Development and application of a model for a NO, storage and reduction catalyst

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 NOx storage and reduction catalyst as part of the simulation environment. A heterogeneous, spatially ID, 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 (HQ and hydrogen, water gas shift and steam reforming reactions, NO/NO2 transformation, oxygen storage, and NO, storage and reduction by CO, H-2 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 NO., storage and reduction catalyst. The NOx 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. (c) 2007 Elsevier Ltd. All rights reserved.