Numerical study of the effects of non-equilibrium plasma on the ignition delay of a methane–air mixture using detailed ion chemical kinetics

Abstract

Researches on non-equilibrium plasmas in ignition and combustion processes have drawn attention of many scientists, because a non-equilibrium plasma-assisted approach provides a useful method to ignite a combustible mixture and stabilize the combustion process. The ignition delay times of methane–air mixtures have been investigated experimentally and numerically; however, the influence of non-equilibrium plasma on the ignition of argon-free methane–air mixtures has seen relatively little discussion. Here, we investigate the ignition delay time of methane–air mixtures via numerical analysis using detailed chemical kinetics. Discharge process and following ignition process are simulated separately, because of significant differences in their time scales and mechanisms. Data on the concentration of atoms and radicals produced in the discharge processes were used as the initial input data to determine the subsequent ignition process because they play an important role in the subsequent ignition process. We focus on the effects of the strength of the reduced electric field, the discharge duration, and the initial temperature on the ignition delay time for zero-dimensional and axisymmetric one-dimensional models. The simulation results showed that the reduced electric field was important in promoting chemical reactions for both the one-dimensional model and the zero-dimensional model; for a constant reduced electric field, longer discharge durations provided more energy to excite the nitrogen, leading to a larger mole fraction of excited nitrogen species during discharge; the gaps between ignition delay times for E/N=0 and E/N⩾50Td were very small at high initial temperatures; however they became very large at low initial temperatures.