Extinction of triple flames at counter-flow

The details of how each premixed flame (PF) merges into the diffusion flame (DF) were presented, focusing on the extinction of triple flames, and compares the extinction with a pure premixed (twin flame) or pure diffusion flame using counter-flow. The triple flames were formed using different fuel concentration streams, i.e., equivalence ratios, composed of methane and dry air. At near extinction, quasi-single flame formed by the merging rich PF (RPF) and lean PF (LPF) was observed. The PPF had a higher maximum strain rates at extinction than the strain rates at extinction converge linearly. According to luminous intensity profile, intermediate product in the rich side of the flame might support reaction in the lean side where RPF merges into DF. As the equivalence ratios of the PPF and the mill flame move towards stoichiometric conditions, the maximum strain rates at extinction converged linearly. The width of the PPF at extinction was constant for all rich and lean stream combinations, indicating that unburnt fuel might exist in the exhaust gas, and shortages of the time to complete some elementally reactions affect this phenomenon. This is an abstract of a paper presented at the 30th International Symposium on combustion (Chicago, IL 7/25-30/2004).