Spark-enhanced ignition and flame stabilization in an ethylene-fueled scramjet combustor with a rear-wall-expansion geometry

Spark ignition processes in an ethylene-fueled scramjet combustor with a rear-wall-expansion geometry were investigated experimentally at the inflow condition of Ma = 2.92 with a stagnation pressure 2.6 MPa and a stagnation temperature 1530 K. Optical measurements including OH∗, CH∗ spontaneous emission and high-speed photography of flame luminosity, were carried out to characterize the ignition and stabilization processes of the flame. Static pressure measurements were also conducted to provide quantitative information of wall-pressure distributions of the combustor. Effects of ignition locations and fuel injection schemes on the ignition possibility, initial flame propagation and flame stabilization processes were studied. It was found that the injection scheme with two parallel injectors (10 mm upstream the cavity) is more favorable for ignition than that with two cascaded injectors (30 mm and 10 mm upstream the cavity). The ignition location near the cavity rear-wall always shows a better ignition performance for both these schemes. It was demonstrated that spark plasma can enhance the combustion during the flame stabilization process. The injection scheme with two cascaded injectors (30 mm and 10 mm upstream the cavity) is more sensitive to the spark plasma than that with two parallel injectors (10 mm upstream the cavity). The injection scheme with two cascaded injectors (30 mm and 10 mm upstream the cavity) is also favorable for the flame stabilization process.