Extinction conditions of non-premixed flames with fine droplets of water and water/NaOH solutions

Interactions of fine droplets of water and water/NaOH solutions with a steady, laminar counterflow methane/air nonpremixed flame are investigated experimentally and numerically. A water atomizer generating a polydisperse distribution of droplet sizes with a median diameter of 20 mum is used in experiments with steady feed rate. Comparisons of the measured flame extinction condition as a function of droplet mass fraction in the air stream indicate a trend similar to that predicted previously using 20 mum monodisperse water droplets. The hybrid Eulerian-Lagrangian numerical model previously developed is generalized to include polydisperse distribution of drop sizes: however, the differences seen between experiments and the numerical predictions at high water mass fractions could not be attributed to variation in size distribution alone. Present experiments support the conclusions of an earlier modeling work that on a mass basis, fine water mist can be as effective as the now-banned gaseous fire suppressant halon 1301. Inclusion of NaOH in water (up to 17.5% by mass) is shown to significantly enhance the fire suppression ability of water by complementing its thermal effects with chemical catalytic radical recombination effects of NaOH.