Inhibition of Laminar Premixed Flames by Halon 1301 Alternatives

Abstract

Halon 1301 (CF3Br) has been banned (by the Montreal Protocol) because of its ozone depleting potential. Even though a critical-use exemption of CF3Br has been granted for commercial aircraft cargo bay applications, the European Union is requiring replacement in new aircraft by 2018 and in existing aircraft by 2040. As a result of the expected phase-out, the FAA tested three alternatives (C2HF5, C3H2F3Br, and C6F12O) in a cargo bay simulator, and under certain conditions, apparent combustion enhancement was observed (even though the agents showed promise in standard tests). To understand the enhancement, experiments and numerical analysis are performed to: 1) test the concepts developed via previous numerical simulations and analysis of the FAA tests, 2) reproduce the phenomena observed in the complex full-scale FAA experiments in laboratory-scale experiments which might serve as a screening tool, 3) provide preliminary validation of recently developed kinetic mechanisms (which are used to understand the phenomena), and 4) examine the performance of potential replacements that were not tested by the FAA.

Two spherically expanding flame experiments were built to measure laminar burning velocity, peak pressure rise, and flame response to stretch. For each experiment, developments included designing the chamber, creating the operating procedure, setting up the necessary data acquisition and operation controls, and developing data reduction and post-processing routines. Numerical modeling with detailed kinetics was performed to interpret experimental results and to validate kinetic mechanisms. The most significant findings of this study include the enhancement of lean CH4-air flames by the proposed alternative agents, the potential of HCFC-123 as a halon replacement, and excellent agreement between burning velocity predictions (with detailed chemical mechanisms) and measurements for hydrocarbon-air flames inhibited by CF3Br, C2HF5, C3H2F3Br, C6F12O, and C2HF3Cl2.