thermomotor

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An engine operated by heat, especially by the expansion of heated air.

from The Century Dictionary.

• noun A heat-engine, particularly a so-called caloric engine, or an air-engine driven by the expansive force of heated air. Compare gas-engine, heat-engine, and caloric engine (under caloric).

from the GNU version of the Collaborative International Dictionary of English.

• noun A heat engine; a hot-air engine.