Vapor engine

an engine worked by the expansive force of a vapor, esp. a vapor other than steam.

See also: Vapor

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
Some suggest that Olds adapted his "Olds Safety Gas & Vapor Engines" to the Morton Traction Truck and may even have sold a few as an Olds "tractor."