Free Piston Type Stirling Engine
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Prototype of a free piston type Stirling engine
In this page, I introduce a prototype of the model free piston Stirling engine. This engine has very simple stracture, because it does not have any crank mechanism. This prototype engine is operated by a candle as the heat source.
Structure of free piston type Stirling engine
This engine has very simple structure as shown in the left figure. In the case of this prototype engine, the power piston, displacer rod and their cylinders are constructed using medical syringes. The diameters are 15mm and 3.5mm. The piston and the rod must have high sealing performance and low friction. The material of the displacer piston is foam polystyrene. The displacer piston must have a low weight. The displacer cylinder uses a vinyl food container. The heat plate is made of copper.
Principle of free piston type Stirling engine
1. The power piston moves down by gravitation.
2. The volume in the engine decreases and the pressure of the working gas becomes higher. The higher pressure raises the displacer and piston and rod.
3. The hot space becomes bigger and the pressure in the engine becomes higher. The power piston then rises due to the higher pressure.
4. The volume decreases and the pressure becomes lower. Then the displacer piston moves down. The cold space becomes bigger and the pressure in the engine becomes lower.
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