Stirling engine

A Stirling engine is a closed-cycle regenerative heat engine with a gaseous working fluid. "Closed-cycle" means the working fluid, the gas which pushes on the piston, is permanently contained within the engine's system. This also categorizes it as an external heat engine which means it can be driven by any convenient source of heat. "Regenerative" refers to the use of an internal heat exchanger called a 'regenerator' which increases the engine's thermal efficiency compared to the similar but simpler hot air engine.

Noted for its high efficiency, quietness of operation and the ease with which it can utilise what would otherwise be waste heat, the Stirling engine is currently exciting much interest as the core component of domestic combined heat and power (CHP) units, the widespread adoption of which could have a significant effect upon worldwide carbon dioxide emissions[1][2].

The Stirling engine was used in small low power applications for nearly two centuries, and saw ever increasing scientific development of its technological potential. The Stirling cycle is notable for its perfect theoretical efficiency; however this ideal has proved notoriously difficult to achieve in real engines, and remains an immense engineering challenge. Nevertheless, the current technology is reasonably advanced, and the designs are useful and versatile. It continues to be used and further developed, and this device holds promise for its ability to provide mechanical or electrical power, heating or cooling in a number of applications wherever a heat source and heat sink are available.

The term "hot air engine" is used generically to include any heat engine with air working fluid. Hot air engines may use any one of several different thermodynamic cycles, including the Brayton cycle, Ericsson cycle or Stirling cycle. Air is one of many possible gases that may be used in a Stirling engine.