Numerical simulation of the synergistic effects of unwanted combustion enhancement by the C3H2F3Br and C2HF5 blends

Abstract

Owing to the restriction of using Halon 1301 (CF3Br) for fire suppression, several alternatives to Halon 1301 have been developed, including C2HF5 (HFC-125), C3H2F3Br (2-BTP), and C6F12O (Novec1230). However, in the Federal Aviation Administration (FAA) Aerosol Can Explosion Test (FAA-ACET), it was found that these alternatives did not suppress lean flames at sub-inert concentrations, but promoted combustion, eventually leading to overpressure. Therefore, they have not been successfully applied in aircraft cargo compartments. Herein, different blend ratios of C3H2F3Br and C2HF5 were used to explore their inhibitory effects on combustion enhancement under lean combustion conditions. A chemical kinetic model was developed and validated using a one-dimensional free-propagation flame simulator. The laminar burning velocity predicted by the model was consistent with the experimental results. The adiabatic flame temperature and overall reaction rate were determined using thermodynamic equilibrium calculations and perfectly stirred reactor (PSR) simulations. By comparing the blend inhibitors with different blend ratios, it was found that the blend of C3H2F3Br and C2HF5 at blend ratios of 25/75 and 50/50 effectively reduced the total heat release and system reactivity. In addition, the blend inhibitor not only weakened the fuel properties of C2HF5, but also further enhanced the bromine-catalysed radical recombination cycle. Notably, a new reaction occurred when C3H2F3Br and C2HF5 were blended into the FAA-ACET chamber: Br + CHF2CF3 = HBr + CF3-CF2, indicating that the Br atoms promoted the decomposition of C2HF5.