State-to-state modeling of NO production by nanosecond electrical discharge in a nitrogen-oxygen mixture at atmospheric pressure

The vibrational non-equilibrium of a N2/N/O2/O/NO/e- mixture, primarily composed of nitrogen, is numerically investigated under discharge and post-discharge conditions, with a focus on the formation of NO molecules. The study is conducted using a reduced electric field of 74 Td and a pulse duration of 200 ns. The numerical model accounts for both heavy particle collisions and electron-heavy particle interactions to accurately capture the complex plasma behavior. The main objectives are to examine the roles of electron-vibrational (e-V) and electron-dissociation (e-D) reactions, as well as to evaluate the effects of slight variations in operating temperature (T = 300, 380, and 500 K), gas recirculation, and pulse repetition frequency. The analysis is performed using a state-to-state model implemented in an in-house, zero-dimensional, time-dependent code, coupled with a Boltzmann equation solver. The results underscore the critical importance of including the full set of vibrational resolved e-V and e-D reactions to avoid underestimating the impact of the discharge. The effect of the temperature, in the investigated range, is clear during the post-discharge and especially at its end, where the atomic densities increase with the temperature and the opposite happens to NO. When the gas recirculation is taken into account, during the discharge-post-discharge cycle, a certain percentage of new gas is entered exactly at the initial set conditions causing a delay in the physical-chemical evolution of the gas itself. Finally, the role of the multiple pulses is studied, observing an enhancement of NO formation for sufficiently high repetition rate.