Thermodynamic modeling and performance analysis of RBCC engine ejector mode considering the inlet forebody drag

The inlet forebody drag (FD) in the ejector mode of an RBCC engine is a crucial factor limiting the engine's net thrust performance. To gain deeper insights of how FD affects net thrust performance, this study developed a thermodynamic model of an RBCC engine that includes forebody drag calculations. Based on the simplifications and assumptions about the characteristics of wave system structures, the model subdivides the velocity range of Ma1.5-2 into two sub-ranges. Using this model, the basic characteristics of FD and engine performance changes within the velocity range under various conditions were analyzed. Results show that FD increases with rocket mainstream flow, decreases with divergent section expansion ratio (ER), and first decreases then increases with secondary fuel equivalence ratio (φ). Engine net thrust (Fnet) increases with rocket mainstream flow and ER, but first increases then decreases with φ. Finally, a genetic algorithm was used to obtain the optimal trend of the φ corresponding to Max-Fnet, Max-Ispnet, and Min-FD within the Ma1.5-2. This paper aims to provide insights into the complex interactions between forebody drag, engine performance, and various influencing factors in the RBCC engines ejector mode, thereby contributing to the optimization and improvement of engine performance.