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Asymmetric particulate filters (PF), where the inlet channel is wider than the outlet channel, are commonly used because of their greater ash capacity. Surprisingly, very few models for asymmetric PFs have been published. This paper considers how to model the soot cake in octo-square asymmetric PFs. Some previous studies have neglected the octahedral shape of the inlet channel and instead assumed that the inlet channels were square. As the correct approach for modelling the soot cake is not obvious, three options are considered. The calculation of soot-loaded channel perimeter and hydraulic diameter (which are important for heat and mass transfer), soot thickness and backpressure as a function of soot loading are given for each geometry. In option 1, the shape of the soot-loaded channel is assumed to be geometrically similar to the soot-free channel.

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.

A one-dimensional numerical model for a Cu-zeolite SCR catalyst has been developed. The model is based on kinetics developed from laboratory microreactor data for the various NH₃-NOX reactions, as well as for NH₃ oxidation. The kinetic scheme used is discussed and evidence for it presented. The model is capable of predicting the conversion of NO and NO₂, NH₃ slip and the formation of N₂O, as well as effects associated with NH₃ storage and desorption. To obtain a good prediction of catalyst temperature during cold start tests, it was found necessary to include storage and desorption of H₂O in the model; storage of H₂O is associated with a sizable exotherm and the subsequent desorption of this water produces a correspondingly large endotherm.

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.