The effect of mixture inhomogeneity and turbulence on the flame front curvature and flame surface density of turbulent planar flames of natural gas

The present study is an extension of our earlier mixing field investigation in partially premixed flames. In the current work, the link between the mixing field and flame structure, and hence flame curvature and surface density are experimentally studied. The flame structure is captured using a high-speed OH-PLIF technique, whereas the crosswise mixing fields were previously presented in our earlier study. A concentric flow slot burner is employed for producing turbulent planar partially premixed natural gas flames at different levels of mixture inhomogeneity. The effects of the level mixture inhomogeneity, the equivalence ratio, the air to fuel stream velocity ratio, and Reynolds number "Re" on the flame characteristics are investigated. The link between the previously reported data on the mixing field and the flame structure are examined. The correlations between the mixing field and the flame structure were clearly observed in the current study. That is, as the mixture becomes highly inhomogeneous, in rich input jet conditions cases, altering Reynolds number and the mixing length led to a pronounced change in both flame structure and flame curvature while altering L/D influences the flame structure. On the other hand, the effects of the mixing length and Reynolds number on the flame structure and curvature in a more homogeneous mixture were not significant. The data showed that the flame surface density was inversely proportional to the level of the mixture inhomogeneity and directly proportional to the Reynolds number. The significant effect of the jet equivalence ratio on the level of mixture inhomogeneity leads to a significant change in the flame structure and flame curvature. In addition, if the mixture inhomogeneity is less pronounced the variation s of the mixing length and Reynolds number lead to minimal effects on the flame structure and flame curvature.