Study On Spreading Kinetics And Fire-fighting Performance Of Aqueous Film-forming Foam Extinguishing Agents

Aqueous film forming foam(AFFF)extinguishing agent is suitable for fighting hydrocarbon fuel fires(Class B fires)because of the dual extinguishing effect of foam and film.For a long time,scholars at home and abroad have focused the research of AFFF fire extinguishing performance on foam properties,and rarely concerned with the role of aqueous film in the process of fire fighting.In view of the fact that the spreading performance of AFFF is mainly determined by the properties of the mixture of fluorocarbon and hydrocarbon surfactant,the spreading kinetics of the mixture and the influence of liquid film on the fire extinguishing performance of hydrocarbon fuel are discussed in this work.The core components of AFFF,fluorocarbon surfactant and sodium 1-hexanesulfonate,were selected to prepare the mixture liquid with the molar ratio of 1:1.The spreading kinetics of the mixed liquid on the surface of cyclohexane,nheptane,aviation kerosene,solvent oil and 0 # diesel oil in one-dimensional and twodimensional directions were studied.The spreading length of liquid film at different time was observed using high-definition camera,and the effects of spreading coefficient and viscosity on spreading rate were studied.The "surface tension-viscosity" mechanism of oil spreading dynamic model on water surface was used to fit,and it was found that the theoretical value was in good agreement with the experimental one.The results show that the spreading rate is positively correlated with the spreading coefficient and negatively related to the fuel viscosity.In addition,the spreading rate decreases with the extension of the spreading time.A certain concentration of mixed liquid can spread on the surface of typical hydrocarbon fuel and form aqueous film with different thickness,which has a certain sealing effect on the oil surface.The sealing effect of liquid film with different thickness on oil vapor was studied by detecting the change of vapor concentration over the closed system at different time.The results show that the greater the thickness of the liquid film is,the better the sealing performance of the same fuel is;and the more volatile the fuel is,the worse the sealing performance is when the thickness of the liquid film is the same.In addition,this dissertation innovatively built an experimental platform to study the influence of liquid film on the fire extinguishing performance of AFFF.By adjusting the amount of compound agent to control its film-forming ability,the influence of aqueous film formation and spreading rate on the fire extinguishing performance of AFFF was studied.Three foam solutions with non spreading performance,poor spreading performance and good spreading performance were used for the fire extinguishing experiments,which were carried out in the oil pan with an inner diameter of 338 mm.The extinguishing times were 33 s,29s and 27 s respectively.The experimental results show that the formation of aqueous film has a positive effect on the fire extinguishing effect.The faster the spreading rate is,the shorter the fire extinguishing time is.