The principle of a Carnot cycle is discussed and the operation of a Carnot engine with an ideal gas is calcuated. Engine efficiency, heating and cooling coefficient of performance are defined and their values calculated for a Carnot engine operating on an ideal gas. In order to bring out the importance of irreversibility during heat transfers in a heat engine, the endoreversible cycle is analysed; the heat transfers at the hot and cold reservoirs are the only source of dissipation. The Stirling engine is described. Work and heat exchange are caculated for an ideal gas undergoing the processes that are involved in Diesel, Otto, Lenoir, Atkinson, Brayton and Rankine engines. The Rankine cycle of a biphasic fluid is analysed also.