Gradient Mechanism of Detonation Initiation for PDE Applications

Abstract

An experimental study of detonation initiation by high–voltage nanosecond gas discharges has been performed in a smooth detonation tube with four–cell discharge chamber designed to realize a gradient initiation mechanism. The chambers were constructed on the basis of our previous studies and introduced analogous cell geometries. The discharge study performed in various chambers has shown that three modes of discharge development are realized under the experimental conditions: a spark mode with high–temperature channel formation, a streamer mode with non–uniform gas excitation, and a transient mode. The mechanisms of deflagration to detonation transition (DDT) under different discharge modes have been proposed and confirmed experimentally. Under spark and transient initiation, simultaneous ignition inside the discharge channel occurs, forming a shock wave and leading to a conventional deflagration to detonation transition (DDT) via an adiabatic explosion. The governing parameters have been established and a significantly higher efficiency in terms of detonation initiation has been achieved due to the enhanced geometry. Successful DDTs have been observed in a stoichiometric propane–oxygen mixture diluted with 40% of nitrogen under energy inputs as low as 200 mJ at initial pressures of 0.8 bar and higher. The run–up distance is within 80 mm, the DDT time is below 0.5 ms. A technique for detonation initiation in fuel–air mixtures in smooth detonation tubes can now be elaborated.