Exergy-based ecological optimisation of a turbofan engine

A novel ecological optimisation is performed by introducing a new coefficient of ecological performance (CEP) defined by propulsive power per unit exergy destruction rate as the objective function for a single spool turbofan engine with an unmixed exhaust considering finite-rate heat transfer from a thermal reservoir at constant temperature. The optimum values for the selected design parameters of compressor pressure ratio, fan pressure ratio, bypass ratio and turbine inlet temperature are determined numerically to maximise this objective function. Furthermore, the overall efficiency, specific thrust, exergy destruction factor, and exergetic sustainability index are considered as the additional objective functions and optimised with respect to the same parameters for comparison. The results show that: i) the compressor pressure ratio range of 15-25.8 provides a good compromise between energy efficiency and ecological performance; ii) a relatively high pressure ratio with a limited flow rate of air through the fan increases ecological performance of the turbofan engine for commercial aircrafts.