This paper presents an optimization method for the civil aircraft environmental control system (ECS) mainly involving two airstreams: the ram airstream for cooling and the bleed airstream for supplying the cabin. The minimum total fuel energy consumption rate (FECR), defined as the weighted sum of the shaft power extraction and propulsive power loss, is obtained under the precondition of the constant outputs in the cooling capacity and outlet pressure. A modified genetic algorithm (GA) is proposed to acquire the optimal values of the heat transfer areas, temperature ratio of bleed air, mass flow rate of ram air, and pressure ratios of the turbine, compressor, and fan. The statistical results show that the multipoint crossover and continuity improvement implemented in the modified GA improve convergence and distribution performance. The probability of reaching a satisfactory result using modified GA is 62.4% higher than standard GA. Due to the decrease of inlet parameters of bleed air and the elimination of power input in the compressor, the FECR of the optimization case can be lowered by 11.0%. In general, the evaluation method considering energy quality together with the modified optimization technique is proved effective in energy-saving design for such energy systems such as ECS with multiple inputs and outputs.

This paper presents a multi-condition design method for the aircraft heat exchanger (HEX), marking with lightweight, compactness, and wide range of working conditions. The quasi-traversal genetic algorithm (QT-GA) method is introduced to obtain the optimal values of five structural parameters including the height, the tube diameter, the tube pitch, and the tube rows. The QT-GA method solves the deficiency of the conventional GA in the convergence, and gives a clear correlation between design variables and outputs. Pressure drops, heat transfer, and the weight of the HEX are combined in a single objective function of GA in the HEX design, thus the optimal structure of the HEX suitable for all the working conditions can be directly obtained. After optimization, the weight of the HEX is reduced to 2.250 kg, more than 20% lower than a common weight of around 3 kg. Based on the optimal structure, the off-design performance of the HEX is further analyzed. Results show that the extreme working conditions for the heat transfer and the pressure drops are not consistent. It proves the advance of the multi-condition design method over the traditional single-condition design method. In general, the proposed QT-GA design method is an efficient way to solve the multi-condition problems related to the aircraft HEX or other energy systems.

The cooled cooling air technology (CCA technology) shows expected performance in solving the growing thermal challenge for advanced aero engines by reducing the temperature of cooling air. The effect of CCA technology on the overall propelling performance with or without adjusting cycle parameters is controversial. Based on this, both the energy and exergy methods have been adopted to elaborate the specific mechanisms of the above energy utilization discrepancy. As a result, the scheme of CCA technology without optimizing cycle parameters has lower propelling work and efficiency with the total exergy destruction increasing 0.5~2%. Oppositely, as for the scheme of CCA with meliorated cycle parameters, the propelling efficiency improved by around 2~4% with total exergy destruction reduced by 1~3.5%. By analyzing the distribution of exergy destruction, the avoidable and unavoidable exergy destruction caused by the combustion chamber, compressors, and turbines accounts for the largest proportion, which indicates that more attention needs to be paid in the future. During the whole flight mission, the percentage of exergy destruction is much higher in supersonic, subsonic cruise, combat, and escape conditions. In conclusion, the improvement of cycle parameters to reduce the exergy destruction should be considered when introducing CCA technology.