Experiments on dynamical motion of buoyancy-induced flame instability under different oxygen concentration in ambient gas

We experimentally investigated the dynamical motion of buoyancy-induced flame instability under different oxygen concentrations in ambient gas for a non-premixed flame, focusing on how the oscillation frequency and amplitude of the flame tip change with oxygen concentration in ambient gas. The oscillation frequency of flame tip ft increases monotonically with increasing oxygen concentration in ambient gas Xo, while the oscillation amplitude at flame tip Am drastically decreases with increasing Xo. The change in the oscillation frequency for different oxygen concentrations can be clearly explained by the use of the theoretical equation proposed by Cetegen and Ahmed [B.M. Cetegen, T.A. Ahmed, Experiments on the periodic instability of buoyant plumes and pool fires, Combustion and Flame 93 (1993) 157-184]. As the flame tip location decreases with increasing Xo, the magnitude of the periodic fluctuation of the interface between hot combustion products and ambient gas becomes small at the flame tip. This leads to a remarkable decrease in the oscillation amplitude of the flame tip in a high oxygen concentration environment.