Effects of Halons and Halon Replacements on Hydrogen-Fueled Laminar Premixed Flames

Abstract

Fundamental unstretched laminar burning velocities and flame response to stretch, as characterized by Markstein numbers, were considered experimentally and computationally. The investigation was limited to laminar premixed flames involving hydrogen burning in air with Halon 1301 (CF 3 Br), nitrogen, and carbon dioxide considered as flame suppressing diluents. Outwardly propagating spherical laminar premixed flames were observed for fuel equivalence ratios of 0.6-1.8, concentrations of oxygen in oxygen/nitrogen mixtures of 21% by volume before dilution with a suppressant, and normal temperature and pressure. Suppressants involved concentrations of the chemically active suppressant, Halon 1301, of 0-2% by volume and 'concentrations of the chemically passive (chemically inert) suppressants, nitrogen and carbon dioxide, of 0-50% by volume. The present flames were sensitive to flame stretch, yielding values of unstretched-to-stretched laminar burning velocities in the range of 0.6-1.2 for levels of flame stretch well below quenching conditions, for example, for Karlovitz numbers less than 0.15. The agreement between measured and predicted unstretched laminar burning velocities was good based on the mechanisms of Mueller et al. for H 2 /O 2 reactions and Babushok et al. for halogen reactions. The resulting flame structure predictions suggest that H and OH radical production and transport are important for flame suppression and preferential-diffusion/stretch interactions; this reflects the strong correlation between laminar burning velocities and the maximum concentrations of H and OH in the reaction zone of the present flames. It also was found that effects of flame suppression that reduced concentrations of H and OH in the reaction zone made the present flames more unstable to preferential-diffusion/stretch interactions, an effect that tends to counteract the beneficial effects of flame suppressants to some extent.