NIST Time|NIST Home|About NIST|Contact NIST

HomeAll Years:AuthorKeywordTitle2005-2010:AuthorKeywordTitle

Mixing and Radiation Properties of Buoyant Luminous Flame Environments. Part 1. Self-Preserving Plumes. Final Report.


pdf icon Mixing and Radiation Properties of Buoyant Luminous Flame Environments. Part 1. Self-Preserving Plumes. Final Report. (9601 K)
Dai, Z.; Sangras, R.; Tseng, L. K.; Faeth, G. M.

NIST GCR 99-769; GDL/GMF-98-02; 128 p. March 1999.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Available from:

National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
Telephone: 1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900.
Website: http://www.ntis.gov
Order number: PB99-140535

Keywords:

fire research; flame research; flame structure; optical properties; refractive index; soot; soot aggregates

Abstract:

An investigation of the structure and optical properties of soot is described, motivated by the need to develop nonintrusive methods for measuring soot properties and to estimate the continuum radiation properties of soot for flame environments. The study included evaluation of Rayleigh-Debye-Gans/polydisperse-fractal-aggregate (RDG-PFA) approximate scattering theory for the optical properties of soot aggregates, the determination of the structure and fractal properties of soot that are needed to make predictions with RDG-PFA theory, and the use of RDG-PFA theory to measure the refractive index and related optical properties of soot. Measured soot optical properties were in good agreement with the predictions of RDG-PFA theory over a broad test range, as follows: soot from both the fuel-rich and fuel-lean regions of buoyant diffusion flames, wavelengths of 350-800 nm, primary particle size parameters as large as 0.46, and soot formed in diffusion flames burning in air for a variety of gaseous and liquid hydrocarbon fuels (acetylene, ethylene, propylene, butadiene, benzene, cyclohexane, toluene and n-heptane). Evaluation of the structure and fractal properties of soot was carried out for a similar range of wavelengths and soot properties showing that soot aggregate fractal properties are relatively independent of flame conditions, yielding a fractal dimension of 1.82 and a fractal prefactor of 8.5, with experimental uncertainties (95% confidence) of 0.08 and 0.5, respectively. The research also yields some helpful relationships between actual and projected soot aggregate properties. Evaluation of the refractive index properties of soot was limited to soot emitted from buoyant turbulent diffusion flames in the long residence time regime (where soot properties are independent of position in the overfire region and characteristic residence time) for the same range of wavelengths and fuels as before. Major findings concerning soot refractive index and related properties are as folows: dimensionless extinction coefficients were relatively independent of fuel type and wavelength and agreed with results from earlier studies within experimental uncertainties; in agreement with recent studies, there was no evidence of a resonance condition in the near uv for soot, similar to graphite; the refractive index functions relevant to absorption and emission, E(m), were relatively independent of fuel type and wavelength and agreed with earlier work for wavelengths greater than 400 nm; and the refractive index functions relevant to scattering, F(m), were also relatively independent of fuel type but increased faster with increasing wavelength than observed during earlier studies.