Meaning of external-combustion

ex•ter•nal-com•bus•tion

Pronunciation: (ik-stûr'nl-kum-bus'chun), [key]
— adj.
  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.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.