Temperature and oxygen effects on oxidation-induced fragmentation of soot particles

Abstract

In this work soot oxidation induced-fragmentation is modeled by using a Multi-Sectional approach. The model has been developed previously and applied successfully, confirming the role of oxidation-induced fragmentation in soot burnout under different combustion conditions. The Multi-Sectional model was used without further modification to understand the mechanism governing the oxidation-induced fragmentation of soot aggregates and particles by modeling particle size distributions (PSDs) previously measured in a two-stage burner under a wide range of temperature and in both fuel-lean and fuel-rich overall conditions. The model was able to reproduce the experimental data in all the investigated conditions both in terms of PSDs and total mass of oxidized particles.An analysis of model results suggested that when temperature decreased, small particles produced by oxidation-induced fragmentation could not be completely oxidized and, thus, could be emitted; on the other hand, when temperature increased, the global oxidation process was more effective and small particles were oxidized and reduced in number concentration.When studying fuel rich conditions, the model predicted that the local presence of a relevant oxygen concentration caused the oxidation-induced fragmentation mechanism, producing small particles, which could eventually be emitted.Finally, a sensitivity analysis was conducted on oxidation-induced fragmentation indicating that aggregate fragmentation controlled soot burnout whereas particle fragmentation was responsible for small particle formation. However, the sensitivity analysis also suggested that both mechanisms were needed for the correct prediction of the evolution of PSDs.