Water Droplets Behavior in Extinguishing Methane-Air Counterflow Diffusion Flames

The behavior of fine water droplets was investigated in a methane-air counterflow diffusion flame, specifically when the water droplets were added to the inlet air feed and used to extinguish the diffusion flame. The water droplets studied had a relatively broad size distribution (from 1 to 60 m), with the number mean diameter of 15 m and Sauter mean diameter of 25 m. With an increase in the velocity gradient, the flame approaches towards the stagnation plane and flame thickness decreases. The flame properties, such as flame location and flame thickness are insensitive to the water mass loading. Along the stagnation stream line, the velocity decreases towards a local minimum just before the flame front. In contrast, the velocity increases in the flame zone due to the thermal expansion, and then decreases towards the stagnation point. In the decelerating zone, the droplet mass flux decreases on approach to the flame zone due to a non-equilibrium in velocity of large droplets between liquid and gas phases. Furthermore, as the droplet-laden air approaches the flame front, the flow stream begins to diverge in the counterflow field. Since the small droplets move away from the burner axis, the divergence of the air flow acts to reduce the water droplet mass flux along the stagnation streamline. Large droplets moving faster than the air flow „catch up ‟ to slower ones just before the flame front, and the mass flux of the droplets tends to increase