A heat engine is a device that converts heat into mechanical energy.
Conceptualising the heat engine: The heat engine must carry a working substance (usually a gas) through a cyclic process in which the system passes through a series of states.
During the cycle:
- the working substance absorbs heat (Qh) from a hot reservoir
- converts part of that heat into mechanical energy (i.e., work output by the engine Wout)
- then expels the rest of the heat (Qc) to a cold reservoir to return to the initial state, and the cycle repeats.
All these cycles comprise of the following basic gas processes: