- Author
- Faeth, G. M. | Koylu, U. O.
- Title
- Structure and Optical Properties of Flame-Generated Soot.
- Coporate
- Michigan Univ., Ann Arbor
- Sponsor
- National Institute of Standards and Technology, Gaithersburg, MD National Aeronautics and Space Administration, Lewis Research Center, Cleveland, OH Office of Naval Research, Washington, DC
- Contract
- NIST-GRANT-60NANB1D1175 NIST-GRANT-60NANB4D1696 NASA-GRANT-NAG3-1245 ONR-GRANT-N00014-93-1-0321
- Book or Conf
- Transport Phenomena in Combustion. Proceedings of the 8th International Symposium on Transport Phenomena in Combustion (ISTP-VIII). Volume 1. July 16-20, 1995, Taylor and Francis, Washington, DC, San Francisco, CA, Chan, S. H., Editors, 19-44 p., 1995
- Keywords
- combustion | soot | structures | optical properties | particle size | aggregates | refractive index
- Identifiers
- soot structure properties; structure of soot emitted from long residence time turbulent diffusion flames; RDG-PFA scattering theory; experimental evaluation of RDG-PFA predictions; computational evaluation of RDG-FA predictions; implications of soot scattering; refractive index properties of soot
- Abstract
- Current understanding of the structure and optical properties of soot is reviewed, emphasizing the soot found in flame environments. Measurements of soot structure have shown that soot consists of nearly spherical and monodisperse primary particles at given flame conditions, with primary particle diameters generally less than 60 nm. These primary particles generally are collected into open-structured (wispy) aggregates that are mas-fractal objects with relatively robust fractal properties, e.g., fractal dimensions of 1.82 ± 0.08 and fractal prefactors of 8.5 ± 0.5, relatively independent of fuel type and flame conditions. These aggregates grow by cluster/cluster aggregation to yield broad aggregate size distributions, with the largest aggregates containing thousands of primary particles and reaching dimensions of several mum. The optical properties of soot are not reliably approximated by either the Rayleigh or the Mie scattering approximations which has lead to the development of approximate Rayleigh-Debye-Gans (RDG) scattering models for polydisperse fractal aggregate populations of soot. The RDG models have been evaluated experimentally, based on measurements of both soot structure and scattering properties, and theoretically, based on numerical simulations to create soot aggregates combined with computations of aggregate scattering properties using more exact theories. These evaluations indicate that the RDG approximation is satisfactory for estimating soot optical properties. Based on these findings, there is potential for obtaining reliable nonintrusive measurements of both soot concentrations and structure in flame environments, which should be helpful for diagnosing problems of particulate matter, pollutant and radiative emissions from combustion processes.