Flame structure and thermal NO_x formation in hydrogen diffusion flames with reduced kinetic mechanisms

Structure and thermal NO_x formation of hydrogen diffusion flames are studied numerically, by adopting a counterflow as a model problem. Detailed kinetic mechanism having twenty-one step hydrogen oxidation is systematically reduced to a two-step mechanism while five-step thermal NO_x chemistry of the extended Zel'dovich mechanism is reduced to one-step. Results show that the extinction strain rates are much higher than those for hydrocarbon flames and the NO_x production can be controlled by increasing strain rates which results in the decrease of flame temperature significantly. Comparison between the results of the detailed and reduced mechanisms demonstrates that the reduced mechanism successully describes the essential features of hydrogen diffusion flames including the flame structure, extinction strain rate and NO_x production.