Experimental investigation on the dynamic combustion–cooling coupled response in ramjet mode of an RBCC engine with annular-to-circular flowpath

To investigate combustion–cooling dynamic coupling in a rocket-based combined cycle (RBCC) engine under ramjet mode, a long-duration experiment was conducted in an annular-to-circular flowpath under a Mach 3 inflow condition using 41 synchronized measurement points. Cold kerosene was injected through inner and outer annular injectors at an equivalence ratio of 0.5. Cooling-channel pressure, cooling kerosene temperature, combustor wall pressure, and wall temperature were measured synchronously. The results show a clear response hierarchy. Wall pressure responds first and rapidly reaches a quasi-steady state. Cooling kerosene temperature and wall temperature develop later due to thermal inertia. Cooling-channel pressure shows the latest response onset. The series regenerative cooling loop shows strong segmental differences. The rocket cooling zone bears the main flow resistance and follows a hydraulic-dominated response mode. The ramjet cooling zone bears the main temperature rise and follows a property-dominated response mode. Its pressure loss shows a 0.071 MPa overshoot at 11.36 s and then decreases and fluctuates at a relatively high level. The wall pressure load and thermal load show spatial non-uniformity and temporal mismatch. The cavity bottom leading edge exhibits the largest pressure rise, temperature rise, and heating rate, corresponding to a high thermal-load category. Different regions show different wall pressure–wall temperature coupled evolution characteristics. The cavity bottom leading edge, cavity trailing edge, and throat show pressure-saturated, coupled-growth, and pressure-pulsation coupled evolution modes, respectively. This study provides a theoretical basis for thermal protection design with dual-side active cooling in annular-to-circular supersonic combustors.