What does a heat engine do?

A heat engine converts thermal energy into mechanical work by exploiting temperature differences between a hot reservoir and a cold reservoir. It operates on thermodynamic cycles, absorbing heat from the hot reservoir, performing work, and releasing some waste heat to the cold reservoir. The efficiency of a heat engine is determined by the ratio of work output to heat input, with limits imposed by the second law of thermodynamics. Common examples include steam engines and internal combustion engines.