Ignition Characteristics of a Supersonic Combustor with Parallel Dual Combustion Zones

The ignition of a dual-combustion-zone supersonic combustor featuring a cavity and a backward-facing step (BFS) are investigated experimentally and numerically. The inflow conditions are Mach 2.52, stagnation pressure 1.6 MPa, and stagnation temperature 1486 K, with ethylene as the fuel at global equivalence ratios ([Formula: see text]) of 0.30, 0.35, and 0.40. The results show that cavity ignition is achieved by spark discharge for all tested conditions, where the spark generates an initial flame kernel confined in the recirculating flow. After a short growth phase limited by radical dissipation, the flame develops into a shear layer flame. In contrast, BFS ignition depends on the equivalence ratio. At [Formula: see text], ignition remains spark-driven, while at [Formula: see text] and 0.40, the BFS undergoes self-ignition followed by flame backpropagation. The self-ignition originates from combustion-induced flow restructuring. The lifted cavity flame compresses the mainstream, forming a high-temperature, high-pressure separation zone that traps fuel–air mixture and enables flame kernel formation. As the energy accumulates, coupled flow and thermal choking stabilize the flame kernel, which transitions to a self-sustained flame. It then propagates upstream through a fuel-rich channel and stabilizes as a BFS flame. These findings provide guidance for optimization and design of novel supersonic combustors.