Spreading kinetics of fluorocarbon surfactants on several liquid fuels surfaces

Abstract

Aqueous film-forming foam (AFFF) is a very important extinguishing agent for hydrocarbon fuel fires. The spreading performance of AFFF is one of the key factors to decide its extinguishing efficiency. There are many parameters that affect the spreading performance of AFFF, but few studies have been done on its spreading mechanism. A method for studying the spreading performance of surfactant solution on different oil surfaces was provided in this work. Additionally, the kinetics of C4-Br/CH3(CH2)5NaO3S, C6-Br/CH3(CH2)5NaO3S and C8-Br/CH3(CH2)5NaO3S equimolar system spread on the surfaces of cyclohexane, n-heptane, aviation kerosene, solvent naphtha and diesel oil 0# were investigated. Meanwhile, the relationship between spreading length and time at 25℃ were obtained and the experimental data were evaluated using the model for surface-tension-viscous regime. The root-mean-square deviation (RMSD) values obtained from the correlation using surface-tension-viscous regime model for all of the systems we studied below 3.41, indicating a good agreement between the experimental and theoretical values. It meant that the surface-tension-viscous regime model could be used to predict the process of the aqueous film formed by surfactant solution spread on the hydrocarbon oils. Furthermore, the theoretical spreading rate (R) and average spreading rate (R¯) from 0 to 50 s of C4-Br/oil, C6-Br/oil and C8-Br/oil systems were also investigated. The results showed that the R decreased with increasing time and the rate of decline slowed down gradually. The R¯ increased with the increase of fluorocarbon chains. In particular, the effect of fuel kinematic viscosity on spreading rate was also very obvious. The greater the kinematic viscosity of fuel, the smaller influence of the surfactant tail length on spreading rate.