Suppression of combustion mode transitions in a hydrogen-fueled scramjet combustor by a multi-channel gliding arc plasma

Abstract A multi-channel gliding arc (MCGA) plasma was utilized to suppress combustion mode transition in a hydrogen-fueled cavity-based scramjet combustor with an inflow speed of Ma2.92. Several optical and electrical techniques, including OH* chemiluminescence, optical emission spectrum, discharge waveform acquisition, and pressure measurements, were employed to show the characteristics of the MCGA discharge and the processes of the combustion mode transitions. When the MCGA is off, the flame frequently oscillates between a cavity shear-layer mode and a cavity-stabilized mode at a low global equivalence ratio, whereas the flame is more likely to be kept in the cavity-stabilized mode when the MCGA is on. The ratio of the cavity-stabilized mode increases from 28.2% to 93% when the plasma is on. The combustion frequently oscillates between a cavity-stabilized mode and a jet-wake stabilized mode at a high global equivalence ratio, but the mode transitions can be suppressed significantly in the presence of the MCGA. The ratio of the jet-wake stabilized increases from 21.9% to 48.8% when the MCGA is on. The Proper Orthogonal Decomposition (POD) method is employed to analyze the oscillation, and it is found that the mean energy content of the large-scale oscillation across the different modes can be significantly suppressed by the MCGA. A plausible explanation can be mainly related to the reactions of N 2 * species with O generated by the MCGA, which increases the temperature in the vicinity of the plasma. The temperature rises spread to the entire cavity with higher backpressure, and results in better mixing and more intense combustion, leading to the suppression of the combustion mode transitions.