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Future heavy-duty diesel (HDD) engines are designed to have higher engine out NOx, for improved fuel economy, while reduction of the emission control technology footprint is also desired. Consequently, higher NOx reduction across compact emission control systems is required. Selective catalytic reduction (SCR) catalyst coating combined with a wall flow particulate filter (SCRF®1) is a technology that enables abatement of NOx emissions in addition to oxidation of soot from diesel engine exhausts. Vanadia based-SCR is well known for NOx reduction and is active for hydrocarbon (HC) and particulate matter (PM) oxidation. This dual functionality (oxidation and reduction reactions) of the V.SCR catalysts plus the filtration achieved by the filter substrate can help certain diesel engine applications achieve the legislative limits with a reduced packaging volume.

In recent years magnetic resonance imaging (MRI) has been shown to be an attractive method for fluid flow visualization. In this work, we show how MRI velocimetry techniques can be used to non-invasively investigate and visualize the hydrodynamics of exhaust gas in a diesel particulate filter (DPF), both when clean and after loading with diesel engine exhaust particulate matter. The measurements have been used to directly measure the gas flow in the inlet and outlet channels of the DPF, both axial profiles along the length and profiles across the channel diameter. Further, from this information we show that it is possible to indirectly ascertain the superficial wall-flow gas velocity and the soot loading profiles along the filter channel length.

Two approaches were adopted to study soot oxidation by NO₂; firstly microreactor tests were performed on soot produced by a soot generator over a range of NO₂ concentrations and temperatures. This enabled measurement to be made under well-controlled conditions. Secondly, soot oxidation measurements were made on an engine bench to obtain data under more realistic, if less controlled, conditions. In the microreactor work NO₂ consumption by soot oxidation and the selectivity of the soot oxidation to CO and CO₂ were measured. The latter was found to vary only slightly with temperature and to be independent of NO₂ concentration. By modeling this data using a 1-dimensional model, rate equations for the soot-NO₂ reaction were determined. These were then tested against the engine data. The soot used in this study was characterized by thermogravimetric analysis, N₂ physisorption and transmission electron microscopy.

The aftertreatment challenge in the non-road market is making the same system work and fit not just in one machine, but in hundreds of different machines, some of which can be used for many different purposes. This huge diversity of applications and the relatively small unit numbers for each application, coupled with the rapid introduction of new standards and the very high performance needed from the engines and machines, requires a sophisticated approach to product development. Furthermore, as emissions requirements become ever more stringent, designing a system to meet the legislation subject to packaging and cost constraints becomes progressively more difficult. This is further exacerbated by increasing system complexity, where more than one technology may be required to control all the legislated pollutants and/or an active control strategy is involved. Also a very high degree of component integration is required.