Simulation Research Of SCR Heat Characteristics

SCR(selective catalytic reduction) system is continuously being analyzed by many researchers worldwide on various concerns due to the stringent nitrogen oxides(NOx) emissions legislation for heavy-duty diesel engines. Urea-SCR includes AdBlue(DEF) as urea source, which subsequently decomposes to NH3(ammonia) being the reducing agent. An accurate and well integrated urea dosing mechanism and SCR temperature are the key factors for the performance of urea-SCR system, as an adequate urea supply will ensure the required availability of reducing agent on the catalyst surface whereas the excess and lacking of the same will result increase in ammonia slip and decrease of system’s deNOx performance, respectively. On other hand, the urea decomposition rate is sensitive to a specific range of temperature. This particular research has been directed to investigate the SCR heat characteristics i.e. temperature of the SCR system for NOx control of diesel engine. The main objective of the study was to to confirm that whether the appropriate temperature is attained for occurrence of urea based catalytic reduction or otherwise and how the system performs on that prescribed temperature range.In order to investigate SCR performance on the basis of deNOx efficiency on different temperature conditions, a CFD model of SCR System(SCR reactor) has been developed on the principles of mass, energy and momentum conservation equations in AVL FIRE ? 2014 by incorporating detailed SCR chemistry and concerned reaction kinetics. On the basis of SCR reaction kinetics, the deNOx efficiency and flow temperature through SCR system has been simulated on different conditions of SCR temperature and with varying concentration of NOx. The model has shown an excellent efficiency on all conditions i.e. the model offered 80% to 95% NOx conversion efficiency. However, the optimum performance of the system has been observed in the temperature range of 250-450oC.To validate the accuracy of the simulated model, simulation results have been authenticated by conducting emission cycle test of a diesel engine equipped with SCR system of similar specification where test results have shown good agreement to the simulation results. The results of CFD model and engine test have also confirmed that SCR can provide excellent deNOx efficiency at the temperature range of 250-450oC. The level of NOx reduction has proven that SCR is the best available technique to comply with the laid down emission legislation and regulating standards.