Experimental investigation of the laminar stagnating premixed flame with fuel concentration oscillation

This study investigates the effect of concentration oscillation on the stagnating laminar premixed flame experimentally. The frequency of the concentration oscillation is 5 Hz and the mean equivalence ratio is set from 0.7 to 0.85. The concentration oscillation is formed by the oscillator with two cylinder piston units which produce alternative ejection of leaner and richer premixture. The velocity fluctuation is suppressed by keeping total flow rate nearly constant with sinusoidal movement of two pistons in 180 degree phase difference in the oscillator. The fuel concentration variation between exit of burner and stagnation plate is visualized by an acetone UVIF. The instantaneous distribution image of the fluorescence of seeded acetone and flame direct images are recorded by a high speed video camera with image intensifier. The flame position variation with concentration oscillation is compared to that without concentration oscillation. The effect of concentration oscillation was seen although there is a small velocity fluctuation. In the leaner case (φ = 0.70), the amplitude of flame position movement due to the concentration oscillation is larger than in near stoichiometric case (φ = 0.85), while the velocity oscillation is nearly the same.