Thermodynamic Analysis of Suppressant-Enhanced Overpressure in the FAA Aerosol Can Simulator

Abstract

The fire suppressant CF 3 Br has been banned for most applications but it is still used in come critical applications for which suitable replacements have not yet been found. One such application is the suppression of cargo-bay fires in aircraft. Recently, the agents C 2 HF 5 (pentafluoroethane, HFC-125), and bromotrifluoropropene (C 3 H 2 F 3 Br, 2-BTP) have been evaluated in a mandated Federal Aviation Administration (FAA) test, in which a simulated explosion of an aerosol can must be suppressed by the agent. Unfortunately, unlike CF 3 Br, either agent, when added at approximately one-half their inerting concentration, created a higher over-pressure in the test chamber than in tests with no agent present (thus failing the test). Similar combustion enhancement has been described in other experiments for certain conditions; however, explanation of the phenomena is lacking. As a first step in understanding this surprising result, the thermodynamics of the chemical systems are examined to predict the over pressure. For all of the cases examined, the over-pressure was predicted well by assuming that the fuel-agent-air ratio is that which produces the peak temperature, or peak CO 2 . The details of the three chemical systems are examined to provide insight into the anomalous behavior.

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

“…In the FAA-ACT, overpressures were observed (indicating an increase in flammability) [4,5]. Similarly, in a constantvolume apparatus at high agent loadings in lean flames, increases in pressure, burning velocity, and flame temperature were observed [23].…”

“…Cup burner tests indicate that 2-BTP is an effective flame extinguisher at concentrations similar to those required by CF 3 Br [1][2][3]. However, it was unexpectedly found that when 2-BTP is added at subinerting concentrations in the U.S. Federal Aviation Authority Aerosol Can Test (FAA-ACT) [4][5][6][7][8] a large overpressure is obtained, causing the agent to fail the test and indicating that 2-BTP is reacting exothermically under these conditions. The development of a fundamental model explaining the chemical basis of these results would be of value to help assess the range of conditions where such behavior might be expected, as well as provide insights that could lead to the development of more effective agents.…”

Fluorinated halon replacement agents in explosion inerting

“…The objective of this work was to develop a laboratory scale experiment to validate the theoretical work of Linteris (2011) andBabushok (2012) for aviation applications. The results of this work support their calculation model.…”

“…Theoretical research into the possible causes for these phenomena included development of calculation models to describe and predict the mechanisms of the specific explosion events (Linteris, 2011;Babushok, 2012). This provided some possible explanations about the chemistry involved.…”

Numerical investigation of the chemical and physical effects of halogenated fire suppressants addition on methane–air mixtures

“…8,9 Several studies have been performed to explain this phenomenon. 10–13 Perfectly stirred reactor simulations have indicated that adding the suppressant to the lean system increases the energy release rate and the overall reaction rate. 10 Thermodynamic equilibrium calculation indicated that the peak pressure rise occurred when the fuel and agent were completely consumed.…”