An
external combustion engine (
EC engine) is a
heat engine where a
working fluid, contained internally, is heated by combustion in an external source, through the
engine wall or a
heat exchanger. The fluid then, by expanding and acting on the
mechanism of the engine, produces motion and usable
work. The fluid is then cooled, compressed and reused (closed cycle), or (less commonly) dumped, and cool fluid pulled in (open cycle air engine).