Comparative Study of Nonequilibrium Plasma Generation and Plasma-Assisted Ignition for Different C2 Hydrocarbons

Abstract

The results of the experimental and numerical study of high-voltage nanosecond discharge afterglow in pure methane, ethane and propane are presented for room temperature and pressures from 2 to 20 Torr. Time-resolved electron density during the plasma decay was measured with a microwave interferometer for initial electron densities in the range between 3×10 11 and 3×10 12 cm -3 and the effective recombination coefficients were obtained. Measured effective recombination coefficients increased with gas pressure and were much higher than the recombination coefficients for simple molecular hydrocarbon ions. The properties of plasma in the discharge afterglow were numerically simulated by solving the balance equations for charged particles and electron temperature. Calculations showed that electrons had time to thermalize prior to the plasma decay. The assumption that cluster hydrocarbon ions are formed during the plasma decay explained the pressure dependence of the measured effective recombination coefficients. It was shown that the loss of electrons was controlled by the dissociative recombination with cluster ions at room electron temperature. Based on the analysis of the experimental data, the rates of three-body formation of cluster ions and recombination coefficients for these ions were estimated.