An experimental study on extinction and stability of stretched premixed flames

Using a counterflow burner and a stagnation flow burner with a water-cooled wall, theeffect of downstream heat loss on the extinction of a stretched premixed flame has been systematically investigated for lean and rich propane/air and methane/air mixtures. Based on results of the concentration limits and flame separation distances at extinction, it is demonstrated that, in accordance with theoretical predictions, extinction by stretch alone is possible only when the deficient reactant is the less mobile one. When it is the more mobile one, downstream heat loss or incomplete reaction is also needed to achieve extinction. A variety of non-steady, non-planar flame configurations, including cellular flames, starshapedflames, groove-shaped flames, and vibrating flames, have been observed. Their response to concentration and flow field variations has been mapped and the possible controlling mechanisms discussed. Minimum and maximum fuel concentration limits of extinction have also been identifiedand discussed on the basis of flammability limits.