On the structure and extinction of interacting lean methane/air premixed flames

Lean methane/air premixed flames are studied numerically, using a detailed chemical model of 74 reaction steps with 28 species, to investigate the flame interaction between two stretched premixed flames with unequal intensities in a counterflow. The finite difference method, time integration and modified Newton iteration are used, and adaptive grid technique and grid smoothing have been employed to adjust the grid system according to the spatial steepness of the solution profiles. The flame structure of the methane premixed flames has four layers, consisting of the radical cutoff layer, the main heat release layer of the methane decomposition, the radical branching layer and the hydrogen and carbon monoxide oxidation layer. Two modes of flame interaction, the strong and weak interactions depending on the differences in the flame intensities, and their respective behaviors are identified. It has been found that heat loss and incomplete reaction are responsible for the flame extinctions in the weak and strong interaction regimes, respectively. The calculated extinction boundaries are in good agreement with the experimental results.