Heat Release Mechanisms in Inhibited Laminar Counterflow Flames.
Heat Release Mechanisms in Inhibited Laminar Counterflow
Flames.
(920 K)
Lee, K. Y.; Cha, D. J.; Hamins, A.; Puri, I. K.
Combustion and Flame, Vol. 104, No. 1/2, 27-40, 1996.
Keywords:
combustion; hazardous materials; waste disposal; laminar
flames; heat release; methodology; inhibitors; flame
stability; radiative heat loss
Abstract:
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 inhibition (which decrease
temperature), and their contribution of heat release
(which increases temperature). Investigations involving
chemical inhibitors have to contend with three
interacting phenomena, i.e., (1) the cooling action due
to the specific heat of the species; (2) the heat
release due to their burning; and (3) inhibition
associated with scavenging of critical radical species.
This study investigated the effect of chloromethane (a
chemical inhibitor due to its halogenation) 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 (which does not
exhibit chemical inhibition or heat release effects) 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. Halogenated
compounds can influence radiative thermal losses from
flames through changes in flame structure that effect
the temperature and soot concentration. Therefore, 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 small
(=2.3%) for all of the flames studied.
