Combustion properties of halogenated fire suppressants

Previous experimental studies have shown that some halogenated fire suppressant agents added to hydrocarbon–air systems can enhance the combustion. For example, their addition to the air stream can widen the flammability limits of lean mixtures, and increase the maximum explosion pressure for constant volume combustion. To explore the experimentally observed combustion enhancement, the combustion properties of pure mixtures of fire suppressants and air/oxygen were studied. Adiabatic combustion temperatures, ignition delays and burning velocities were calculated for several typical fluorinated fire suppressant agents (CF3H, C2F5H, C3F7H and C3F7COC2F5) in mixtures with air, and CF3Br and CF3I in air and oxygen. Calculated burning velocities are in the range 0.37–2.5 cm/s at initial temperature 400 K (stoichiometric air mixtures of CF3H, C2F5H, C3F7H, C3F7COC2F5, 1 bar). The results show that the fluorinated agents possess sufficient energy to participate in combustion processes, and can support combustion with burning velocities which should be measurable (for some of the systems) at slightly elevated initial temperatures. Simulated ignition delays for C3F7H and C3F7COC2F5 are shorter than for propane for the analyzed range of temperature (1000–1500 K), and those for C2F5H/air mixtures are comparable with propane in a lower temperature range (1000–1250 K).