Wartsila SP Tech 2008 Derating

Derating: a solution forhigh fuel savings and lower emissions Rudolf Wettstein1 & David Brown2 ­ Wärtsilä Switzerland Ltd, Winterthur ­ Summary This paper sets out ways to achieve worthwhile reductions in the fuel consumption of Wärtsilä low-speed engines when designing newbuildings. The key approach is to use the flexibility offered by the full power/speed layout field to select a better layout point at a derated power with a lower BSFC and also possibly a higher propeller efficiency. Introduction Fuel efficiency and environmental friendliness are high on the list of requirements for ship propulsion engines from today’s shipping- and shipbuilding industries. Thus Wärtsilä is committed to creating better technology in these areas that will benefit both the customers and the environment. Yet it is often forgotten by many ship designers and those specifying low-speed main engines that advantage can be taken of the power/speed layout field of Wärtsilä low-speed engines to select an engine rating point with a still lower fuel consumption. The concept of the power/speed layout field for low-speed marine diesel engines originated in the 1970s. The layout options were step-by-step widened until, in 1984, our low-speed engines began to be offered with a broad power/speed layout field. An engine’s contracted maximum continuous rating (CMCR) can be selected at any point in the power/ speed field defined by the four corner points: R1, R2, R3 and R4 (Fig. 1). The rating point R1 is the maximum continuous rating (MCR) of the engine. Most recently, the layout fields for certain engines, the RT-flex82C, RTA82C, RT-flex82T and RTA82T, are extended to increased speeds for the R1+ and R2+ points (Fig. 2). The extended fields offer widened flexibility to select the most efficient propeller speed for lowest daily fuel consumption, and the most economic propulsion equipment, 1 ­ Engine power, %R1 100 Higher propulsive efficiency R1 0 -1 ∆BSFC -2 g/kWh -3 -4 -5 -6 -7 80 R3 Lower specific fuel consumption 70 C on st an 90 tt or qu Rx e lin e R4 R2 60 70 80 90 100 Engine speed, %R1 Fig. 1: Typical layout field for RTA and RT-flex engines. The contracted maximum continuous rating (CMCR) can be selected at any point, such as Rx, within the layout field. The ∆BSFC is the reduction in full-load BSFC for any rating point Rx relative to that at the R1 rating. [08#044] 2 ­ Rudolf Wettstein is Director, Marketing & Application Development, Ship Power, Wärtsilä Switzerland Ltd. David Brown is Manager, Marketing Support, Wärtsilä Switzerland Ltd. namely the propeller, shafting, etc. One basic principle of the engine layout field is that the same maximum cylinder pressure (Pmax) is employed at all CMCR points within the layout field. Thus the reduced brake mean effective pressure (BMEP) obtained at the reduced power outputs in the field results in an increased ratio of Pmax/BMEP and thus lower brake specific fuel consumption (BSFC). The other principle behind the layout field is © Wärtsilä Corporation, June 2008 ­ —1— Engine power. In general. 4: Since the 1980s engine ratings have been selected over a steadily smaller area of the layout field. This is the line through a CMCR rating point such that any point on the line represents a new power/speed combination that will give the same ship speed in knots.000 tdw to 0. %R1 100 R1 R1+ Engine power.22 for container ships larger than 3000 TEU and 0. Rating points at lower speeds on the rating line require a larger propeller diameter and give a greater propulsive efficiency. 3: For a given ship. [08#049] that the lower CMCR speeds allow flexibility in selection of the optimum propeller with consequent benefits in propulsion efficiency and thus lower fuel consumption in terms of tonnes per day. a rating line (slope α) can be applied to the layout field so that all rating points on that line would give the same ship speed with a suitably optimized propeller. June 2008 ­ 60 70 80 90 100 Engine speed. such as design draught and ballast draught limitations. bulk carriers and general cargo ships up to about 10. %R1 100 R1 90 Rx2 Rx1 Rating line slope = α 90 R3 80 R3 80 70 R4 R2 R2+ R4 R2 80 90 Engine speed.000 tdw. One feature to be borne in mind when selecting the rating point for the derated engine is the rating Fig. 2: For the RT-flex82C.15 for tankers. The maximum diameter is often determined by operational requirements. as well as class recommendations concerning propeller–hull clearance (pressure impulse induced by the propeller on the hull). %R1 100 60 70 80 90 100 Engine speed. %R1 . Afterwards RTA engines were frequently selected at ratings in the lower part of the layout field to gain the benefits of —2— © Wärtsilä Corporation. The points on the rating line all require the same propeller type but with different adaptations to suit the power/speed combination. Usually the selected propeller speed depends on the maximum permissible propeller diameter. %R1 100 Area of recent CMCR selection R1 90 Area of CMCR selection in the 1980s 80 R3 line (Fig. It can range from 0. lower speeds of rotation require larger propeller diameters and thereby increase the total propulsive efficiency. RT-flex82T and RTA82T engines the layout fields are extended to the ratings R1+ and R2+ at the same powers as R1 and R2 respectively but with increased shaft speed. Fig. 70 R4 R2 Changing engine selection strategies When the broad layout field was introduced in RTA engines in 1984 it was widely welcomed by shipowners and shipbuilders. RTA82C. The slope of the rating line (α) depends broadly upon the ship type.25 for tankers and bulk carriers larger than 30. ­ [08#051] ­ Engine power. 3). %R1 Fig. US$/tonne 380cSt HFO 500 400 300 200 100 2004 2005 2006 2007 2008 Fig. Depending on bunker costs.Bunker price. such a strategy can have a very attractive pay-back time. under the pressure of first costs and softening bunker prices the strategy was changed and the selected power/speed combination has. The consequent fuel saving may make for an acceptable payback time on the additional investment cost. a Capesize bulk carrier. bunker prices have steadily climbed. In addition it is important to bear in mind that the fuel savings measures discussed here will also result in lower NOX emissions in absolute terms. a Panamax container ship and a Post-Panamax container ship. rising by some 85 per cent in the course of 2007 from US$ 270 to US$ 500 per tonne (Fig. The four case studies are for a Suezmax tanker. It would justify any efforts to increase the overall efficiency of the complete propulsion system. If a carbon trading scheme is imposed on shipping it would give further economic advantage to reducing fuel consumption and further help to pay for any necessary extra investment costs. The result is that bunkers are now the dominant part of ship operating costs. These cases demonstrate that such engine derating can be an advantageous solution with remarkable saving potential. —3— © Wärtsilä Corporation. been selected to be closer to the R1 rating (Fig. ­ [08#045] ­ lower fuel consumption. 4). Such drastic increases in bunker prices give a strong impetus to reduce fuel costs. The green bars indicate the mean price for each year. Derating engines for greater fuel savings In the following pages are some case studies for ship installations for which an engine is selected with an extra cylinder without increasing the engine’s power. Yet. The chart shows the average price of 380 cSt heavy fuel oil (HFO) from various ports around the world from 2004 to 2008. Further impetus to implementing such changes in engine selection strategy will come from a future need to cut CO2 emissions. June 2008 ­ . more recently. They include estimations of the respective pay-back times for the additional engine costs. However. during the past 15 years or so. 5: Bunker prices have considerably increased in recent times. They can also justify additional investment cost such as selecting an engine with an extra cylinder. 5). if a seven-cylinder engine is employed instead.6 64.0 165.780/95 20. In the engine/propeller layout for this ship as shown in figure 6.4% —4— © Wärtsilä Corporation. June 2008 ­ . g/kWh: – 100% load: – 90% load: Daily fuel consumption.000 0 8690 472 7RT-flex68-D 680 2720 4:1 21. US$: Engine length.000 – 309. mm: Piston stroke.4 per cent.6 8.780/95 18. kW / rpm: CMCR.7 169.0 16.614/86.6 164. mm: Engine mass.3) through a common design point for the same ship service speed (knots). Length overall: Beam: Design draught: Scantling draught: Sea margin: Engine service load: about 274 46–50 16 17 15 90 m m m m % % Table 2: Main engine options ­ Alternative engines: Cylinder bore.7 17. mm: Stroke/bore ratio: MCR. The calculation of annual fuel costs given in table 2 is based on 6000 hours running with heavy fuel oil Table 1: Typical ship parameters for a Suezmax tanker costing US$ 500 per tonne. LCV 42.7 MJ/kg: – LCV 40. kW / rpm: BMEP at CMCR. US$: Fuel saving.5 and six years depending on the bunker price of US$ 600–400 per tonne respectively (Fig.853. tonnes/day: – ISO fuel. A similar case may be made for a Capesize bulk carrier as it would be similar in size and speed to a Suezmax tanker and would thus require a similar engine.9 16.544.902/91. However.910/95 18.4 96.8 162. tonnes: 6RT-flex68-D 680 2720 4:1 18.6 67. %: Annual fuel costs.Case 1: Suezmax tanker & Capesize bulk carrier ­ In this case. kW/rpm: BSFC at CMCR. the daily fuel consumption can be reduced by some 3. the CMCR points for the two alternative engines are on the same rating line (α = 0.8 100 8.460/89. a typical Suezmax tanker might be specified with a six-cylinder Wärtsilä RT-flex68-D main engine.5 MJ/kg: – As percentage.000 9870 533 –3. bar: CSR at 90% CMCR. The resulting payback time for the extra cost associated with the additional engine cylinder is estimated to be between 3. 7).2 70.8 68. The calculations of the payback are based on an interest rate of eight per cent. [08#052] 18.460 kW 89. HFO: $600/tonne $500/tonne $400/tonne 2. June 2008 ­ .3 CMCR 18.6 rpm CSR 16. 7: Variation of payback times from fuel savings according to bunker costs for the derated engine with an extra cylinder for a typical Suezmax tanker.0 Bunker price. [08#144] Investment approx.0 Fig.0 0 2 4 6 8 10 12 14 Years —5— © Wärtsilä Corporation. kW 22.000 16.614 kW 86.902 kW 91. ($) 1.780 kW.7 rpm 75 80 85 90 95 100 Engine speed.000 Constant ship speed α = 0. 95 rpm 6RT-flex68-D Fig. 6: Engine/propeller layouts for a typical Suezmax tanker with a derated seven-cylinder RT-flex68-D engine compared with a six-cylinder engine at the full MCR power and speed.000 CSR 16.000 7RT-flex68-D 20.Case 1: Suezmax tanker & Capesize bulk carrier ­ Engine power. rpm Millions US$ 3.7 rpm Design point CMCR = R1 18. 000 – 348. tonnes: 8RT-flex82C 820 2646 3.3 166. kW / rpm: CMCR.680/102 35.6 164. the CMCR points for the two alternative engines are on the same rating line (α = 0.0% 16.000 0 14.5 15 90 m m m m % % Table 4: Main engine options Alternative engines: Cylinder bore.790. %: Annual fuel costs. if a nine-cylinder engine is employed instead.2) through a common design point for the same ship service speed (knots). In the engine/propeller layout for this ship as shown in figure 8.0 32. However.5 169.480/97.000 16.160/102 19.2 12 13.5 32.7 MJ/kg: – LCV 40. g/kWh: – 100% load: – 90% load: Daily fuel consumption. June 2008 ­ .544/98. mm: Piston stroke.Case 2: Panamax container ship ­ In this case.5 130. the daily fuel consumption can be reduced by some two per cent.4 134. Table 3: Typical ship parameters for a Panamax container ship The calculation of annual fuel costs given in table 4 is based on 6000 hours running with heavy fuel oil costing US$ 500 per tonne.0 166. Length overall: Beam: Design draught: Scantling draught: Sea margin: Engine service load: about 295 32.500 1140 —6— © Wärtsilä Corporation.0 137. kW / rpm: BSFC at CMCR. mm: Engine mass.160/102 36. The resulting payback time for the extra cost associated with the additional engine cylinder is estimated to be between four and seven years depending on the bunker price of US$ 600–400 per tonne respectively (Fig. kW / rpm: BMEP at CMCR.250/94.138. LCV 42.2:1 40.3 98 – 2.2:1 36. tonnes/day: – ISO fuel.5 17.5 MJ/kg: – As percentage.1 100 17. 9). The calculations of the payback are based on an interest rate of eight per cent. US$: Fuel saving. bar: CSR at 90% CMCR.055 1020 9RT-flex82C 820 2646 3. a typical Panamax container ship with a container capacity of up to 5000 TEU might be specified with an eight-cylinder Wärtsilä RT-flex82C main engine. mm: Stroke/bore ratio: MCR. US$: Engine length.6 127. HFO: $600/tonne 3.0 0 2 4 6 8 10 12 $500/tonne $400/tonne Fig.250 kW 94.2 34.850 kW 97.3 rpm 85 90 95 CSR 32.544 kW 98. kW 42.0 Bunker price.000 9RT-flex82C 38.5 rpm 32.0 1.0 2. rpm Millions US$ 4.5 rpm Design point CMCR = R1+ 36. 8: Engine/propeller layouts for a typical Panamax container ship with a derated nine-cylinder RT-flex82C engine compared with an eightcylinder engine at the full MCR power and speed.000 40. June 2008 ­ .000 Constant ship speed α = 0. [08#145] Investment approx. 102 rpm Fig.Case 2: Panamax container ship ­ Engine power. [08#062] 36. ($) 14 Years —7— © Wärtsilä Corporation.000 100 105 Engine speed.000 CMCR 35.000 8RT-flex82C CSR 32. 9: Variation of payback times from fuel savings according to bunker costs for the derated engine with an extra cylinder for a typical Panamax container ship.160 kW. 9 18.8 233. bar: CSR at 90% CMCR.4 per cent.000 23.000 0 21. kW / rpm: BSFC at CMCR. US$: Fuel saving. The resulting payback time for the extra cost associated with the additional engine cylinder is estimated to be between two-and-a-half and four years depending on the bunker price of US$ 600– 400 per tonne respectively (Fig. tonnes: 11RT-flex96C 960 2500 2.4% 30.0 163. In the engine/propeller layout for this ship as shown in figure 10.000 – 762. mm: Stroke/bore ratio: MCR. Length overall: Beam: Design draught: Scantling draught: Sea margin: Engine service load: about 325 42.8 13 14. 11).5 15 90 m m m m % % Table 6: Main engine options ­ Alternative engines: Cylinder bore. kW / rpm: CMCR.360/102 65. a typical Post-Panamax container ship with a container capacity of around 7000 TEU might be specified with an eleven-cylinder Wärtsilä RT-flex96C main engine.2 245. if a 12-cylinder engine is employed instead. kW / rpm: BMEP at CMCR.6:1 66. June 2008 ­ . tonnes/day: – ISO fuel.230 2050 —8— © Wärtsilä Corporation. The calculations of the payback are based on an interest rate of eight per cent.330/102 19. US$: Engine length.919/98.7 MJ/kg: – LCV 40.327/95.5 171.550 1910 12RT-flex96C 960 2500 2.738. the CMCR points for the two alternative engines are on the same rating line (α = 0. However.2) through a common design point for the same ship service speed (knots).6 59.4 59.500.6:1 72.0 166.697/98. LCV 42.Case 3: Post-Panamax container ship ­ In this case.5 168. mm: Engine mass. g/kWh: – 100% load: – 90% load: Daily fuel consumption.8 239 252 100 31.6 – 2. the daily fuel consumption can be reduced by some 2.9 97.330/102 66. %: Annual fuel costs. Table 5: Typical ship parameters for a Post-Panamax container ship The calculation of annual fuel costs given in table 6 is based on 6000 hours running with heavy fuel oil costing US$ 500 per tonne. mm: Piston stroke.5 MJ/kg: – As percentage. 919 kW 98. 10: Engine/propeller layouts for a typical Post-Panamax container ship with a derated 12-cylinder RTflex96C engine compared with an 11-cylinder engine at the full MCR power and speed.000 Constant ship speed α = 0.0 Bunker price. June 2008 ­ .5 rpm 100 105 Engine speed.000 60.697 kW 98.000 CMCR 65.000 12RT-flex96C 70.5 rpm 58.000 Design point CMCR = R1 66.0 2. HFO: $600/tonne $500/tonne $400/tonne Fig.327 kW 95. 102 rpm 68.0 0 2 4 6 8 10 12 14 Years Investment approx.000 90 95 CSR 59. rpm Millions US$ 8. [08#146] 4. 11: Variation of payback times from fuel savings according to bunker costs for the derated engine with an extra cylinder for the typical Post-Panamax container ship. [08#127] 11RT-flex96C 64.330 kW.Case 3: Post-Panamax container ship ­ Engine power.2 66.000 CSR 59. kW 72.000 62. ($) —9— © Wärtsilä Corporation.0 6.9 rpm Fig. 1:1 9720/124 9720/124 19. then the BSFC at full load is reduced by 4. the D version of this engine was announced. However.7 163.1 100 4. mm: S/B ratio: MCR.000 – 124. g/kWh: – 100% load: – 90% load: Daily fuel consumption. Furthermore the engine would need to be tested and approved by the Classification Society for both ratings with all the necessary emissions certification. it can be frustrating to buy more ‘engine’ than seems necessary. %: Annual fuel costs. tonnes/day: – ISO fuel.000 © Wärtsilä Corporation. mm: Piston stroke.513. US$: Fuel saving.637. Then for a later date.6 35. kW / rpm: CMCR. lower minimum running speeds. Yet there is an interesting option to retain an ability to utilise the full available installed engine power.7 171 167.5 g/kWh.5 8748/119. the engine could be re-adapted to the higher output.2 97. The concept would be to set up the engine for the derated output at the chosen reduced service speed.Case 4: Derating without adding an engine cylinder It is also feasible to apply a derated engine to obtain fuel savings in such a way that an additional engine cylinder is not required. shafting and ancillary equipment to meet the requirements of the envisaged higher power.7% 4. however.000 when operating for 6000 running hours a year with heavy fuel oil costing US$ 500 per tonne. There would.3 – 2. There are already a number of standard ship designs delivered and on order with RT-flex50-B or even the original RT-flex50 engine. be Table 7: Options for the Wärtsilä RT-flex50 engine type a modest increase in cost of the D version for the higher-efficiency turbochargers used. or 2. Even greater savings are possible if the engine is derated to a lower running speed (rpm) at the derated power to gain the benefits of a better propulsion efficiency.1 per cent and the BSFC at full-load was reduced by 2 g/kWh compared with the B version.1:1 10. in which the engine power was increased by 5. kW / rpm: BMEP at CMCR. bar: CSR at 90% CMCR. US$: 6RT-flex50 500 2050 4.7 MJ/kg: – LCV 40. Wärtsilä RT-flex low-speed engines incorporate the latest electronically-controlled common-rail technology for fuel injection and valve actuation. Derating with flexibility to full rating Although derating offers attractive economics. RT-flex technology as an important contribution to fuel saving Wärtsilä RT-flex technology plays an important role in fuel saving. bringing benefits in lower fuel consumption. but the extra cost would soon be repaid by the fuel cost savings. So it would be perfectly feasible to install a derated RT-flex50-D in further newbuildings to the same ship designs and obtain the benefit of the substantial savings in operating costs.000 0 — 10 — 6RT-flex50-D 500 2050 4. kW / rpm: BSFC at CMCR.2 37. this needs corresponding provisions in the selection and design of the propeller. The result is great flexibility in engine setting. For a typical bulk carrier with a six-cylinder RT-flex50 engine this can translate into annual savings of US$ 124. The overall dimensions of the D version are identical to those of the B and original versions of the RT-flex50.7 165. smokeless operation Alternative engines: Cylinder bore.2 36. even up to the full R1 rating for future use to obtain higher ship service speeds. LCV 42.470/124 9720/124 19. Thus if a ‘-D’ engine is derated to the same cylinder power output as the original version of the RT-flex50. In October 2007. An example of this can be seen with the Wärtsilä RT-flex50 engine.5 8748/119.7 per cent (see Table 7).5 MJ/kg: – As percentage.0 34. June 2008 ­ . Conclusion The paper shows that there are techniques to achieve worthwhile reductions in the fuel consumption of Wärtsilä low-speed engines when designing newbuildings. If you have a project for which you wish to explore the fuel-saving possibilities through derating as set out in this paper. Moreover. [1] Owing to the interaction between fuel economy and NOX emissions. It must also not be forgotten that any fuel savings achieved at the ship design stage will have benefits in also reducing exhaust emissions. Wärtsilä RTA and RT-flex engines are all fully compliant with the NOX emission regulation of Annexe VI of the MARPOL 1973/78 convention. there is always the possibility that fuel saving measures will have an impact on NOX emissions. July 2004.com — 11 — © Wärtsilä Corporation. German Weisser. Our experts will be delighted to calculate various alternatives for your evaluation. June 2008 ­ .wartsila. Wärtsilä Switzerland Ltd. References 1. The key approach is to use the flexibility offered by the full power/speed layout field to select a better layout point with a lower BSFC and Published June 2008 by: Wärtsilä Switzerland Ltd PO Box 414 CH-8401 Winterthur Tel: +41 52 262 49 22 Fax: +41 52 262 07 18 www. then please contact your nearest Wärtsilä office. As with all new marine engines nowadays. also possibly a higher propeller efficiency. ‘Fuel saving with RT-flex’.at all running speeds. Not only do RT-flex engines have a lower partload fuel consumption than RTA engines but they can be adapted through Delta Tuning so that their part-load fuel consumtion is even lower. the engines in the Wärtsilä portfolio will be adapted to meet the coming IMO NOX reduction level Tier II. and better control of other exhaust emissions.