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RESEARCH PAPERS: Radiative Transfer

Spectral Extinction Coefficients of Soot Aggregates From Turbulent Diffusion Flames

[+] Author and Article Information
Ü. Ö. Köylü

Department of Chemical Engineering, Yale University, New Haven, CT 06520-8286

G. M. Faeth

Department of Aerospace Engineering, The University of Michigan, Ann Arbor, MI 48109-2118

J. Heat Transfer 118(2), 415-421 (May 01, 1996) (7 pages) doi:10.1115/1.2825860 History: Received May 01, 1995; Revised December 01, 1995; Online December 05, 2007

Abstract

The spectral extinction coefficients of soot aggregates were studied in the fuel-lean (overfire) region of buoyant turbulent diffusion flames. Extinction measurements were carried out in the wavelength region of 0.2–5.2 μm for flames fueled with acetylene, propylene, ethylene, and propane, burning in air. The present measurements were combined with earlier measurements of soot morphology and light scattering at 0.514 μm in order to evaluate the spectral soot refractive indices reported by Dalzell and Sarofim (1969), Lee and Tien (1981), and Chang and Charalampopoulos (1990). The specific extinction coefficients and emissivities were predicted based on Rayleigh–Debye–Gans theory for polydisperse fractal aggregates, which has been recently found to be the best approximation to treat optical cross sections of soot aggregates. The results indicated that available refractive indices of soot do not predict the spectral trends of present measurements in the ultraviolet and infrared regions. Soot complex refractive index was inferred to be m = 1.54 + 0.48i at 0.514 μm, which is surprisingly in best agreement with the values reported by Dalzell and Sarofim (1969). Additionally, specific extinction coefficients of soot aggregates varied with wavelength as λ−0.83 from the visible to the infrared. Finally, soot refractive indices were found to be relatively independent of fuel type for the visible and infrared spectral regions over the H/C ratio range of 0.08–0.22.

Copyright © 1996 by The American Society of Mechanical Engineers
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