Physical Aspects of Nucleation and Growth of Soot Particles

  • G. Prado
  • J. Lahaye

Abstract

In order to shed light on the physical mechanisms of soot formation, two different soot producing systems were investigated: thermal decomposition of benzene and methane and laminar premixed flat flames. The experimental techniques used to measure the size and number density of soot particles were either electron microscopy or laser light scattering and absorption. In some experiments both techniques were used in a complementary fashion. Soot consists essentially of agglomerates of a number of small spherical carbon particles. Electron micrographs obtained from collected soot yield a reliable size distribution and number concentration of the individual spherical elements, providing information on particle nucleation, coalescent coagulation and surface growth. The in situ optical methods, on the other hand, see only the true agglomerate, providing complementary information on particle agglomeration.

A mechanism involving irreversible combination of colliding units appears to give satisfactory correlations of the experimental results. The chemical nature of soot nuclei is not well established. A possibility is that large polyaromatic molecules (PAH) undergo coagulation, forming the first spherical nuclei. In the early stages of particle growth, coalescent collisions between particles dominate the process resulting in a decreasing number density of particles of increasing diameter. During this stage, the growing particles maintain an approximately spherical shape. Dehydrogenation occuring in the condensed phase has the effect of increasing the particle viscosity, and at a later stage, collisions are no longer coalescent. Chain-forming collisions become predominant. In both stages gas-phase hydrocarbon species attach to the surface of growing particles, providing the bulk of the soot mass fraction. Experimental results from the previously mentioned soot-producing systems are presented and discussed within the general frame of this mechanism.

Keywords

Nucleation Rate Soot Particle Surface Growth Premix Flame Soot Formation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media New York 1981

Authors and Affiliations

  • G. Prado
    • 1
  • J. Lahaye
    • 2
  1. 1.Massachusetts Institute of TechnologyCambridgeUSA
  2. 2.Centre de Recherches sur la Physico-Chimie des Surface SolidesC.N.R.S.MulhouseFrance

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