基于国Ⅵ标准柴油机 SCR 排放标定试验研究分析

文章为了检验选择性催化还原(selective catalytic reduction, SCR)系统在尾气排放中的各方面性能,对柴油机进行AVL后处理台架搭建测试,在集成式后处理系统柴油机氧化催化器(diesel oxidation catalyst, DOC)+柴油颗粒捕集器(diesel particulate filter, DPF)+SCR+氨氧化催化器(ammonia slip catalyst, ASC)的技术路线下,完成系统裸排、背压、WHTC排放、尿素结晶、传感器校对、开闭环标定等一系列测试;研究后处理系统对柴油机造成的排放阻力和温度损失,讨论氮氧化物 $ \left(NO_{x}\right) $的转化率与氨 $ \left(NH_{3}\right) $存储量之间的关系以及两者关系在不同排气流量和不同温度下的变化规律,并研究SCR系统对比柴油机原排所起的功效。结果表明: $ NO_{x} $的转化效率随着 $ NH_{3} $存储量增大而逐渐变大,随着排气流量增大呈负指数增长,在一定温度下随温度呈正指数增长,超过一定温度后受催化剂材料约束;SCR系统造成的温损和压阻均在可接受范围内,且对 $ NO_{x} $有可观的转化效率,在混合器改进后效率有所提升,可满足国VI排放标准。

In order to test the performance of selective catalytic reduction (SCR) system in exhaust emissions, a diesel engine AVL post-treatment bench was built. Under the technical route of integrated post-treatment system with diesel oxidation catalyst (DOC) + diesel particulate filter (DPF) + SCR + ammonia slip catalyst (ASC), a series of tests were completed, such as system bare discharge, back pressure, WHTC discharge, urea crystallization, sensor calibration, open and closed loop calibration, etc. The emission resistance and temperature loss of diesel engine caused by the post-treatment system were explored, and the relationship between $ NO_{x} $ conversion efficiency and ammonia ( $ NH_{3} $) storage was proved. The relationship between the SCR system and diesel engine exhaust was further studied with different exhaust flow rate and different temperature. The results show that the $ NO_{x} $ conversion efficiency increases gradually with the increase of $ NH_{3} $ storage, increases negatively with the increase of exhaust flow rate, and increases positively with the temperature at a certain temperature. And it is also constrained by the catalyst material exceeding a certain temperature. The temperature loss and pressure resistance caused by the SCR system are within the acceptable range, and the conversion efficiency of $ NO_{x} $ is considerable. After the improvement of the mixer, the efficiency is improved and can meet the China Vl emission standard.