Enhancement of the detonability of hydrogen-oxygen mixture by use of nanosecond plasmas. *

This experimental work aims at highlighting the effects of a non-equilibrium, nanosecond plasma at moderate pressure on the detonability of hydrogen-oxygen mixture. Two detonability parameters were investigated, namely: (A) the detonation cell width and (B) the distance for the deflagration-detonation transition. The experiments were carried out in the stoichiometric H₂:O₂ composition at initial pressures ranging from 100 to 200 mbar for (A) and from 200 to 1400 mbar for (B). ICCD imaging, back current shunt technique, sooted-plate technique and  schlieren imaging were used to characterize the plasma and the detonation. The effect of a nanosecond plasma ahead of a detonation front reduces significantly the detonation cell width in the region where the plasma was applied. The effect is instantaneous and reproducible at all the pressures. The experiments also bring out differences in the deflagration to detonation process between a classical spark plug igniter and a self-designed multi-channel nanosecond plasma igniter.  The differences for transition length and time, flame speed and the ignition of the mixture are presented for both devices. The efficiency of the plasma igniter is underlined by schlieren imaging. Overall the work brings experimental evidences of the effect of the predissociation of a combustible mixture by nanosecond plasma on the behavior of a detonation wave.