What is a heat engine?

(N/A) heat engine is a device that converts heat energy into mechanical work. It operates by taking heat from a high-temperature reservoir (source),performing work on the surroundings,and rejecting the remaining heat to a low-temperature reservoir (sink). The efficiency of a heat engine is defined as the ratio of the work done to the heat absorbed from the source,given by $\eta = \frac{W}{Q_H} = 1 - \frac{Q_L}{Q_H}$,where $W$ is the work done,$Q_H$ is the heat absorbed from the source,and $Q_L$ is the heat rejected to the sink.