byl_2141_final - Stirling Engine Marten Byl 12/12/02 1 x Te...

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Unformatted text preview: Stirling Engine Marten Byl 12/12/02 1 x Te Th Tc =0 R Figure 1: Schematic of Stirling Engine with key variables noted. Introduction In the undergraduate class 2.670 at M.I.T., the students explore basic manufacturing tech- niques by building a stirling engine. The class is concluded by all of the students running their engines at the same time. As the students discover, the stirling engine is very sensi- tive to manufacturing tolerance, specifically the fit of the components determines both the friction in the engine and air leakage out of the engine. The purpose of this project was to develop a model of the stirling engine that accurately predicts the effects of leakage and friction on engine performance. 1 Stirling Engines Figure 1 shows a simple schematic of a stirling engine with key parameters noted. The concept of a stirling engine is fairly simple. The engine consist of heat source, in our case an alcohol ame, and a heat sink, ambient air, an enclosed cylinder, a heat piston, a power piston, and a ywheel connected to the two pistons by a set of linkages. The concept is that the heat owing through the air in the enclosed cylinder is modulate by the position of the heat piston. When the heat piston is located directly over the ame the heat ow into the engine is minimized while the heat ow out of the cylinder to the heat sink is maximized. Similarly, when heat ow in is maximize, heat ow out is minimized. While the heat piston is moving, the power piston is also moving thus converting the thermal energy being captured by the air into mechanical motion. The ywheel then stores this mechanical energy, thus allowing the mechanical power to ow both in and out of the engine. The geometry of the linkages determines the relationship between the motion of the power piston and the heat piston. Figure 2 shows an animation of the stirling engine in operation. Frame A shows the engine in the starting angular position. In the starting position, we see that the heat cylinder S S S S S S A B C D E F Figure 2: Animation of stirling engine in operation. is positioned to maximize the heat in-ow while at the same time the power piston is positioned to maximize output power. In frame B, we see the engine has rotated such that output power is minimized while the heat input area is reducing. In frame C, we see that heat outow is nearing maximum while mechanical power may actually be owing back into the engine. Frames D and E, show the transition back to heat in ow and mechanical power outow. Frame F shows the engine moving back into the maximum thermal power in and mechanical power out position. I would like to thank Katherine Lilienkamp for allowing me to use her matlab code to generate these animations....
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byl_2141_final - Stirling Engine Marten Byl 12/12/02 1 x Te...

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