Heat Engine Cycle

Heat engine: device that converts HEAT into WORK over a cycle.

Takes heat Q_h from a hot reservoir, dumps heat Q_c to a cold reservoir, produces work W = Q_h − Q_c.

Efficiency: η = W/Q_h = 1 − Q_c/Q_h.

Real engines: gasoline (Otto cycle), diesel (Diesel cycle), gas turbine (Brayton), steam (Rankine).

Maximum possible efficiency: Carnot's η = 1 − T_c/T_h.

Heat engines are CYCLIC: return to initial state, ΔU = 0 over cycle, Q_net = W_net.

On PV diagram: clockwise closed loop. Enclosed area = net work output.

Kelvin-Planck statement (2nd law): No engine can convert 100% of heat to work in a cycle.