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This site is dedicated to the understanding, designing, and building of Stirling Engines. Understanding includes to some extent some math and some background in engineering thermodynamics. We have included some information about the latter. Please, please feel free to make comments, suggestions, and ask questions. This site will always be under development and your contributions are most welcome.

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Thank You and have fun ..... Zig Herzog

Introducing the Stirling Engine

At a time when thermodynamics and Carnot efficiency were still decades away the Reverend Robert Stirling (Oct. 25, 1790 - June 6, 1878), a Scot, applied for patents on what is now known as a Stirling engine including the invention of the 'Economiser' now known as the regenerator. At that time, 1816 that is, Reverend Stirling was just 26, hence the accompaning picture was created some time after that.

Three major aspects make the Stirling engine truely unique. Unlike gasoline, diesel, and various jet engines a Stirling engine receives its heat externally and the heat is supplied continuously. This makes it possible to burn a large variety of fuels and even use the sun light or just any hot body as a heat source. Because the heat is supplied continuously the burning fuel combusts almost completely emitting little carbon monoxide, hydrocarbons, and nitrogen oxides in comparison to internal combustion engines. The disadvantage is of course that the heat has to be transferred through the engine walls which is probably one of the big reasons Stirling engines have a hard time competing with the internal combustion engine.

A second attribute of Stirling engines is that the working fluid ( ususally one of the commonly available gases like air, hydrogen, helium etc ) is completely contained inside the engine, save for unintentional leaks.

Lastly, the Stirling engine with its generator can theoretically achieve a thermodynamic efficiency equal to the maximum possible, the Carnot efficiency. If you are interested why there is such a theoretical maximum click here. The Carnot efficiency and its companion the Carnot cycle are named after Nicolas Léonard Sadi Carnot a French fellow (1 June 1796 - 24 August 1832). By the way, the 't' at the end of his name is silent.

The Carnot efficiency can be calculated rather easily :

η = 'work produced' divided by 'heat supplied' = 1 - Tc / Th

where Tc = absolute temperature at which heat is removed
Th = absolute temperature at which heat is supplied

Absolute temperature in degree Kelvin (K) = temperature in degree Celsius (C) + 273.15
Absolute temperature in degree Rankine (R) = temperature in degree Fahrenheit (F) + 491.67 (491.67=1.8*273.15).
η = the greek letter eta is frequently used as a symbol for efficiency.
As there is no temperature below 0 K there is no cyclic engine operating between the same temperature with an efficiency greater than that indicated by the equation for the Carnot efficiency. Again, if you are curious about this feel free to click here.

Last revised: 01/14/15