The stringent limits of emission standards require advanced emission control technologies to be used in modern on and off highway diesel engines. They include both in-cylinder and aftertreatment measures where the latter now have become almost mandatory. Selective catalytic reduction aftertreatment systems are widely used for nitrogen oxide (NOX) conversion in exhaust gases into harmless N2. To reduce time and costs, at the design stage of SCR systems numerical modelling is applied. Mathematical models and methods providing high prediction accuracy with and acceptable level of computational efforts are required. In this work an approach for complete simulation of SCR systems based on the coupling of commercial CFD software with developed multichannel 1D catalyst model is presented. The first one is used to carefully describe processes occurring upstream in the catalytic converter, particularly, during urea water solution injection and flow mixing. As a result, the distributions of flow parameters at catalyst inlet are derived. They are subsequently imported as boundary conditions into a developed multichannel catalyst model that allows one to take them into account when calculating NOx conversion efficiency. Based on the proposed approach a SCR system was simulated. The effect of non-uniform distributions of NH3 concentration and the gas flow velocity at the catalyst inlet on its performance was investigated. It has been shown that they have a great impact on NOX conversion and should be taken into account during the catalyst modelling.

One of the key issues of the modern engine development is to comply with today’s stringent emission standards. It forces the manufacturers to enhance in-engine and after treatment emission reduction technologies continuously. The selective catalytic reduction (SCR) is still the most effective technique for nitrogen oxides removal from exhaust gases of vehicles with diesel engines. Numerical modelling is widely used for SCR systems development and assessment. In this paper, a simplified one-dimensional numerical model of diesel SCR catalyst, which was implemented in Matlab, is described. The algorithm for automatic mesh generation describing real cross-section geometry of the catalyst block and the calculation procedure allowing to take into account non-uniform distribution of the gas flow parameters at the catalyst inlet are presented. Model was validated by the experimental data available in the literature. Numerical simulations for the full-scale modern SCR catalyst were carried out. The effect of the gas velocity non-uniformity at the catalyst inlet on the overall NOx reduction efficiency was evaluated.

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Selective catalytic reduction systems are widely applied as a NOX emission control technology in modern onand off highway diesel engines. Considering the stringent limits of emission standards, they should ensure high rates of conversion efficiency. To achieve that at the design stage numerical modelling is used to optimize physical and chemical processes. New mathematical models and methods that can provide the reduction of calculation time and related costs keeping the acceptable level of prediction accuracy are desired. In this study a methodology for calculating SCR systems based on the use both of CFD models and simplified catalyst models are presented. The capabilities of the suggested numerical approach were demonstrated during the simulations of a SCR system where the influence of UWS injection angle on NOX reduction efficiency was investigated.

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