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Diesel particulate filters (DPF) are now a mandatory part in diesel exhaust aftertreatment systems in order to achieve compliance with current emission legislations. However future demands for further NOx and CO₂ reductions combined with a maximum amount of allowed particle numbers per ccm lead to special requirements for the DPF substrate material. On the one hand high filtration efficiency of soot particles in the nanometer scale has to be reached and on the other hand high porosities and large pore sizes have to be realized to support catalytic coating. In order to have a base material composition which can easily be modified to meet current and future demands a new SiC substrate, called XP-SiC, was developed. The technology of the XP-SiC is based on a reaction forming process of coextruded silicon and carbon particles to SiC. This new manufacturing process leads to a unique microstructure with a sponge-like appearance and a high porosity in the range of 50% - 70%.

The current paper describes a methodology for combustion bowl assessment for diesel engines. The methodology is based on the application of Computational Fluid Dynamics (CFD) following a Design of Experiments (DoE) procedure. In this work the 3D CFD simulation was performed by the commercial CFD code AVL-FIRE for different combustion bowls from intake valve closing (IVC) to exhaust valve opening (EVO). The initial conditions (at IVC) and boundary conditions were obtained from 1D simulation. Since the work was concentrated on the spray injection, mixing, combustion as well as bowl aerodynamics only a sector mesh was employed for the calculations. A DoE procedure was also used for this simulation work in order to minimize the number of simulation runs and at the same time maintaining the accuracy required assessing the influences of different bowl geometry, spray and intake air motion parameters.

In this study, an investigation was made on a heavy duty diesel engine using both conventional diesel combustion mode and a partially premixed combustion (PPC) mode. A segment mesh was built up and modeled using the commercial CFD code AVL FIRE, where only the closed volume cycle, between IVC and EVO, was modeled. Both combustion modes were validated using experimental data, before a number of heat flux boundary conditions were applied. These conditions were used to evaluate the engine response in terms of engine performance and emission levels for the different percentage of heat rejection. The engine performance was measured in terms of specific fuel consumption and estimated power output, while the calculated net soot and accumulated NOx mass fractions were used for comparing the emission levels. The results showed improved efficiency for both combustion types, but only the PPC combustion mode managed that without increasing the production of NOx emissions severely.