Measurements of the optical properties of soot, emphasizing refractive indices, are reported for visible wavelengths (350–800 nm). The experiments considered soot in the fuel-lean (overfire) region of buoyant turbulent diffusion flames in the long residence time regime where soot properties are relatively independent of position in the overfire region and residence time. Flames fueled with acetylene, propylene, ethylene, and propane that were burning in still air provided a range of soot physical and structure properties. Measurements included soot composition, density, structure, gravimetric volume fraction, and scattering and absorption properties. These data were analyzed to find soot fractal dimensions, refractive indices, refractive index functions, and dimensionless extinction coefficients assuming Rayleigh-Debye-Gans scattering for polydisperse mass fractal aggregates (RDG-PFA theory). RDG-PFA theory was successfully evaluated using measured scattering properties. Soot fractal dimensions were independent of both fuel type and wavelength, yielding a mean value of 1.77 with a standard deviation of 0.04. Refractive indices were independent of fuel type within experimental uncertainties and were in reasonably good agreement with earlier measurements for soot in the fuel-lean region of diffusion flames due to Dalzell and Sarofim (1969). Dimensionless extinction coefficients were independent of both fuel type and wavelength, yielding a mean value of 5.1 with a standard deviation of 0.5, which is lower than earlier measurements for reasons that still must be explained.

1.
Batten
C. E.
,
1985
, “
Spectral Optical Constants of Soots From Polarized Angular Reflectance Measurements
,”
Appl. Optics
, Vol.
24
, pp.
1193
1199
.
2.
Chang
H. Y.
, and
Charalampopoulos
T. T.
,
1990
, “
Determination of the Wavelength Dependence of Refractive Indices of Flame Soot
,”
Proc. R. Soc. London A
, Vol.
430
, pp.
577
591
.
3.
Charalampopoulis
T. T.
,
1992
, “
Morphology and Dynamics of Agglomerated Particulates in Combustion Systems Using Light Scattering Techniques
,”
Prog. Energy Combust. Sci.
Vol.
18
, pp.
13
45
.
4.
Choi
M. Y.
,
Mulholland
G. W.
,
Hamins
A.
, and
Kashiwagi
T.
,
1995
, “
Comparisons of the Soot Volume Fraction Using Gravimetric and Light Extinction Techniques
,”
Combust. Flame
, Vol.
102
, pp.
161
169
.
5.
Dalzell
W. H.
, and
Sarofim
A. F.
,
1969
, “
Optical Constants of Soot and Their Application to Heat Flux Calculations
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
91
, pp.
100
104
.
6.
Dobbins
R. A.
, and
Megaridis
C. M.
,
1991
, “
Absorption and Scattering of Light by Polydisperse Aggregates
,”
Appl. Optics
, Vol.
30
, pp.
4747
4754
.
7.
Dobbins
R. A.
,
Mulholland
G. W.
, and
Bryner
N. P.
,
1994
, “
Comparison of a Fractal Smoke Optics Model with Light Extinction Measurements
,”
Atmospheric Environment
, Vol.
28
, pp.
889
897
.
8.
Dyer
T. M.
,
1979
, “
Rayleigh Scattering Measurements of Time-Resolved Concentration in a Turbulent Propane Jet
,”
AIAA J.
, Vol.
17
, pp.
912
914
.
9.
Faeth
G. M.
, and
Ko¨ylu¨
U¨. O¨.
,
1995
, “
Soot Morphology and Optical Properties in Nonpremixed Turbulent Flame Environments
,”
Combust. Sci. Tech.
, Vol.
108
, pp.
207
229
.
10.
Farias
T.
,
Carvalho
M. G.
,
Ko¨ylu¨
U¨. O¨.
, and
Faeth
G. M.
,
1995
, “
Computational Evaluation of Approximate Rayleigh-Debye-Gans/Fractal-Aggregate Theory for the Absorption and Scattering Properties of Soot
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
117
, pp.
152
159
.
11.
Felske
J. D.
,
Charalampopoulos
T. T.
, and
Hura
H.
,
1984
, “
Determination of the Refractive Indices of Soot Particles From the Reflectivities of Compressed Soot Pellets
,”
Combust. Sci. Tech.
, Vol.
37
, pp.
263
284
.
12.
Habib
Z. G.
, and
Vervisch
P.
,
1988
, “
On the Refractive Index of Soot at Flame Temperature
,”
Combust. Sci. Tech.
, Vol.
59
, pp.
261
274
.
13.
Jullien, R., and Botet, R., 1987, Aggregation and Fractal Aggregates, World Scientific Publishing Co., Singapore, pp. 45–60.
14.
Ko¨ylu¨, U¨. O¨., 1992, “Emission, Structure and Optical Properties of Overfire Soot From Buoyant Turbulent Diffusion Flames,” Ph.D. Thesis, The University of Michigan, Ann Arbor, Michigan.
15.
Ko¨ylu¨
U¨. O¨.
, and
Faeth
G. M.
,
1992
, “
Structure of Overfire Soot in Buoyant Turbulent Diffusion Flames at Long Residence Times
,”
Combust. Flame
, Vol.
89
, pp.
140
156
.
16.
Ko¨ylu¨
U¨. O¨.
, and
Faeth
G. M.
,
1994
a, “
Optical Properties of Overfire Soot in Buoyant Turbulent Diffusion Flames at Long Residence Times
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
116
, pp.
152
159
.
17.
Ko¨ylu¨
U¨. O¨.
, and
Faeth
G. M.
,
1994
b, “
Optical Properties of Soot in Buoyant Laminar Diffusion Flames
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
116
, pp.
971
979
.
18.
Ko¨ylu¨
U¨. O¨.
, and
Faeth
G. M.
,
1996
, “
Spectral Extinction Coefficients of Soot Aggregates from Turbulent Diffusion Flames
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
118
, pp.
415
421
.
19.
Ko¨ylu¨
U¨. O¨.
,
Faeth
G. M.
,
Farias
T. L.
, and
Carvalho
M. G.
,
1995
, “
Fractal and Projected Structure Properties of Soot Aggregates
,”
Combust. Flame
, Vol.
100
, pp.
621
635
.
20.
Lee, S. C., and Tien, C. L., 1980, “Optical Constants of Soot in Hydrocarbon Flames,” Eighteenth Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, pp. 1159–1166.
21.
Manickavasagam
S.
, and
Mengu¨c
M. P.
,
1993
, “
Effective Optical Properties of Coal/Char Particles Determined from FT-IR Spectroscopy Experiments
,”
Energy and Fuel
, Vol.
7
, pp.
860
869
.
22.
Martin
J. E.
, and
Hurd
A. J.
,
1987
, “
Scattering from Fractals
,”
J. Appl. Cryst.
, Vol.
20
, pp.
61
78
.
23.
Medalia
A. I.
, and
Heckman
F. A.
,
1969
, “
Morphology of Aggregates—II. Size and Shape Factors of Carbon Black Aggregates from Electron Microscopy
,”
Carbon
, Vol.
7
, pp.
567
582
.
24.
Rosner
D. E.
,
Mackowski
D. W.
, and
Garcia-Ybarra
P.
,
1991
, “
Size- and Structure-Insensitivity of the Thermophoretic Transport of Aggregated ‘Soot’ Particles in Gases
,”
Combust. Sci. Tech.
, Vol.
80
, pp.
87
101
.
25.
Rudder
R. R.
, and
Bach
D. R.
,
1968
, “
Rayleigh Scattering of Ruby-Laser Light by Neutral Gases
,”
J. Opt. Soc. Amer.
, Vol.
58
, pp.
1260
1266
.
26.
Tien
C. L.
, and
Lee
S. C.
,
1982
, “
Flame Radiation
,”
Prog. Energy Combust. Sci.
, Vol.
8
, pp.
41
59
.
27.
Vaglieco
B. M.
,
Beretta
F.
, and
D’Alessio
A.
,
1990
, “
In-Situ Evaluation of the Soot Refractive Index in the uv-Visible from the Measurements of Scattering and Extinction Coefficients in Rich Flames
,”
Combust. Flame
, Vol.
79
, pp.
259
271
.
28.
Viskanta
R.
, and
Mengu¨c
M. P.
,
1987
, “
Radiation Heat Transfer in Combustion Systems
,”
Prog. Energy Combust. Sci.
, Vol.
13
, pp.
97
160
.
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