Response and flamelet structure of stretched premixed methaneair flames

Effects of strain on the structure of premixed laminar flames are investigated numerically for various counterflow configurations that can develop in turbulent flow. Lean to stoichiometric methaneair flames are considered. The computations are based on both a mechanism of elementary reactions and, alternatively, a mechanism consisting of four global reactions. Comparisons of results as obtained from both mechanisms are presented through the paper. First, attention is focused on an asymmetrical configuration, where one of the counterflowing supply streams carries a cold, reactive mixture of methane and air, and the other the respective mixture of hot equilibrium combustion products. Second, a symmetrical twin-flame configuration is studied that can be produced by directing two identical reactant streams toward each other. Third, the limiting case of low strain rates is considered. Attention is focused on the asymmetrical flow configuration which is particularly relevant for flamelet-models of premixed turbulent combustion. In view of incorporation into such models, computed profiles of the thermochemical variables are plotted versus a reactive-scalar progress variable. For all flow geometries extinction limits are determined and differences in corresponding results are discussed.