Thermodynamic analysis and investigation on performance optimization of the RBCC engine ejector mode

The rocket-based combined cycle (RBCC) engine is expected to emerge as the next generation of power system for vehicles within the atmosphere. The ejector mode performance is critically governed by the air pressurization ratio and rocket-to-air energy conversion efficiency. However, research in this area remains limited at present. This research conducted a study on ejector mode performance optimization through a combination of thermodynamic analysis and modeling, numerical simulation, and experiment. The thermodynamic process of the ejector mode operation was analyzed. A rocket-air pressurization model was established, and this model was then used to conduct performance evaluation of the engine. Based on numerical simulation and experiment, the optimal performance matching mechanism among the air pressurization ratio, thrust gain and energy conversion efficiency in a real engine was studied. The results show that as the bypass ratio increases, the air pressurization ratio gradually decreases, while the secondary combustion heating ratio gradually increases. Optimal performance requires a compromise between the air pressurization ratio and the secondary combustion heating ratio, achieved by regulating the bypass ratio. The upper boundary of thrust gain is achieved at bypass ratios of 4.68 (Ma0), 4.95 (Ma0.8) and 6.65 (Ma1.6), with corresponding thrust gains of 11.0%, 43.7% and 117.2%, respectively. The higher the pressure in the rocket chamber, the more conducive it is to increasing the air pressurization ratio and the engine performance. The increase in incoming flow velocity and the elevation of flight altitude are beneficial for enhancing the bypass ratio and the performance of the ejector mode.