INFLUENCE OF CF3I, CF3BR, AND CF3H ON THE HIGH-TEMPERATURE COMBUSTIONOF METHANE

The effects of a number of flame retardants (CF3I, CF3Br, and CF3H) on the high-temperature reactions of methane with air in a plug flow rea ctor are studied by numerical simulations using the Sandia Chemkin Cod e.(1) The dependence of (a) the ignition delay and (b) time for substa ntially complete reaction as a function of temperature and additive co ncentrations are calculated. In agreement with experiments, the igniti on delay can be increased or decreased by the addition of retardants. The reaction time is always increased by additives. The mechanism for these effects has been examined. It is concluded that the ignition del ay is controlled by the initial retardant decomposition kinetics, whic h releases active species into the system. These species can either te rminate or initiate chains. The reaction time is largely a function of the concentrations of the active radicals H, OH, and O that are forme d during the combustion process. It is shown that their concentrations , particularly those of H atoms, are lowered in the presence of the re tardants. We find that the chemical mechanism governing reaction time is very similar to that which controls the flame velocity and a correl ation between decreases in flame velocity and H-atom concentration is demonstrated. The calculations suggest that relative reaction time and I-I-atom concentrations should be effective measures for the estimati on of retardant effectiveness. Copyright (C) 1996 by The Combustion In stitute