An engine is a machine designed to convert energy into useful mechanical motion. In common usage, an engine burns or otherwise consumes fuel, and is differentiated from an electric ...
http://en.wikipedia.org/wiki/Engine

engine n. A machine that converts energy into mechanical force or motion. Such a machine distinguished from an electric, spring-driven, or hydraulic
http://www.answers.com/topic/engine

A car engine is one of the most amazing machines we use on a daily basis. Learn all about car engines and the different types of combustion engines.
http://www.howstuffworks.com/engine.htm

The internal combustion engine is an engine in which the combustion of a fuel (normally a fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber.
http://en.wikipedia.org/wiki/Internal_combustion_engine

engine: see diesel engine diesel engine, type of internal-combustion engine invented by the German engineer Rudolf Diesel and patented by him in 1892.
http://encyclopedia2.thefreedictionary.com/engine