Effects of temperature and turbulence on characteristics and morphological variations of urea deposits in urea-SCR systems. A study using SEM and XRD

The Urea-Water Solution (UWS) is sprayed into the diesel engine exhaust gases of automobiles in order to generate reducing agent NH₃ in Urea-Selective Catalytic Reduction (SCR) systems adopted to diesel engines of modern automobiles to mitigate oxides of nitrogen (NO_x). Although it is a very efficient technique, deposit formation at low temperatures is a major concern. The growth of deposits not only reduces the efficiency of NH₃ generation but also generates non-depleting complex compounds. The temperature of exhaust gas and the Reynolds number of the flow have significant effects on this deposit formation. In this study, the compositional variation and the crystallinity of the deposits are investigated using Energy Dispersive X-ray Spectroscopy (EDX) and X-ray diffraction analysis (XRD) with respect to variation in temperature and flow rate at the preliminary stage. The elemental analysis is done for different samples using EDX that indicates urea as a major constituent in most of the deposits for a temperature range of 423-523K for overdosed conditions. The XRD results indicate the evolution of various traces of urea-related compounds at different temperatures and for turbulent flow of Reynolds Number 9000-32000. Using Scanning Electron Microscopy (SEM), the morphological variations of the deposits have been studied for various temperature and flow conditions. The comparative study of the morphology of deposits during the initial stages of deposit formation indicates an extent to which growth can occur and probable areas of deposits for further growth.