How do Stirling Engines Work?

Stirling engines are heat engines that convert a temperature difference into mechanical work by alternately heating and cooling a quantity of working fluid in a closed cycle.  For 19th century Stirling engines this working fluid is usually air.  Later high power and high efficiency Stirling engines use pressurised hydrogen or helium.

Mechanical work is extracted by heating the working fluid and causing it to expand against a piston.  It is then moved to a cold space where it’s cooled and compressed before being returned to the hot space, repeating the cycle. 

 There are various mechanical arrangements for doing this:

 Alphas use two cylinders with a piston in each and an approximate 90-degree crank angle between them (hot cylinder leading cold cylinder).  The Hayward Tyler, WhisperGens, and LSM 17.2 engines in this collection are all alpha style (WhisperGens are double alphas, having 4 pistons).

 Betas use a piston and a displacer (usually but not always a loose-fitting piston) in one cylinder, also with an around 90-degree phase angle between them (displacer leading piston). Most of the LSM engines, the Heinricis, Ericsson, Phillips crycoolers, Infinia free piston engines and Ringbom in this display are betas. 

 Gamma’s also use a piston and displacer at ~90 degrees to each other, but in separate cylinders, or separated by a bulkhead.  The Stirling original replica, Lehman, Jost fan, Robinson, and model “coffee cup” engines in this display are all gammas.

Peter Lynn for the Mahan Heritage Centre, 2025