Gliding spark plasma: Physical principles and performance in direct pyrolysis of methane

The pulsed plasma with divergent electrodes, producing gliding spark discharge, and its capability in methane reformation is examined in this research. In comparison to the conventional pulsed plasmas with parallel electrodes, nearly 5-35% improvements in conversion rates and energy efficiencies are obtained. Contrary to the conventional DC or AC glide arcs where the plasma channel has a comparable velocity with the gas flow one, the movement velocity of the plasma channel in glide pulsed plasma is found to be 50-100 m/s that is much higher than the gas flow velocity of 0.2 m/s. A simulation of pressure waves in the cavity of the reactor shows that the spark channels are formed at the moving node points of interfering self-stimulated acoustic waves. The mobile plasma channel causes the fresh reactant gas envelopes to be better exposed to the plasma and conversion, rather than dissociating the products, resulting in higher selectivities of unstable hydrocarbons. While energy conversion efficiency exceeds 75%, the conversion rate as high as about 50% is obtained, which is comparable with the records obtained by high temperature arc based technologies. The average temperature of the reactor hardly exceeds 150 °C in the present study.