An external combustion, open-diesel cycle heat engine

An external combustion engine is presented where the pressure of the hot gas (heat source) is less than the pressure of the cold gas (heat sink). The pressure difference allows a spontaneous flow of gas from the low temperature reservoir to the high temperature reservoir without pumps, thus minimizing the number of moving parts; during this flow, the gas is heated by an external combustion chamber. Work output occurs when gas flows from the hot gas reservoir to the cold gas via a free-piston engine whose cycle is essentially a diesel cycle