Cellular instabilities of n-butane/air flat flames probing by PLIF-OH and PLIF-CH2O laser diagnosis

摘要

The structure and instability characteristics of non-adiabatic fuel-rich n-butane/air cellular flames on McKenna burner were experimentally investigated at atmospheric pressure. Planar Laser Induced Fluorescence (PLIF-OH and PLIF-CH2O) flame diagnosis technology was utilized to probe the flame structure under varied equivalence ratio and inflow mixture velocity respectively. Results show that, the equivalence ratio plays an important role in forming cellular flames. The flat, wrinkled and cellular flames appear in turn when increasing equivalence ratio and inflow velocity. Differed to the separated cells of cellular flames appeared in direct Digital camera images and PLIF-OH images, the PLIF-CH2O images clearly display that all cellular flames are connected. In the PLIF-OH images of cellular flames, the OH radical fluorescence signal intensity is higher in the convex region toward unburned mixture than in the concave region, but in PLIF-CH2O images, the fluorescence signal intensity is nearly unchanged in both convex and concave regions. Quantitative stand-off distance and amplitude data probed by PLIF-OH and PLIF-CH2O diagnosis together reveal that the onset of non-adiabatic n-butane/air cellular flames on flat flame burner is dominantly governed by diffusive-thermal mechanism.