An Experimental Facility for Rapid Testing of SCR Systems

Abstract

Urea-SCR (selective catalytic reduction) has become the principal technology used to lower NOx emissions in automotive compression ignition engines. Although the technology is well known and developed, the stricter emissions� limits force engineers to implement new approaches to reduce warm-up time and improve the mixing process of the urea-water solution with the exhaust gases while avoiding a solid deposit formation. The exhaust system�s design is optimized using 3D numerical methods, but the validation of the design�s performance requires prototype testing on an engine dynamometer, where it is difficult to decouple and adjust the exhaust gas composition and temperature as in the numerical model; and thus it is problematic to verify the model. In this study we propose an experimental facility for rapid testing of SCR systems in simulated and precisely controlled engine-relevant conditions. The experimental set-up presented here uses heated atmospheric air with an addition of nitrogen oxides to simulate exhaust gases. Several parameters can be studied: the SCR�s overall NOx reduction, NH3 distribution, pressure drops and urea deposit formation. In this study we focus on the NH3 uniformity index at the inlet to the catalyst, which is not measured directly. In the set-up discussed here, the concentration of nitrogen oxides and ammonia is measured at the outlet of the catalyst. As the catalyst�s channels are parallel and the concentration of nitrogen oxides at the inlet is known, the ammonia distribution at the inlet can be calculated. In order to verify the measurement, we compared the experimental results with numerical simulations performed for the same conditions. The verification was done for different operating points to avoid any influence of specific conditions on the results. The experimental set-up and numerical model gave comparable results, which suggests that the set-up can be used for fast verification of the prototype�s performance.