Flame-seed structures: Original structures of nonpremixed flames in mixing layers of methane, ethane, propane and DME

The ultimate structure of an edge-flame near the extinction limit was experimentally investigated using a fuel-air mixing layer within a narrow channel. An interesting flame structure was discovered which is a nonpremixed-flame branch enclosed by two distinctive asymmetric premixed-flame branches. Experimental conditions that could most clearly distinguish the three flame branches were analyzed using methane ethane propane and dimethyl ether fuels. Flame morphologies and their sensitivities to the fuel concentration gradient were investigated and chemiluminescence trajectories along the three flame branches for various fuels were compared on a ternary diagram. Conclusively each fuel displayed a unique morphological and chemiluminescent flame structure near its extinction limit. This unique flame structure can bridge the gap between various laminar flame structures called flame-seed thereby delineating the inter-connections among various laminar flame structures.