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

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 N-2(v), O-2(v) and CH4(v) as well as the electronically excited species O-2(a(1)Delta(g)) and O-2(b(1)sigma(+)(g)) 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 N-2 electronically excited species produce abundant O and H, which is conducive to the formation of the methane oxidation intermediates. e + O-2 = e + O + O(D-1) in the NRP discharge and e + O-2 = e + O-2(a(1)Delta(g)) in the synergistic discharge play the crucial roles in the methane/air plasma enhance ignition, respectively.

Automated summary

Plasma assisted combustion has the potential to reduce ignition delays and control pollutant emissions. When combining nanosecond repetitive pulsed (NRP) discharge with DC discharge, selectively exciting vibrational and electronic states in molecules can enhance ignition efficiency in methane/air plasma combustion. The kinetic effect of plasma on ignition enhancement surpasses the thermal effect, with the synergistic discharge showing stronger effects compared to NRP discharge.