Heat Engine

A heat engine is a device that accepts heat from a high temperature reservoir, T_H , performs externalwork, W, and rejects heat to a low temperature reservoir T_L. The diagram shows a practical realization of this device,a single cylinder spark ignited internal combustion engine. The high temperature "reservoir" is replaced by the heat input from the combustion of fuel and oxygen, the output work is the mechanical shaft work, and the low temperature "reservoir" is replaced by heat transported in the exhaust gases and lost to the cooling water.

In this Ballard diagram, the combustion temperature is 2573 K, the water temperature 398 K and the air temp. is 290 K. The estimated overall efficiency is 20%.