The near-field structure of a planar methane jet flame

Direct numerical simulations (DNS) are conducted of a preheated planar meth ane jet diffusion flame for Various flow conditions. The fuel stream is a m ixture of methane and nitrogen, and the oxidizer stream is air. The chemist ry is modeled via the 1-step global mechanism of Bhui-Pham (1992). The flam e behavior is assessed for various oxidizer stream temperatures, fuel strea m velocities and nitrogen dilutions of the fuel stream. Consistent with exp erimental results, the root mean square (rms) values of temperature show tw o local maxims and a local minima on either side of the jet centerline and the probability density function (PDF) of temperature displays bimodality w ithin the intermittent flow regions. Analyses of the post-ignition region o f the flame in mixture fraction space indicate that as the conditional aver age values of the temperature increase downstream, those of the reaction ra te decrease. The near-field characteristics of the flame are strongly influ enced by the dilution of the fuel stream. An increase in the fuel dilution results in the increase in flame-vortex interactions, flame thickness and f inite-rate chemistry effects. Peak values of the tangential strain rate and the curvature, calculated on the flame surface, are also increased. The co rrelations between the scalar dissipation rate and the strain rate improve significantly when the interactions between the flame and the vorticity fie ld increase. The analyses of the flowfield show that the laminar flamelet m odel compares favourably with the DNS in the regions where the flame curvat ure is small.