Inhibition of Combustion by Bromine-Free Polyfluorocarbons I. Burning Velocities of Methane Flames Containing Polyfluoroalkylamines

To estimate the inhibition effect of several bromine-free polyfluoroalkylamines such as (CF3CF2)(3)N, (CF3)(2)NCF2CF3, (CF3)(2)NCF2CHF2, and (CF3)(2)NCF=CF2 on flame propagation, the laminar burning velocity was measured for a mixture of 9.5% methane, 90.0% air, and 0.5% inhibitor, at an initial temperature of 298 +/- 2K and a pressure of 1 atm. All of the polyfluoroalkylamines inhibited flame propagation less than CF3Br (Halon 1301), but more than CH3CHFCF3 (FM200). Calculations showed that the inhibition effect of polyfluoroalkylamines was caused not only by physical factors, but also by a chemical process in which fluoric species capture chain carriers (H, O, and OH) of combustion reactions to form stable HF molecules. The inhibition efficiencies of polyfluoroalkylamines were found to be higher than those of polyfluoroalkanes because of polyfluoroalkylamines decomposition to reactive polyfluoroalkyl radicals in the lower temperature region of each flame. The application of polyfluoralkylamines to fire-extinguishers was also discussed.