Nanosecond pulsed discharge in a propane-air mixture: Ignition and energy deposition

The study examined the possibility of using nanosecond pulse discharges as a new ignition and assisted combustion method to solve ignition and combustion stabilization problems encountered in new combustion technologies. To better understand how temperature and the presence of radicals affect nanosecond discharge ignitions, spatiotemporal profiles of rotational and vibrational N2(X) temperatures were measured through spontaneous Raman scattering in a lean propane-air mixture and compared with previous results obtained in air to obtain the space- and time-resolved measurements necessary to validate the kinetic modeling of the discharge in presence of hydrocarbons. The study aims to contribute to a better understanding of the initial ignition processes in stoichiometric mixture (first observed at 1 µs) and the rapid displacement of the flame front in propane-air mixtures. In the analyzed propane-air mixture, the gas heated slightly more rapidly than in air. This temperature increase might have occurred in the release of energy resulting from dissociation of propane due to quenching by metastable species. The presence of traces of CO confirmed this assumption. The energy transfer processes were identical in all other respects and occurred over the same time scales in air and in the propane-air mixture. Once the flame in the stoichiometric mixture was ignited, it propagated through a cylindrical channel whose diameter was identical to that of the volume of gas heated to above 900 K in the lean propane-air mixture. This early ignition and the spreading of the flame kernel demonstrate the combined effect of radicals and temperature on the nanosecond discharge ignition process. The resulting new database makes it possible to validate simulations of the vibrational kinetics involved in nanosecond discharges of a lean propane-air mixture and provides a first step toward modeling flame initiation.