially modeling of the exhaust ports. The flow coefficients are measured in an arrangement similar to the following figure: Figure 7-6: Exhaust Port Modeling The measured mass flow rate is related to the isentropic mass flow rate calculated with the valve area and the pressure difference across the port. The model shown on the bottom left of the above figure would produce mass flow rates which are too high (too low in the case of a nozzle shaped exhaust port), because the diffuser modeled causes a pressure recovery increasing the pressure difference at the entry of the pipe modeling the port. The mass flow rate is calculated with the increased pressure difference and the valve area, and is therefore greater than the measured one. This problem can be overcome either by a correction of the flow coefficients or by switching to a model as shown on the bottom right of the above figure. Due to modeling the pipe as a straight diameter pipe with flange area, there is no pressure recovery. However, the flow coefficients need to be corrected by the ratio of the different areas. This can be done easily by the scaling factor. For modeling a multi-valve engine two options are available: 1. A pipe is connected to each valve (refer to Figure 7-7, left side): The branched part of the intake and exhaust port is modeled by two pipes and a junction. For this junction, the refined model should be used exclusively, as the constant pressure model causes very high pressure losses. This modeling is required only if the two valves feature different valve timings, the geometry of the runner attached to each valve is different or a valve deactivation systems is used. User’s Guide BOOST Version 4.0.4 23-Jun-2004 7-5 2. All intake and all exhaust valves are modeled by one pipe attachment (refer to Figure 7-7, right side): The number of valves is taken into account by specifying the flow coefficients and scaling factor in such a way that the total effective flow area of all considered valves is obtained. This modeling is preferred as it requires fewer elements and is therefore less complicated and more efficient. Figure 7-7: Modeling Multi-Valve Engines 7.2. Analysis of Results The BOOST post-processor assists the user efficiently in the analysis of calculation results, as it allows several trends to be displayed over crank angle simultaneously. This makes the comparison of pressure or mass flow histories over crank angle very simple at different locations in the engine model. An important parameter for the analysis of gas dynamic pressure wave motion is the crank angle interval, which is required by a pressure wave to propagate over a certain distance. The speed of the pressure wave propagation is determined by the speed of sound and the flow velocity (a ± u). Mostly the Mach number of the flow in the pipe is relatively low, which allows the influence of the flow velocity to be neglected. In this case, the crank angle interval required for the propagation of a pressure wave over one meter distance can be calculated from the following formula: a n v W ⋅ = 6 (7.2.1) w v pressure wave propagation speed [degrees CRA/m] n engine speed [rpm] a speed of sound [m/s] The speed of sound can be calculated from the gas temperature in the pipe. A typical value for the intake system is 345 m/s. In the exhaust system, the speed of sound varies typically between 550 m/s (diesel engines) and 650 m/s (gasoline engines). When using the Equation 7.2.1, it should be noted that the influence of the flow velocity is neglected. BOOST Version 4.0.4 User’s Guide 7-6 23-Jun-2004 Another important effect in the analysis of gas dynamic calculation results is the characteristics of the pressure wave reflection: • At an open pipe end (α ∼1.0), a pressure wave is reflected as a depression wave, and a depression wave as a pressure wave. • At a closed pipe end (α ∼0), a pressure wave is reflected as a pressure wave, and a depression wave as a depression wave. The reflection of pressure waves at a plenum is more complex, as normally the pressure in the plenum varies over time. For that reason, the characteristics of the pressure wave reflection depend on the volume of the plenum: • If the plenum is very large, the pressure in the plenum remains almost constant and the reflection characteristics are similar to those of a pipe open to the ambient as discussed above. • If the plenum volume approaches zero, the variation of the pressure in the plenum is similar to the pressure variation inside the pipe. The behavior of diffusers and cones is also of special interest. A pressure wave propagating into a diffuser is weakened due to the expansion resulting from the increasing cross- section. As a consequence, depression waves are reflected by the diffuser: • If a depression wave propagates into a diffuser, the depression wave is also weakened and pressure waves are reflected. • If a pressure wave propagates into a cone, the pressure wave becomes stronger and pressure waves are reflected. • If a depression wave propagates into a cone, the depression wave becomes stronger and depression waves are reflected. 7.3. Important Trends This section summarizes some typical influences of important parameters on engine performance. They may be used to get an overview of required parameter modifications in an engine model to obtain calculated performance characteristics closer to the target engine performance. The example figures shown in this chapter reflect the general trend. They were obtained from a simplified model of a 4-cylinder SI engine. The actual influence of the parameter varied may be different on other engines due to the presence of other effects. The influence of heat transfer is two-fold. It influences the heating of the fresh charge during the gas exchange and thus the volumetric efficiency. This effect is more pronounced from low to mid-engine speeds as more time is available for the heat transfer to take place. Secondly, the heat transfer influences the efficiency of the high pressure cycle by influencing the wall heat losses. Figure 7-8 shows the effect of the variation of the in- cylinder heat transfer on the engine performance. User’s Guide BOOST Version 4.0.4 23-Jun-2004 7-7 Figure 7-8: Influence of In-Cylinder Heat Transfer on Engine Performance The influences of the flow coefficients and wall friction losses are more pronounced at high engine speeds, where the flow velocities in the system are relatively high. They have little influence on engine performance in the low and mid-speed range. Figure 7-9: Influence of Port Flow Coefficients on Engine Performance Intake valve closing mainly influences the volumetric efficiency of the engine. Advanced intake valve closing improves the engine air flow at low engine speeds and retarded intake valve closing favors high engine speeds. BOOST Version 4.0.4 User’s Guide 7-8 23-Jun-2004 Figure 7-10: Influence of IVC on Engine Performance Figure 7-11: Influence of EVO on the Engine Performance There may be a significant influence of the valve train dynamics and/or of the differences between the valve clearances between a cold and hot engine on the engine air flow characteristics. This depends on valve train design. Inertia effects in the intake system may be used for a gas dynamic supercharging of the engine. This effect is important at higher engine speeds because the inertia of the gas in the intake runner becomes significant only at high velocities. Another possibility of gas dynamic supercharging is the use of resonance effects in the intake system. The resonance frequency of such system can be determined roughly from the Helmholtz formula: User’s Guide BOOST Version 4.0.4 23-Jun-2004 7-9 V l A a f ⋅ ⋅ ⋅ = π 2 (7.3.1) f resonance frequency [Hz] a speed of sound [m/s] A pipe cross-section [m²] l tuning pipe length [m] V plenum volume [m³] By selecting the dimensions, a resonance system may be tuned to low or high speeds. A tuning for low speeds can be achieved with a long tuning pipe, a large plenum volume and a small pipe cross-section. However, the plenum is usually located between the tuning pipe and the cylinders, which provide the excitation of the resonance system. For this reason, a large plenum volume lowers the resonance frequency but also increases the damping of the excitation, which is detrimental to gas dynamic tuning. The effects of these two tuning strategies can be seen in the following figures. If the length of the air feed pipe to the intake receiver is varied, as defined in the following sketch, it mainly influences the low frequency resonance peak in the volumetric efficiency curve. Figure 7-12: Air Feed to Intake Receiver BOOST Version 4.0.4 User’s Guide 7-10 23-Jun-2004 Figure 7-13: Influence of Air Feed Pipe Length on Engine Performance Using the dimensions of the air feed pipe for tuning purposes depends on the number of cylinders. The excitation of the low frequency system decreases when the number of cylinders is increased. Figure 7-14: Influence of Number of Cylinders on Engine Performance Although the intake runner length as shown in the next sketch, determines the high frequency resonance, it has also a certain influence on the low frequency peak. User’s Guide BOOST Version 4.0.4 23-Jun-2004 7-11 Figure 7-15: Intake Running Length Figure 7-16: Influence of Intake Runner Length on Engine Performance The performance characteristics of two-stroke engines are more unstable than four-stroke engines. This is caused by the strong interference between the intake and exhaust systems during the scavenging period. As a consequence, a large number of cycles must be calculated until steady conditions are achieved. Minor inaccuracies in the engine model or minor modifications to an engine configuration may result in large differences in the engine performance. The tuning of a two-stroke engine with symmetrical port timing can almost be achieved via the exhaust system alone, as the conditions in the cylinder at the beginning of the high pressure cycle are determined by exhaust port closing. For this reason, the influence of combustion on the gas exchange process is also relatively strong (via the exhaust gas temperature and the speed of sound in the exhaust system). This is not the case for four- stroke engines. BOOST Version 4.0.4 User’s Guide 7-12 23-Jun-2004 7.4. Turbocharger Matching Another application of BOOST is to determine a suitable compressor and turbine size for a turbocharged engine. The simplified turbocharger model with its three calculation modes (turbine layout, boost pressure and waste gate calculation) supports the user in this task. The following steps outline the procedure for the layout of a conventional waste gate turbocharger: 1. The first step is to estimate the air flow requirement for engine full load at the engine speed when the waste gate starts to open. A common layout is around maximum torque speed. The air flow can be calculated from the target Brake Mean Effective Pressure (BMEP), Brake Specific Fuel Consumption (BSFC) and the required Air/Fuel Ratio. The latter is estimated from emission targets considerations. 9 10 16 . 2 ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ = ⋅ c D air n BSFC n V BMEP AFR m (7.4.1) air m ⋅ air flow [kg/s] AFR air fuel ratio [-] BMEP brake mean effective pressure [bar] D V displacement [l] n engine speed [rpm] c n 1 for two stroke engines 2 for four stroke engines BSFC brake specific fuel consumption [g/kWh] 2. With another estimate of the intake manifold temperature and the volumetric efficiency of the engine, the target BOOST pressure is calculated from 10 6 ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ = ⋅ n V n T R m P D V c m air m η (7.4.2) m P intake manifold pressure [bar] R gas constant of air, 287 J/kg K m T intake manifold temperature [K] V η volumetric efficiency related to intake manifold conditions [-] 3. Substituting Equation 7.4.1 into Equation 7.4.2 yields 9 10 6 . 3 ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ = V m m T R BSFC BMEP AFR P η (7.4.3) User’s Guide BOOST Version 4.0.4 23-Jun-2004 7-13 4. With the pressure loss of the inter cooler and air cleaner, the compressor pressure ratio is known cleaner amb cooler m co P P P P ∆ − ∆ + = Π co Π compressor pressure ratio [-] cooler P ∆ inter cooler pressure loss [bar] amb P ambient pressure [bar] cleaner P ∆ air cleaner pressure loss [bar] 5. Using a turbine layout calculation, an equivalent turbine discharge coefficient and an operating point of the engine in the compressor map is obtained. Making two additional calculations with the first turbine discharge coefficient at the lowest engine full load speed in the BOOST pressure calculation mode and at the highest full load speed in the waste gate calculation mode, yields another two operating points of the engine in the compressor map. The compressor pressure ratio for the waste gate calculation can be determined again from Equation 7.4.3. Figure 7-17 shows the three operating points in the compressor map. Figure 7-17: Engine Operating Line in the Compressor Map 6. With this information a suitable compressor can be selected. If the compressor is too small, the rated speed operating point is beyond the speed limit of the compressor or in the choked flow region, Figure 7-18. BOOST Version 4.0.4 User’s Guide 7-14 23-Jun-2004 Figure 7-18: Engine Operating Line in the Compressor Map (compressor too small) If the compressor is too large, low and/or mid speed operating points are located left of the surge line in Figure 7-19. Figure 7-19: Engine Operating Line in the Compressor Map (compressor too large) User’s Guide BOOST Version 4.0.4 23-Jun-2004 7-15 If the correct compressor is selected, the entire engine operating line is located within the map, Figure 7-20. Figure 7-20: Engine Operating Line in the Compressor Map (correct compressor) 7. To determine the necessary turbine, the equivalent turbine discharge coefficient must be converted to a swallowing capacity and plotted in the turbine map, Figure 7-21. Figure 7-21: Engine Operating Point in the Turbine Map 8. After selecting possible turbines and compressors, the calculations must be repeated in the BOOST pressure and waste gate calculation modes to consider the actual efficiencies and swallowing capacities from the maps. For turbochargers with variable turbine geometry, the turbine layout calculation mode may be used at all engine speeds. The location of the engine operating point in the compressor and turbine map must be checked and the actual efficiencies compared to the assumed efficiencies of the calculation. If a larger difference between the efficiencies is detected, the calculation must be repeated with updated efficiencies. User’s Guide BOOST Version 4.0.4 23-Jun-2004 8-1 8. LITERATURE This guide contains important information about the theoretical basis used for the development of the code. For further reading, refer to the following list: General Literature: [G1] Heywood, J. B., Internal Combustion Engine Fundamentals, McGraw-Hill, 1988, ISBN 0-07-100499-8 [G2] Pischinger, R. et al., Thermodynamik der Verbrennungskraftmaschine, Springer, 1989, ISBN 3-211-82105-8 [G3] Benson, R. S., The Thermodynamics and Gas Dynamics of Internal Combustion Engines, Volume 1, Clarendon Press, Oxford, 1982, ISBN 0-198562101 [G4] Shapiro, A. H., The Dynamics and Thermodynamics of Compressible Fluid Flow, Volume 1/2, Ronald Press Company, 1954 [G5] Fried, E., Flow Resistance (A Design Guide for Engineers), I.E. Idelchick Hemisphere Publishing Corporation, 1989, ISBN 0-89116-435-9 [G6] Watson, N. and Janota, M. S., Turbocharging the Internal Combustion Engine, The Macmillan Press Ltd., London, ISBN 0-33-24290-4 [G7] Laimböck, F. J., The Potential of Small Loop-Scavenged Spark-Ignition Single- Cylinder Two-Stroke Engines, SP 847 Society of Automotive Engineers, Inc., Warrendale, PA 15096-0001 [G8] Engine Terminology and Nomenclature – General, NN, SAE - Standard J604, sl, June 1995 Pipe Flow: [P1] Giannattasio, P. et al., Applications of a High Resolution Shock Capturing Scheme to the Unsteady Flow Computation in Engine Ducts, Imech 1991, C430/055 [P2] Harten, A. et al., High Order Accurate Essentially Non-Oscillatory Schemes III, Journal of Computational Physics, Volume 71, Number 2, August 1987 [P3] Winterbone, D. E. and Pearson, R. J., Design Techniques for Engine Manifolds, Wave Action Methods for IC Engines, Professional Engineering Publishing, 1999. [P4] Winterbone, D. E. and Pearson, R. J., Theory of Engine Manifold Design, Wave Action Methods for IC Engines, Professional Engineering Publishing, 2000. [P5] Onorati, A., Nonlinear fluid dynamic modeling of reactive silencers involving extended inlet/outlet and perforated ducts, Noise Control Eng. J. 45 (1), 1997 [P6] Bartsch, P., Bachner, B., Borzi, A. and Schuemie, H. A., On the Simulation of a Concentric Tube Resonator, 5 th ISAIF, Gdansk, 2001 [P7] Konstandopoulos, A. G., Kostoglou, M., Skaperdas, E., Papioannou, E., Zarvalis D., and Kladopoulou, E., Fundamental Studies of Diesel Particulate Filters: Transient Loading, Regeneration and Ageing, SAE 2000-01-1016 , 2000. [P8] Konstandopoulos, A. G., Skaperdas, E., Warren, J., and Allansson, R., Optimise Filter Design and Selection Criteria for Continuously Regenerating Diesel Particulate Traps, SAE 1999-01-0468, 1999. BOOST Version 4.0.4 User’s Guide 8-2 23-Jun-2004 [P9] Peters, B. and Gosman, A. D., Numerical Simulation of Unsteady Flow in Engine Intake Manifolds, SAE 930609 , 1993. [P10] Shah, R. K. and London, A. L., Laminar Flow Forced Convection in Ducts: A Sourcebook for Compact Heat Transfer Exchange Analytical Data, Academic Press, 1978. [P11] Peters, B. and Dziugys, A., Numerical Modeling of Electrified Particle Layer Formation on the Surface of Filtration Fabric, Environmental Engineering , 9:4:191-197, 2001. [P12] Peters, B. and Dziugys A., Numerical Simulation of the Motion of Granular Material using Object-oriented Techniques, Comput. Methods Appl. Mech. Eng. , 191:1983-2001, 2002. Cylinder: [C1] Woschni, G. and Anisits, F., Eine Methode zur Vorausberechnung der Änderung des Brennverlaufs mittelschnellaufender Dieselmotoren bei geänderten Betriebsbedingungen, MTZ 34, 1973 [C2] Hires, S. D., Tabaczynski, R. J. and Novak, J. N., The Prediction of Ignition Delay and Combustion Intervals for a Homogenous Charge Spark Ignition Engine, SAE 780232 [C3] Andree, A. and Pachernegg, S. J., Ignition Conditions in Diesel Engines, SAE 690253 [C4] Rhodes, D. B. and Keck, J. C., Laminar Burning Speed Measurements of Indoline- Air-Dilunet Mixtures at High Pressures and Temperatures, SAE 850047 [C5] Woschni, G., A Universally Applicable Equation for the Instantaneous Heat Transfer Coefficient in Internal Combustion Engines, SAE 6700931 [C6] Woschni, G., Einfluß von Rußablagerungen auf den Wärmeübergang zwischen Arbeitsgas und Wand im Dieselmotor, in proceedings to „Der Arbeitsprozeß des Verbrennungsmotors“, Graz 1991 [C7] Hohenberg, G., Experimentelle Erfassung der Wandwärme von Kolbenmotoren, Habilitationsschrift TU-Graz, 1980 [C8] Zapf, M., Beitrag zur Untersuchung des Wärmeübergangs während des Ladungswechsels in einem Viertakt-Dieselmotor, MTZ 30, 1969 [C9] Gorenflo, E., Einfluß der Luftverhältnisstreuung auf die zyklischen Schwankungen beim Ottomotor, Wiesloch, VDI Fortschrittsberichte , Reihe 12, Nr 322 [C10] Noske, G., Ein quasi-dimensionales Modell zur Beschreibung des ottomotorischen Verbrennungsablaufes, Eggenstein, VDI, Fortschrittsberichte, Reihe 12, Nr 211 [C11] Jungbluth, G. und Noske, G., Ein quasi-dimensionales Modell zur Beschreibung des ottomotorischen Verbrennungsablaufes – Teil 1, MTZ 52, 1991 [C12] Jungbluth, G. und Noske, G., Ein quasi-dimensionales Modell zur Beschreibung des ottomotorischen Verbrennungsablaufes – Teil 2, MTZ 52, 1991 [C13] Vibe, I. I., Brennverlauf und Kreisprozeß von Verbrennungsmotoren, Verlag Technik, Berlin, 1970 User’s Guide BOOST Version 4.0.4 23-Jun-2004 8-3 [C14] Hiroyasu, H. and Kadota, T., Models for Combustion and Formation of Nitric Oxide and Soot in Direct Injection Diesel Engines, in SAE Paper 760129, pages 513-526. 1976 [C15] Hiroyasu, H., Kadota T. and Arai, M., Development and Use of a Spray Combustion Model to Predict Diesel Engine Efficiency and Pollutant Emissions (Part 1. Combustion Modelling), Bulletin of the JSME, 26:569-575, 1983 [C16] Imanishi, T., Yoshizaki, K. and Hiroyasu, H., Simulation Study of Effects of Injection Rate Profile and Air Entrainment Characteristics on D.I. Diesel Combustion, in SAE Paper 962059, pages 135-144, 1996 [C17] Yoshizaki, K., Nishida, T. and Hiroyasu, H., Approach to Low NOx and Smoke Emission Engines by Using Phenimenogical Simulation, in SAE Paper 930612, 1993 [C18] Chmela, F. and Orthaber, G., Rate of Heat Release Prediction for Direct Injection Diesel Engines Based on Purely Mixing Controlled Combustion, SAE Paper 1999 01 0186 [C19] Chmela, F., Orthaber, G. and Schuster, W., Die Vorausberechnung des Bennverlaufs von Dieselmotoren mit direkter Einspritzung auf der Basis des Einspritzverlaufs, MTZ 59 (1998) 7/8 [C20] Wolfer, H., Der Zündverzug im Dieselmotor, VDI-Forschungsarbeiten, Heft 392, VDI-Verlag GmbH Berlin (1938) [C21] Bargende, M., Hemispherical Flame Propagation – A Tool for Simulating Internal Combustion Effects, In 4 th Symposium, The Working Process of the Internal Combustion Engine, Technical University - Graz, September 1993. [C22] Blizzard, N. C. and Keck, J. C., Experimental and Theoretical Evaluation of Turbulent Burning Model for Internal Combustion Engines, SAE 740191. [C23] Tallio, K. V. and Colella, P., A Multi-Fluid CFD Turbelent Entrainment Combustion Model: Formulation and One-Dimensional Results, SAE 972880. [C24] Tabaczynski, R. J., Ferguson, C. R. and Radhakrishnan, K., A Turbulent Entrainment Model for Spark Ignition Engine Combustion, SAE 770647. [C25] Tabaczynski, R. J., Trinker, F. H. and Shannon, B. A. S., Further Refinement and Validation of a Turbulent Flame Propagation Model for Spark Ignition Engines, Combustion and Flame, 1980. [C26] Groff, E. G., An Experimental Evaluation of an Entrainment Flame-Propagation Model, Combustion and Flame, 1987. [C27] Poulos, S. G. and Heywood, J. B., The Effect of Chamber Geometry on Spark Ignition Engine Combustion, SAE 830334. [C28] Heywood, J. B., Internal Combustion Engine Fundamentals, McGraw-Hill International Editions, 1986. [C29] Morel, T., Rackmil, C. I., Keribar, R. and Jennings, M. J., Model for Heat Transfer and Combustion in Spark Ignited Engines and it’s Comparison with Experiments, SAE 880198. BOOST Version 4.0.4 User’s Guide 8-4 23-Jun-2004 [C30] Jennings, M. J., Multi-Dimensional Modeling of Turbulent Premixed Charge Combustion, SAE 920589. [C31] Bielert, U., Klug, M. and Adimiet, G., Application of Front Tracking Techniques to the Turbulent Combustion Processes in a Single Stroke Device, Combustion and Flame, 1996. Acoustics: [A1] Blair, G. P. and Spechko, J. A., Sound Pressure Levels Generated by Internal Combustion Engine Exhaust Systems, SAE Automotive Congress, Detroit, January 1972, SAE 720155 [A2] Blair, G. P. and Coates, S. W. Noise Produced by Unsteady Exhaust Efflux from an Internal Combustion Engine, SAE Automotive Congress, Detroit, January 1973, SAE 730160 [A3] Coates, S. W. and Blair, G. P., Further Studies of Noise Characteristics of Internal Combustion Engines, SAE Farm Construction and Industrial Machinery Meeting, Milwaukee, Wisconsin, September 1974, SAE 740713 Turbocharger: [T1] Turbocharger Nomenclature and Terminology, SAE – Standard J 922, sl, June 1995 [T2] Turbocharger Gas Stand Test Code, SAE – Standard J 1826, sl, March 1995 User’s Guide BOOST Version 4.0.4 23-Jun-2004 9-1 9. APPENDIX 9.1. Running The Executable 9.1.1. Command Line It is recommended to run the BOOST executable from the graphical user interface (Simulation|Run). However, it is also possible to run the BOOST executable (calculation kernel) on its own from a shell or command prompt. This executable (boost or boost.exe) can be found in the platform dependent bin directory of the BOOST installation ($BOOST_HOME). It is also possible to use command line arguments and input file specification for this executable. Running the executable without any command line arguments will result in a command prompt requesting the input file name. This is similar behavior to previous BOOST releases. This section also includes important information on the directories from which gas property files and other auxiliary files used by BOOST are loaded. 9.1.1.1. Options Command line arguments are specified using a preceding dash (-). For some options only a single command line option or input files will be processed. That is, in some cases if multiple command line options are used followed by a BOOST input file (e.g. boost – help –v 4t1cal.bst) only the first command line option is processed before termination. See details on each option for more information. 1. Version (-v) This displays the current version number of the BOOST executable to screen. > ./boost -v v4.0.3 BOOST Version 4.0.4 User’s Guide 9-2 23-Jun-2004 2. Help (-help) This is used display some information on the executable, how to use it and a support contact. > ./boost -help A V L B O O S T Version: v4.0.3 Platform: ia32-unknown-winnt Build: <build date> Usage: boost [-v|-help|-dirs|-plat|-what|-lic] or boost [-verbose] [-debug<number>] [-atm|-burn] [-stop] <filename(s)> Options: -v Print version number -help Print this help information -dirs Print directory information -plat Print platform type -what Print executable information -lic Print license information -verbose Run in verbose mode -debug<number> Run in debug level <number> mode Debug level from 0 (min) to 5 (max) -stop Stop on error (multiple bst only) Run modes: (default is cycle simulation) -atm Aftertreatment analysis -burn High pressure analysis Examples: boost 4t1calc.bst boost -atm aftertreatment.atm boost -burn burn.brn Support:
[email protected] This message will also be displayed for any unrecognized options. 3. Directories (-dirs) This option displays the directories used by BOOST when executed on input files in the same manner. User’s Guide BOOST Version 4.0.4 23-Jun-2004 9-3 > ./boost -dirs A V L B O O S T Version: <Version> Platform: <platform> Build: <build date> Executable directory: <executable directory> Working directory: <working directory> BOOST_HOME: <BOOST_HOME if set> If BOOST_HOME has not been set then a message stating this will be displayed rather than a blank following the BOOST_HOME. 4. Platform (-plat) This displays the build platform for the executable. > ./boost -plat ia32-unknown-winnt 5. What (-what) This displays more detailed information on the executable. The information displayed is similar to the UNIX ‘what’ command. > ./boost -what AVL BOOST v4.0.3 ia32-unknown-winnt (Jun 27 2003 09:15:19) 6. License (-lic) This displays information on the available licenses. > ./boost -lic AVL BOOST v4.0.3 checking licenses.... $Id: @(#) ASTFlexlm v8.4 (Feb 12 2003 13:30:36) ia32-unknown- winnt $ Searching for feature "boost_main" version: "4.0" .... found This license is available Searching for feature "boost_advanced" version: "4.0" .... not found Searching for feature "boost_basic" version: "4.0" .... not found Searching for feature "boost_acoustic" version: "4.0" .... not found Searching for feature "boost_hpa" version: "4.0" .... not found Searching for feature "boost_egat" version: "4.0" .... found This license is available Searching for feature "boost_charging" version: "4.0" .... not found Searching for feature "boost_control" version: "4.0" .... not found Searching for feature "boost_external" version: "4.0" .... not found AVL BOOST v4.0.3 finished checking licenses BOOST Version 4.0.4 User’s Guide 9-4 23-Jun-2004 7. Verbose (-verbose) This option also runs the input file(s) through the solver. All messages that are written to the input file are also sent to the screen. 8. Debug (-debug<number>) This option also runs the input file(s) through the solver. A number must also be given from 0 (minimum) to 5 (maximum). This selects debug options for certain features so that more checks are done. This typically causes a longer run time and an earlier exit due to errors. 9. Stop (-stop) This option stops a multiple simulation run (e.g. ./boost *.bst) whenever a fatal error occurs. 9.1.1.2. File Search Paths BOOST uses a number of auxiliary input files such as the gas property files. These files are opened by BOOST from the following directories, listed in order of priority: 1. Same directory as the BOOST input file. 2. BOOST_HOME files directory ($BOOST_HOME/../files) 3. BOOST_HOME files directory ($BOOST_HOME/../../files) 4. Same directory as the BOOST executable. 5. Current working directory. This is usually the same as 1 or 4 but can be different. 6. Parent directory of the BOOST input file. As soon as the particular file is successfully opened from any of these directories BOOST will stop searching and continue. If it fails to open the file from any of these directories the run will fail unless the file has been specified as optional. Optional files are sometimes used for developmental features. No message is generated for failing to open an optional file. The error message includes the list of the directories specified above. The command line argument for directories (-dirs) can be used if BOOST has problems opening these files. If a file exists in more than one of the allowed locations, the first successfully opened file will be used and the other(s) ignored. A RUNINFO message type specifying the name and path of the file loaded will be written. This is true for optional files also. User’s Guide BOOST Version 4.0.4 23-Jun-2004 9-5 9.1.2. Batch Mode 9.1.2.1. Create Model with GUI The model set-up and the creation of the kernel input files ( *.bst) has to be done with help of the GUI. The bst-files are created as follows: 1. Select Simulation | Run from the Menu bar. 2. In the Run window select Model Creation, deselect Simulation and then select Run. 9.1.2.2. Preparing the Batch File: For this example run.bat was used for the name of the batch-file. The working directory is D:\support\Batch_test\boost This means in this case all bwf-files for this run are in this directory and the example BOOST files are: test1.bst test2.bst test3.bst The following lines shows the content of run.bat ================= Start of run.bat================== #!/bin/sh cd "D:\support\Batch_test\boost\test1.Case_Set_1.Case_1" boost_batch v=4.0 simulation test1 cd "D:\support\Batch_test\boost\test2.Case_Set_1.Case_1" boost_batch v=4.0 simulation test2 cd "D:\support\Batch_test\boost\test3.Case_Set_1.Case_1" boost_batch v=4.0 simulation test3 exit ================= End of run.bat================== 9.1.2.3. Start the Run Open a “bash-window” from the desktop Start | Programs | AVL | AWS3.1 | Bash Start the batch-file with the command: sh run.bat BOOST Version 4.0.4 User’s Guide 9-6 23-Jun-2004 9.2. Required Input Data The following list is a summary of data required as input for a BOOST model. 9.2.1. Engine Data bore, stroke, number of cylinders, con rod length, numbering of cylinders, principle arrangement of manifolds (diagram or sketch) compression ratio, firing order and firing intervals, number of valves, inner valve seat diameters, valve lift curves, cold valve clearances, flow coefficients of the ports (incl. reference area), swirl number (incl. definitions) 9.2.2. Turbocharging System Data compressor and turbine maps including efficiencies, mass flow characteristic of waste-gate valve, intercooler size and hot effectiveness 9.2.3. Fuel Data lower heating value, stoichiometric air-fuel ratio 9.2.4. Boundary Conditions ambient pressure, ambient temperature, max. permissible charge air temperature, pressure loss of air cleaner and intercooler, pressure loss of exhaust system, dimensions of engine compartment 9.2.5. Drawings detailed drawings of the complete intake and exhaust system, (including all receivers, mufflers, throttles and pipes), drawings of the cylinder head, (including the port geometry, flange areas and valve positions) User’s Guide BOOST Version 4.0.4 23-Jun-2004 9-7 9.2.6. Measurements measured full load performance of the engine, (BMEP, BSFC, air-fuel ratio, fuelling, air flow, volumetric efficiency), mean pressures and temperatures in the intake and the exhaust system, (including location of the measuring points), combustion data, cylinder pressure traces, friction measurement results (including definition of procedure) 9.2.7. For Transient Simulation Inertia of engine and power consumption devices Inertia of rotor assembly (TC) Inertia of supercharger reduced to drive shaft (mechanically driven compressors) BOOST Version 4.0.4 User’s Guide 9-8 23-Jun-2004 9.3. Available Channel Data Element Actuator Channel Units Sensor Channel Units Global Load Torque Nm External (Ext.Cnt.) - Speed rpm Mean Speed rpm Speed Gradient rpm/s Mean Speed Gradient rpm/s Ambient Pressure Pa Ambient Temperature K Crank Angle (Ext. Cnt.) deg Absolute Crank Angle (Ext. Cnt.) deg LOAD 0-1 Load Torque Nm Engine Torque Nm Mean Engine Torque Nm Time (Ext. Cnt.) S BMEP Pa System Boundary Pressure Pa Pressure Pa Temperature K Temperature K Flow Coefficient 0-1 Flow Coefficient 0-1 Residual Gas Concentration (Ext) kg/kg Residual Gas Concentration (Ext.) kg/kg A/F Ratio kg/kg A/F Ratio kg/kg Fuel Concentration (Ext.) kg/kg Fuel Concentration (Ext.) kg/kg Internal Boundary Pressure Pa Pressure Pa Temperature K Temperature K Residual Gas Concentration (Ext.) kg/kg Residual Gas Concentration (Ext.) kg/kg A/F Ratio kg/kg A/F Ratio kg/kg Fuel Concentration (Ext.) kg/kg Fuel Concentration (Ext.) kg/kg Cylinder Fuelling (Int) kg Pressure Pa Start of Injection (Int) deg Temperature K Ignition Timing deg A/F-Ratio kg/kg Piston Wall Temperature K Mean Piston Wall Heat Flow W Head Wall Temperature K Mean Head Wall Heat Flow W Liner Segment Wall Temperature K Mean Liner Segment Heat Flow W Intake Port Wall Temperature K Mean Intake Port Wall Heat Flow W User’s Guide BOOST Version 4.0.4 23-Jun-2004 9-9 Element Actuator Channel Units Sensor Channel Units Cylinder Exhaust Port Wall Temperature Mean Exhaust Port Wall Heat Flow W Intake Cam Phasing (VC) deg Mean Liner Wall Heat Flow W Exhaust Cam Phasing (VC) deg (Octane Number (Quad)) - Cooler Coolant temperature K Coolant temperature K Heat flow J/s Measuring Point Pressure Pa Mean Pressure Pa Temperature K Mean Temperature K Mass Flow kg/s Mean Mass Flow kg/s Residual Gas Concentration kg/kg Fuel Concentration (Ext) kg/kg A/F Ratio kg/kg Plenum Pressure Pa Mean Pressure Pa Temperature K Mean Temperature K Residual Gas Concentration kg/kg Fuel Concentration kg/kg A/F Ratio kg/kg Turbocharger VTG-Position (VTG) 0-1 Rotational Speed rpm Mean Rotational Speed rpm Turbocompressor Clutch-Engagement (full) 0-1 PDC Clutch-Engagement (full) 0-1 Fuel injector Flow Coefficient 0-1 A/F-Ratio kg/kg Restriction Flow Coefficient 0-1 Conditions ECU for ECU Element only Ext External Mixture Preparation Int Internal Mixture Preparation VC Valve Controlled Ports VTG VTG-Turbine full Full Model of TCP and PDC Quad Quasi-dimensional, Vibe 2 Zone, Table 2 Zone BOOST Version 4.0.4 User’s Guide 9-10 23-Jun-2004 9.4. Compiling and Linking BOOST The BOOST installation includes all the files necessary to create a new executable to use more advanced features such as the user defined element. This section covers the platform specific operations necessary to create this new executable. 9.4.1. NT Visual Studio A new BOOST executable can be created on Windows 98/2000/NT/XP using Microsoft Visual Studio, Microsoft Visual C++ (Version 6.0) and HP (Compaq) Visual Fortran (Version 6.6C). A ready-to-use visual studio project can be requested at
[email protected]. Further information can also be found at http://www.compaq.com/fortran/visual/faq.html http://msdn.microsoft.com/vstudio/techinfo/techfaq.asp 9.4.2. UNIX The BOOST static library, the main object, and all the precompiled fortran 90 module files (*.mod) are available on each of the supported UNIX platforms. The recommended practice is to create a Makefile to build the new executable which links the platform specific libraries and objects to create the new executable. Makefiles also can be requested at
[email protected]. 9.5. Using the BOOST Dynamic Link Library The BOOST installation includes dynamic link libraries (or shared objects) of the calculation kernel on all the supported platforms (boost.dll). This is used for links to external programs (e.g. AVL CRUISE or MATLAB/Simulink). The BOOST dynamic link library is dynamically loaded at run time by the linking program. 9.5.1.1. Loading Problems Some possible problems during loading are listed below together with their solution. • Entry Point Not Found The problem is that an older version of dformd.dll is being used. This can be updated from the installation CD or downloaded from the following web site: http://www.compaq.com/fortran/visual/redist.html In this example the problem has occurred using the MATLAB s-function link so the dformd.dll used by MATLAB needs to be updated. The location of dformd.dll that needs to be updated is installation dependent (e.g. C:\MATLAB6p5\bin\win32\dformd.dll). User’s Guide BOOST Version 4.0.4 23-Jun-2004 9-11 9.6. Flow Coefficients Directions FLOW COEFFICIENTS INFLOW OUTFLOW System Boundary Flow into pipe * Flow out of pipe ** Plenum Flow into plenum Flow out of plenum Variable Plenum Flow into plenum Flow out of plenum Air Cleaner Flow into cleaner Flow out of cleaner Catalyst Flow into catalyst Flow out of catalyst Air Cooler Flow into cooler Flow out of cooler Junction (Constant Pressure) Flow into junction Flow out of junction User defined Element Flow into element Flow out of element * (typically less than 1 for flow from large volume into pipe) ** (typically 1 for flow out of pipe into a large volume ) The outflow coefficient should generally be less than one (flow into a pipe from a volume) but this is dependent on the actual volume (and other factors) so there is no hard and fast rule. The exception is the system boundary where the outflow (pipe to boundary) should typically be one and the inflow (boundary to pipe) less than one. Refer to the online help (Flow Coefficients - Standard Values) for more information. BOOST Version 4.0.4 User’s Guide 9-12 23-Jun-2004 9.7. Variation Parameters from V3.3 to V4.0 For the advanced BOOST v3.3 user the following equivalence table may be helpful. Variation Parameters in v.3.3 Parameter Type Path to Specify this Parameter in v. 4.0 Engine Speed m Simulation Control | General | Engine Speed Fuelling m Cylinder | Combustion | Fuelling | Fuel Mass Throttle Setting m Restriction | Flow Coefficients | Flow Coefficients (for both directions) Intake Valve Closing/Phase Shift m Cylinder/Modification/Intake Valve Closing (Phase Shift) Intake Valve Closing/Adjusted Cam Length (IO constant) m Cylinder/Modification/Intake Valve Closing (Modified cam length) Exhaust Valve Opening/Phase Shift m Cylinder/Modification/Exhaust Valve Closing (Phase Shift) Exhaust Valve Opening/Adjusted Cam Length (IE constant) m Cylinder/Modification/Exhaust Valve Opening (Modified Cam length) Intake Valve Opening/Fixed Exhaust Valve Closing m Cylinder/Modification/Intake Valve Opening only Intake Valve Opening/Modified Exhaust Valve Closing m Cylinder/Modification/Intake Valve Opening combined with Exhaust Valve Closing (Same direction) Exhaust Valve Closing/ Fixed Intake Valve Opening m Cylinder/Modification/Exhaust Valve Closing only Exhaust Valve Closing/ Modified Intake Valve Opening m Cylinder/Modification/Exhaust Valve Closing combined with Intake Valve Opening (Opposite direction) Cam Spread m Cylinder/Modification/Cam Spread Boost Pressure m Turbocharger/Simplified Model/Compressor pressure ratio User’s Guide BOOST Version 4.0.4 23-Jun-2004 9-13 Turbine Size m Turbocharger/Full Model/Turbine/ Mass Flow scaling factor Positive Displacement Compressor (PDC) Mass Flow m Turbocharger/Full Model/Compressor /Compressor Scaling/Mass Flow scaling factor Pipe Length m Pipe/General/Pipe length Pipe Diameter m Pipe/General/Pipe diameter Element Position m Pipe/General/Pipe length (of related pipes) Plenum Volume m Plenum/General/Volume Control Valve Setting m Restriction/Flow coefficients/Flow coefficients Start of Combustion SOC m,d Cylinder/Combustion/Vibe, Double Vibe, Vibe 2-Zone, Constant volume/Start of Combustion Combustion Duration CD m,d Cylinder/Combustion/Vibe, Vibe 2-Zone, Double Vibe (Vibe1,Vibe2), Woschni/Anisits, Hires et al/Combustion duration Combustion Duration/Timing of Mass Fractions m Cylinder/Combustion/Vibe/Combustion duration (Timing of Mass Fraction will be possible in BOOST v4.1) Compression Ratio m Cylinder/General/Compression ratio Parameter type: main/dependent BOOST V 3.3 list of dependent variation parameters according to main variation parameters. Operation process, Element: Main variation parameter • Dependent variation parameter Path in BOOST V 4.0 Combustion: Engine speed • Fuelling Cylinder/Combustion/Fuelling/Fuel Mass Combustion: Engine speed, Throttle Setting • A/F-Ratio Cylinder/Initialization/Initial Gas Composition/Ratio value Combustion: Engine speed, Fuelling, Throttle Setting • Start of Combustion Cylinder/Combustion/Vibe/Start of Combustion • Combustion Duration Cylinder/Combustion/Vibe/Combustion duration • Vibe Shape Parameter m Cylinder/Combustion/Vibe/Shape parameter m • Ignition Timing Cylinder/Combustion/Hires et al, Quasidimensional, KCM, KCS/Ignition Timing • Ignition Timing Cylinder/Combustion/AVL MCC/Ignition Delay Calibration Factor BOOST Version 4.0.4 User’s Guide 9-14 23-Jun-2004 • Ignition Timing Cylinder/Combustion/Woschni Anisits, Hires et al/Ignition Delay • Ignition Timing Cylinder/Combustion/Vibe, Double Vibe, Vibe 2 Zone, Const. Volume/Start of Combustion Heat Transfer: Engine speed, Fuelling, Throttle Setting • Piston Temperature Cylinder/Heat transfer/Piston/Wall Temperature • Cylinder Head Temperature Cylinder/Heat transfer/Cylinder Head/Wall Temperature • Liner Temperature (Piston at TDC) Cylinder/Heat transfer/Liner/Wall Temp. (Piston at TDC) • Liner Temperature (Piston at BDC) Cylinder/Heat transfer/Liner/Wall Temp. (Piston at BDC) • Port Wall Temperature… Cylinder/Valve Port Specifications/Port/Wall Temp. • Pipe Wall Temperature… Pipe/General/Wall Temperature • Plenum Wall Temperature… Plenum/Heat Transfer/Wall Temperature Valve Timing: Engine speed, Fuelling, Throttle Setting • Intake Cam Phasing Cylinder/Modification/Intake Valve Closing (Phase Shift) • Exhaust Cam Phasing Cylinder/Modification/Exhaust Valve Closing (Phase Shift) Chamber Data: Engine speed, Fuelling, Throttle Setting • Fuel Fraction Cylinder/Chamber/Combustion/Fuel Fraction • Combustion Start Cylinder/Chamber/Combustion/Vibe/Start of Combustion • Combustion Duration Cylinder/Chamber/Combustion/Vibe/Combustion Duration • Shape parameter m Cylinder/Chamber/Combustion/Vibe/Shape Parameter m • Wall Temperature Cylinder/Chamber/Combustion/Wall Heat TransferWall Temperature Intake Valve Closing by: Intake Valve Closing • Phase Shift Cylinder/Modification/Intake Valve Closing (Phase Shift) • Adjusted Cam Length (IO constant) Cylinder/Modification/Intake Valve Closing (Modified Cam length) Exhaust Valve Opening by: Exhaust Valve Opening • Phase Shift Cylinder/Modification/Exhaust Valve Closing (Phase Shift) • Adjusted Cam Length (IO constant) Cylinder/Modification/Exhaust Valve Closing (Modified Cam length) Intake Valve Opening by: Intake Valve Opening • Fixed Exhaust Valve Closing Cylinder/Modification/Intake Valve Opening only User’s Guide BOOST Version 4.0.4 23-Jun-2004 9-15 • Modified Exhaust Valve Closing Cylinder/Modification/Intake Valve Opening combined with Exhaust Valve Closing (Same direction) Exhaust Valve Closing by: Exhaust Valve Closing • Fixed Intake Valve Opening Cylinder/Modification/Exhaust Valve Closing only • Modified Intake Valve Opening Cylinder/Modification/Exhaust Valve Closing combined with Intake Valve Opening (Opposite direction) Exhaust Valve Closing by: Exhaust Valve Closing • Fixed Intake Valve Opening Cylinder/Modification/Exhaust Valve Closing only • Modified Intake Valve Opening Cylinder/Modification/Exhaust Valve Closing combined with Intake Valve Opening (Opposite direction) Turbocharger data (only simplified model): Engine Speed, Fuelling: • Equivalent discharge coefficient Turbocharger/Simplified Model/Equiv. Turbine Discharge Coeff. • Maximum compressor pressure ratio Turbocharger/Simplified Model/Compressor Pressure Ratio • Compressor efficiency Turbocharger/Simplified Model/Compressor Efficiency • TC-overall efficiency Turbocharger/Simplified Model/Turbo Charger overall Efficiency Turbocompressor data (only if a constant operating point is specified): Engine Speed: • Pressure ratio TurboCompressor/Simplified Model/Pressure ratio • Isentropic efficiency TurboCompressor/Simplified Model/Isentropic Efficiency • Mechanical efficiency TurboCompressor/Simplified Model/Mechanical Efficiency Positive displacement compressor data (only if a constant operating point is specified): Engine Speed: • Corrected mass flow/volume flow TurboCompressor/Full Model/Compressor/Compressor Scaling/Massflow Scaling Factor • Temperature increase/isentropic efficiency TurboCompressor/Full Model/Compressor/Compressor Scaling/Efficiency Offset • Power consumption/total efficiency TurboCompressor/Full Model/Compressor/Power consumption/total efficiency