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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 NOx 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 NOx. 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 NOx. 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 NOx effect at low temperatures.
Date of Publication: Dec. 2008