DOC/SCR组合方式及关键参数对NOx转化效率的影响

在柴油机中等转速下，通过改变柴油机氧化催化器（DOC）和选择性催化还原催化器（SCR）的组合方式，以及改变喷嘴位置、两级SCR载体间距和催化剂成分，获得各种条件下的NOx转化效率，为优化组合方式和关键参数提供重要数据支撑。结果表明：增加尿素喷嘴与SCR入口的相对距离，NOx转化效率升高，喷嘴距离为45 cm较为合适；载体间距的增大，NOx转化效率先略有升高，后急剧下降，间距为2 cm较为合适；载体体积增大，NOx转化效率明显升高，在满足目标NOx转化效率的前提下，载体体积不宜过大；DOC与SCR的组合方式对NOx转化效率具有明显差异，前置DOC能够有效的提高NOx转化效率；在催化条件下，NOx转化效率由高到低排序为：铜基 > 钒基 > 铁基；对于复合催化剂而言，铜铁复合基>铁铜复合基。

Influence of combinations and key parameters on NOx conversion efficiency in DOC/SCR system

Based on the condition of medium speed of diesel engine, the NOx conversion efficiency were obtained by changing the combination modes between DOC and SCR components, varying the position of the nozzle, the intervals of two SCR substrates and the catalyst composition, in order to provide important data support for optimizing the combination mode and the key parameters. The results showed that increasing the relative distance between the urea's nozzle and the SCR substrate, NOx conversion efficiency increased, and the distance of 45 cm was the optimized distance. Increasing the interval of the SCR substrates, NOx conversion efficiency increased firstly and then decreased sharply, and the interval of 2 cm was the optimized distance. Increasing the substrate volume, and NOx conversion efficiency increased significantly, while the substrate volume was not suitable to be larger after meeting the target of NOx conversion efficiency. The NOx conversion efficiency could be significantly affected by the changing the combination mode between DOC and SCR substrate, and the pre-DOC can effectively improve the NOx conversion efficiency. Under catalytic conditions, the descending order of NOx conversion efficiency was:Copper-based > Vanadium-based > Iron-based;under the composite catalysts condition, the descending order was:Copper-Iron complex based > Iron-Copper complex based.