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Removal of NOx from lean Diesel exhaust can be achieved by the use of selective catalytic reduction technology. The supplied reductant is often ammonia, either as urea or as ammonia gas released from a storage medium. Experiments have been carried out on an engine test rig run to steady state conditions using NOx composed mainly of NO, with ammonia gas as the reductant. This was essentially a 1D study because a long 10 degree diffuser was used to provide uniform temperature and velocity profile to the SCR catalyst brick in the test exhaust system. Tuning of the standard reaction, the NO SCR reaction, in a kinetic scheme from the literature and adjustment of the ammonia adsorption kinetics achieved improved agreement between the measurements and CFD simulations. This was carried out for studies at exhaust gas temperatures between 200 and 300 °C. The effect of diffuser geometry upstream of the SCR catalyst on NOx conversion was then investigated experimentally using a 180 degree sudden expansion as a 3D diffuser. These were also steady state studies with the exhaust NOx composed mostly of NO. The SCR brick was short, 45 mm in length, to provide a rigorous test of the kinetics. Observed NOx conversion profiles for ammonia supplied in quantities ranging from deficient to excess showed that the combined influence of temperature and velocity profiles upstream of the SCR was apparent in this 3D case. 2D axially symmetric CFD simulations have been carried out to model the 3D case and the predictions are discussed and compared with engine test data in this paper. INTRODUCTION Removal of NOx from lean Diesel exhaust can be achieved by the use of selective catalytic reduction technology and this is one of the methods of choice to achieve the Euro 6 targets for passenger cars by 2014. The supplied reductant is often ammonia, supplied either as an aqueous urea spray or as ammonia gas released from a storage medium. Experiments have been carried out on an engine test rig run to steady state conditions using NOx composed mainly of NO, with ammonia gas as the reductant. The engine was run without EGR so that significant and easily measurable levels of NOx were produced. A series of experiments has been carried out aimed at providing a data set for validation of a CFD model. Initial experiments under 1D conditions have provided data that have enabled a kinetic scheme to be tested and modified. This data was obtained using a novel engine test configuration that removed uncertainty with regards to the effect of non-uniformity in the flow field on the kinetics. In real exhaust systems on passenger cars, packaging constraints determine the design of the exhaust and this is often non-ideal so that a mal-distributed flow field is supplied to the SCR catalyst. In a second set of experiments discussed in this paper the flow was supplied to the catalyst via a 180 ° diffuser. This gave a mal-distributed axially symmetric 3D flow field for experimental purposes, and therefore provided a test of the model's capability with non-uniform flow. A CFD model has been developed based on kinetics that are available in the open literature. The kinetic scheme of Olsson et al. [1] has been used because it is a complete scheme, for a form of copper zeolite, and it is a simple scheme that uses Tuning the Standard SCR Reaction Kinetics to Model NO Conversion in a Diesel Engine Exhaust SCR Catalyst System Under Steady State Conditions in 1D and 3D Geometries Using Ammonia Gas as the Reductant 2012-01-1636 Published 09/10/2012 S. F. Benjamin, M. Gall and C. A. Roberts Coventry University, UK Copyright © 2012 SAE International doi:10.4271/2012-01-1636 THIS DOCUMENT IS PROTECTED BY U.S. AND INTERNATIONAL COPYRIGHT. It may not be reproduced, stored in a retrieval system, distributed or transmitted, in whole or in part, in any form or by any means. Downloaded from SAE International by Stephen Benjamin, Wednesday, July 18, 2012 05:03:47 AM

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Tuning the Standard SCR Reaction Kinetics to Model NO Conversion in a Diesel Engine Exhaust SCR Catalyst System Under Steady State Conditions in 1D and 3D Geometries Using Ammonia Gas as the Reductant