Study on the operating modes of an ethylene-fueled hollow air-breathing rotating detonation engine under varying inflow velocities

In this study, ethylene–air rotating detonation was successfully realized in a leading-edge expanded hollow combustor under the incoming flow condition where the air total temperature corresponded to Mach 2.5. The test results show that when the small-hole fuel injection scheme on the wall is adopted, the incoming flow velocity significantly affects the stable operation of the air-breathing rotating detonation engines. When the isolator reaches supersonic conditions, the combustor can establish a stable detonation mode only within a specific lean equivalence ratio range. As the flow rate and axial velocity increase, it becomes more and more difficult to organize detonation combustion. This is mainly manifested in a significant increase in the time for deflagration-to-detonation transition and a narrowing of the detonative equivalence ratio range. However, once detonation is successfully initiated, under high-speed conditions and with a certain equivalence ratio, the intensity of the detonation wave will increase due to the injection of more reactants. Within the entire detonation range, the velocity of the rotating detonation engines can reach 85%–90% of the CJ velocity. A method was developed to determine whether the isolator is fully affected by the forward motion shock wave. By checking if the first PCB pressure fluctuation at the isolator inlet reaches 10% of the local static pressure, the states of the isolator can be classified into two types: fully affected and partially affected. In the detonation mode, the static pressure inside the combustor also increases significantly, and this pressure rises as the equivalence ratio and the incoming flow velocity increase. The impact of the pressure disturbance caused by the detonation wave on the supersonic incoming flow is significantly greater than that in the other two operating modes.