A Chemical Kinetic Mechanism for 2‐Bromo‐3,3,3‐trifluoropropene (2‐BTP) Flame Inhibition

Abstract

In this work, we report a detailed chemical kinetic mechanism to describe the flame inhibition chemistry of the fire-suppressant 2-bromo-3,3,3-trifluoropropene (2-BTP), under consideration as a replacement for CF 3 Br. Under some conditions, the effectiveness of 2-BTP is similar to that of CF 3 Br; however, like other potential halon replacements, it failed an U.S. Federal Aviation Authority (FAA) qualifying test for its use in cargo bays. Large overpressures are observed in that test and indicate an exothermic reaction of the agent under those conditions. The kinetic model reported herein lays the groundwork to understand the seemingly conflicting behavior on a fundamental basis. The present mechanism and parameters are based on an extensive literature review supplemented with new quantum chemical calculations. The first part of the present article documents the information considered and provides traceability with respect to the reaction set, species thermochemistry, and kinetic parameters. In additional work, presented more fully elsewhere, we have combined the 2-BTP chemical kinetic mechanism developed here with several other submodels from the literature and then used the combined mechanism to simulate premixed flames over a range of fuel/air stoichiometries and agent loadings. Overall, the modeling results qualitatively predicted observations found in cupburner tests and FAA Aerosol Can Tests, including the extinguishing concentrations required and the lean-to-rich dependence of mixtures. With these data in hand, in a second phase of the present work, we perform a reaction path analysis of major species under several modeled conditions. This analysis leads to a qualitative understanding of the ability of 2-BTP to act as

Theoretical Kinetic and Mechanistic Studies on the Reactions of CF3CBrCH2 (2-BTP) with OH and H Radicals

“…This Br abstraction was not considered in the study by Chen et al [4], while Zhang et al [5] reported Br abstraction for 1-BTP with a high barrier 42.3 kca/mol. This is of great interest when one realizes that the C-Br bond is the weakest bond in 2-BTP [6,10]. It can be explained by the fact that the interaction between the nucleophilic OH and the electrophilic H is much stronger than that between OH and Br (halogens are normally nucleophilic).…”

“…A great amount of studies have been focused on the inhibition chemistry mechanism, minimum extinguishing concentration, and combustion enhancement/suppression of 2-BTP by using theoretical calculation, model simulation or experiment [5,6,7,8,9,10,11,12,13,14,15,16,17]. According to previous studies, 2-BTP was considered to have a similar suppression performance to CF 3 Br given that both molecules contain a bromine atom and a CF 3 group [7,11].…”

“…Unfortunately, 2-BTP failed in the mandated FAA aerosol can test (FAA-ACT), like other potential replacements, i.e., C 2 HF 5 (HFC-125) and C 6 F 12 O (Novec 1230) [7,11,18]. In order to better understand why it promoted a higher overpressure when added at sub-inerting concentration and then reduced during the test, Babushok and Burgess et al developed a chemical kinetic mechanism to describe the flame inhibition chemistry of 2-BTP [10,11]. However, in their model, the unimolecular decomposition and radical-induced decomposition (notably by OH and H) pathways for 2-BTP were incomplete and most of the kinetic data were obtained from estimation.…”

“…However, in their model, the unimolecular decomposition and radical-induced decomposition (notably by OH and H) pathways for 2-BTP were incomplete and most of the kinetic data were obtained from estimation. Using the chemical model developed, Babushok and Linteris et al [9,10,11] conducted numerical simulations on the premixed flames, thermodynamic equilibrium, and perfectly stirred-reactors to explore the inhibition and enhancement performance for 2-BTP and other potential replacements under wide combustion conditions. Their studies indicated that the enhancement phenomenon for 2-BTP, when added to lean hydrocarbon-air mixtures, results from the fuel-like property and the increase of the heat release, and the reactions of 2-BTP with OH and H radicals play a significant role in combustion chemistry [9,10,11].…”

“…Using the chemical model developed, Babushok and Linteris et al [9,10,11] conducted numerical simulations on the premixed flames, thermodynamic equilibrium, and perfectly stirred-reactors to explore the inhibition and enhancement performance for 2-BTP and other potential replacements under wide combustion conditions. Their studies indicated that the enhancement phenomenon for 2-BTP, when added to lean hydrocarbon-air mixtures, results from the fuel-like property and the increase of the heat release, and the reactions of 2-BTP with OH and H radicals play a significant role in combustion chemistry [9,10,11]. For instance, almost 80% of the 2-BTP is consumed by reacting with H radical for a stoichiometric CH 4 -air flame with 1% loading, forming the inhibition species (CF 3 , Br and HBr) and hydrocarbons [11].…”