A
hot air engine (historically called an
air engine or
caloric engine) is any
heat engine that uses the expansion and contraction of
air under the influence of a temperature change to convert
thermal energy into
mechanical work. These engines may be based on a number of thermodynamic cycles encompassing both open cycle devices such as those of
Sir George Cayley and
John Ericsson and the closed cycle engine of
Robert Stirling. Hot air engines are distinct from the better known internal combustion based engine and steam engine.