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A computational, three-dimensional approach to investigate the behavior of diesel soot particles in the micro-channels of wall-flow Diesel Particulate Filters is presented. The KIVA3V CFD code, already extended to solve the 2D conservation equations for porous media materials [1], has been enhanced to solve in 2-D and 3-D the governing equations for reacting and compressible flows through porous media in non axes-symmetric geometries. With respect to previous work [1], a different mathematical approach has been followed in the implementation of the numerical solver for porous media, in order to achieve a faster convergency as source terms were added to the governing equations. The Darcy pressure drop has been included in the Navier-Stokes equations and the energy equation has been extended to account for the thermal exchange between the gas flow and the porous wall.

In the last decades the continuously tightening limitations on pollutant emissions has led to an extensive adoption of after-treatment devices on the exhaust systems of modern internal combustion engines. While these devices are primarily introduced for reducing and controlling the emissions, they also play an important role influencing the wave motion inside the exhaust system and so affecting the acoustics and the performances of the engine. In this paper a novel approach is proposed for the modeling of two after-treatment devices: the catalyst and the Diesel Particulate Filter. The models are based on a fast quasi-3D approach, named 3Dcell, originally developed by the authors for the acoustic modeling of silencers. This approach allows to model the wave motion by solving the momentum equation along the three directions.

A novel base metal-palladium catalytic coating was applied on commercial silicon carbide wall flow diesel filters and tested in an engine test bench. This catalytic coating limits the NO2 formation and even removes NO2 within a wide temperature range. Soot combustion, HC conversion and CO conversion properties are comparable to current platinum-based coatings, but at a lower cost. This paper compares the results from engine bench tests of present commercial solutions as regards NO2-, HC-, CO-removal and soot combustion with the novel coating. Furthermore, emission test results from base metal-palladium coated diesel particulate filters installed on operating taxis and related test cycle data are presented. A significant reduction in NO2 emission compared to present technology is measured.

A new fast and efficient parallel numerical solver for reacting and compressible flows through porous media has been developed in the OpenFOAM® (Open Field Operation and Manipulation) CFD Toolbox. With respect to the macroscopic model for porous media originally available in OpenFOAM®, a different mathematical approach has been followed: the new implemented solver makes use of the physical normal components resulting from the velocity expansion in the unit orthogonal vector basis to compute the Darcy pressure drop across the porous medium. Also, an additional sink term to account for the increased flow friction over the porous wall has been included into the momentum equation. In the new solver, the pressure correction equation is still able to achieve a faster convergency at very low permeability of the medium, also when it is associated with grid non-orthogonality.

The development of thermally durable zeolite NH3/Urea-SCR formulations coupled with that of high porosity filters substrates has opened the way to integrate PM and NOx control into a single device, namely an SCR-coated Diesel Particulate Filter (SCRF). A few experimental works are already present in the literature regarding SCRF systems, mainly addressing the DeNOx performances of the system (in both presence and absence of soot) under both steady state and transient conditions. The purpose of the present work is to perform a simulation study focused on phenomena which are expected to play key roles in SCRF systems, such as coupling of reaction and diffusion phenomena, soot effect on DeNOx activity, SCR coating effect on soot regeneration and filtration efficiency and competition between soot oxidation and DeNOx processes involving NO2.

This work presents the experimental investigation of Diesel Particulate Filter (DPF) regeneration and a calibration procedure of a 1D DPF simulation model based on the commercial software AVL BOOST v. 5.1. Model constants and parameters are fitted on the basis of a number of steady state DPF experiments where the DPF is exposed to real engine exhaust gas in a test bed. The DPF is a silicon carbide filter of the wall flow type without a catalytic coating. A key task concerning the DPF model calibration is to perform accurate DPF experiments because measured gas concentrations, temperatures and soot mass concentrations are used as model boundary conditions. An in-house-developed raw exhaust gas sampling technique is used to measure the soot concentration upstream the DPF which is also needed to find the DPF soot burn rate.

Many of the materials which have been developed for use as particle filters in the exhaust of diesel engines have characteristics which give rise to significant problems in practical use. Due to its special characteristics, it is shown that SiC is very well suited for use as the base material for particulate filters. The physical and thermal properties of porous SiC substrate material as applied to diesel particulate filters have been determined and are presented. Experimental results from several types of filter regeneration processes in exhaust gas systems confirm the improvements in the area of thermal load and reduction in temperature level during regeneration. The reduction in temperature during regeneration is shown to be consistent with the high thermal conductivity of SiC.

Recent studies have shown that SiC provides substantial advantages for use as the material for wall flow diesel particulate filters. In addition to very advantageous thermal properties, it has been shown that SiC based filter material has higher permeability than Cordierite. This paper presents a comparison of the basic flow characteristics of SiC based and Cordierite based wall flow filter material, expressed in terms of parameters which are basic materials properties that are independent of filter geometry. In addition, the flow characteristics of the particulate matter collected on the filter during engine operation are presented. The results show that the advantageous flow characteristics observed with the basic filter material are retained for loaded filters, up to very high loadings.

Silicon Carbide (SiC) has been shown to have a high melting/decomposition temperature, good mechanical strength, and high thermal conductivity, which make it well suited for use as a material for diesel particulate filters. The high thermal conductivity of the material tends to reduce the temperature gradients and maximum temperature which arise during regeneration. The purpose of this paper is to experimentally investigate the thermal loading which arise under regenerations of varying severity. An experimental study is presented, in which regenerations of varying severity are conducted for uncoated SiC and Cordierite filters. The severity is varied through changes in the particle loading on the filters and by changing the flow conditions during the regeneration process itself. Temperature distributions throughout the filters are measured during these regeneration.

The paper presents a 2-dimensional model for the calculation of the regeneration process in a wall flow diesel particulate filter. The model includes heat transfer by conduction and convection, a model for particle combustion based on diffusive burning of individual particles, and flow through the channels and across the filter walls. It was found that only the pressure drop across the walls need be considered for normal regeneration conditions. Comparisons between model predictions and experimental results for spatial dependent temperature time histories, and integrated degree of regeneration are used to validate the model. The validations were carried out for a series of severe regenerations, where there are large changes in flow and temperature throughout the process. Relative magnitudes of energy flows due to combustion, convection, and conduction are presented, as well as parametric studies of the effects of temperature, oxygen concentration and soot loading.

Studies were performed with three commonly used additive metals, cerium copper, and iron, with a conventional and a low sulfur fuel in order to investigate fuel additive effects on engine particulate emissions before a particulate filter. Measurements were made on a 4 cylinder direct injection diesel engine and included total particulate mass, soluble organic fraction for both fuels, and polynuclear aromatic hydrocarbon emissions for the low sulfur fuel. The cerium based additive reduced the emissions with both fuels, with the largest effect being on the non-SOF fraction. With the other additives and the high sulfur fuel, non-SOF emissions were increased, increasing total particulate emissions. Copper was found to reduce the polynuclear aromatic hydrocarbons, and cerium was found to have the least effect. The use of an SiC wall flow filter reduced particulate and polynuclear aromatic emissions by over 90%.