An external combustion engine in which heat is applied through the wall of a chamber within which a gas is successively heated and cooled, alternately expanding and contracting to power a piston inside the chamber. Its advantages include: exceptional silence, lack of vibration, long life, high efficiency, extremely low emissions and adaptability to many different kinds of fuel. Its main drawbacks are the need for extremely effective seals, inflexible control systems, and cost.

A heat engine of the reciprocating (piston) where the working gas and a heat source are independent. The working gas is compressed in one region of the engine and transferred to another region where it is expanded. The expanded gas is then returned to the first region for recompression. The working gas thus moves back and forth in a closed cycle.

a closed-cycle, regenerative heat engine which uses an external combustion process, heat exchangers, pistons, a 'regenerator' and a gaseous working fluid contained within the engine to convert heat to mechanical work (motion)

a completely different beast