Experimental investigation of multichannel plasma igniter in a supersonic model combustor

Reliable and fast ignition of scramjet engine is quite important in consideration of high velocity and low pressure of inlet air. Successful ignition requires that sufficient ignition energy be injected into the flame kernel so that the flame propagates outwardly beyond the critical initial radius of the critical flame. Larger critical flame initiation radius is required during the preliminary stage of scramjet engine so advanced ignition technology for scramjet engines is urgently needed. In this study, multichannel plasma igniter (MCPI) is proposed to induce a relatively larger ignition kernel for the purpose of achieving successful ignition in scramjet engines. Ignition experiments in a model scramjet combustor fueled by ethylene were conducted with inflow conditions of Ma = 2.52, stagnation pressure P0 = 1.6 MPa and stagnation temperature T0 = 1600 K. Ignition processes of SI and MCPI at different fuel injection schemes were captured by CH∗ chemiluminescence imaging and flame luminosity imaging technology. Results reveal that MCPI with five channels generates 5 times more ignition energy than SI and MCPI can generate much larger plasma volume and activated area which can induce a relatively larger initial flame kernel. The CH intensity of MCPI was about 2.2 times larger than that of conventional SI. Besides, it was shown that the lean ignition limit of scramjet combustor through MCPI was extended by 20-26% than that through SI and the ignition time was reduced by approximately 50%. MCPI with an injection 10 mm upstream the cavity demonstrates the best performance in this study.