To understand the characteristics of the separated stratified premixed swirl methane/air flame, effects of the Stratification Ratio (SR) on the structure of the separated stratified premixed swirl flame are experimentally investigated. Methane is used as the fuel in the experiment, and the change of the mean flame configurations-or the macrostructures-characterized by flame CH* chemiluminescence, including flame stabilization, flame front and flashback, etc. are measured by varying the SR at normal temperature and pressure. We observe the changes in the method of flame stabilization and the main heat release zone. Under the combined influence of the corner recirculation zone, lip recirculation zone and principal recirculation zone, flame stabilization points appear at four locations, including the downstream of the central body, the rims of the lip and the edge of the main tube exit, as the SR varies. Hence, 6 new modes of the separated stratified premixed swirl flame are first proposed:Y mode, V mode, symmetric D mode, wrinkled mode, narrow W mode and wide W mode, which are different from the modes of the stratified premixed swirl flame in other research. The results show that the SR has an important impact on the flame macrostructure and flame self-excitation, which can be explained by rich burn, lean burn and flammable limit of methane.
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