Start/unstart hysteresis characteristics driven by embedded rocket of a rocket-based combined-cycle inlet

The RBCC (rocket-based combined-cycle) engine integrates a rocket engine into the flow passage of the ramjet engine, thereby significantly broadening the operating range and becoming one of the potential solutions for the reusable space transportations. The embedded rocket, as one of the core components of an RBCC engine, is strongly coupled to other components, such as the inlet and combustor, and can induce significant impacts on the inlet start behaviors. For the stable operation of the RBCC inlet, the start/unstart hysteresis characteristics and the reliable start boundaries driven by embedded rocket are experimentally and numerically studied. The results show that due to the function of embedded rocket jet, the inlet start/unstart hysteresis range of Mach number rises from Mach 1.79-1.87 to 1.85-1.90, and the back pressure hysteresis range changes from P-c/P-infinity of 3.9-5.8 to 4.7-5.8. Meanwhile, during the increasing and decreasing process of the embedded rocket pressure, the inlet undergoes a transition between start and unstart, accompanied by hysteresis phenomena as well. Furthermore, three different control strategies are proposed for the start of RBCC inlet. Similar to the traditional ramjet inlets, the RBCC inlet can self-/re-start by reducing the back pressure. Particularly, owing to the synergistic effect of embedded rocket jet and back pressure, the RBCC inlet can self-/re-start by reducing the embedded rocket pressure from P-rocket/P-infinity = 58 to 39 in the "embedded rocket dominated" cases, while the inlet self-/re-start can be achieved by increasing the rocket pressure from P-rocket/P-infinity = 20 to 39 in the "back pressure dominated" cases.