Numerical Investigation of the Flow across the Static Mixer with the Injection of Urea-water-solution for Automotive Scr-system

Selective catalytic reduction (SCR) technique has been widely used for the abatement of the nitrogen oxides (NOX) emissions from diesel engines for decades. The urea-water solution (UWS) spray over the exhaust gases of diesel engines is one of the important methods used for exhaust after-treatment systems. The urea water solution is extensively injected in the upstream of the catalyst to generate the evaporated product ammonia and thereby, employed in the SCR catalyst as a reductant of NOX. In this work, to comprehend the significance of ammonia, the urea-water solution is modelled to investigate the phenomenon of distribution of ammonia at the entrance of the SCR catalyst system. Three types of mixers are considered which are installed in the upstream regime of the domain and the effect of each mixer is addressed by the pressure drop over the entire domain. This study has also focused towards the mixing enhancement of the evaporated ammonia and exhaust gas stream by examining the effectiveness of mixer with the uniformity index chart. Thermolysis reactions of the evaporated urea are solved as volumetric reactions using finite rate/eddy dissipation model. The evaporation of urea is simulated using convection-diffusion controlled model where the urea decomposes to ammonia needed for SCR system.