Temperature Regions of Optimal Chemical Inhibition of Premixed Flames.
Temperature Regions of Optimal Chemical Inhibition of
Premixed Flames.
(165 K)
Rumminger, M. D.; Babushok, V. I.; Linteris, G. T.
Combustion Institute, Symposium (International) on
Combustion, 29th. Volume 29. Part 1. Proceedings.
July 21-26, 2002, Sapporo, Japan, Combustion Institute,
Pittsburgh, PA, Chen, J. H.; Colket, M. D.,
Editor(s)(s), 329-336 pp, 2002.
Keywords:
premixed flames; chemical inhibition; temperature; flame
models; flame speed; flame inhibition
Abstract:
Chemically active fire suppressants may, due to their
properties Or the means by which they are added to
flames, have strong inhibition effects in particular
locations in a flame. To study the spatial effects of
chemically active inhibitors, numerical experiments are
conducted in which the rates of reactions of model
inhibitors are varied in spatial regions defined by
temperature. The influence of three types of spatial
regions are investigated, those with the inhibitor (1)
active only within a narrow temperature band (off-
on-off), (2) active below a cutoff temperature (on-of!),
and (3) active above a (:utoff temperature (off-on). The
effect of several localized chemical perturbations on
the burning velocity are studied, including the
variation of the H + O2 <-> OH + 0 or the CO + OH <->
CO2 + H reaction rate and catalytic scavenging of
radicals by an idealized perfect inhibitor or by CF 3Br
(halon 1301). The results indicate that the flame speed
is reduced most when the perturbation location
corresponds to the regions of maximum radical volume
fraction or maximum chain-branching reaction rates. Each
of the chemical perturbations has a negligible effect
below 1200 K. Calculations for CF 3Br-inhibited flames
indicate a temperature of maxi- mum influence that is
higher than previous suggestions for Br-based
inhibitors. Calculations for flames with the H + O2 rate
perturbed or with addition of the perfect inhibitor
indicate that the important region for flame inhibition
in lean, rich, and stoichiometric flames corresponds to
the position of the peak H-atom volume fraction. The
results of this work demonstrate that the burning
velocity is sensitive to inhibition over a relatively
small spatial region of the flame. Simulations with
stepwise activation and deactivation of an inhibitor
show that the effect of the inhibitor is small when the
activation or deactivation temperature is below 1700 K.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899