Synergistic effect of low-voltage nanosecond-pulsed discharges for scramjet cavity ignition

Nanosecond-pulsed high-frequency discharges (NPHFDs) have been an ignition technology of interest due to their efficient production of active radicals and excited species with low overall energy input. However, a drawback is the fast rise time and high peaks in voltage and current that often produce significant electromagnetic interference which can be detrimental to electronic components in the region of the ignition system. The current work experimentally investigated the ignition of a cavity-based flameholder using a burst of low-voltage nanosecond discharges in comparison to single, high-voltage nanosecond discharges. Experiments were conducted in a Mach-2 flow with stagnation temperature and pressure of 589 K and 483 kPa, respectively. The cavity was directly fueled with ethylene to test ignition across an equivalence ratio range of 0.67 – 1.58. Low-voltage bursts of nanosecond pulses produced low- and high-current discharges. The low-current pulses were found to pre-condition the discharge region and establish breakdown, whereas the high-current discharges (breakdown) ultimately governed ignition. High-frequency bursts (300 kHz) with low voltage per pulse (∼1.5 kV) successfully ignited the cavity with 89 % lower voltage and at least 53 % lower energy compared to single pulse cases while not significantly impacting the time to ignition. These results show that utilizing a burst of low-voltage nanosecond pulses is a promising method of reducing NPHFD device requirements without a loss in ignition performance.