Experimental study of fuel decomposition and hydrocarbon growth processes for cyclohexane and related compounds in nonpremixed flames

• Published in: Combustion and flame 2004-01, Vol.136 (1-2), p.155-167
• Main Authors: McEnally, Charles S., Pfefferle, Lisa D.
• Format: Article
• Language: English
• Subjects: Applied sciences; Burners; Combustion of gaseous fuels; Combustion. Flame; Diffusion; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Inorganics; Soot; Theoretical studies. Data and constants. Metering
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/j.combustflame.2003.09.012

C1 to C12 stable hydrocarbons, soot volume fraction, several major species, and gas temperature have been measured in a series of methane/air coflowing nonpremixed flames whose fuel was separately doped with 2000 ppm of cyclohexane, cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, and benzene. The cyclohexadienes mostly dehydrogenated to benzene, while cyclohexane and cyclohexene mostly decomposed to C2, C3, and C4 hydrocarbons. Addition reactions were the main benzene source in the cyclohexane-doped flame, whereas both addition and dehydrogenation were important benzene sources in the cyclohexene-doped flame. Reaction pathways were identified in each flame from the hydrocarbon product distributions and from calculated rate constants of relevant reactions. Dehydrogenation was a minor pathway in the cyclohexane- and cyclohexene-doped flames because unimolecular dissociation, not H-atom abstraction, consumed the dopants and their conjugate radicals in these nonpremixed flames. The maximum soot volume fraction correlated poorly with the maximum benzene mole fraction in the cyclohexadiene-doped flames, which indicates that benzene formation was not a rate-determining step to soot production in those flames.