尿素SCRにおける還元剤噴霧の分散性・分解過程に関する検討

抄録

 Urea SCR (Selective Catalytic Reduction) is a promising technique to reduce NOx emissions from diesel engines. In order to apply Urea SCR with high NOx reduction efficiencies, it is necessary to supply the reductant to the exhaust gas for it to be uniformly distributed over the cross section of the exhaust pipe. In addition, it is desirable that the supplied reductant be converted into NH3 as much as possible within the distance between the injection nozzle of the reductant and the inlet of catalyst. In line with these considerations, the present study investigated how spray characteristics influence the spray distribution in space and the evaporation and the thermolysis process of urea water droplet. A simplified 2-D spray model considering droplet size, injection angle, droplet size distribution and flow distribution was proposed. Calculation results revealed that spraying the reductant with smaller sized droplets could be effective in promoting the quick conversion of urea-water solution into NH₃. Moreover, it was found that a hollow cone spray whose droplet size distribution had a flat shape could lead to high uniformity of the reductant over the cross section of the exhaust pipe.