Investigation of Flame Stabilization in a Dual-Mode Scramjet Combustor Using a Pulsed Nanosecond Discharge

This study investigates the impacts of a nanosecond, repetitively-pulsed discharge on optical emission and pressure measurements in an ethylene-fueled, dual-mode scramjet combustor. The experiments were performed in the University of Virginia Supersonic Combustion Facility (UVASCF). High frame rate (50-100 kHz) spectrally filtered images, optical emission spectra, and high frequency pressure measurements were synchronously acquired to assess the improvements induced by the discharge-coupled cavity compared to nominal fuel-lean and low temperature cavity flameholding operation. Increased production of relevant excited-state hydrocarbon combustion radicals (OH*, CH*, and C2*) was observed during discharge actuation across all test cases in both spectrally filtered images and emission spectra. Spatial distribution of increased emission varied for each combustion radical. The impacts of the discharge were observed to depend on local fuel availability and were enhanced at lower stagnation temperatures. Spatial and modal analyses revealed that the discharge instigated forward shifts and an increase in width of the reaction zone for all interrogated intermediate species. Assessment of CH* temporal dynamics in the cavity and cavity shear layer showed that nanosecond discharge actuation increased CH* production throughout the shear layer with a maximum increase observed at 3.5 µs from peak discharge emission. This study presents new findings on dual-mode scramjet flameholding enhancements provided by nanosecond discharges through observation of hydrocarbon combustion radical production on relevant timescales for plasma-enhanced combustion.