Response of a Cylindrical Premixed Flame to Periodic Concentration Fluctuation

Abstract

Response of a cylindrical premixed flame to periodic concentration fluctuation was investigated. The flame was formed in a porous cylinder by percolating the mixture uniformly through the cylinder wall. The burner used here was devised so as to fluctuate the mixture concentration (equivalence ratio) only in the radial direction of the flow (vertically to the cylindrical flame surface) without varying the flow field. With this burner the time variations of burning velocity, burnt gas temperature and flame luminosity were measured for the lean methane-air mixture in the range of fluctuation frequency from 3 Hz to 50 Hz, and the results were examined from the viewpoint of flame curvature effects. The results show that the variation width of the burning velocity of the dynamic flame is larger than that of the static flame corresponding to the concentration fluctuation. Burnt gas temperature and flame luminosity also exhibit similar tendencies. The magnification ratio of the variation width depends on the flame curvature and the large flame curvature makes the flame sustainable even for the mixture leaner than the flammability limit of the static flame.