Laser ablation ignition modes in a cavity-based supersonic combustor

A numerical and experimental study was conducted to investigate the Laser Ablation (LA) ignition mode in an ethylene-fueled supersonic combustor with a cavity flameholder. The experiments were operated under a Mach number 2.92 supersonic inflow, with stagnation pressure of 2.4 MPa and stagnation temperature of 1600 K. Reynolds-averaged Navier-Stokes simulations were conducted to characterize the mixing process and flow field structure. This study identified four distinct LA ignition modes. Under the specified condition, laser ablation in zero and negative defocusing states manifested two distinct ignition modes termed Laser Ablation Direct Ignition (LADI) mode and Laser Ablation Re-Ignition (LARI) mode, correspondingly. LA ignition in a local small cavity, created by depressing the flow field regulator, could facilitate the ignition mode transforming from LARI mode to Laser Ablation Transition Ignition (LATI) mode. On the other hand, the elevation of the flow field regulator effectively inhibited the forward propagation of the initial flame kernel and reduced the dissipation of LA plasma, further enhancing the LADI mode. Based on these characteristics, the LADI mode was subdivided into strong (LADI-S) and weak (LADI-W) modes. Facilitating the transition of ignition modes through alterations in the local flow field could contribute to attaining a more effective and stable LA ignition.