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Effect of CF3I Compared to CF3Br on OH and Soot Concentrations in Co-Flowing Propane/Air Diffusion Flames.


pdf icon Effect of CF3I Compared to CF3Br on OH and Soot Concentrations in Co-Flowing Propane/Air Diffusion Flames. (954 K)
Smyth, K. C.; Everest, D. A.

Combustion Institute, Symposium (International) on Combustion, 26th. Proceedings. Volume 1. July 28-August 2, 1996, Napoli, Italy, Combustion Institute, Pittsburgh, PA, 1385-1393 pp, 1996.

Keywords:

combustion; soot; diffusion flames; propane

Abstract:

The recent halt in the production of CF3Br because of its deleterious effect on stratospheric ozone levels has intensified the search for new suppressants with comparable properties. In contrast to most proposed alternatives, earlier investigations of CF3I have reported excellent extinction efficiencies, sometimes superior to CF3Br on a molar basis. These findings have spurred an interest in elucidating more clearly the chemical effects produced by iodine-containing suppressants. In the present study, OH and soot concentrations have been measured using fluorescence imaging and laser-induced incandescence methods, respectively, in a co-flowing, axisymmetric, atmospheric-pressure propane/air diffusion flame inhibited by CF3Br and CF3I. In addition, broadband molecular fluorescence (attributed to polycyclic aromatic hydrocarbons) has been monitored, and peak temperatures have been measured using two-line OH laser-induced fluorescence. Overall, the two suppressants behave similarly when added to both the air and fuel streams, with the most notable exception being the greaer enhancement of soot production for CF3Br addition at subextinction concentrations. CF3I is found to slightly superior to CF3Br under our experimental conditions in terms of [1] requiring smaller mole fraction concentrations at extinction and [2] producing less within-flame soot. The reductions in the OH concentrations with agent additions are essentially the same for CF3I and CF3Br.