For a detailed examination of soot particle morphology and its regional variation within a laminar coannular propane diffusion flame at atmospheric pressure, the thermophoretic sampling technique for extracting soot particle, which is based on subjecting a cold surface for short exposure time to precisely defined regions of the flame, has been used. The morphological features provide not only valuable qualitative information on soot particle agglomeration, surface growth, and oxidation, but also quantitative data on primary particle ＆ agglomerate sizes as a function of flame coordinates. Observations with a series of T.E.M. photographs consistently show an increasing primary particle size with height above the burner in the low and intermediate regions of the flame. The size then decreases through oxidation as the particles move to the tip of the flame. Also, the radial size distributions of primary particle ＆ agglomerate were obtained and the results indicate the existence of toroidal zone of maximum soot volume fraction which exists 1-2mm inside of the flame surface.
