Buoyant Turbulent Jets and Flames. Part 2. Refractive Index, Extinction and Scattering Properties of Soot. Annual Report.
Buoyant Turbulent Jets and Flames. Part 2. Refractive
Index, Extinction and Scattering Properties of Soot.
Krishnan, S. S.; Faeth, G. M.
NIST GCR 00-796; GDL/GMF-99-02; 119 p. September 2000.
Sponsor:National Institute of Standards and Technology,
Available from: National Technical Information Service
(NTIS), Technology Administration, U.S. Department of
Commerce, Springfield, VA 22161.
1-800-553-6847 or 703-605-6000;
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turbulent jets; turbulent flames; buoyant plumes;
buoyant flow; soot; extinction; diffusion flames
Extinction and scattering properties at wavelengths of
250-5200 nm were studied for soot emitted from large
buoyant turbulent diffusion flames where soot properties
are independent of position in the overfire region and
characteristic flame residence time. Flames burning in
still air and fueled with both gas (acetylene, ethylene,
propane and propylene) and liquid (benzene, toluene,
cyclohexane and n-heptane) hydrocarbon fuels were
considered. Extinction and scattering measurements were
interpreted to find soot optical properties using
(RDG/PFA) theory after establishing that this theory
provided good predictions of scattering patterns and
ratios of total scattering/absorption cross sections.
Effects of fuel type on soot optical properties were
comparable to experimental uncertainties. Measured
depolarization ratios were correlated with the primary
particle size parameter, completing RDG/PFA methodology
needed to make soot extinction and scattering
predictions. Measurements of dimensionless extinction
coefficients were in good agreement with earlier
measurements for similar soot populations and were
relatively independent of wavelength for wavelengths of
400-800 nm where a mean value of 8.4, averaged over fuel
type and wavelength, was observed. The refractive index
function for absorption was in good agreement with
earlier reflectometry measurements in the visible but
was larger than these measurements in the infrared.
Similarly, present measurements of the refractive index
function for scattering agreed with earlier
reflectometry measurements for wavelengths of 400-550 nm
but otherwise increased with increasing wavelength more
rapidly than the rest. Finally, ratios of total
scattering/absorption cross sections were relatively
large in the visible and near-infrared, with maximum
values as large as 0.9, suggesting greater potential for
scattering from soot particles to affect flame radiation
properties than previously thought.