Low-Btu gas mixtures—I. Methane oxidation rates for a wide range of equivalence ratios

Abstract

We present estimates for the effective oxidation rates of methane over a wide range of equivalence ratios using Ar as primary diluent and CO or H 2O as additives. The rate of disappearance of methane has been monitored in a fuel-rich CH 4O 2Ar mixture by direct measurements of the change in transmission for He-Ne laser radiation at 3.392 μ behind reflected shock waves. The rate of formation of water with time has been obtained in independent absolute i.r. emission measurements near 6.75 μ on stoichiometric CH 4O 2Ar mixtures with and without added water. We have found empirically that a number of data correlations may be used and that the overall rates of disappearance of CH 4 and of formation of H 2O were the same during the post-induction period behind reflected shock waves. The rates of concentration changes with time to which we refer are average rates observed during the post-induction periods. The temperatures ( T max ) for which the oxygen-atom concentrations are a relative maximum were found to be close to the arithmetic means between the initial temperatures ( T 5) behind reflected shock fronts and the final equilibrium temperatures. The numerical values found for the correlation parameters as functions of the temperature during the post-induction oxidation are not sensitive to the prior admixture of CO or H 2O but vary with mixture ratio. The overall methane conversion rates are directly useful in defining burner designs for the utilization of highly diluted mixtures (i.e. low-Btu gas systems) containing primarily CH 4. Our results are not applicable to low-Btu gas mixtures containing such reactive species as H 2 or NH 3.