A quasi-two-dimensional model for describing regeneration events in the continuous regeneration-diesel particulate filter (CR-DPF) is presented, in which computational grids of the diesel particulate filter are provided in the discretization of physical domains in the axial and wall thickness directions. In the model, gas and particle flows, pressures, temperatures, and soot distributions in the inlet/outlet channels and wall, together with both continuous regeneration and active regeneration reactions, are considered. Rate constants of the chemical reactions are calibrated using results of soot oxidation tests in a mini flow reactor and engine bench tests. The distributions of loaded soot mass, filter temperature, and pressure during both continuous and active regenerations have been analysed using this model. The analysis shows that the predicted pressure drop across the diesel particulate filter is in good agreement with the data obtained in an engine bench test. The processes of soot loading including the deep wall filtration phase and the subsequent soot cake layer formation phase have been successfully predicted by calculation based on the model. It is also shown that soot accumulates mainly in the upstream area in the filter wall and at the front and rear parts in the axial direction when the soot accumulation amount is small. The reason for this uneven accumulation is presumed to result from the large pressure differences between the inlet and outlet channels at these locations.
Many heavy-duty commercial vehicles are now equipped with urea-selective catalytic reduction (SCR) systems, which can reduce NO x emissions sufficiently to meet the requirements of legislation such as Japan's New Long-term Diesel Emissions Regulations. However, in order to meet even stricter exhaust emissions regulations (and fuel consumption standards) due to be imposed in many parts of the world in the near future, urea-SCR systems with greater catalytic efficiency combined with diesel particulate filters (DPFs) will be needed. Therefore, in the study presented here the scope for enhancing the efficiency of a urea-SCR system was explored by optimizing the urea dosing system and injection strategies, and the gas flow in the exhaust pipe. However, since improving the catalysis parameters could have the greatest overall effect on conversion efficiency, work focused on modifying the catalyst materials to increase their adsorption capacity for the NH 3 reducing agent, and thus increase the collision frequency between NO x and NH 3 absorbed on the surface of the catalyst. In addition, the oxidation parameters of the oxidation catalyst were optimized, which enhanced the NO x conversion efficiency of the system, not only in a steady cycle but also in a transient cycle. Following these adjustments, a DPF-plus-SCR system with the new catalytic material delivered 90 per cent conversions of NO x and particulate matter to N 2 and CO 2 respectively, in the JE05 test cycle.In addition, a new concept, a miniaturized 'urea-SCR with DPF function system' was proposed and tested, which delivered 90 per cent NO x conversion rates and 90 per cent reductions in particulate matter emissions in the JE05 test cycle.
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