External-combustion engine and Heat engine

External-combustion engine noun - A heat engine in which ignition occurs outside the chamber (cylinder or turbine) in which heat is converted to mechanical energy.

Heat engine and external-combustion engine are semantically related. In some cases you can use "Heat engine" instead a noun phrase "External-combustion engine".

Heat engine noun - Any engine that makes use of heat to do work.

External-combustion engine and heat engine are semantically related. Sometimes you can replace phrase "External-combustion engine" with "Heat engine", this phrases are similar.