Wall-flow particulate filters are the basis to meet particulate emission standards concerning number and mass limits. The required balance between filtration efficiency and pressure drop demands the availability of computational tools able to predict and diagnose their combined response. In this paper a filtration model coupled with a gas dynamic particulate filter (PF) model based on the theory of packed beds of spherical particles is presented. The model takes as main assumption the experimentally well-known low soot penetration inside the porous wall. From this basis the description of the changes in filtration efficiency, pressure drop and deposits distribution are approached as a function of the soot loading level. The soot penetration inside the porous wall is shown to be a critical parameter dependent on the Peclet number. The transition from deep bed to cake filtration regime is also analysed accounting for macro-and micro-scale transition. Finally, the model is validated against experimental data obtained from several PFs. Flow properties advection along channels and the appropriate definition of the soot penetration and deposition dynamics lead to great accuracy in the modelling of the filtration efficiency, both overall and as a function of the particle size, as well as pressure drop.

ElsevierSerrano Cruz, JR.; Climent Puchades, H.; Piqueras Cabrera, P.; Angiolini, E. (2014). Analysis of fluid-dynamic guidelines in diesel particulate filter sizing for fuel consumption reduction in post-turbo and pre-turbo placement. Applied Energy. 132:507-523. doi:10.1016/j.apenergy.2014.07.043.Analysis of fluid-dynamic guidelines in diesel particulate filter sizing for fuel consumption reduction in post-turbo and pre-turbo placement AbstractWall-flow particulate filters are in the present days a standard aftertreatment system widely used in diesel engines to reduce particle emissions and meet emission regulations. This paper deals with the analysis of the macro-and meso-geometry definition of the DPF monoliths from a fluid-dynamic modelling approach. Focus is driven to the analysis of the influence on pressure drop and hence on engine fuel economy.The influence of the DPF volume on the engine performance is analysed with a gas dynamic software including both post-turbo and pre-turbo placement under clean and soot loading conditions. A swept in cell density is also considered for different thermal integrity factors. This approach allows analysing the trends in pressure drop and cell unit geometric parameters defining the monolith thermal and mechanical performance. A discussion considering constant specific filtration area and constant filtration area is performed providing a comprehensive understanding of the DPF and engine response as volume and cellular geometry are changed. Results are leading to rigorously justify known but usually empirical guidelines for DPF design in post-turbo applications. A discussion on the potential for monolith volume reduction in pre-turbo applications with respect to the post-turbo baseline is addressed. This is based on the very low sensitivity of fuel consumption and pressure drop both to volume reduction and soot and ash loading with pre-turbo DPF configuration.

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The use of aftertreatment systems in reciprocating internal combustion engines is currently mandatory in order to comply worldwide with emission standards. Among these systems, the wall-flow diesel particulate filter (DPF) is in charge of the particulate matter removal. The DPF is conventionally placed downstream of the turbine. However, its placement upstream of the turbine is growing in interest because of the benefits in specific fuel consumption, passive regeneration and aptitude to downsizing. In the current work an in-house 1D wall-flow DPF model is applied to evaluate the effect of the DPF downsizing on filtration efficiency. Both pre-and post-turbine placement are considered in presence of clean and soot loaded substrates. Volume reduction is approached considering diameter and length variation. In parallel, the cell density is also varied modifying the meso-geometry, i.e. cell size and porous wall thickness, imposing constant thermal integrity factor. The sensitivity to this last parameter is also analysed being its influence of second order in comparison to volume and cellular geometry effects. The lower Peclet number in the pre-turbine placement leads to higher filtration efficiency than post-turbine location comparing at the same DPF volume. Diameter based volume reduction provides slightly better results in filtration efficiency because of the way the filtration velocity field is varied. This general behaviour involves additional advantages to the potential for volume reduction of pre-turbine DPFs. Thus, different strategies with boundaries defined by volume reduction at constant filtration area or at constant specific filtration area can be approached looking for the best balance between fuel economy reduction and filtration efficiency increase with pre-turbine DPF placement.