Direct numerical simulation of turbulent non-premixed methane-air flames

Turbulent non-premixed stoichiometric methane-air flames have been studied using the direct numerical simulation approach. A global one- step mechanism is used to describe the chemical kinetics, and molecular transport is modeled with constant Lewis numbers for individual species. The effect of turbulence on the internal flame structure and extinction characteristics of methane-air flames is evaluated. The flame is wrinkled and in some regions extinguished by the turbulence, while the turbulence is weakened in the vicinity of the flame due to a combination of dilatation and a 25:1 increase in kinematic viscosity across the flame. Reignition followed by partially-premixed burning is observed in the present results. Local curvature effects are found to be important in determining the local stoichiometry of the flame, and hence, the location of the peak reaction rate relative to the stoichiometric surface. The results presented in this study demonstrate the feasibility of incorporating global-step kinetics for the oxidation of methane into direct numerical simulations of homogeneous turbulence to study the flame structure