Linked from
The 20 pages that link to Heat engine, each with the reason it gives.
ThermodynamicsRelated: Its performance is bounded by thermodynamic laws.
EntropyRelated: Entropy places a ceiling on the fraction of heat convertible to work.
Thermal energyRelated: It uses a temperature difference to extract useful work from thermal energy.
Work (thermodynamics)Related: Its useful output is work produced during a thermodynamic cycle.
Irreversible processRelated: Irreversible effects reduce the work an engine can extract from heat.
Laws of thermodynamicsRelated: The laws determine its energy balance and maximum efficiency.