Influence of Urea-SCR system parameters on NOx conversion rate and liquid film

Nitrogen oxides conversion rate, ammonia slip, and urea crystallization are major problems in the application of the selective catalytic reduction systems of diesel engine. Based on the bench test, the selective catalytic reduction system model was proposed with the code AVL Fire to investigate these problems. The research results indicate that the increasing ammonia/nitrogen oxides feed ratio contributes to reduce the emission of nitrogen oxides. However, the excessive supply of urea-water solution causes the increase of ammonia slip and liquid film. Nitrogen oxides conversion rate reaches a higher level when the exhaust temperature is 450°C. The performance of the system goes worse as the exhaust flow rate increases. The location of the mixer has a huge impact on the flow streamline. The formation of the liquid film and the interaction between the pipe and the droplets depend on the flow streamline. The mixer location is optimized to reduce the quantity of ammonia slip and liquid film based on the numerical study.