Kinetic ignition enhancement of diffusion flames by nonequilibrium magnetic gliding arc plasma

Kinetic ignition enhancement of CH₄-air and H₂-air diffusion flames by a nonequilibrium plasma discharge of air was studied experimentally and numerically through the development of a well-defined counterflow system. Measurements of Ignition temperatures and major species, as well as computations of rates of production and sensitivity analyses, were performed to understand the kinetic enhancement pathways for ignition by plasma discharge of air. It was found that plasma discharge of air led to significant kinetic ignition enhancement illustrated by large decreases in the ignition temperatures for a broad range of strain rates. Examination of the radical and NO_x production in the plasma showed that the enhancement was caused primarily by the catalytic effect of NO_x. The results of numerical simulations of the counterflow burner with preheated air and NO_x addition showed the existence of different ignition regimes, which appeared due to the competition between radical production by NO_x and other pathways, as well as heat release. There were two ignition regimes for small concentrations of NO_x and three ignition regimes for large concentrations of NO_x. Numerical simulations agreed well with the experimental measurements and suggested a new strategy for plasma-assisted ignition in supersonic flow, where a combination of thermal and nonthermal plasma would work more efficiently for ignition enhancement.