Combustion organization strategies for a variable geometry RBCC combustor under low total temperature conditions

A rocket-based combined cycle (RBCC) engine experiences a low Mach number phase during flight operations. Through combustor geometry adjustment technology, the engine can combust more efficiently under low-temperature inflow conditions during this phase, thereby improving the engine efficiency. In this paper, we investigate the fuel blending and combustion processes in rocket ramjet and pure ramjet modes under Ma 2.5 low-temperature inflow conditions, analyze the fuel combustion and flow and engine performance changes under different operating modes, and propose a new method for centralized heat release combustion organization under low-temperature inflow conditions. The method is based on the RBCC engine combustor with a geometry throat and relies on both direct-connect experiments and numerical calculations. The results show that (1) when the primary rocket operates, its jet reacts with the inflow in the shear layer and ignites the kerosene fuel injected by the pylons, forming a high-temperature zone downstream of the fuel pylons. When the primary rocket stops working, this flame is stabilized in the low-speed reflux region at the exit of the rocket by injecting a small equivalent ratio of fuel in the isolator to mix with the air. This approach can be a good substitute for the rocket jet to stabilize the flame. (2) When the primary rocket operates, the secondary fuel is mainly concentrated in the area from the fuel pylons to the geometric throat. After the rocket is turned off, the interval of heat release from combustion is also concentrated in the combustor from the fuel pylons to the geometric throat. (3) After the primary rocket stops working, the performance of the combustor improves significantly.