- Author
-
Dobbins, R. A.
|
Santoro, R. J.
|
Semerjian, H. G.
- Title
- Interpretation of Optical Measurements of Soot in Flames.
- Coporate
- Brown Univ., Providence, RI
National Bureau of Standards, Washington, DC
- Report
-
Paper 83-1516,
- Book or Conf
- American Institute of Aeronautics and Astrronautics. Thermophysics Conference, 18th. Paper 83-1516. June 1-3, 1983,
Montreal, Canada,
208-237 p.,
1983
- Keywords
-
soot
|
particle size distribution
|
light scattering
|
optical properties
|
agglomerates
|
scaling
|
data analysis
|
equations
|
void spaces
- Abstract
- The mean cross sections for directional scattering and extinction are calculated for absorbing spheres obeying the log normal size distribution function using Mie theory. These properties are used to calculate the dissymmetry ratios, the scattering-extinction ratios, and the depolarization ratios for polydispersions of specified complex refractive index. The use of this information to deduce particle volume fraction, the various mean sizes and the width of the distribution, and the particle number concentration is discussed. Optical observations of agglomerated soot in flames in our laboratory and elsewhere are reviewed. The incompatability of these observations with the Mie theory for polydispersions of absorbing spheres noted by D'Alessio et al is confirmed. It is concluded that this conflict arises because the loosely packed, low density agglomerates have an effective refractive index that is significantly reduced below that of the particulate material. The downward scaling of the refractive index in the manner suggested in the past for macroscopic aggregates of soot material with distributed finite void spaces alleviates the incompatabilities. When the particles display the characteristics of Mie scattering, it is possible to determine the soot volume fraction, the width of the distribution function and various mean diameters, the agglomerate number concentration, and the effective refractive index of the soot agglomerates from certain optical observations. The solution for the soot properties is recovered from the observed data by the minimization of an aggregate relative error of the observations using a method for the least squares minimization of nonlinear functions. Illustrative examples based on recent observations in a laminar ethene/air diffusion flame are provided.