Optimization of flame kernel ignition and evolution induced by modulated nanosecond-pulsed high-frequency discharge

Abstract

The enhanced growth of ignition kernels through modulation of nanosecond pulsed high-frequency discharges is investigated quantitatively in a reactive flow. High-frequency discharge and new notions of rotational temperature effective coupling per subsequent pulse (> 30 kHz) existing within the breakdown regime have led to the discovery of the “fully-recoupled” regime. The evolution of flame kernels is observed in a methane-air mixture at an equivalence ratio of 0.6 flowing at 12.5 m/s, with an interelectrode gap of 1.7 mm. Energy deposition into the flow per pulse was previously found to be 2.9 ± 0.23 mJ/pulse, where the number of pulses per effective modulation type was 10 (≈ 30 mJ). By holding average power constant through each pulse train, the Constant Pulse Repetition Frequency partially-coupled and decoupled regimes were directly compared against the (Modulated Pulse Repetition Frequency fully-recoupled regime through kernel growth measurements via high-speed schlieren. It was found that by utilizing the inter-pulse coupling of rotational temperatures through Modulated Pulse Repetition Frequency, the ignition probability and kernel area increased as to create the fully-recoupled regime as a new form of ignition optimization.