ANALYSIS OF CF3Br INHIBITION MECHANISM ON METHANE PREMIXED COMBUSTION
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Halon 1301 (CF3Br) has been widely used for many years due to its high extinguisher efficiency at low concentrations, high dispersion capabilities, and good chemical stability at standard conditions. It represents an ideal fire suppressant for those inhabiting close environments such as aircrafts, ships, oil platforms, etc where evacuation is almost impossible. Despite these advantages, bromofluorocarbons are associated with the ozone layer destruction as suggested by Rowland and Molina in 1973. Considering the importance of the stratospheric ozone layer which protects life on Earth from solar radiation, in 1987 the Montreal protocol banned the production of substances with high ozone depletion potential, including Halon 1301. This ban has led to the necessity of finding cleaner alternatives with similar Halon 1301 capabilities; however, no substance has been found to meet such criteria. Progress in this field requires a better understanding of flame inhibition mechanisms, since much of the current knowledge on inhibition is empirical and unclear. Considering this lack of knowledge, the main objective of this work is to obtain further insight into the kinetic effects of CF3Br as an inhibitor of hydrocarbon combustion, especially methane. Numerical analysis is used to simulate premixed flames using Chemkin. Experimental validation is carried out using a shock tube where premixed combustion is achieved at atmospheric pressure over a range of temperatures using mixtures of methane, oxygen, and an inhibitor highly diluted in argon. Reaction progress is monitored using OH* chemiluminescence at 310 nm, a photomultiplier tube and a narrowband filter. Parameters such as ignition delay times and the resulting OH* time histories are used to compare the results from the experiment with the model predictions. Methane chemistry is based on GRI 3.0, CF3Br chemistry is from the mechanism of Westbrook (1983), and the OH* chemistry is modeled using the mechanism of Hall and Petersen (2007). The results herein show the chemical mechanism compares well with experiment for ignition times, but some improvement can be made with respect to OH-radical concentration histories.
