Numerical Simulation On Urea-SCR Catalytic Convertor And Optimization On Its Structural Parameters

The Urea-SCR is presently considered the most promising technique for the removal of nitrogen oxides from the exhaust of heavy-duty diesel vehicles. The catalytic converter is an important part of the SCR system. Its structures have significant impact on SCR performances. Beacause of the restrictive relation between conversion ratio of NOx and pressure loss, the structural design and selection are hard to satisfy both requirement at the same time.Ror this reason, the numerical simulation on the influences of structural parameters to conversion ratio of NOx and small pressure loss and structural parameters optimization are performed in this paper. The main research content and innovation are as follows.(1) Based on the reaction mechanism of SCR and mathematical model of catalytic convertor, the influences of structural parameters to conversion ratio of NOx and pressure loss are researched. The results show that larger cross-sectional area,shorter length and thinner wall thichness are benefit to the SCR performances. But the influences of length, cell per square inch and washcoat thickness are more complicated.(2) The quadrtic polynomial model and Kriging model is established, based on the samples of parameters which got through Latin Hypercube method. And then the precision of both model are calculated and compared.The results show that he precision of Kriging model is higher.It can be used to replace the numerical simulation.(3) Taking high conversion ratio of NOx and small pressure loss as the optimization goal, with monolith volume, length, cell per square inch, wall thickness and washcoat thickness as design variables, the optimization is solved by NSGA-Ⅱusing Kriging model as the approximate model. Validated by numerical simulation, the conversion ratio of NOx was more than95%and pressure loss is lower than1kPa.