Behavior of methane-oxygen-nitrogen mixtures near flammability limits

Abstract

Results of the detailed calculations using one-dimensional adiabatic premixed flame model for mixtures near inflammable compositions are reported. The effect of nitrogen as a diluent on the flame structure and speed are studied for stoichiometric and fuel-lean mixtures of methane and oxygen. The results indicate that while a fundamental limit in terms of a cut-off composition may not exist for the mathematical solution, the numerical solutions show an asymptotic limiting behavior as extreme compositions are reached. An attempt is made to explain the limits on the basis of rapid depletion of radical species and a steep increase in the flame thickness. Oscillations-which sometimes are said to indicate inflammability limits-are found to be of numerical origin.