Finite-Time Thermodynamic Analysis of Combined Heat Engines

The maximum power output and the efficiency at that power of a combined heat engines are analysed by using Curzon and Ahlborn's finite-time analysis. The efficiency at the maximum power of the combined reversible and irreversible heat engines has been obtained. This work also shows that when the engines are internally irreversible, the combined cycle delivers less power and has lower efficiency than an endoreversible combined heat engines. An expression is derived to relate the maximum power output ratio (irreversible/endoreversible) to the corresponding cycle efficiency ratio. It is shown by that relation that the efficiency ratio is much higher than the power ratio and they become identical when the irreversible cycle is very close to the endoreversible one.