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

Kinetic ignition enhancement of H
₂
diffusion flames by a nonequilibrium plasma discharge of H
₂
- and CH
₄
-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 H
₂
O and CH
₄
governed the ignition processes in the system. With air as the oxidizer, ignition was enhanced from the plasma-produced NO
_x
. With H
₂
addition to the oxidizer, H
₂
O formation significantly increased the ignition temperature. However, with plasma activation, the inhibitive effect of H
₂
O was significantly reduced because of the dominant role of NO
_x
. With CH
₄
addition to the oxidizer, the ignition temperatures increased due to the radical quenching by H
₂
O or CH
₄
, 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 H
₂
O and CH
₄
because of the overwhelming catalytic NO
_x
effect at low temperatures.