Kinetic Ignition Enhancement of $\hbox {H}_{2}$ Versus Fuel-Blended Air Diffusion Flames Using Nonequilibrium Plasma

Kinetic ignition enhancement of H₂ diffusion flames by a nonequilibrium plasma discharge of H₂- and CH₄-blended oxidizer 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 conducted to identify the important kinetic pathways. It was found that the competition between the catalytic effect of NO_x and the inhibitive effects of H₂O and CH₄ governed the ignition processes in the system. With air as the oxidizer, ignition was enhanced from the plasma-produced NO_x. With H₂ addition to the oxidizer, H₂O formation significantly increased the ignition temperature. However, with plasma activation, the inhibitive effect of H₂O was significantly reduced because of the dominant role of NO_x. With CH₄ addition to the oxidizer, the ignition temperatures increased due to the radical quenching by H₂O or CH₄, depending upon the strain rate. The results showed that the inhibitive effects were significantly decreased with plasma activation. Unlike vitiated air ignition, plasma-enhanced ignition for fuel-air mixtures can suppress the inhibitive effects of H₂O and CH₄ because of the overwhelming catalytic NO_x effect at low temperatures.