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Stirling engine

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Stirling engine
Gamma model

This engine is a compromise between the alpha engine and the beta engine. In a cylinder the displacer assumes its function. In the other cylinder, the operating piston controls the variations of the global volume and recovers energy. This type of engine is frequently used to take advantage of small differences in temperature between cold source and hot source.

1. The four basic stages :

Compared to the ideal cycle described in the page "The principles", the different phases of the cycle of a gamma engine are less differentiated. However, the following drawings seek to represent them.

1.1. Heating :

Heating Heating Heating

During this phase, the engine piston moves slightly, the overall volume is minimal. In contrast, the displacer carries out a long race and the gas is heated.

1.2. Expansion :

Expansion Expansion Expansion

The displacer moves little. In contrast, the operating piston carries out more than 70% of its race. It recovers energy.

1.3. Cooling :

Cooling Cooling Cooling

The displacer carries out most of his race: the gas is cooled. The operating piston moves little.

1.4. Compression :

Compression Compression Compression

The displacer remains at the top: the gas is cold. However, the piston engine performs the majority of its race: it compresses the gas by yielding mechanical energy

The following animation shows the complete cycle of a gamma engine:

Animation of the complete cycle of a gamma engine

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2. The PV diagram :

2.1. The volume variations :

Volume variations

2.2. The PV diagram :

PV diagram

This diagram is characteristic of the engine described above.
The calculations were made with TM = 290 K (17°C) et Tm = 348 K (75°C) .

The volume covered by the operating piston is 5 times lesser than the one covered by the displacer.

The theoretical efficiency would be 17%.

One can see that this cycle is clearly different from the theoretical cycle.

The important thing is to have the gray area as large as possible. It is representative of the work recovered during a cycle (see the page ."the principles").

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This site was created and is maintained by Pierre Gras. Thank you with all the people who contributed their shares: articles, photographs, vidéos, worksheets… The author is opened with any suggestion allowing to improve this site for happiness of everybody. Finally, a big thank you to Robert Stirling !

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