Study of propagating methane flames in strained mixing layers using 4-step reduced chemistry*

Flames propagating along strained mixing layers exhibit interesting structures depending on the local flow conditions. If the imposed strain rate is small, a tribraichial flame is found with a lean premixed wing on one side and a rich premixed wing on the other, followed by a trailing diffusion flame. When this strain rate is increased, these premixed wings merge with the trailing diffusion flame, forming an edge flame structure. Further increase in the strain rate leads to a retreating edge flame, subsequently extinguishing at a particular strain rate. These aspects of triple-flame propagation and its structure in the canonical counterflow configuration are studied through numerical integration of the conservation equations using a reduced four-step model for the combustion chemistry. In particular, a parametric study of flame propagation speed vs. strain rate is carried out for two different combination of feed-stream mixtures (methane-air and the methane-oxygen) and the results are compared with predictions employing the one-step Arrhenius chemistry.