The ignition characteristics of the close dual-point laser ignition in a cavity based scramjet combustor

The ignition processes of single-point laser ignition (LI) and dual-point LI were experimentally investigated in a cavity-based Mach 2.52 scramjet combustor fueled with ethylene. The stagnation temperature and total pressure of the supersonic inflow were 1486 K and 1.6 MPa, respectively. The results indicate that the ignition performance of dual-point LI with a plasma distance of 3 mm is the same as the single-point LI. However, further increasing the plasma distance to 7 mm degrades the ignition performance of dual-point LI. Therefore, dual-point LI is not superior to single-point LI in the scramjet combustor, which is contradictory to the investigations performed in quiescent premixed combustible mixtures. The reason is that the high turbulence intensity and strain rate in the cavity recirculation flow (similar to 100 m/s) lead to serious plasma and flame quenching instead of enhancing the flame propagation. Therefore, expanding the spatial distribution of the plasma by dual-point LI method, which might result in significant radical loss and heat loss, is not recommended for igniting a scramjet combustor.