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With the introduction of stringent emission standards in the US in 2007 (Tier II Bin8, 5) an exhaust aftertreatment for NO x reduction is required for compliance with the emission regulations. A new approach consists in the synergetic combination of existing technologies NSC (NO x Storage Catalyst) and SCR (Selective Catalytic Reduction) with onboard generation of ammonia as the reducing agent for the SCR. It is shown in this work that the performance of the combined system exceeds those of each one considered separately, especially after ageing. The generation of ammonia is correlated to the ammonia selectivity during the regeneration of the NSC. The selectivity is primarily dependent on the temperature, A/F ratio (Air/Fuel) and the rich time. It is shown that the development of a suitable control strategy leads to a high level of NO x reduction under transient conditions in an FTP driving cycle. Due to the complexity and high development costs of current exhaust aftertreatment systems, modelling and simulation were identified as an important aspect in the development process. A system simulation tool named ExACT ( Exhaust Gas Aftertreatment Components Toolbox) developed at Daimler is presented. By using the simulation already at an early stage, specific development work can be carried out prior to the experimental work on an engine test bench. [ABSTRACT FROM AUTHOR]

Abstract: To fulfil future emission standards for diesel engines, combined after-treatment systems consisting of different catalyst technologies and particulate filters (DPF) are necessary. For designing and optimising the resulting systems of considerable complexity, a purely experimental approach is time and cost consuming. Therefore, effective simulation models for different catalyst technologies and DPF have been developed and integrated into a common simulation environment ExACT (Exhaust After-treatment Components Toolbox). A key issue is robustness and scalability of the models as the applications range from passenger cars to heavy-duty commercial vehicles. The publication focuses on the development and validation of a model for the storage and reduction catalyst as part of the simulation environment. A heterogeneous, spatially 1D, physically and chemically based mathematical model of the catalytic monolith has been developed. A global reaction kinetic approach has been chosen to describe reaction conversions on the washcoat surface. Twenty-two reactions are considered, describing the most important processes in the converter: oxidation of carbon monoxide, hydrocarbons (HC) and hydrogen, water gas shift and steam reforming reactions, transformation, oxygen storage, and storage and reduction by CO, and HC. Reaction kinetic parameters have been evaluated from a series of laboratory experiments. These have been performed to evaluate transient behaviour of a commercial storage and reduction catalyst. The storage dynamics and total storage capacity have been evaluated from isothermal adsorption experiments at different temperatures. To investigate the regeneration behaviour, periodic operation with variations of rich phase conditions (temperature and the inlet gas composition) has been applied. The model was validated with the data from passenger car dynamometer test bench and heavy-duty commercial vehicle engine test bench measurements. The results show the applicability of the model over this wide range in size and operating conditions, underlining the suitability of the chosen modelling approach to the requirements. Series of simulations have been carried out to study the effects of varying operation conditions on the converter performance and overall conversions. [Copyright &y& Elsevier]

Abstract: Dynamic simulation of the smart catalytic converter, proposed by Daimler AG, is presented. The smart catalytic converter combines NOx storage, on-board ammonia production and selective catalytic reduction (SCR) and functions in a dual-mode operation, alternating between lean burn and rich burn. It relies on intrinsic dynamic operation and synchronization of all units and its development demands a reliable dynamic simulator. A platform capable of simulating the dynamic behavior of multiple-unit aftertreatment system was developed based on COMSOL package. Predictive kinetic models were developed for NOx storage unit that includes ammonia formation function and for NH3-SCR unit. Using these kinetic models, two-unit smart catalytic converter was simulated on the developed simulator. The results of the simulator were validated using two-unit experimental data. The simulator was also employed to control and optimize the performance of smart catalytic converter. It was shown that the simulator is vital for optimization of lean and rich periods in order to ensure stable lean–rich cycles. [Copyright &y& Elsevier]