Stirling Engine

A Stirling engine is a closed cycle heat engine that converts heat into mechanical work by repeatedly expanding and contracting a fixed quantity of gas, usually air, sealed permanently inside the machine, rather than by burning fuel inside a cylinder the way an internal combustion engine does; a component called a regenerator stores and returns heat within the gas as it shuttles between a hot zone and a cold zone, which is what distinguishes a true Stirling engine from earlier hot air engines. Scottish clergyman Robert Stirling patented the design in 1816, describing the regenerator in his own patent as an economiser, and by 1818 an engine built to his design was already pumping water at an Ayrshire quarry; his brother James Stirling later built larger industrial versions in the 1840s, though these eventually gave way to steam engines. The Philips company revived serious research into the engine from the 1930s through the 1950s, producing the MP1002CA generator set by 1951, and the Swedish Navy went on to adopt Stirling engines during the 1980s and 1990s as air independent propulsion for its submarines, letting them run submerged for extended periods without surfacing. Because it can run on any external heat source, the Stirling engine remains in use today in concentrated solar power systems and small residential combined heat and power units.