Study of nanosecond discharges in different H$_2$ air mixtures at atmospheric pressure for plasma-assisted applications*

This paper presents 2D simulations of nanosecond pulsed discharges between two point electrodes in different H$_2$/air mixtures and in air at atmospheric pressure. A fluid model is coupled with detailed kinetic schemes for air and different H$_2$/air mixtures to simulate the discharge dynamics. First, as the positive and negative ionization waves propagate in the interelectrode gap, it has been observed that in H$_2$/air mixtures with equivalence ratios between 0.3 and 2, major positive ions produced by the nanosecond discharge are N$_2^+$, O$_2^+$ and HN$_2^+$. The discharge dynamics is shown to vary only slightly for equivalence ratios of the H$_2$/air mixture between 0.3 and 2. Then, as the discharge transits to a nanosecond spark discharge, we have studied the different chemical reactions that lead to fast gas heating and to the production of radicals, as O,H and OH. Both thermal and chemical effects of the nanosecond spark discharge are of interest for plasma assisted combustion applications.