Flame inhibition by aqueous solution of Alkali salts in methane and LPG laminar diffusion flames

Abstract

Finely atomized water mist (diameter <100 μm) is a promising fire suppressant showing high effectiveness and no toxicity. The effectiveness can be improved further by mixing a small concentration of alkali compounds with pure water. The present work investigates the effectiveness of alkali compounds in counterflow diffusion flames of methane and LPG (38% propane, 62% n-butane by mass). In methane flames the inhibitors ranked by suppression effectiveness follows: KHCO3 ≈ CH3COOK > K2CO3 > K2C2O4.H2O ≈ Na2CO3 > NaHCO3 > CH3COONa > NaC3H5O3 > NaBr > C4H5NaO6.H2O. The effectiveness of the inhibitors increases linearly with solution concentration. Only the potassium salts were tested in LPG flames, and the ranking obtained is CH3COOK > KHCO3 ≈ K2CO3 > K2C2O4.H2O. The numerical models qualitatively capture the experimental trends; however, they underpredict the suppression effectiveness. Detailed sensitivity analysis and reaction pathway diagram analysis suggest that the rate constants of the recombination reactions, species entropy, and L-J collision diameters need careful consideration for improving the model predictions.