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This paper will review several different emission control systems for heavy duty diesel (HDD) applications aimed at future legislations. The focus will be on the (DOC+CSF+SCR+ASC) configuration. As of today, various SCR technologies are used on commercial vehicles around the globe. Moving beyond EuroVI/US10 emission levels, both fuel consumption savings and higher catalyst system efficiency are required. Therefore, significant system optimization has to be considered. Examples of this include: catalyst development, optimized thermal management, advanced urea dosing calibrations, and optimized SCR inlet NO:NO2 ratios. The aim of this paper is to provide a thorough system screening using a range of advanced SCR technologies, where the pros and cons from a system perspective will be discussed. Further optimization of selected systems will also be reviewed. The results suggest that current legislation requirements can be met for all SCR catalysts under investigation.

Sulphur poisoning and regeneration of NOx trap catalysts have been studied in synthetic exhausts and in an engine bench. Sulphur gradually poisoned the NOx storage sites in the axial direction of the NOx trap. During sulphur regenerations, hydrogen was found to be more efficient than carbon monoxide in removing the sulphur from the trap. The sulphur regeneration became more efficient the richer the environment (λ<1) and the higher the temperature (at least 600°C). H2S was found to be the main product during the sulphur regeneration. However, it was possible to reduce the H2S formation and instead produce more SO2 by running with lambda close to one or by pulsing lambda. Even if a relatively large amount of sulphur was removed from the NOx trap, these methods gave a much less efficient regeneration per sulphur atom removed than when running relatively rich constantly. Finally, a model that could explain this observation was proposed.

For a NOx trap catalyst to work properly, it is important that the times for the lean period and the rich spikes are correctly calculated in the engine management system (EMS). This paper deals with the development of a physically based NOx trap model for implementation in the EMS. The catalyst was divided into different segments (complete mixed cells) to correctly mimic the axial distribution of stored NOx and the axial temperature profile. Furthermore, the model included physical steps as adsorption, desorption, storage and release of NOx. The model also includes the storage and reduction of O2 and a simplified model of the heat release from the oxidation of the reductants. The model could successfully describe the process of storage and release in a short time interval. However, problems to describe the function of the NOx trap occurred after longer time in the vehicle because of inaccurate estimation of the input variables.