Simultaneous CH3 and CH2O imaging in premixed turbulent flames for instantaneous flame structure visualization

Abstract Photofragmentation laser-induced fluorescence (PF-LIF) of methyl radical ( CH 3 ) and planar laser-induced fluorescence (PLIF) of formaldehyde ( CH 2 O ) were simultaneously carried out in premixed methane-air turbulent flames to visualize flame structure and extract quantitative features of CH 3 and CH 2 O layers. A CH 3 layer is located along the edge of a CH 2 O layer, and they partially overlap with each other. CH 3 is closer to the reaction zone of a premixed flame compared with CH 2 O that is regarded as a typical marker of the preheating zone. The results show that the CH 3 can be served as a flame marker for the transitional zone between the preheating zone and the reaction zone. The thicknesses of CH 3 and CH 2 O layers and their distances were then quantitatively estimated to reduce the influence of layer merging and strong curvature. It was found that the broadening of CH 2 O layers against turbulence is more sensitive than that of CH 3 layers. In stoichiometric and rich flames, layer broadening was clearly observed even with a slightly increased Karlovitz number.