Generation of Non-Equilibrium Plasma in the Gliding Arc Discharge

Drexel University, Philadelphia PA

Investigators

Abstract

This is a study of plasma parameters generated in the gliding-arc discharge propagating in both plane and coaxial geometries , especially near the equilibrium-to-nonequilibrium transition point. The gliding air in the plane parallel to the gas flow is the base case; a cylindrical gliding-arc configuration adds tangential velocity independently controlled by external magnetic fields. Arc propagation velocities, geometry, electric fields, and power inputs are determined by optical imaging synchronized with voltage-current measurements. Additional information on plasma conditions is obtained by spectrally resolved imaging, microwave interferometry, and infrared spectroscopy. A concomitant theoretical study focuses on kinetic mechanisms of the equilibrium-to-nonequilibrium transition. Kinetics of excited and charged particles are modeled under conditions when both thermal ionization and nonequilibrium ionization mechanisms are important. Critical values of the electric field and gas temperature in the transition plasmas are identified and compared to experimental findings. The gliding arc is a hybrid type of atmospheric-pressure air discharge that provides relatively high levels of electron density, current, and power (typical of thermal plasmas) along with relatively low temperature and high electric field (typical of cold nonequilibrium plasmas). The gliding-arc discharge, moving in a gas flow between divergent electrodes, contains periodic self-triggered transitions of atmospheric-pressure thermal arc into a nonequilibrium discharge. In this transition, the plasma cools rapidly while electron density remains on the thermal-plasma level.