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byl_2141_final

# byl_2141_final - Stirling Engine Marten Byl 1 x Te R Th Tc...

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Stirling Engine Marten Byl 12/12/02 1

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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 ﬂame, and a heat sink, ambient air, an enclosed cylinder, a ”heat” piston, a ”power” piston, and a ﬂywheel connected to the two pistons by a set of linkages. The concept is that the heat ﬂowing 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 ﬂame the heat ﬂow into the engine is minimized while the heat ﬂow out of the cylinder to the heat sink is maximized. Similarly, when heat ﬂow in is maximize, heat ﬂow 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 ﬂywheel then stores this mechanical energy, thus allowing the mechanical power to ﬂow 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-ﬂow 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 outﬂow is nearing maximum while mechanical power may actually be ﬂowing back into the engine. Frames D and E, show the transition back to heat in ﬂow and mechanical power outﬂow. 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 1 x Te R Th Tc...

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