Inter-cavity flame dynamics for ignition and flameholding in a dual-cavity scramjet

To investigate the effects of ignition position on flame propagation and combustion characteristics in a dual-cavity scramjet combustor, comparative experiments were conducted under upstream cavity ignition (UCI) and downstream cavity ignition (DCI) conditions in a direct-connect supersonic combustor facility at an inflow Mach number of 2.52. Synchronized schlieren and CH* chemiluminescence imaging systems were employed to visualize flow and flame dynamics during ignition and flameholding processes. For both ignition positions in the present study, the flame initially propagates downstream, then migrates upstream, and finally stabilizes above the upstream cavity. During inter-cavity propagation, the flame leading edge anchors in the near-wall low-velocity zone, and the flame propagation path within the unignited cavity follows the local recirculation direction. Combustion-induced backpressure shifts the shock train upstream; the resulting shock–flame interaction enhances flame propagation toward the unignited cavity and intensifies combustion during the first inter-cavity propagation in the DCI case, whereas this phenomenon is not observed in the UCI case. During flameholding, both cases exhibit cyclic oscillations with temporary flame weakening near the downstream cavity. Under UCI, the oscillation frequency progressively increases until premature flameout occurs, while under DCI, the frequency remains lower without acceleration; both cavities provide stronger flame stabilization, and the flame leading edge oscillates over a smaller range.