Approximate methods for estimating the optical properties of flame-generated soot aggregates were evaluated using existing computer simulations and measurements in the visible and near-infrared portions of the spectrum. The following approximate methods were evaluated for both individual aggregates and polydisperse aggregate populations: the Rayleigh scattering approximation, Mie scattering for an equivalent sphere, and Rayleigh-Debye-Gans (R-D-G) scattering for both given and fractal aggregates. Results of computer simulations involved both prescribed aggregate geometry and numerically generated aggregates by cluster-cluster aggregation; multiple scattering was considered exactly, considered using the mean-field approximation, and ignored using the R-D-G approximation. Measurements involved the angular scattering properties of soot in the postflame regions of both premixed and nonpremixed flames. The results show that available computer simulations and measurements of soot aggregate optical properties are not adequate to provide a definitive evaluation of the approximate prediction methods. The simulations involve either exact solutions for small aggregates where effects of multiple scattering are small, or approximate solutions of uncertain accuracy for the large aggregates of interest for practical flames. The measurements are limited to conditions where soot aggregate structure is not known, and for relatively large scattering angles where the various approximations yield similar results. Within these limitations (for aggregates larger than the Rayleigh scattering regime) the approximate theories performed as follows: Rayleigh scattering generally understimated scattering, Mie scattering for an equivalent sphere yielded unreliable results, while basic and fractal aggregate R-D-G scattering yielded best results for given and fractal aggregates, respectively. However, existing simulations suggest significant effects of multiple scattering for soot aggregates (except near soot inception conditions) that are not included in R-D-G scattering so that improved approximate optical theories for soot aggregates should be sought.
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Research Papers
Radiative Properties of Flame-Generated Soot
U¨. O¨. Ko¨ylu¨,
U¨. O¨. Ko¨ylu¨
Department of Aerospace Engineering, The University of Michigan, Ann Arbor, MI 48109-2140
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G. M. Faeth
G. M. Faeth
Department of Aerospace Engineering, The University of Michigan, Ann Arbor, MI 48109-2140
Search for other works by this author on:
U¨. O¨. Ko¨ylu¨
Department of Aerospace Engineering, The University of Michigan, Ann Arbor, MI 48109-2140
G. M. Faeth
Department of Aerospace Engineering, The University of Michigan, Ann Arbor, MI 48109-2140
J. Heat Transfer. May 1993, 115(2): 409-417 (9 pages)
Published Online: May 1, 1993
Article history
Received:
May 1, 1992
Revised:
September 1, 1992
Online:
May 23, 2008
Connected Content
A companion article has been published:
Separated Flow in a Low-Speed Two-Dimensional Cascade: Part II—Cascade Performance
Citation
Ko¨ylu¨, U. O., and Faeth, G. M. (May 1, 1993). "Radiative Properties of Flame-Generated Soot." ASME. J. Heat Transfer. May 1993; 115(2): 409–417. https://doi.org/10.1115/1.2910693
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