Analysis and modelling of particulate matter filtration in internal combustion engine exhaust aftertreatment systems

The ltration of Particulate Matter (PM) in the Exhaust Systems of the Internal Combustion En- gines (ICE) is one of the main aftertreatment solutions that allowed to comply with progressively more restrictive regulations on engine emissions. While very ecient to this aim, Particulate Filters may be the cause of dierent drawbacks such as additional fuel penalties, increased costs and impact on the system durability. Therefore, a proper balance among these dierent issues is key for the design of such emission control components and systems. Although the experimental analysis is still required to guarantee the real performances of af- tertreatment systems, numerical simulation seems to be the most convenient strategy to cope with their development, optimization and control of one in this case. In fact, after a specic validation by comparing results with a limited set of experimental data, a virtually unlimited number of combina- tion of the design and operating parameters may be numerically tested with a remarkable reduction of time and costs. However this is advantage may be only apparent, as the technical challenges presented by advanced numerical modeling are more than a few: the Particulate Filter behavior is intrinsically character- ized by processes acting on a very wide set of characteristic space and time scales. The latter in fact ranges from the description of the exhaust gases ow occurring at a scale in the order of the length of the device, down to the nanoparticle deposition process occurring at the micro-pores scale of the porous media. Furthermore, the design of any Exhaust Aftertreatment component or system requires both the understanding of the eects of parameter design and control on long-term oper- ation as well as a detailed analysis of microscopic uid dynamic processes (e.g. Brownian motion eects on nanoparticle ltration). All the mentioned eects must be properly represented in the model. The main objective of this PhD dissertation consists thus of the development of two alternative numerical models which allow to cope with this multiscale problem: a simplied macroscale and a detailed multiscale one. While each of the model is able to describe problems on the reference time and space scale, their coupling may be eectively used for a complete design procedure of such components within Diesel or gasoline ICE exhaust systems. The simplied macroscale model will be rst introduced to study a simplied long-term operation of a Particulate Filter, or to implement real-time control strategies; then a detailed multiscale one, capable of analyzing basic ltration and uid dynamic processes in the component, will be described. The eects of key design parameters such as channel shape, porous media specications and fuel type will be commented for both the approaches, along with the description of the processes and of the main parameter trade-os in terms of eciency, fuel consumption, costs and durability.