Combustion promotion and extinction of premixed counterflow methane/air flames by C6F12O fire suppressant

Along with the phase-out of CF3Br (Halon 1301), several agents have been proposed as halon replacements for use in suppressing fires in aircraft cargo bays. However, these potential drop-in replacements were found to have a promotion effect on the explosion of an aerosol can, which tested by the US Federal Aviation Administration. Motivated by this problem, we measured the laminar burning velocity of premixed methane/air flames with added one of these agents, C6F12O (Novec 1230), in the counterflow configuration, for fuel/air equivalence ratios of 0.63, 0.68, 0.74, and 0.82. C6F12O was added at levels up to 3.5% by volume fraction to each mixture. Numerical simulations were performed using the detailed kinetic mechanism. The predicted results were in good agreement with the experimental measurements. The burning velocity for the very lean flames (phi=0.63) was increased with C6F12O added at low concentrations due to the additional heat release from C6F12O reaction, whereas for higher equivalence ratios (phi=0.68-0.82), it always decreased with all added agent concentrations. The extinction stretch rates have also been measured using the counterflow technique to gain further insight into the promotion/inhibition behavior of C6F12O in ultra-lean (phi<0.63) flames. The results showed that C6F12O has larger promotion effect for the ultra-lean conditions. Sensitivity analyses showed that lean flames are more sensitive to the fluorinated reactions compared to the rich. In addition, direct images of hydrocarbon flame inhibition by fluorinated ketone were provided for the first time to help interpret the experiments.