Inhibition of premixed and non-premixed flames with fine droplets of water and solutions

Inhibition/extinction of premixed and non-premixed methane/air flames with fine droplets of water and solutions containing several chemical agents has been investigated experimentally. While solutions allow delivery of much higher concentrations of chemical agent to the flame front than otherwise possible, the non-premixed flame extinction results indicate saturation (or condensation) of the agent at some effective temperature below the flame temperature. Based on the chemical additives considered, on a molar basis, the following order of effectiveness is observed: KOH > NaCl > NaOH. The inhibition of premixed flames by similar size droplets indicates insensitivity to NaOH mass fraction in the water. This insensitivity was related to the shorter residence time of the droplets (13 mum median diameter) through the premixed flame structure. Detailed comparison of the premixed and non-premixed flame inhibition/extinction with pure water droplets supports the importance of droplet residence time and optimum droplet size in controlling the interaction of droplets with the flame front.