Engines with an External Heat Supply

In engines that use external combustion , also known as “ hot air engines ”, no heat input to the working fluid is produced by combustion in the engine. Instead, the heat input is produced by external combustion, which may be continuous, and is achieved via a heat exchange through cylinder walls or heat exchangers. Two types of external heat engines have been studied for many years: the Stirling engine and the John Ericsson engine . Unlike the reciprocating internal combustion engine, or to a lesser extent the gas turbine, these engines can operate with any form of heat input, as this heat comes from an external source. Traditional fossil fuels, as well as renewable energies such as biomass and solar energy, can be used.