Dynamics and Suppression Effectiveness of Monodisperse Water Droplets in Non-premixed Counterflow Flames

In situ measurements of velocity and size distributions of initially monodisperse water mists of initial diameters ranging from 14 lm to 42 lm seeded into the air stream of non-premixed propane/air counterflow flames are reported. Droplets were generated piezoelectrically, and the size and velocity distributions and the number density were determined by phase-Doppler particle anemometry. Droplets having initial diameters of 18 lm underwent complete vaporization in a counterflow flame at a strain rate of approximately 170 s 1, while droplets of 30 lm penetrated slightly beyond the visible flame zone. Measurements of the effect of water droplets on the extinction strain rates of propane/air counterflow flames were performed. Droplets having initial diameters of 14 lm and 30 lm where found to have similar suppression effectiveness, while droplets of 42 lm were substantially less effective at reducing the extinction strain rates. Both the 14 lm and 30 lm water droplets were found to be more effective, on a mass basis, than CF3Br. The present experimental results are in excellent agreement with the predictions of recent modeling studies exploring the behavior of various sized water droplets in counterflow flame.