Kinetic Modelling of Soot Oxidation: The Effect of Soot Structure

Kirsten  Leistner, University of Paris Pierre et Marie Curie / IFP

The modelling of Diesel particulate filters (DPF) is of crucial importance due to the ever-more stringent regulations on particulate emissions. Soot oxidation is a complex process and a detailed description challenging, because of the varied character of soot and the formation and migration of surface complexes. Not surprisingly, most studies use very simplified kinetic schemes (< 10 steps). Global kinetic parameters are relatively well documented in literature, but do not allow for a kinetic representation of the differing oxidation behaviour of soots. Elementary or semi-global parameters however, lend themselves to expressing idiosyncrasies such as reaction rates and product ratios. However, calibrating this type of parameter requires more information, such as the experimental profiles of all reaction products The objective of the current PhD thesis carried out at IFP Energies nouvelles is to develop a flexible kinetic model for the oxidation of carbon particles and subsequently link it to a 3D model describing DPF regeneration.

In this context, the study proposed for presentation concerns the kinetics of the oxidation of diesel soot and other carbon materials and its dependence on material structure. Kinetics-limited oxidation experiments of graphite, a carbon black, flame soot, diesel soot and coke in a fixed bed reactor are modelled. A fixed bed reactor model was implemented in the IFP Exhaust library of the simulation software AmeSim. Simulations of this model allow for calibration of a three-step semi-global surface mechanism for each of the materials. Experimental CO and CO2 profiles of the oxidation of diesel soot and graphite are presented. A kinetics-based approach to modelling the effect of carbon structure on reactivity is proposed. The structure-dependence of the reactivity of soot and other carbon materials is described by expressing semi-global activation energies and pre-exponential factors in terms of carbon content. This approach allows for reproduction of carbon consumption rates and CO/CO2 selectivity.

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