Control of a Flame Holding Cavity in a Mach 2 Combustor by Quasi-Direct Current Electric Discharge

The quasi-DC (Q-DC) electric discharge is explored for plasma-assisted combustion and plasma-based flow control in scramjet environments. The Q-DC electric discharge generates a high power, filamentary plasma and is applied in Mach 2 airflows using the supersonic blowdown wind tunnel SBR-50 at the University of Notre Dame and Research Cell-19 at the Air Force Research Lab. The plasma filaments are coupled to the flow in a two-way relationship: the flow affects the plasma morphology and parameters and the plasma filaments affect the flow structure and thermodynamics. The intense, local heating of the gas immediately surrounding and within the plasma filaments leads to expansion and causes an oblique shock wave to form in a supersonic flow. Utilization of this plasma-generated shock wave as an active control technique in a supersonic combustor with a flame holding cavity is explored thoroughly in this work by examining the electrical parameters of the electric discharge, plasma parameters, plasma morphology, the resulting impact on the flow field, efficacy of the design/placement of the electrode array, and finally how the plasma influences combustion stability in a supersonic flame holding cavity. Impinging the shock wave onto the shear layer of the cavity increases the static pressure in the cavity flame holder and affects the fuel mixing and entrainment from the core flow. The Q-DC electric discharge was demonstrated in this way to increase the fuel-to-air ratio inside the cavity positively affecting the combustion stability. Novel configurations of the Q-DC electric discharge were also explored to improve its stable and predictable operational in a metallic environment as well as to utilize more resulting effects of the plasma filaments on the flow field than just the oblique shock wave generated by the plasma. An external magnetic field was applied to the Q-DC electric discharge to manipulate the length and morphology of the plasma filaments. The Q-DC electric discharge was also tested in a configuration on the same wall as and upstream of the flame holding cavity. In this configuration the plasma filaments acted as an ignition source in addition to the flow control authority. Overall, the Q-DC electric discharge was successfully demonstrated as a flow control technology for a scramjet combustor and as a supersonic combustion-assistance technique.