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Heat Release Mechanisms in Inhibited Laminar Counterflow Flames.


pdf icon 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.