Conceptual design and optimization of scramjet engines using the exergy method

Abstract

The exergy-based multi-disciplinary optimization (MDO) method has been applied to conceptual design of a scramjet engine by analyzing the available energy in each subsystem within a highly integrated and high efficiency required vehicle. Regarding the conceptual design of a scramjet, the stream thrust method has been adopted to calculate each subsystem’s in/out area, i.e., inlet, isolator, combustor and nozzle. Next, a newly developed evaluation program was utilized to evaluate the performance of the vehicle’s internal flow. With the calculated state parameters obtained from the evaluation program results, the exergy analysis was then performed. Subsequently, genetic algorithm and non-dominated sorting genetic algorithm were used to optimize the design variables. The maximum exergy efficiency was measured and the specific impulse (Isp) optimization was conducted separately, and a multi-objective optimization containing both was also investigated. The results demonstrated that the optimization objective with exergy efficiency was suitable for long-endurance vehicles and high-efficiency fuel utilization, the maximum Isp was suitable for high acceleration and high thrust, and the Pareto front could address both needs. It was also found that the cycle static temperature ratio and static pressure ratio of the nozzle should be specifically set at an optimized value to obtain the maximum exergy efficiency and Isp.