external-combustion

[ik-stur-nl-kuh m-buhs-chuh n]
adjective
  1. noting or pertaining to an engine, as a steam engine, in which fuel ignition takes place outside the cylinder, turbine, or the like, in which heat energy is transformed into mechanical force.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018