- Author
- Dobbins, R. A.
- Title
- Optical Measurements of Soot Fractal Aggregates in an Ethene Diffusion Flame.
- Coporate
- Brown Univ., Providence, RI
- Sponsor
- National Institute of Standards and Technology, Gaithersburg, MD
- Book or Conf
- Pennsylvania State University. Biennial Conference on Carbon, 19th. June 25-30, 1989, 400-401 p., 1989
- Keywords
- soot | aggregates | diffusion flames | soot aggregates
- Identifiers
- optical cross sections; polydisperse fractal aggregates
- Abstract
- Advancements in the use of laser diagnostic experiments have provided the incentive for definitive optical cross sections for aggregated particles produced in flames. The interpretation the laser scattering experiment in the past has relied on either Rayleigh theory or the Lorenz-Mie theory applicable for spherical particles. It was noted by D'Allesio et al. that the latter theory gave inconsistencies when applied to soot particles in flames. These workers noted that the particles size found from the dissymetry of scattered light was 60% or more greater than the size found from the ratio of the 90 deg scattering to extinction. It is now well documented that the particles produced in the more heavily sooting flames are aggregates of nearly monodisperse, nearly spherical, primary particles and that these aggregates are mass fractals. The latter can be described by [equation] where n= number of primary particles per aggregate, Rg is the radius of gyration, Df is the fractal dimension, and kf a constant of proportionality. Aggregates which are the product of cluster-cluster growth have a fractal dimension [equation]. Further, such aggregates are polydisperse because n is a discrete variable within any given aggregate population. Thus a size probability distribution function (SPDF) of the discrete variable n is required to describe an aggregate population. The first two moments of the QSPDF are n1 and n2, and they enter into the calculation of the optical cross sections. The first moment n1 is the average number of primary particles per aggregate.