The improvement of blowout limit in partially/fully premixed flames with geometrically modified bluffbody bases

The improvement of the lean blowout limit of bluffbody stabilized methane flames is investigated. The flame configuration consists of a hybrid of partially and fully premixed flames, which is produced by injecting methane jets from a streamline-shaped bluffbody into a fully premixed methane/air crossflow. Additional geometric modifications from the original bluffbody base are such that the base has two-dimensionally modified geometries and three-dimensional local cavities. We observe that the blowout limit of the hybrid configuration is extended by up to ~12% (in terms of the equivalence ratio of the crossflow) with the modified geometries. Gas chromatographic sampling and particle image velocimetry (PIV) show that high fuel mole fraction regions coexist with regions of low speed flow for the modified geometries. Further PIV analysis shows that the downstream flow fields of the modified bases generally have a larger number of incoherent vortices and lower strain rate in comparison with those of the unmodified base.