Heat Release Mechanisms in Inhibited Laminar Counterflow Flames.
Heat Release Mechanisms in Inhibited Laminar Counterflow
Flames.
(858 K)
Lee, K. Y.; Cha, D. J.; Puri, I. K.; Hamins, A.
American Society of Mechanical Engineers. Fire,
Combustion, and Hazardous Waste Processing. HTD-Vol.
296. November 6-11, 1994, Chicago, IL, American Society
of Mechanical Engineers, NY, Acharya, S.; Annamalai, K.;
Presser, C.; Skocypec, R. D., Editor(s)(s), 25-36 pp,
1994.
Keywords:
combustion; hazardous materials; waste disposal; laminar
flames; heat release; methodology; inhibitors; flame
stability; radiative heat loss
Abstract:
Both the chemical kinetic and thermal channels of
inhibition must be simultaneously characterized in order
to understand the effectiveness of chemical agents on
flame stability. However, due to the participation of
inhibitors in flame chemistry, it is difficult to
concurrently characterize the complex interaction
between their cooling action, and the chemical kinetic
effects due to them. Investigations involving chemical
inhibitors have to contend with three interacting
phenomena, i.e., (Chang et al., 1987) the cooling action
due to the specific heat of the species: (Karra et al.,
1988) the heat release due to their burning; and (Pitz
and Westbrook, 1990) inhibition associated with
scavenging of critical radical species. This study
investigated the effect of chloromethane (a chemical
inhibitor) on the heat release in methane-air
nonpremixed flames. For comparison, the effect on the
heat release due to the purely thermal action of
nitrogen was also investigated. The flames were
experimentally and numerically studied in a counterflow
configuration, and the heat release was calculated from
simulations involving detailed chemistry. When inert
suppressants were added to the oxidizer stream of a
nonpremixed flame, the global heat release decreased.
Chloromethane addition to the fuel stream, however,
increased the heat release. Whereas addition of
nitrogen narrowed the heat release region, chloromethane
addition to the oxidizer altered the flame
stoichiometry, such that the heat release profiles were
markedly different. A thorough investigation of flame
stability must consider the importance of heat losses
through radiative emission. Halogenated compounds can
influence flame emission through changes in flame
structure including increases in temperature and soot
concentration. For these reasons, a small
Schmidt-Boelter type gauge was used to measure the
radiative flux through a cylindrical control volume
surrounding the flame, and the total radiation emitted
from the flame was calculated by integrating the emitted
flux. The results show that as nitrogen was added to
the methane-air base flame, the radiative heat loss
fraction decreased slightly. When chloromethane was
added to the oxidizer stream, the radiative heat loss
fraction increased substantially (=40%). Values of the
radiative heat loss fraction remained relatively
unchanged (=2.3%) for all of the flames studied.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899