A kinetic model for flame inhibition by antimony-halogen compounds in hydrocarbon flames is developed. Thermodynamic data for the relevant species are assembled from the literature, and calculations are performed for a large set of additional species of Sb-Br-C-H-O system. The main Sb- and Br-containing species in the combustion products and reaction zone are determined using flame equilibrium calculations with a set of possible Sb-Br-C-H-O species, and these are used to develop the species and reactions in a detailed kinetic model for antimony flame inhibition. The complete thermodynamic data set and kinetic mechanism are presented. Laminar burning velocity simulations are used to validate the mechanism against available data in the literature, as well as to explore the relative performance of the antimony-halogen compounds. Further analysis of the premixed flame simulations has unraveled the catalytic radical recombination cycle of antimony. It includes (primarily) the species Sb, SbO, SbO, and HOSbO, and the reactions: Sb+O+M=SbO+M; Sb+O+M=SbO+M; SbO+H=Sb+OH; SbO+O=Sb+O; SbO+OH+M=HOSbO+M; SbO+HO=HOSbO+OH; HOSbO+H=SbO+HO; SbO+O+M=SbO+M. The inhibition cycles of antimony are shown to be more effective than those of bromine, and intermediate between the highly effective agents CFBr and trimethylphosphate. Preliminary examination of a Sb/Br gas-phase system did not show synergism in the gas-phase catalytic cycles (i.e., they acted essentially independently).

A kinetic model of inhibition by the potassium-containing compound potassium bicarbonate is suggested. The model is based on the previous work concerning kinetic studies of suppression of secondary flashes, inhibition by alkali metals and the emission of sulfates and chlorides during biomass combustion. The kinetic model includes reactions with the following gas-phase potassium-containing species: K, KO, KO, KO, KH, KOH, KO, KO, (KOH), KCO, KHCO and KCO. Flame equilibrium calculations demonstrate that the main potassiumcontaining species in the combustion products are K and KOH. The main inhibition reactions, which comprise the radical termination inhibition cycle are KOH+H=K+HO and K+OH+M=KOH+M with the overall termination effect: H+OH=HO. Numerically predicted burning velocities for stoichiometric methane/air flames with added KHCO demonstrate reasonable agreement with available experimental data. A strong saturation effect is observed for potassium compounds: approximately 0.1% volume fraction of KHCO is required to decrease burning velocity by a factor of 2, however an additional 0.6% volume fraction is required to reach a burning velocity of 5 cm/s. Analysis of the calculation results indicates that addition of the potassium compound quickly reduces the radical super-equilibrium down to equilibrium levels, so that further addition of the potassium compound has little effect on the flame radicals.

The influence of CFI on the burning velocity of methane-air flame is experimentally and numerically studied. Experimental results demonstrate that the inhibition effectiveness of CFI is very close to that of CFBr. A detailed kinetic model of flame inhibition by CFI is presented, based on an updated version of a previous model. The kinetic model contains 1072 reactions with 115 species including 10 iodine-containing species. Modeling results demonstrate good agreement with experimental data, and both experiments and calculations show that CFI is only slightly less effective at reducing the burning velocity than CFBr. The flame structure predicted from numerical simulations is analyzed and shows that main reactions of the inhibition cycle of CFI are: H+HI=H+I; H+I+M=HI+M; I+I+M=I+M; H+I=HI+I; I+CH+M=CHI+M; H+CHI=CH+HI; I+HCO=HI+CO; HI+OH=HO+I and O+HI=I+OH.