Ignition modes of a cavity-based scramjet combustor by a gliding arc plasma

A gliding arc discharge was employed to ignite an ethylene-fueled scramjet combustor with an inflow speed of Ma = 2.92. Flame chemiluminescence and Schlieren photography were recorded simultaneously with CH* emission images and discharge waveforms for showing the ignition characteristics in the cavity. The direct ignition mode and the re-ignition mode can be identified. In the direct ignition mode, the initial flame can be directly ignited. In the re-ignition mode, the flame kernel is unable to form an initial flame in the early stage of the ignition process, which can be found from the quenching CH* emission of the flame kernel. The CH* emission can be seen again although its quenching lasts for similar to 700 mu s and the re-ignition of the initial flame can be developed to further establish a cavity-stabilized flame. Local equivalence ratio, the instantaneous power of the gliding arc, the area of the flame kernel, and the moving trail of the flame play important roles in determining the ignition modes of the scramjet combustor. The re-ignition mode is more likely to be observed in the local fuel-lean environment and exhibits a longer flame propagation time (1.6 times) and a smaller flame kernel (15%) than those of the direct ignition mode. (C) 2020 Elsevier Ltd. All rights reserved.