Stirling engine

Stirling engine, type of external-combustion engine invented in Scotland by the Rev. Robert Stirling in 1816. Long in disuse, the Stirling engine has recently been reinvestigated as a possible substitute for the gasoline engine, but so far has not proved practical. Different versions of the Stirling engine exist, but all involve a gas (usually air) circulating in a closed system of cylinders and pistons and deriving energy from an external source of heat.