Spectral Extinction Coefficients of Soot Aggregates From Turbulent Diffusion Flames

1996 ◽  
Vol 118 (2) ◽  
pp. 415-421 ◽  
Author(s):  
U¨. O¨. Ko¨ylu¨ ◽  
G. M. Faeth
Keyword(s):  
Cross Sections ◽  
Turbulent Diffusion ◽  
Diffusion Flames ◽  
Complex Refractive Index ◽  
Wavelength Region ◽  
Refractive Indices ◽  
Extinction Coefficients ◽  
The Best Approximation ◽  
Turbulent Diffusion Flames ◽  
Infrared Spectral

The spectral extinction coefficients of soot aggregates were studied in the fuel-lean (overfire) region of buoyant turbulent diffusion flames. Extinction measurements were carried out in the wavelength region of 0.2–5.2 μm for flames fueled with acetylene, propylene, ethylene, and propane, burning in air. The present measurements were combined with earlier measurements of soot morphology and light scattering at 0.514 μm in order to evaluate the spectral soot refractive indices reported by Dalzell and Sarofim (1969), Lee and Tien (1981), and Chang and Charalampopoulos (1990). The specific extinction coefficients and emissivities were predicted based on Rayleigh–Debye–Gans theory for polydisperse fractal aggregates, which has been recently found to be the best approximation to treat optical cross sections of soot aggregates. The results indicated that available refractive indices of soot do not predict the spectral trends of present measurements in the ultraviolet and infrared regions. Soot complex refractive index was inferred to be m = 1.54 + 0.48i at 0.514 μm, which is surprisingly in best agreement with the values reported by Dalzell and Sarofim (1969). Additionally, specific extinction coefficients of soot aggregates varied with wavelength as λ−0.83 from the visible to the infrared. Finally, soot refractive indices were found to be relatively independent of fuel type for the visible and infrared spectral regions over the H/C ratio range of 0.08–0.22.

Optical Properties of Overfire Soot in Buoyant Turbulent Diffusion Flames at Long Residence Times

1994 ◽  
Vol 116 (1) ◽  
pp. 152-159 ◽  
Author(s):  
U¨. O¨. Ko¨ylu¨ ◽  
G. M. Faeth
Keyword(s):  
Optical Properties ◽  
Residence Time ◽  
Cross Sections ◽  
Turbulent Diffusion ◽  
Rayleigh Scattering ◽  
Diffusion Flames ◽  
Model Performance ◽  
Turbulent Diffusion Flames ◽  
Angle Scattering ◽  
Time Regime

The optical properties of soot were studied for the fuel-lean (overfire) region of buoyant turbulent diffusion flames in still air. Results were limited to the long residence time regime where soot structure is independent of position in the overfire region and residence time for a particular fuel. Measurements included scattering, absorption, and extinction cross sections at 514.5 nm and extinction cross sections at 632.8 and 1152 nm for flames fueled with acetylene, propylene, ethylene, and propane. The measurements were used to evaluate scattering predictions based on the Rayleigh-Debye-Gans (RDG) approximation for randomly oriented poly disperse fractal aggregates of spherical primary soot particles having constant diameters. The present soot aggregates exhibited significant departures from Rayleigh-scattering behavior at 514.5 nm, with forward scattering roughly 100 times larger than wide-angle scattering and ratios of scattering to absorption cross sections in the range 0.22–0.41, increasing with increasing propensity of the fuel to soot. The approximate RDG theory generally provided an acceptable basis to treat the optical properties of the present overfire soot aggregates, although additional measurements in the Guinier (small angle) regime are needed for a definitive evaluation of model performance.

Extinction and Scattering Properties of Soot Emitted From Buoyant Turbulent Diffusion Flames

2000 ◽  
Vol 123 (2) ◽  
pp. 331-339 ◽  
Author(s):  
S. S. Krishnan ◽  
K.-C. Lin ◽  
G. M. Faeth
Keyword(s):  
Refractive Index ◽  
Cross Sections ◽  
Turbulent Diffusion ◽  
Diffusion Flames ◽  
Absorption Cross ◽  
Fuel Type ◽  
Total Scattering ◽  
Turbulent Diffusion Flames ◽  
Near Ultraviolet ◽  
Good Agreement

Extinction and scattering properties at wavelengths of 250–5200 nm were studied for 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 flame residence times. Flames burning in still air and fueled with gas (acetylene, ethylene, propane, and propylene) and liquid (benzene, toluene, cyclohexane, and n-heptane) hydrocarbon fuels were considered. Measured scattering patterns and ratios of total scattering/absorption cross sections were in good agreement with predictions based on the Rayleigh-Debye-Gans (RDG) scattering approximation in the visible. Measured depolarization ratios were roughly correlated by primary particle size parameter, suggesting potential for completing RDG methodology needed to make soot scattering predictions as well as providing a nonintrusive way to measure primary soot particle diameters. Measurements of dimensionless extinction coefficients were in good agreement with earlier measurements for similar soot populations and were independent of fuel type and wavelength except for reduced values as the near ultraviolet was approached. The ratios of the scattering/absorption refractive index functions were independent of fuel type within experimental uncertainties and were in good agreement with earlier measurements. The refractive index function for absorption was similarly independent of fuel type but was larger than earlier reflectometry measurements in the infrared. Ratios of total scattering/absorption cross sections were relatively large in the visible and near infrared, with maximum values as large as 0.9 and with values as large as 0.2 at 2000 nm, suggesting greater potential for scattering from soot particles to affect flame radiation properties than previously thought.

Optical Properties in the Visible of Overfire Soot in Large Buoyant Turbulent Diffusion Flames

2000 ◽  
Vol 122 (3) ◽  
pp. 517-524 ◽  
Author(s):  
S. S. Krishnan ◽  
K.-C. Lin ◽  
G. M. Faeth
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Turbulent Diffusion ◽  
Diffusion Flames ◽  
Complex Refractive Index ◽  
Mean Value ◽  
Index Function ◽  
Turbulent Diffusion Flames ◽  
Visible Wavelengths ◽  
Good Agreement

Nonintrusive measurements of the optical properties of soot at visible wavelengths (351.2–800.0 nm) were completed for soot in the overfire region of large (2–7 kW) buoyant turbulent diffusion flames burning in still air at standard temperature and pressure, where soot properties are independent of position and characteristic flame residence time for a particular fuel. Soot from flames fueled with gaseous (acetylene, ethylene, propylene, and butadiene) and liquid (benzene, cyclohexane, toluene, and n-heptane) hydrocarbon fuels were studied. Scattering and extinction measurements were interpreted to find soot optical properties using the Rayleigh-Debye-Gans/polydisperse-fractal-aggregate theory after establishing that this theory provided good predictions of scattering patterns over the present test range. Effects of fuel type on soot optical properties were comparable to experimental uncertainties. Dimensionless extinction coefficients were relatively independent of wavelength for wavelengths of 400–800 nm and yielded a mean value of 8.4 in good agreement with earlier measurements. Present measurements of the refractive index function for absorption, Em, were in good agreement with earlier independent measurements of Dalzell and Sarofim and Stagg and Charalampopoulos. Present values of the refractive index function for scattering, Fm, however, only agreed with these earlier measurements for wavelengths of 400–550 nm but otherwise increased with increasing wavelength more rapidly than the rest. The comparison between present and earlier measurements of the real and imaginary parts of the complex refractive index was similar to Em and Fm.[S0022-1481(00)02203-9]

Refractive Indices at Visible Wavelengths of Soot Emitted From Buoyant Turbulent Diffusion Flames

1997 ◽  
Vol 119 (2) ◽  
pp. 230-237 ◽  
Author(s):  
J.-S. Wu ◽  
S. S. Krishnan ◽  
G. M. Faeth
Keyword(s):  
Standard Deviation ◽  
Residence Time ◽  
Diffusion Flames ◽  
Fractal Dimensions ◽  
Mean Value ◽  
Refractive Indices ◽  
Fuel Type ◽  
Extinction Coefficients ◽  
Turbulent Diffusion Flames ◽  
Visible Wavelengths

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.

Soot formation in ducted turbulent diffusion flames

AIAA Journal ◽  
1991 ◽  
Vol 29 (6) ◽  
pp. 932-935 ◽  
Author(s):  
T. Neill ◽  
I. M. Kennedy
Keyword(s):  
Turbulent Diffusion ◽  
Diffusion Flames ◽  
Soot Formation ◽  
Turbulent Diffusion Flames

Density Variations Effects in Turbulent Diffusion Flames: Modeling Of Unresolved Fluxes

2014 ◽  
Vol 186 (10-11) ◽  
pp. 1370-1391 ◽  
Author(s):  
Sylvain Serra ◽  
Vincent Robin ◽  
Arnaud Mura ◽  
Michel Champion
Keyword(s):  
Turbulent Diffusion ◽  
Diffusion Flames ◽  
Turbulent Diffusion Flames

scholarly journals Soot modeling in turbulent diffusion flames: review and prospects

2021 ◽  
Vol 43 (4) ◽  
Author(s):  
Sebastian Valencia ◽  
Sebastián Ruiz ◽  
Javier Manrique ◽  
Cesar Celis ◽  
Luís Fernando Figueira da Silva
Keyword(s):  
Turbulent Diffusion ◽  
Diffusion Flames ◽  
Turbulent Diffusion Flames

scholarly journals Mixing process in turbulent diffusion flames.

1989 ◽  
Vol 55 (510) ◽  
pp. 517-522 ◽  
Author(s):  
Kohoichi SUZUKI ◽  
Kinichi TORIKAI ◽  
Kiyoshi SAKUMA
Keyword(s):  
Turbulent Diffusion ◽  
Diffusion Flames ◽  
Mixing Process ◽  
Turbulent Diffusion Flames
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