Nanosecond Pulsed Plasma Discharges in High-speed Methane-Air Flow: Effects of Velocity on Plasma Morphology and Ignition Development

The Nanosecond Pulsed High-Frequency Discharges (NPHFD) is a promising ignition method in high-speed flows like scramjets and ramjets, where ignition is challenging. This study investigates NPHFD ignition in high-velocity subsonic fuel-air mixtures (up to 80 m/s) under controlled conditions, focusing on the effects of flow velocity, number of pulses, inter-pulse time, and plasma morphology on ignition probability and flame kernel development. Key findings include plasma elongation, where hot and ionized gas from preceding discharges promotes subsequent discharge elongation. This phenomenon alters the understanding of pulse-kernel interactions, which can facilitate successful ignitions in previously disadvantaged conditions. Preliminary results show significant impacts of flow velocity on ignition probabilities, with plasma elongation mitigating destructive pulse-kernel interactions. Identified inter-pulse coupling regimes—fully coupled, partially coupled, and decoupled—depend on discharge elongation and flow conditions, offering new insights for optimizing plasma-induced combustion processes in high-velocity environments.