Numerical investigation on plasma assisted ignition of methane/air mixture excited by the synergistic nanosecond repetitive pulsed and DC discharge

Abstract

Plasma assisted combustion provides possibilities for reducing ignition delays and controlling pollutant emissions. The zero-dimensional plasma and combustion models have been built up to numerically investigate the effects of the synergistic nanosecond repetitive pulsed (NRP) and DC discharge on the methane/air plasma assisted ignition. The synergistic discharge means exerting the low voltage DC discharge after the NRP discharge in one period of the discharge plasma. The simulation results indicate that the selective excitation of the vibrationally excited species N2(v), O2(v) and CH4(v) as well as the electronically excited species O2(a1Δg) and O2(b1Σg +) by the synergistic discharge is superior to that by the NRP discharge when the electron energy has been deposited into different molecular degrees of freedom. The plasma kinetic effect on the ignition enhancement is highly efficient since it can break though the threshold of the thermal effect. Both the kinetic effect and the thermal effect of the NRP discharge on ignition enhancement are relatively weaker than those of the synergistic discharge. Besides, reactions involved the N2 electronically excited species produce abundant O and H, which is conducive to the formation of the methane oxidation intermediates. e + O2 = e + O + O(1D) in the NRP discharge and e + O2 = e + O2(a1Δg) in the synergistic discharge play the crucial roles in the methane/air plasma enhance ignition, respectively.