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Title: Determination of soot scattering coefficient from extinction and three-angle scattering in a laminar diffusion flame

Abstract

The total scattering coefficient is determined from three multiangle scattering measurements at different heights above the burner in a nonsooting laminar ethylene diffusion flame. The local extinction coefficient is determined from multichord extinction measurements. The above analysis quantifies the contribution from scattering to extinction without knowledge of the soot primary particle diameter or the morphology of the aggregates, and the absorption coefficient can now be determined. The primary particle diameter, the number density of primary particles, the average number of primary particles in an aggregate, and the width of the lognormal distribution function for the number of primary particles in an aggregate are calculated using the absorption coefficient and assumed constant values for the fractal dimension, the fractal prefactor, and the complex refractive index for soot. The values for the primary particle diameter obtained from the in situ measurements in this study compare well with those obtained from transmission electron microscopic measurements of thermophoretically sampled soot aggregates in a previous study at all heights in the diffusion flame, while the calculated soot structure parameters compare well with previous studies only at heights between 30 and 50 mm above the burner. (author)

Authors:
; ; ;  [1]
  1. Department of Mechanical Engineering, The Pennsylvania State University, University Park, PA 16802 (United States)
Publication Date:
OSTI Identifier:
20880649
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 149; Journal Issue: 1-2; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; SOOT; SCATTERING; PARTICLE SIZE; COMPARATIVE EVALUATIONS; ETHYLENE; LAMINAR FLAMES; ABSORPTION; DISTRIBUTION FUNCTIONS; DENSITY; ALBEDO; FLAME EXTINCTION

Citation Formats

Iyer, Suresh S., Litzinger, Thomas A., Lee, Seong-Young, and Santoro, Robert J. Determination of soot scattering coefficient from extinction and three-angle scattering in a laminar diffusion flame. United States: N. p., 2007. Web. doi:10.1016/J.COMBUSTFLAME.2006.11.009.
Iyer, Suresh S., Litzinger, Thomas A., Lee, Seong-Young, & Santoro, Robert J. Determination of soot scattering coefficient from extinction and three-angle scattering in a laminar diffusion flame. United States. doi:10.1016/J.COMBUSTFLAME.2006.11.009.
Iyer, Suresh S., Litzinger, Thomas A., Lee, Seong-Young, and Santoro, Robert J. Sun . "Determination of soot scattering coefficient from extinction and three-angle scattering in a laminar diffusion flame". United States. doi:10.1016/J.COMBUSTFLAME.2006.11.009.
@article{osti_20880649,
title = {Determination of soot scattering coefficient from extinction and three-angle scattering in a laminar diffusion flame},
author = {Iyer, Suresh S. and Litzinger, Thomas A. and Lee, Seong-Young and Santoro, Robert J.},
abstractNote = {The total scattering coefficient is determined from three multiangle scattering measurements at different heights above the burner in a nonsooting laminar ethylene diffusion flame. The local extinction coefficient is determined from multichord extinction measurements. The above analysis quantifies the contribution from scattering to extinction without knowledge of the soot primary particle diameter or the morphology of the aggregates, and the absorption coefficient can now be determined. The primary particle diameter, the number density of primary particles, the average number of primary particles in an aggregate, and the width of the lognormal distribution function for the number of primary particles in an aggregate are calculated using the absorption coefficient and assumed constant values for the fractal dimension, the fractal prefactor, and the complex refractive index for soot. The values for the primary particle diameter obtained from the in situ measurements in this study compare well with those obtained from transmission electron microscopic measurements of thermophoretically sampled soot aggregates in a previous study at all heights in the diffusion flame, while the calculated soot structure parameters compare well with previous studies only at heights between 30 and 50 mm above the burner. (author)},
doi = {10.1016/J.COMBUSTFLAME.2006.11.009},
journal = {Combustion and Flame},
number = 1-2,
volume = 149,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • Neutron scattering techniques have been applied to the study soot particles in an ethylene diffusion flame. Primary particle sizes have been determined as a function of height-above-the-burner. The practicality of the method has been demonstrated. (author)
  • An analysis is developed for predicting extinction of the diffusion flame that is established when an oxidizing gas flows about the nose of a vaporizing fuel body. Use is made of the limit of a large ratio of the activation energy to the thermal energy at the flame for the overall combustion process, since this limit encompasses all cases of practical interest. By revealing a correspondence with the asymptotic flame structure of a counterflow diffusion flame analyzed earlier, the theory makes available explicit formulas, in term of a Damkoehler number, for study of gas-phase extinction in the present geometry. Frommore » these results a simplified but reasonably accurate method is developed for obtaining, from experimental data on extinction, kinetic information concerning the overall oxidation process occurring in the vicinity of extinction. Curves calculated from a parametric study are presented to facilitate application of the technique, and the procedure is illustrated for methanol burning in oxygen-nitrogen mixtures.« less
  • The dimensionless extinction coefficient (K{sub e}) of soot must be known to quantify laser extinction measurements of soot concentration and to predict optical attenuation through smoke clouds. Previous investigations have measured K{sub e} for post-flame soot emitted from laminar and turbulent diffusion flames and smoking laminar premixed flames. This paper presents the first measurements of soot K{sub e} from within laminar diffusion flames, using a small extractive probe to withdraw the soot from the flame. To measure K{sub e}, two laser sources (635 nm and 1310 nm) were coupled to a transmission cell, followed by gravimetric sampling. Coannular diffusion flamesmore » of methane, ethylene and nitrogen-diluted kerosene burning in air were studied, together with slot flames of methane and ethylene. K{sub e} was measured at the radial location of maximum soot volume fraction at several heights for each flame. Results for K{sub e} at both 635 nm and 1310 nm for ethylene and kerosene coannular flames were in the range of 9-10, consistent with the results from previous studies of post-flame soot. The ethylene slot flame and the methane flames have lower K{sub e} values, in some cases as low as 2.0. These lower values of K{sub e} are found to result from the contributions of (a) the condensation of PAH species during the sampling of soot, (b) the wavelength-dependent absorptivity of soot precursor particles, and, in the case of methane, (c) the negligible contribution of soot scattering to the extinction coefficient. RDG calculations of soot scattering, in combination with the measured K{sub e} values, imply that the soot refractive index is in the vicinity of 1.75-1.03i at 635 nm.« less
  • Laser scattering/extinction tests on a coannular ethene diffusion flame were analyzed using cross sections for polydisperse aggregates. Using an improved experimental arrangement that allowed simultaneous measurement of light scattering at multiple angles, it was possible to determine the fractal dimension of the aggregates in the flame. The analysis also yields the mean-square radius of gyration, the aggregate number concentration, the average number of primary particles per aggregate, as well as the volume average of the volume-mean diameter as a function of height or residence time along the particle path of maximum soot concentration in this flame. These results lead tomore » the conclusion that soot aerosol dynamic processes in the laminar ethene flame are partitioned into four regions. Low in the diffusion flame there is a region of particle inception that establishes the number of primary particles per unit volume that remains constant along a prescribed soot pathline. In the second region, there is sustained particle growth through the combined action of cluster-cluster aggregation (CCA) accompanied by heterogeneous reactions contributing to monomer-cluster growth. Oxidation processes occur in the third region where CCA continues. If aggregate burnout is not complete in the oxidation region, then smoke is released to the surroundings in the fourth region where reactions cease but clusters continue to grow by CCA. The experiments yield the CCA growth rate within the flame which compares favorably with the theoretical value. The similarities and differences between this data reduction and the traditional analysis based on the use of cross sections for Rayleigh spheres and Mie theory spheres is discussed.« less
  • A simplified model of soot formation, based on a laminar flamelet approach and developed, in earlier studies, with a view to subsequent turbulent flame prediction, is extended to include oxidation. The model is evaluated against detailed measurements in a two-dimensional laminar diffusion flame on a Wolfhard-Parker burner. The freestream compositions are modified to raise the stoichiometric condition ({zeta}{sub st} = 0.475), thereby adjusting the flame shape to make the burn-out regime readily accessible to measurement and to substantially raise the temperature levels throughout the flame--peak measured temperature was {approximately} 2,550 K. These temperatures are more relevant to many practical systemsmore » than those typically realized in small-scale laminar flame experiments and therefore provide some insight into the extrapolation necessary for practical application. The principal oxidizing species is shown to be the hydroxyl radical, introduced into the prediction from a flamelet calculation as a function of the mixture fraction, the characteristic scalar variable for the complete composition field. The simplified representation of sooting processes in terms of volume fraction and number density is then readily adapted to incorporate soot oxidation and is shown to satisfactorily embrace the enhanced temperature range.« less