Investigation on Ignition Enhancement Mechanism in a Scramjet Combustor with Dual Cavity

Abstract

The spark ignition and flame stabilization of kerosene in a dual-cavity scramjet combustor is investigated with the isolator entrance Mach number of 2.52, total pressure of 1.6 MPa, and stagnation temperature of 1486 K, which corresponds to flight condition. The effects of dual-cavity configuration on ignition and flameholding were analyzed. Two distinct cavity-organized flame regimes were found: cavity flame and cavity shear-layer flame. The driving force of the transition of flame stabilization mode from cavity flame to cavity shear-layer flame is the high pressure resulted from combustion, which occurs in the cavity. The dual-cavity flameholding scheme can promote the ignition ability. First, the downstream cavity could stabilize the flame convected from the upstream cavity. Second, compared with the upstream cavity, the downstream cavity is a more suitable ignition location because the fuel has a longer distance for evaporation and mixing. The boundary-layer separation and upstream moving of precombustion shock train are responsible for the contraflow flame propagation process. Also, an unstable boundary-layer/cavity-stabilized combustion is found during the flame transition process. This phenomenon results from the interaction between the cavity recirculation zones and the separation zone immediately upstream of T1 cavity, which is caused by the strong shock/boundary-layer interactions, as the shock train is pushed upstream.