Experimental and numerical investigation on the urea-deposit formation at different severities in selective catalytic reduction systems

Complex Exhaust Aftertreatment System (EATS) designs with Selective Catalytic Reduction (SCR) system can suffer deposit problems due to the liquid film formation in critical regions. Experimentally validated numerical prediction methods can help detect these problematic areas to eliminate deposit formation problems in product development and ongoing product development stages of EATS. This study investigates the spray-wall interaction, the liquid film formation at different severities, the liquid film evaporation by injecting Urea Water Solution (UWS) into an impingement plate in a non-uniform flow medium under different operating conditions, experimentally and numerically. The experimental set-up includes a backward facing step flow through an impingement plate. During experiments, after a specified time, the UWS injection was stopped, and a non-uniform liquid film evaporation due to non-uniform flow was also investigated, separately. Experimental and finite volume based numerical studies show that the liquid film layer formed in the stagnant flow regions has greater risks in terms of deposit formation than the other regions in an EATS. The wall cooling occurred mostly on the spray footprint portion of the impingement plate due to the liquid film formation during UWS injection, the liquid film in this part was rapidly evaporated after UWS injection was stopped and no deposit formation was observed in this part for each case under study. Experimental and numerical studies show that deposit formation occurred in the stagnant regions where the liquid film did not evaporate. The numerical results agree well with the experimental results and they demonstrate the predictive capability of the numerical model for the deposit formation.