Study On Foaming Mechanism And Extinguishing Performance Of Aqueous Film-Forming Foam Extinguishing Agents

Aqueous film forming foam extinguishing agent（AFFF）has the function of double extinguishing of foam and aqueous film.It is an important extinguishing agent for extinguishing oil fires.It is widely used in hangar,ship,oil field and other fields.The International Civil Aviation Organization（ICAO）designated AFFF to extinguish aircraft and aviation fuel fire is the main extinguishing agent.AFFF aqueous film can prevent evaporation of oil and isolate oxygen,and foam can shield the thermal radiation of flame.It is obvious that the performance of foam has an important effect on the extinguishing performance of AFFF.Previous studies on AFFF foaming properties have focused on the effect of foam on fire suppression.Little attention has been given to the effect of foaming conditions on foam performance.The complete foaming kinetics model of AFFF has not been established.This thesis studies the foaming performance and foam stability of AFFF,and the influence of foaming performance on fire extinguishing performance.（1）The environmental friendly four carbon chain fluorocarbon surfactant（FSA,the core component of AFFF）was selected as the research object of foaming and foam stability.The effects of parameters such as concentration,aeration flow rate and mesh diameter on foam performance were investigated.Foaming was performed by automatic foaming apparatus.The real-time state of foam was observed by video system,and the foaming rate at different concentrations,aeration flow and mesh aperture was recorded.In this thesis,the foaming kinetic equation of fluorocarbon surfactant at 25℃was established as dV/dt =k₀ωu^0.9592φ^0.0767.It is found that the concentration,aeration flow and screen aperture are positively correlated with the foaming rate.（2）The foaming performance of a new type of foam extinguishing agent,which was invented by ourselves,was used to study the foam stability of AFFF.By measuring the conductivity,the time of 50%liquid analysis(t_1/2)was measured.The effect of aeration flow rate,concentration and foam stabilizer on the foam stability was investigated.The results show that the inflation rate has little effect on foam stability.t_1/2 gradually increases and then decreases with the increase of concentration.When the concentration reaches 10 m M（mmol/L）,t_1/2 is 300 s,and the foam stabilizing performance is the best.When the concentration continues to increase to 20 m M,t_1/2 gradually decreases,and the foam stabilizing performance gradually decreases;The addition of stabilizer increased the stability of AFFF.When the mass fraction of alkyl glucoside（APG）reached 0.5%,t_1/2 was 350 s,and the foam stability was the best.APG foam stability decreased continuously.When the mass fraction of fatty alcohol polyoxyethylene ether glucoside（AEG）reaches 1.0%,t_1/2 is 390 s,and the foam stability is the best.The stability of AEG is decreased.（3）In addition,this thesis creatively built an experimental platform to study the influence of foaming and foam stabilizing performance on AFFF fire extinguishing performance.The fire extinguishing experiment was carried out on an oil pan with an area of 380 cm²,and the fire extinguishing time corresponding to different foaming rate and t_1/2 was compared.The experimental results show that the foaming rate has a positive effect on the fire extinguishing time When the foaming rate reaches 8.18 m L/s,the fire extinguishing time is 26 s.When t_1/2increases from 300 s to 390 s,the fire extinguishing time is shortened from 28 s to 19 s and then increased to 21 s.when t_1/2 is 360 s,the best fire extinguishing effect is 19 s.Comprehensively considered,in the process of liquid fire fighting,when the foaming rate of AFFF reaches more than 8 m L/s and the 50%liquid separation time is controlled within 350 s～390 s,AFFF has excellent foaming performance and foam stability,and can play a better fire extinguishing effect.