Phenomenological Models of Soot Processes in Combustion Systems

摘要

The fuel sooting trends in pre-mixed and diffusion flames follow opposite directions due to the different influences of temperature. In pre-mixed flames as the temperature rises the rate of oxidative attack on the soot precursors increases faster than the rate of precursor formation through pyrolysis. Thus the higher the temperature the less is the tendency to soot. In the pre-mixed flame all aliphatics form some acetylene which is the monoelement for precursor formation and all fuels essentially follow the same nucleation route. Aromatics oxidize partially through carboxyl radicals formed during attack on the ring and thus aromatic mixtures burn 'richer' than corresponding aliphatic mixtures of the same stoichiometry. The dominant factors in diffusion flames are the temperature and fuel structure. Here the higher the temperature, the greater is the rate of fuel pyrolysis and the propensity to soot. Thus fuel structures which during pyrolysis form strongly conjugated (polar) species most readily soot. A pure acetylenic polymerization route is too slow to predict the early nucleation of soot particles and the presence of ions cannot predict the difference of isomers to soot in diffusion flames. Thus it has been postulated that only conjugated species which have polar resonance structures can undergo the fast reactions necessary. (Author)