CFD Analysis in Control of Urea Injection for an Automotive SCR Application

Abstract

Selective Catalytic Reduction (SCR) has proven to be the front runner for the removal of nitrogen oxides (NOX) from exhaust gas. BS-VI emission regulations present a challenge from the control point of view, so as to achieve high NOx conversion while keeping the ammonia slip under control. This thesis mainly focus upon finding the internal mechanism occurred inside the SCR. The behaviour of urea-droplet inside the SCR are investigated through CFD Ansys Simulations. The flow uniformity , temperature dependency of deposits, evaporation tendency of the mixture near the substrate are also found. The effect of insulation of convertor cone, mass flow rate of exhaust and inlet cone length, turbulent and swirling flow, effect of different geometries in injection system, effect of different temperature ranges are further studied. Various simulations are also performed in both transient and steady states in order to find the injectors and sprays directions, the deposits at wall formation, and evaporation tendency are also investigated. With the help of above results we can predict the parameters such as reqiured mass flow rate of emissions, position of injection of urea spray, time for the spray etc, that can optimize the Exhaust system and provides less harmful atmosphere. These results are validated experimentally by the exhaust system suppliers for heavy commercial vehicles.