Numerical calculations have been performed on the ignition of methane-oxygen-argon mixtures due to dissociation of molecular oxygen into ground state oxygen atoms. The computations are caried out using a time and spatially dependent fluid mechanics model in one-dimension coupled with a detailed oxidation mechanism for methane. A calculation of the minimum ignition energy as a function of equivalence ratio shows that ignition by oxygen dissociation is clearly different from laboratory experimental results of spark ignition. Whereas the minimum spark ignition energy occurs at Math for methane-oxygen-argon mixtures, the computations show a steadily declining minimum ignition energy from Math. Increasing the amount of oxygen dissociation decreases the induction time and increases the flame propagation rate during tht early part of the burning. This enhanced flame propagation rate lasts only until the oxygen atom concentration relaxes to a level which is typical of a flame moving at a constant speed. Calculation of reaction rates and the rates of change of concentrations due to convection, expansion, diffusion, and reaction helps to explain the variation in minimum ignition energy with equivalence ratio. These results demonstrate the efficiency of igniting lean mixtures with oxygen atoms and indicate the potential advantages to be gained from ignition by a combination of oxygen atoms and heat.
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