Extinction and flame structure of lean premixed and diffusion combined flames formed in a counter flow are investigated experimentally and numerically. The extinction limits can be divided into two regions. One is a diffusion flame dominant extinction region (DF-DE) in which equivalence ratio of LPF side (φ L) at extinction limit is decreasing linearly with increasing fuel concentration of DF side (χ U). The other is a lean premixed flame dominant extinction region (LPF-DE) in which effect of χ U on extinction φ L is increasing with increasing χ U. In these two regions, the flame structures and its φ L dependence are different greatly. In the DF-DE, the temperature has symmetrical profile regardless of φ L and the temperature peak is located near DF. Since DF has higher temperature than LPF, LPF is thermally supported than DF. Temperature gradients between two reaction zones are decreasing with increasing φ L, while laminar burning velocity (S L) and burnt gas width (W B) are constant regardless of φ L. On the other hand, in the LPF-DE, the temperature has asymmetrical profile and the temperature peak leans to the LPF side. That is, the temperature gradient of LPF side is very steep compared with the DF side. Since LPF has higher temperature than DF, DF is thermally supported than LPF. Temperature gradients between two reaction zones are constant regardless of φ L, while S L and W B are increasing with increasing φ L.
|ジャーナル||Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B|
|出版ステータス||Published - 2012|
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