Alterations of Regenerative Displacers in Stirling Engines

1. Alterations of Regenerative Displacers in Stirling Engines In Conjunction with: Steve Wilhelm, PhD, Brown University Andrew Wilhelm, Physics Major, West Point Stephen F. Austin University Physics Department Alex Wilhelm Dash Gordon Introduction: This study is being preformed to find an efficient use of the landfill gas to create power. The experiment included researching, building, and testing a Stirling engine. Specifically, the study is being preformed to determine if a smaller or larger regenerative displacer is more effective for creating energy. The heat source in our project will be a small candle, but the landfill gas being burned at the moment could easily be applied to a Stirling engine. This study could potentially increase the efficiency of the application of a Stirling engine being fueled by landfill gas. The Stirling engine as the most basic operation utilizes the “closed thermodynamic regenerative cycle” (“SESUSA” 2002). The engine consists of a fixed amount of contained gas within a chamber. There are two properties that allow this engine to work. When a fixed amount of gas is contained in a fixed volume, and heat is applied, the molecules in the gas will heat up and the pressure increases. The other property of gas is that when a fixed amount of gas is compressed the temperature of the gas will increase. The displacer type of engine has one piston and a displacer that controls when the gas is heated and cooled. This engine is similar to ours that it also has two heat sources that are separated, the hot and the cold. The regenerative displacer is a sealed piston that moves in a linear direction and provides the heat when the gas is compressed. The displacer is a loose piston that allows the air to move around it, this allows the air to heat when the displacer is at the top of the master cylinder and cool when the displacer is near the bottom of the displacer. When the displacer is near the top, the gas can heat and expand making the regenerative displacer move, and creates the work. When the displacer piston is near the bottom of the master cylinder the gas has the heat drawn away through the cold source pulling the regenerative displacer in and compresses the gas. • To obtain data, the researchers attempted the following steps: • Build a stirling engine (see note below) • Run engine, noting RPM. • Change the volume of the regenerative displacer by 15% approx. Under no other changes, repeat run. Note RPM. • Referenced from the first size, decrease size of displacer. Repeat experiment. • Remove displacer, repeat experiment. • Analyze data found. Run more tests to obtain more accurate/meaningful data. • (For a more accurate description of how to build, refer to final paper or design provided by: Stephen F. Austin State University – Physics Department) Methodology: Data: Using the design attempted, a speed of approximately 120 RPM would have been attained. The engine, under no circumstances would run without a displacer. Conclusions: We were not able to complete this experiment as we did not have to capability to build a functioning stirling engine. Over a multi-day period we built three (3) distinct stirling engines. All were not able to sustain a rotation, and thus the experiment failed. The research team, was very lucky too have 14 hours of help from a PhD chemist (Brown University), and 4 hours of from a Physics major from West Point. However, they also failed in getting the said engines to function. However, setbacks aside, the researchers still feel strongly that any increase in the volume of the displacer would result in a decline in the efficiency of the engine. An increase in the total volume would decrease the total heat available per unit of air, thus decreasing the rotation speed. There would be less power, hence fewer RPM. To find the most efficient size for the displacer, multiple tests would need to occur with a working engine.