Combustion inhibition and enhancement of premixed methane–air flames by halon replacements

Abstract Apparent combustion enhancement by some halon replacement fire suppressants (proposed for use in aircraft cargo bays) has been observed in full-scale, constant-volume tests at the FAA. In order to explore the phenomena, laboratory-scale constant-volume combustion experiments were performed. The maximum explosion pressure and burning velocity were measured for methane–air flames with added CF 3 Br (Halon 1301), C 6 F 12 O (Novec 1230), C 3 H 2 F 3 Br (2-BTP), and C 2 HF 5 (HFC-125). The explosion pressure, for initially stoichiometric flames, was increased mildly (up to 11% and 6%) with C 6 F 12 O and C 2 HF 5 added at low concentrations, while at lean conditions ( Φ  = 0.6), it was increased about 50% for added C 6 F 12 O, C 3 H 2 F 3 Br, or C 2 HF 5 , at agent volume fractions X a = 0.02, 0.03, and 0.06. The burning velocity for initially stoichiometric flames was always decreased with addition of any of the agents, whereas, for the lean conditions, it increased with added C 6 F 12 O or C 2 HF 5 (32% and 14%, at X a = 0.01 and 0.03). Burning velocities at higher initial pressure (3 bar) and temperature (400 K) showed lower inhibition effectiveness (than at ambient conditions) for the stoichiometric flames, and larger enhancement for the lean flames (and the effect was due primarily to the temperature increase). CF 3 Br did not increase the explosion pressure or burning velocity for any of the tested conditions. Equilibrium calculations were used to interpret the experiments. The present work is consistent with the FAA results and previous analysis of the full-scale tests.