Understanding overpressure in the FAA aerosol can test by C3H2F3Br (2-BTP)

Abstract

Thermodynamic equilibrium calculations, as well as perfectly-stirred reactor (PSR) simulations with detailed reaction kinetics, are performed for a potential halon replacement, C3H2F3Br (2-BTP, C3H2F3Br, 2-Bromo-3,3,3-trifluoropropene), to understand the reasons for the unexpected enhanced combustion rather than suppression in a mandated FAA test. The high pressure rise with added agent is shown to depend on the amount of agent, and is well-predicted by an equilibrium model corresponding to stoichiometric reaction of fuel, oxygen, and agent. A kinetic model for the reaction of C3H2F3Br in hydrocarbon-air flames has been applied to understand differences in the chemical suppression behavior of C3H2F3Br vs. CF3Br in the FAA test. Stirred-reactor simulations predict that in the conditions of the FAA test, the inhibition effectiveness of C3H2F3Br at high agent loadings is relatively insensitive to the overall stoichiometry (for fuel-lean conditions), and the marginal inhibitory effect of the agent is greatly reduced, so that the mixture remains flammable over a wide range of conditions. Most important, the flammability of the agent-air mixtures themselves (when compressively preheated), can support low-strain flames which are much more difficult to extinguish than the easy-to extinguish, high-strain primary fireball from the impulsively released fuel mixture. Hence, the exothermic reaction of halogenated hydrocarbons in air should be considered in other situations with strong ignition sources and low strain flows, especially at preheated conditions.

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

“…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].…”

“…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].…”

Theoretical analysis and simulation of methane/air flame inhibition by sodium bicarbonate particles

“…This phenomenon might also explain overpressure increase observed in the FAA-ACT experiments [18] where the introduction of inhibition powders actually led to faster flames and higher overpressures. Many authors [38][39][40][41] have proposed an explanation for the observed overpressure increase based on thermodynamic equilibrium calculations and perfectly stirred reactor simulations. A non-uniform inhibitor distribution prior to ignition, and the subsequent flame surface increase, may also explain the increase in pressure during these experiments.…”

Numerical Investigation of the Chemical Effect and Inhibition Effect Improvement of C3H2F3Br (2-BTP) Using the Perfectly Stirred Reactor Model

“…There are kinetic limitations when using the equilibrium simulations to predict the explosive pressure in FAA-ACT test. However, PSR simulations cannot only understand kinetic limitations [6] but also evaluate inhibition effectiveness of different agents through overall reaction rate during blow-out [15]. The PSR model is a classical idealization of the combustion process in which both physical and chemical mechanisms of fire suppression can be considered.…”

“…Babushok et al studied the combustion properties of halogenated fire suppressants [5] and calculated that approximate peak burning velocities of the pure 2-BTP-air flames were 1.15 cm/s, 2.15 cm/s, and 3.5 cm/s for initial mixture temperatures of 300 K, 400 K, and 500 K, respectively [1]. Afterwards, Linteris et al found when compressively preheated, 2-BTP/air mixture can support low-strain flames which are much more difficult to extinguish [6]. Pagliaro et al measured the laminar burning velocity of 2-BTP experimentally.…”