Stirling engine
An external combustion engine in which the working fluid expands when heated, driving the working piston. An auxiliary piston transfers the fluid to a colder region. It is then compressed by the working piston and transferred by the auxiliary piston to the hot region to start the cycle again. Helium under pressure is often used as the working medium.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
