Gradient Mechanism of Detonation Initiation Under Action of High-Voltage Nanosecond Discharge

An experimental study of detonation initiation by high-voltage nanosecond gas discharge has been performed in a smooth detonation tube with a four-cell discharge chamber designed to enable a gradient initiation mechanism. Stoichiometric propane-oxygen mixtures were used at initial pressures from 0.2 to 1 bar. Detonation was formed within four transverse tube sizes at initial pressures higher than 0.2 bar for the propane-oxygen mixture and higher than 0.8 bar for the diluted mixture with 40% nitrogen. The discharge energy inputs were 0.2-0.3 J. The time of detonation formation was below 0.5 ms for all conditions. Combined with the focusing effect of the converging reducer, the gradient mechanism of detonation formation similar to the one suggested by Zeldovich has been shown to be the governing process. The value of the ignition delay time gradient, formed by nonuniform radical production during streamer discharge and following rapid plasma thermalization, has been estimated to be consistent with the condition on the gradient mechanism.