Investigation of the impact of NRP discharge frequency on the ignition of a lean methane-air mixture using fully coupled plasma-combustion numerical simulations

The ignition of an atmospheric pressure laminar premixed methane/air mixture by Nanosecond Repetitively Pulsed (NRP) discharges in a pin-pin configuration is studied using fully coupled plasma-combustion numerical simulations. These simulations are performed using the AVIP code specifically developed for low temperature plasma modeling and coupled to the combustion code AVBP. A reduced chemical scheme for plasma-assisted combustion previously derived and validated is used to investigate the effect of the frequency of NRP discharges and the benefits of their chemical enhancement. It is observed that the induced shock wave produced by strong discharges is of major importance for ignition and can lead to quenching of the ignition kernels through strong induced recirculation of gases. Increasing the frequency of the discharges reduces this effect by depositing less energy at each discharge and accumulating energy more homogeneously between the electrodes, leading to a faster and more stable ignition. The minimum energy necessary to ignite decreases with increasing frequency and at the highest studied frequency (100 kHz) ignition has been achieved with 30% less energy than with a single-pulse discharge.