Ethylene Ignition by Nanosecond-Pulsed Plasma under High-Temperature and High-Velocity Conditions

Combustion in high-speed systems presents unique challenges attributed to short residence time of gas in a combustion chamber, which, combined with high turbulence, often leads to rapid quenching and prevents successful ignition. The nanosecond-pulsed high-frequency discharge (NPHFD) ignition method has demonstrated the potential to overcome these limitations by enabling precise control of key parameters, such as pulse repetition frequency, pulse number, and pulse energy, thereby optimizing energy deposition. This study investigates the dynamics of wall-based NPHFD ignition in heated, high-speed (U = 100 m/s, T = 300°C) ethylene-air mixtures emulating scramjet cavity conditions (U = 36 - 147 m/s, T = 300°C). Ignition probability of the wall-based geometry was studied as a function of varying frequency (1 - 200 kHz), temperature (T = 20 - 300°C), flow velocity (U = 10 - 120 m/s), equivalence ratio (Φ = 0.2 - 0.6), and number of pulses (N = 25 - 100). The kernel was captured using a high-speed Schlieren imaging system and a high-speed infrared camera equipped with a CO₂ filter. Results indicate that elevated temperature, frequency, and number of pulses affect the probability drastically, resulting in successful ignition occurring at lower equivalence ratio and frequency when compared to this obtained in low-flow (U = 10 m/s) at standard room conditions (T = 20°C, P = 1 atm); however, increasing velocity presents an opposite effect causing ignition probability to decrease. These findings provide critical insights into NPHFD ignition, supporting the optimization of wall-based and subsequent scramjet cavity ignition.