[Type text] December 10, 2010 EAST UNDERGRADUATE FELLOWSHIP STIRLING ENGINE Nicholas Randall | Faculty Advisor Daniel Martinez, PhD which is ice. This project was based off an engine found on a website (Boyd 2005). such as solar. In 1816. which will cause the power cylinder to move back and forth depending on whether there is an increase in pressure or a decrease in pressure. and transportation. but still used external combustion. Stirling engines are undergoing a new phase of development using a number of energy sources. The purpose of having the hot and the cold source is to create a pressure difference between the displacement cylinder and the power cylinder. 2010 Purpose The purpose of this project is to fabricate a walking beam Gamma type Stirling engine and test the engine characteristics when operating using an external heat source. Introduction One of the purposes of this project was to understand the laws and principles of a Stirling Cycle. the power 1 . geothermal. et al. the engines beca me widely used for pumping water out of the ground (Boyle et al.Nicholas Randall December 10. et al. et al. 2009). The reason Stirling engines have been used in high and low scale applications is because of the power to volume ratio. The Stirling engine only added 30% efficiency (Cullen. Stirling engines are used to produce electricity from the sun's energy by putting one part of the Stirling engine in a device that will collect the sun's heat. The second law states that heat would flow from hot to cold and can only flow from cold to hot if there is work done upon it. Some research has been done on making a hybrid car with an internal combustion engine and a Stirling engine by using the exhaust gases to power the Stirling engine. One source of energy is created by using a Sterno gel fuel. After Stirling’s invention. The ability to access the medium scale could allow for a number of opportunities in thermal generation. Robert Stirling was awarded a patent for an external combustion engine he designed and built to help reduce the horrendous accidents that frequently occurred with steam engines boilers that were in use at that time. the longterm goals of the project are to understand the laws of thermodynamics as they apply to the Stirling engine. 2003). The other energy source is a cooling source at the top of the engine. Additionally. and biomass. The Stirling engine requires two sources of energy creating a difference in temperatures. electricity generation. The Stirling engine works on the laws of thermodynamics mainly the first and second law. In biomass power plants a Stirling engine is used to recover heat that would be lost in the combustion process and they are able to generate power from Stirling engine output (Obara. 2005). This engine used a walking-beam configuration in conjunction with a gamma configuration of a Stirling engine and was adapted for use with this project. When the pressure increases (expansion). The first law states that energy is neither created nor destroyed but it just changes form. The other purpose of this project was to take the knowledge learned and apply it to building a model of a Stirling engine. Stirling engines are used in either very high scale or very low scale applications with little utilization in between. Stirling engines have also been used in a geothermal application to drive heat pumps for pumping hot water out of the ground (Lian. 2008). Robert Stirling made an engine that did not require a boiler to run. This made for some complications by using steel pipe instead of a can. We needed to be able to seal one end but have the other end accessible so that we could try different displacer pistons. The first displacer piston that was made was too small. you have one end already sealed. This creates momentum which drives the engine. Once the plate was finished. so the displacer piston was changed out. it was bolted on to the top of the pipe with a high temperature silicone to get a good seal (figure 7). 9). Holes were drilled in the top of the pipe. The plate had to have a grove in it so that pipe would bolt down and seal properly on the plate. Also there had to be a bevel put on the outside edge of the pipe so the welding bead would have someplace to sit (figure 2). the next thing was to choose a design to build an engine. Displacer piston The displacer piston was made from an empty tin can and a 1/8” brass rod . The top plate was bolted on using eight hex head machine screws. By only drilling two holes in either end of the can and attach the displacer piston rod with silver solder on either end of the can. instead of a can we used a 3” steel pipe for the main cylinder. There was a hole drilled and tapped in the side of the displacement cylinder about half-way up from the bottom so the power piston assembly could be attached by screwing it into the displacement cylinder and sealing it with high temperature silicone (figures 7. The design was based off a tin can Stirling engine with a walking beam with some modifications (Boyd 2005). This process was done by first machining the end of the pipe on the lath so the end was perfectly flush (figure 4). Power piston assembly The next step was to make the power piston assembly which was made out of a bronze sleeve bearing and the piston was made from a piece of aluminum stock (figure 8). One of the complications was that with a can. Displacement cylinder assembly For the main displacement cylinder assembly. the power cylinder will get sucked inward. which consists of a separate power cylinder and displacement cylinder.Nicholas Randall December 10. The first thing it was replaced with was a 2 . This was done by a professional welder (figure 3). 2010 cylinder gets pushed outward and when the pressure decreases (compression). which will cause the power piston to move in a linear direction which causes the flywheel to turn. Then there were eight holes drilled in the top of the pipe set apart at 45 degrees from one another (figure 5). There had to be a grove cut in the plate so the pipe would sit down in the plate (figure 1). The top steel plate had a center hole in it which had a 3/8” bolt running through it serving as a guide for the displacer piston rod (figure 7). The displacement cylinder will displace the air. Once that was done there were threads tapped into the holes. We used the gamma configuration. Methods Once all the preliminary work was done. This was done by welding a plate on the bottom end of the pipe but there was trouble getting an airtight seal at first. This was done by putting the pipe on a turn table that was bolted to a milling machine so the pipe was standing on end (figure 6). The next can was an aluminum can. Assembly of the flywheel. The two masts. Because it was aluminum. Then. The next thing was another tin can but instead of using a tomato paste can. it was an imported mandarin orange can (figure 10) and the main differences were that this new can had smooth sides and was a little taller. it was light and smooth on the sides. The old walking beam was a piece of wood that was thicker than it needed to be and therefore added extra weight. 2010 bigger tin can. Research was done to figure out the optimal ratio for the displacer piston to the displacer cylinder. The new walking beam was much lighter because it was much thinner than the original. The structure was made out of wood and consisted of two masts and a base supported by four legs. it allowed for the engine to be put on top of the flame so that the wood would not catch on fire. The optimal ratio was a diameter of 2 3/4”. but this allowed the displacer piston to move from side to side and hit the displacer cylinder walls. which was made from hardwood. The base was modified by cutting off half of it because having an open flame under a wooden base was a safety hazard. but they were still binding at certain points. The new flywheel was made from fiberboard. and structure There was a structure created to hold all of the parts into place. The walking beam was centered between the flywheel and the displacer piston rod. One of the problems with the connecting rods is that they were binding and to help this problem. the measurements that were taken from the engine were compared to other engines that were researched. we first bent the rods so that they were able to flex. By cutting off the base. This was the initial set-up. there was a more direct approach at reaching the optimal size displacer piston. The problem with the aluminum can was that. 3 . But this also caused a problem with having insufficient support for the engine. This flywheel was much lighter but had to be mounted in a different way than the previous flywheel by using a collar and then putting a bolt through the collar. connecting rods. there was an aluminum base made that allowed us to put the flame underneath the engine and still be sturdy. figure 11) . To fix that problem. the timing of the engine would be off. aluminum cans don’t work as well because they have a dimple on the bottom of the can which allows air to get trapped under the can. The rods were replaced with wire to get rid of the binding problem. But this caused problems with friction so with the new flywheel just had one support. as a displacer.Nicholas Randall December 10. but there was trouble with this set-up so the design was changed by running tests and figuring out which parts were causing problems. The original design for the mast for the flywheel was to have two supports lined up parallel so that a shaft would run through them. and a length of 4” (table 1. we used aluminum tape to tape over the dimple so that it was flat. Otherwise. one supported the flywheel and the other supported the walking beam. After the mandarin orange can. walking beam. The mast supporting the walking beam had to have several holes drilled in it so that the height of the walking beam could be adjusted (figure 13). To resolve this problem. a radius of 1 3/8”. (figure 12). The original flywheel was found to be too heavy. the volume stays the same. The displacer piston moves up. There were several weeks of research before the project was started. there would be a loss of power due to the fact that the pressure was escaping through the bigger guide sleeve hole instead of going to the power piston to do work. The process between stage one and two is isothermic. but still have some rigidness to keep the displacer piston going up and down in a straight line so it wouldn’t hit the sides of the displacer cylinder. The walking beam was connected to the flywheel by a double-hooked brass rod. The next step was to connect the displacer piston rod to the walking beam which was done by connecting to a joint that had two pivot points to prevent the rod from flexing too much and getting bound on the displacer cylinder guide sleeve. If the hole was too big. Between the processes of three and four. being the ideal cycle. The second law is in effect by allowing for heat to transfer from the heat source to the displacer cylinder. and the pressure increases (expansion) and pushes out the power piston. Results Thermodynamics. 2010 The other problem with the brass rod was that it was causing too much friction in the displacement rod guide sleeve and to get rid of the friction a bigger hole drilled in the guide sleeve. which allowed the brass rod to pivot around the flywheel. The first law is used to explain what happens in the Stirling Cycle. The Carnot cycle. Assembly of the engine Assembling the engine consisted of putting together the power piston assembly which screwed into the main displacer piston cylinder and the displacer cylinder was screwed down to the base for stability. Volume is increasing. The temperature increases.Nicholas Randall December 10. and pressure is decreasing (compression). In the stage between two and three. The Stirling Cycle is made up of four different stages. This was to understand the Stirling cycle and terminology that goes along with it. The assembly was tested without the power piston hooked up. The test was to spin the flywheel gently to see how many times the flywheel would spin around without stopping or getting hung up on something. Stirling Cycle Understanding the Stirling Cycle was one of the key principles behind this project. the volume decreases. does not work in reality because you’ll never use the full amount of heat that is put into an engine. The first law states that you can use heat energy to transfer into mechanical work. the temperature is isothermic. The final conclusion was to go with a thinner rod for the displacer piston so that it would allow for some flexibility. temperature drops. and this causes a decrease in pressure (compression) which pulls in the power piston. temperature stays constant. the pressure is 4 . After this it was time to hook up the power piston to the flywheel then the engine assembly was complete and was in the test and debugging stage. The energy input that you put in will never equal the energy that you get out due to heat loss within the cycle. they improved the performance and made it easier to see what other problems there were. The changes that were made to the structure and components did not solve the problem of the engine not running. it helped to make it easier to line up the engine for timing. This way was better in the sense that the flywheel moved a lot easier. but it didn’t allow us to hook up anything to it. By changing the walking beam. The power piston is at the maximum outward push and the displacer starts to move up. and the volume is isovolumetric. Another change that needs to be made is to run thermalcouples to the engine so the efficiency of the engine could be measured and it would also help to troubleshoot the engine so that the engine would run. there were several problems that had to be overcome. Future Plans One of the future plans is to redesign the base for optimal efficiency. The cycle repeats (table 2) The objective: During the process of building this engine. This involved changing the setup for the flywheel so that the connecting rod from the power piston to the flywheel would be straight. so there is less air getting displaced. However. 2010 increasing (expansion). the steel-wool pad is a good thermal mass because it allows for air to rush through it when it is going up and down as a displacer piston which allows a rapid heating and cooling. The result of changing the first displacer piston provided more power but was still too heavy and had a tendency to cause drag. was not enough force to turn the flywheel a full turn. What didn’t work is the mechanical configuration that was designed. Another thing would be to change the displacer piston to a steel-wool scrubber pad which allows the shape and size of the displacer piston to be changed. This is done by the fact that steel- 5 . The first thing that was done to improve the power output was to change out the displacer piston in order to try to get more power by displacing more air. Also. But. This caused the power piston to move in and out accordingly. The next plan is to use a similar set-up but attach a pulley to the flywheel so that it would be possible to hook something else to it. One of the things that needs to be done is to raise the mast that holds the walking beam so the connecting rod can be run from the power piston underneath the raised walking beam because there was trouble with the piston connecting rod running into the mast of the walking beam. there was a table produced by calculating different ratios that were found on other Stirling engines of the size of the displacer cylinder to the displacer piston (table 1).Nicholas Randall December 10. To figure out the optimal displacer piston size. it didn’t make the difference between the engine running and not running. The engine would work when the displacer piston was moved up and down by hand. A result of changing the flywheel was that the flywheel was lighter. To have the engine placed so that there would be no strains on different parts of the engine and to have everything perfectly lined up to minimize any drag. This works until the piston is too big and it doesn’t have any room to move up and down. due to the force that the power piston was putting out. Conception if combination of gasengine-driven heat pump and water-loop heat pump system. 6 . Eexergy analysis of the woody biomass Stirling engine and PEM-FC combined system with exhaust heat reforming. 2005. Urieli. J. Z. Park.Nicholas Randall December 10. New York. D. and J. 2010 wool is porous. Huang. 2011 and I have created a website at sites. The Philips Stirling engine. C. P.com/site/usmstirlingengine/ that describes the process that I went through to build this engine and make this project. W. Yao. S. NY. Lian. Boyle. 2010 Energy system feasibility study of an Otto cycle/Stirling cycle hybrid automotive engine. Stirling engine and plans.google. A. G. International Journal of Hydrogen Energy 33: 2289-2299. Bristol. 2008. The porous material allows heat to be trapped so that it stores the heat to be used in a later process.com/stirling/. References Boyd.. I. http://boydhouse. 2005.. Tanno. Everett. M. Stirling cycle engine analysis. I. S. Ramage. 1991. In Energy Systems and Sustainability. Berchowitz. M. 322-327. Obara. International Journal of Refrigeration 28: 810-819. Accessed October 12. Oxford University Press. Hoshi and S. This is called the regenerative process. Adam Hilger. S. Baik. D. Y. New York. Elsevier. 2010.. Hargreaves. Publishing This research will be presented at Thinking Matters in spring. Cullen. and Y. 1984. Sasaki.. The Stirling engine. Energy 35: 1017-1023. B. B.. McGovern. Kito. 4 1.5625 l 3. 7 .4633 Vpc 1.Nicholas Randall December 10.6 2. Vdc= volume of displacement cylinder.74004 1.8225 4. Cycle 1 to 2 volume increases temperature stays constant (isothermic) pressure decreases Cycle 2 to 3 volume stays constant (isovolumetric) temperature decreases pressure decreases Cycle 3 to 4 volume decreases temperature stays constant (isothermic) pressure increases Cycle 4 to 1 volume stays constant (isovolumetric) temperature increases pressure increases Table 2.318345 3.1025 1. l= length(height) of piston. V= volume. and temperature standpoint.38 r2 2.5 2. This is the process of the Stirling Cycle when looking at it from a pressure.778417 Final Dimensions 1.096722 4.809325 4.096722 1. Calculations for optimal displacement piston size. r= radius. These calculations allowed me to determine the optimal size of the displacer piston by working with the pressure/volume equation.9 2.35 1.7 2.96 3.5 1.551142 3.95 Vdc Vpc . 2010 Appendix: Tables and Figures d 3 2.3 1.69 1.608212 23. Vpp= volume of power piston.45 1. volume and temperature table.Vpp 24.884956 Pressure/volume equation p1V 1-p2V 2 Table 1.276743 Vpp Vdc-(Vpc-Vpp) 0.35 1. d= diameter.809325 1.4 1. Pressure. Green is the optimal zone of the displacer piston and then the orange is the average of the two green rows.8 2. volume.8225 1.75 r 1.25 2.96 1.417915 4.7 2.25 1.89 3. Vpc= volume of power piston cylinder.8 2. Figure 2.Nicholas Randall December 10. Grooved plates. 8 . Groves were made by using a milling machine and a turn table. Beveled edge of displacement cylinder. 2010 Figure 1. Put the beveled edge on displacement cylinder for welding on a steel plate. 2010 Figure 3. The pipe is on the lath. Cleaning ends. Figure 4.Nicholas Randall December 10. and using a cutting tool to clean the end of the pipe so that it is flush. Professionally welded the plate onto a pipe to make a displacer cylinder. 9 . Drilling holes in end of pipe.Nicholas Randall December 10. 2010 Figure 5. Holes were drilled in the end of the pipe so I could tap in threads for bolting on the end plate. 10 . 11 .Nicholas Randall December 10. 2010 Figure 6. This is the set-up that was used to drill the holes in the end of the pipe for bolting on the plate. Set-up on milling machine. Nicholas Randall December 10. Displacement cylinder assembly. 2010 Figure 7. This is the displacement cylinder with the top plate bolted on and the displacement piston and guide rod sleeve attached. 12 . The power piston is a 1" piece of aluminum stock made into a piston. The power piston cylinder is a brass sleeve bearing. 2010 Figure 8. Displacement cylinder assembly with power piston assembly attached. There was high-temperature silicone. which has a red color.Nicholas Randall December 10. Power piston assembly. disassembled. used to seal all potential leaks. Figure 9. 13 . The object to the far left is a jig made out of wood for cutting cans on the lath. Displacer piston with silver solder attaching the brass rod. The blue can was the optimal size. 14 . Figure 11.Nicholas Randall December 10. 2010 Figure 10. Arrangement of displacer cylinders for testing. Displacer piston. These are the displacement cylinders that I cut after making the table of calculations (table 1). Figure 13. The main purpose of this is to link the displacer with the power piston and provide momentum for a continuous cycle. Mast. flywheel. This is the assembly of the structure without the engine.Nicholas Randall December 10. 15 . walking beam. 2010 Figure 12. This mast is adjustable to adjust the height of the walking beam by inserting the walking beam into one of the three holes. Adjustable mast. and structure. The beta type engine is when the mechanical configuration has the power piston and the displacer piston in the same cylinder C Closed cycle engine.The stroke that decreases the volume of the cylinder and increases the pressure of the cylinder D Diaphragms. with a regenerator in between them Atmosphere.The engine working fluid never leaves the engine like in a Stirling engine Compression. one hot. and argon.When the reaction that produces thermal energy happens outside the engine. 2010 Glossary A Air. 16 .Is a flexible material that is used instead of a piston or in conjunction with a piston Displacer.is a device that pushes matter from a side to another side or place Displacer Piston.pushes the working fluid from one side to the other side and in most Stirling engines is connected to the power piston by some mechanical means by a quarter turn.Measurement in thermodynamics for the amount of work that cannot be used in a closed thermodynamic system Ericsson Cycle. one cold.A unit of pressure (atm) B Beta Stirling engine.The surrounding gases near the earth surface and is made up of mostly nitrogen. oxygen.The alpha configuration uses two power cylinders.The ability to do work for duration of time Entropy.Nicholas Randall December 10. Air is also one of the working fluids most Stirling engines use Alpha Stirling engine.Works like the Stirling Cycle but the volume is what changes in the Ericsson Cycle instead of the pressure Expansion-To move apart from one another External combustion. E Energy. Force that is uniformly spread across an area. An example is an internal combustion engine. Friction. 2010 F Free piston.The piston that is used to convert energy to mechanical motion Pressure. In the gamma configuration. Also known as adiabatic. Often measured as pressure per square inch (psi). G Gamma Stirling engine.The energy that is produced by when two contacting surfaces are rubbing together. the displacement and the power cylinders are separate.When the engine’s working fluid is used once and then pushed out of the engine.Nicholas Randall December 10.A mechanical device that moves thermal energy Helium. H Heat engine.The amount of work done in a certain time period Power Piston.A different mechanical configuration of the Stirling engine.Needs heat to produce mechanical energy Heat pumps.A working fluid in some Stirling engines I Isocaloric process. O Open cycle engines.A working fluid in some Stirling engines Hydrogen.Is when heat does not transfer from one place to another place.A cylinder that moves in a linear direction inside another cylinder Power. The piston moves up and down by the increase and decrease of pressures in the cylinder.A piston that is not attached to anything mechanically. producing the result of thermal energy. R Regeneration -What happens when heat is moved by a working fluid thus cooling the area 17 . P Piston. The amount of heat that an object can store V Vacuum.Nicholas Randall December 10.A piece of metal that will absorb thermal energy Stirling Cycle.The amount that an object can expand by a certain amount of heat Thermal Mass.A heat engine T Thermal efficiency.The measure of the device’s performance thermally Thermal expansion.Created by a change in pressures from a higher pressure to a lower pressure W Working fluid.The fluid or gas in an engine that carries heat so it can be reused in the regenerator 18 . 2010 S Schmidt Theory.The way calculations are made on the efficiency of a Stirling engine Sink.How a Stirling engine works in principle Stirling engine.
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