Soot Formation via Gelation in an Acetylene/Air Diffusion Flame
Abstract
Gelation is usually thought of in terms of liquid systems, the formation of gelation gels or the sol to gel transition being common examples. However, under certain conditions acetylene/air diffusion flames create copious amounts of large ( ~mm) soot particles. In this paper we present evidence that these large particles are a result of an aerosol gelation process. At low acetylene flow rates, light scattering shows submicron clusters of soot in both the luminous and nonluminous regions of the flame. This soot shows a weak size dependency with flow rate. As the flow rate is increased, a threshold occurs in which large, 10's μm soot clusters suddenly appear. These large clusters have a DLCA morphology with a fractal dimension of ca. 1.8 with as many as 10^8 monomeric particles per cluster.(C.M. Sorensen and G.D. Feke, Aerosol Sci. Tech. \underline25), 328 (1996). High speed photographs of the flame show these cluster are very dense, i.e., they nearly touch. Optical volume fraction measurements indicate a gel would form when soot cluster sizes are ca. 50μm, the same as the measured cluster sizes. Kinetic measurements indicate that the growth kinetics necessary to create these large clusters is ca. 10^3 faster than the Brownian kinetics responsible for ``normal'' soot growth.(C. Oh and C.M. Sorensen, J. Aerosol Sci. to appear 1997.) Thus a novel kinetics must be at work, and we propose it is gelation.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 1997
- Bibcode:
- 1997APS..MAR.D4123S