Effects of Electrode Properties on Transition Limit to Big-Arcs in Combustion Gas Plasma Boundary Layer.

Abstract

Effects of physical properties of cathode materials on the transition of discharge mode in the boundary layer of combustion gas plasma have been investigated experimentally. At the transition to big-arcs, micro-arc currents fluctuate and some micro-arcs with arc current beyond a critical value grow up to big-arcs, breaking through the thermal boundary layer, whereas most of the micro-arcs with arc current below a critical value remain as micro-arcs adjacent to the electrode wall surface. The micro-arc currents at the transition to the big-arc mode become smaller for the copper electrode than for the stainless-steel and the titanium electrodes. In the case of a copper electrode with lower boiling point and latent heat of evaporation, the electrode material will evaporate rapidly and ionize at the high-temperature spot in spite of its high thermal conductivity, which easily results in micro-arc growth to big-arcs. It is concluded that the electrode materials having both infusible properties and high thermal conductivity can suppress the transition to big-arcs.