Inhibition effectiveness of halogenated compounds

A numerical study of the inhibition efficiency of halogenated compounds was carried out for C-1-C-2 hydrocarbon-air laminar premixed flames. The inhibition efficiency of CF3Br, CF3I, CF3H, C2HF5, C2F6, and CF, additives was interpreted using an additive group method. In agreement with measurements, the calculated burning velocity decreased exponentially with increasing additive concentration over a wide concentration range. The inhibition parameter Phi proposed by Fristrom and Sawyer indicating inhibition efficiency was modified to take into account the exponential dependence of burning velocity on inhibitor concentration. The inhibition indices for halogen atoms and groups important in the inhibition process were determined for stoichiometric conditions. The physical and chemical effects of the additives were studied. With increasing additive concentration, the chemical influence of an inhibitor saturates and the physical influence increases. Therefore, use of a composite inhibitor composed of a mixture of an effective chemical inhibitor with a high heat capacity diluent may be beneficial. The contribution of physical and chemical components on inhibitor influence are estimated near extinction. A procedure for determination of a regeneration coefficient, which indicates an effective number of catalytic cycles involving inhibitor during the combustion process, is suggested. The regeneration coefficient of HBr in stoichiometric methane-air flame with 1% CF3Br added is approximately 7. (C) 1998 by The Combustion Institute.