Carnot heat engine
![Axial cross section of Carnot's heat engine. In this diagram, abcd is a cylindrical vessel, cd is a movable piston, and A and B are constant–temperature bodies. The vessel may be placed in contact with either body or removed from both (as it is here).[1]](/Images/godic/202412/18/Carnot-engine-18240029.png")
![Carnot engine diagram (modern) - where an amount of heat QH flows from a high temperature TH furnace through the fluid of the](/Images/godic/202412/18/Carnot_heat_engine_2.svg0029.png")
![real ideal engines (left) compared to the Carnot cycle (right). The entropy of a real material changes with temperature. This change is indicated by the curve on a T-S diagram. For this figure, the curve indicates a vapor-liquid equilibrium (See Rankine cycle). Irreversible systems and losses of heat (for example, due to friction) prevent the ideal from taking place at every step.](/Images/godic/202412/18/Real_vs_Carnot.svg0029.png")
A Carnot heat engine is an engine that operates on the reversible Carnot cycle. The basic model for this engine was developed by Nicolas Léonard Sadi Carnot in 1824. The Carnot engine model was graphically expanded upon by Benoît Paul Émile Clapeyron in 1834 and mathematically elaborated upon by Rudolf Clausius in 1857 from which the concept of entropy emerged.