分子筛型SCR对车用柴油机排放改善的试验研究

摘要

The combination of DOC and SCR aftertreatment system was widely used for commercial diesel engine to meet National Ⅳ and Ⅴ emission regulations.Different kinds of SCR have different influences on the final exhaust emissions significantly.The ESC and ETC tests are carried out to research the exhaust emission on a 2.8 L diesel engine with a vanadium-based SCR catalyst.The results show that NOx and PM emissions of molecular sieve SCR in ETC improve by 19% and 33% respectively compared with vanadium-based SCR.The NOx catalytic conversion efficiency of molecular sieve SCR is obviously higher than that of vanadium-based SCR under low exhaust temperature or large exhaust flow rate conditions.However, using the molecular sieve SCR, the particulate number is 7% more than that of vanadium-based SCR and the large particle matter is easily broken up into different small particle matter.Both kinds of SCR catalysts can reduce CO and HC emissions by up to 20%.%商用车柴油机多采用DOC+SCR的后处理系统来满足国Ⅳ、国Ⅴ排放标准的要求,而不同类型SCR的催化特性对最终污染物排放影响也不同.试验获取了一支铜基分子筛型SCR,基于1台2.8 L柴油机和一支钒基SCR,运行了车用柴油机稳态循环(ESC)和瞬态排放循环(ETC),研究并分析了其对柴油机污染物的减排特性.结果表明,相较于钒基SCR,运行ETC循环时分子筛型SCR对发动机NOx和PM排放的减排效率分别提升19%和33%;分子筛型SCR对NOx的低温转化效率更高,且由于对排气流量不敏感,在高空速工况下其转化效率显著高于钒基SCR;分子筛型SCR对颗粒物个数的减排效率弱于钒基SCR,达7%以上,容易将大质量颗粒物分解为小质量颗粒物;两种SCR均对CO和HC具有一定的减排效果,减排率可达20%左右.