Carnot cycle

An ideal reversible, but unattainable, cycle of energy transformation that explains the operation of a perfect heat engine. The four events that occur in a Carnot cycle are: 1. An isothermal expansion of the working fluid from A to B. Heat energy is neither added to nor taken from the air. The temperature remains constant at T1. 2. An adiabatic expansion from B to C with the temperature changing from T1 to T2. 3. An isothermal compression from C to D at temperature T2. 4. An adiabatic compression of the gas from D to A, returning it to its original conditions.