Bulk soot formation

Emissions of soot on the other hand represent a smaller fraction of the overall emission, but are probably of greater concern from the standpoint of visibility and health effects. It has been suggested that soot emissions from fuel oil flames result from processes occurring in the vicinity of individual droplets (droplet soot) before macroscale mixing of vaporized material, and from reactions in the bulk gas stream (bulk soot) remote from individual droplets. Droplet soot appears to dominate under local fuel lean conditions (1, 2), while bulk soot formation occurs in fuel rich zones. Factors which are known to affect soot formation from liquid fuel flames include local stoichiometry, droplet size, gas-droplet relative velocity and fuel properties (primarily C H ratio). 

Both diffusional flame calculations and detailed spatial mapping indicate that the nondispersed injection mode produces a vapor cloud that is characterized by diffusionally controlled combustion and bulk heating while subjecting the droplets to near isothermal conditions. The soot produced in this cloud is strongly influenced by bulk diffusion limitations and as such represents a bulk soot formation extreme. It was found that fuel changes had little effect on the overall soot yield due to this diffusion control. Lower gas temperatures and richer conditions were found to favor soot formation under bulk sooting conditions, probably due to a decrease in the oxidation rate of the soot. 

This chapter complements Refs. 21 and 22 in reviewing the progresses made on the transient, convective, multicomponent droplet vaporization, with particular emphasis on the internal transport processes and their influences on the bulk vaporization characteristics. The interest and importance in stressing these particular features of droplet vaporization arise from the fact that most of the practical fuels used are blends of many chemical compounds with widely different chemical and physical properties. The approximation of such a complex mixture by a single compound, as is frequently assumed, not only may result in grossly inaccurate estimates of the quantitative vaporization characteristics but also may not account for such potentially important phenomena as soot formation when the droplet becomes more concentrated with high-boiling point compounds towards the end of its lifetime. Furthermore, multi-... 

The reason for this poor definition of materials is found in the process of their formation, namely difficult to control polymerization reactions. Such reactions also occur in catalytic reactions with small organic molecules. The nature of carbon deposits therefore reflect all the complexity of the bulk carbon materials One aim of this article is to describe the structural anc chemical complexity of carbon or soot in order tc provide an understanding of the frequently observec complexity of the chemical reactivity (e.g. in reac tivation processes aiming at an oxidative removal o deposits). 

Sources of atmospheric aerosol particles are bulk-to-particle conversion, gas-to-particle conversion, and combustion processes. Bulk-to-particle conversion includes the formation of sea salt, dust, and biogenie partieles. Gas-to-particle formation involves either new particle formation from aerosol precursor gases, or growth of preexisting particles by mass transfer processes between the gas and the partiele phase. Particles derived from gas-to-partiele eonversion processes are also called secondary aerosol particles. Other partieles, sueh as from bulk-to-partiele eonversion processes or combustion particles (soot, fly ash), are called primary aerosol particles. 

---