Hot air engine

A hot air engine is any heat engine that uses the expansion and contraction of air under a changing temperature to convert thermal energy into mechanical work, repeatedly heating and cooling air inside a cylinder to move a piston. Guillaume Amontons demonstrated an early heat-powered wheel in 1699, one of the first recorded attempts at an air engine, though early designs were not practically successful. The type matured significantly with Robert Stirling's 1818 engine, which added a component he called an economiser, now known as a regenerator, that stored and recovered heat between cycles and sharply improved efficiency; that feature is central to what became known as the Stirling engine. The closed-cycle Stirling design is distinguished from earlier open-cycle hot air engines built by engineers such as George Cayley and John Ericsson. By the mid-1800s commercial manufacturers were producing reliable hot air engines for practical uses such as pumping water.