Effectiveness Of Potassium Salts In Inhibiting N-Heptane Fire And Ethanol Fire

Fire is a major disaster affecting people's lives and property safety that threatens people's production and life seriously.In order to reduce the hazards of fire,people are committed to finding an efficient and clean fire extinguishing substance.Water mist just meets this requirement that has good fire extinguishing effect,and the fire extinguishing performance has been further improved after adding chemical agents.As a class of ordinary water mist additive,potassium salts can extinguish fire by capturing flame free radicals such as H,O,OH and interrupting combustion chain reaction.To study the different fire extinguishing effects of water mist containing potassium salts on n-heptane fire and ethanol fire,and to analyze the chemical reactions between potassium salts and combustion free radicals in the process of fire extinguishing from the point of view of kinetics,will help people fully understand the effect of potassium salts in the process of fire extinguishing,and help people screen out the most effective potassium salt additive to maximize the fineness of fire extinguishing effect of water mist.In this paper,the minimum extinguishing concentration of ultra-fine water mist with several kinds of potassium salts to inhibit n-heptane and ethanol flame are measured,and the differences of fire extinguishing effect of these kinds of potassium salts are compared and analyzed from the experimental point of view.Then,the change of Gibbs free energy of the spontaneous reactions of potassium hydroxide with flame free radicals are calculated by HSC Chemistry software to determine the spontaneous reactions occurring in the temperature range of 0-1500K.At last,the minimum effective retention time of nitrogen and potassium hydroxide to inhibit n-heptane and ethanol fire and the changes of flame free radicals are simulated by Chemkin software,and the differences of mechanism of potassium hydroxide to inhibit n-heptane fire and ethanol fire are explored from the perspective of sensitivity analysis and path analysis.These results are as follows:?1?The change trend of the minimum extinguishing concentration and the reduction rate of the minimum extinguishing concentration of ultra-fine water mist with various of potassium salts inhibiting n-heptane fire and ethanol fire are consistent:potassium oxalate>potassium acetate>potassium nitrate>potassium carbonate>potassium bicarbonate>potassium chloride>potassium dihydrogen phosphate;the minimum extinguishing concentration for ultra-fine water mist with various of potassium salts inhibiting heptane fire are smaller than that of ethanol fire.The reduction rate of minimum fire-extinguishing concentration of ultra-fine water mist containing potassium chloride,potassium oxalate,potassium carbonate and potassium acetate for inhibiting ethanol fire are higher than that for inhibiting n-heptane fire.The reduction rate of minimum fire extinguishing concentration of ultra-fine water mist containing potassium dihydrogen phosphate for inhibiting n-heptane fire is higher than that of ethanol fire.The reduction rate of minimum fire extinguishing concentration of ultra-fine water mist containing potassium nitrate or potassium bicarbonate for inhibiting n-heptane fire is not significantly different from that of ethanol fire.?2?In the Chemkin kinetic calculation,the minimum effective retention time of nitrogen inhibiting n-heptane combustion mechanism is 0.39 ms,and the minimum effective retention time of nitrogen inhibiting ethanol combustion mechanism is 0.55ms.With the increase of nitrogen content,the slope of the minimum effective residence time of high concentration nitrogen for n-heptane combustion mechanism is higher than that of ethanol combustion mechanism.With the increase of the molar fraction of potassium hydroxide,the change slope of the minimum effective residence time of high concentration potassium hydroxide for ethanol combustion mechanism is higher than that of n-heptane combustion mechanism.?3?With the increase of nitrogen and potassium hydroxide in the PSR reactor,the number of free radicals in the whole combustion system decrease.The decreasing trend of H and OH free radicals in n-heptane system inhibiting by nitrogen is higher than that in ethanol fire system.Potassium hydroxide inhibits the decreasing trend of flame free radical content in n-heptane fire system,which is lower than that in ethanol fire system.?4?For the more sensitive reactions in the combustion mechanism of n-heptane and ethanol,the absolute value of sensitivity coefficient of potassium hydroxide inhibition system is larger than that of nitrogen inhibition system.In these temperature sensitive reactions,potassium hydroxide inhibits the newly adding potassium-containing reaction of R389?KO+OH=KOH+O?in ethanol combustion system,while potassium hydroxide inhibits the combustion of n-heptane without newly addition of potassium reactions.In these free radical sensitive reactions,potassium hydroxide inhibits the newly adding potassium reactions of R389?KO+OH=KOH+O?,R393?KO+O=KO+O₂?and R395?KO+H=KO+OH?in ethanol combustion system,while potassium hydroxide inhibits n-heptane combustion system without newly adding potassium reactions.