The influence of flow rotation on droplet combustion and evaporation are experimentally studied by using a burning liquid-pool system, and numerically investigated by considering a nonreactive, rotating, stagnation-point flow, respectively. The experiment involves measurements of flame temperature, flame position and evaporation rate of the liquid pool, observations of the recirculation zone and the soot layer, and identification of flame extinction. A finite-volume method is employed to numerically solve the corresponding transport equations. Calculated results show that in the vicinity of the liquid surface, both convection and diffusion transports are weakened by the flow rotation, resulting in the suppression of the evaporation strength of liquid; the recirculation zone can be identified and compared with experimental observation. For the steady burning of an ethanol pool in a swirling air jet, it is found that as the angular velocity increases, the diffusion flame shifts closer to the upper burner, has a larger flame thickness, experiences a smaller flame stretch, but suffers from the reduction of mass diffusion of ethanol vapor to the flame. However, the evaporation rate of ethanol is usually decreased with increasing angular velocity. In the flame extinction experiment, the critical volumetric oxygen concentration at extinction first decreases to a minimum value and then increases with angular velocity. It is generally concluded that flow rotation reduces the rates of both droplet combustion and evaporation.
Cool-flame extinction during n-alkane droplet combustion in microgravity
