Experimental and Chemical Kinetics Study of the Effects of Halon 1211 (CF₂BrCl) on the Laminar Flame Speed and Ignition of Light Hydrocarbons

Abstract

In this study, the effect of Halon 1211 (CF2BrCl) on the ignition delay time and laminar flame speed of CH4, C2H4, and C3H8 were investigated experimentally for the first time. The results showed that the effects of Halon 1211 on the ignition delay time are strongly dependent on the hydrocarbon: the ignition delay time of CH4 is significantly decreased by Halon 1211 addition, while a significant increase in the ignition delay time was observed with C2H4 for the lowest temperatures investigated. Ignition delay times for C3H8 were slightly increased, mostly on the low-temperature side and for the fuel-rich case. A significant reduction in the laminar flame speed was observed for all of the fuels. A tentative chemical kinetics model was assembled from existing models and completed with reactions that have been determined in the literature or estimated when necessary. The experimental results were reproduced satisfactorily by the model, and a chemical analysis showed that most of the effects of Halon 1211 on the ignition delay times of C2H4 and C3H8 are due to the consumption of H radical through the reaction HBr + H ⇄ Br + H2. In the case of methane, the CF2 radical promotes the formation of H via CF2 + CH3 ⇄ CH2:CF2 + H, which then promotes the branching reaction H + O2 ⇄ OH + O. The laminar flame speed results can be explained using catalytic cycles involving Br atoms that are similar to those reported in the literature for CF3Br. This study exhibits the need for a better estimation of the chlorine atom chemistry during the combustion of hydrocarbons in the presence of fire suppressants.

Reaction Kinetics of HBr with HO2: A New Channel for Isotope Scrambling Reactions

“…The gas phase chemical reactions of small bromine-containing species continues to attract interest in atmospheric and combustion applications. In combustion chemistry, , it is known that the introduction of halogen species can act as an inhibitor such as used in flame retardants. , Mathieu et al, e.g., have recently discussed the influence of radical reactions such as C 2 H 3 + Br = C 2 H 3 Br and Br + HO 2 = HBr + O 2 on the laminar flame speed and ignition delay time for hydrocarbon combustion. The sensitivity of combustion observables to the rates of elementary bromine processes motivates the need to continue to improve the accuracy of rate coefficients used in chemical modeling.…”