柴油机SCR尿素喷射方式研究

鉴于柴油机选择性催化还原系统尿素喷射特性与氮氧（NO_x）转化效率密切相关，本文搭建SCR系统小样试验台，NO和NH₃作为主要试验用气，研究了不同氨氮比和不同温度条件下V₂O₅-WO₃/TiO₂催化剂的氨存储、氨泄漏以及NO_x转化效率的影响.结果表明:氨氮比越大，氨存储量的建立时间越短，NO_x转化效率的提升就越快；氨氮比为0.22时，15 s内NO_x转化效率从0增大到4.3%；当氨氮比为0.30时，15 s内NO_x转化效率从0增大到8.7%；随着氨氮比的增大氨泄漏会提前出现；氨氮比先大后小的喷射方法有利于改善NO_x转化效率.采用氨氮比先大后小的喷射方法，进行ETC标准循环测试，NO_x比排放从8.26 g/（kW·h）减少到1.91 g/（kW·h），NH₃泄漏均值为5×10-6，峰值为18×10-6，满足国V排放法规要求. 

Research on SCR Urea Injection Method of Diesel Engine

The characteristics of urea injection and NO_x conversion efficiency are closely related.A SCR test bench was built based on V₂O₅-WO₃/TiO₂ catalyst,and NO,NH₃ and O₂ feed streams were dosed by mass flow controllers.The effect of normalized stoichiometric ratio (NSR) and catalyst temperature on ammonia storage,ammonia slip and NO_x conversion efficiency was studied.The results show that the influence of NSR and temperature on ammonia storage,ammonia slip and NO_x conversion efficiency is obvious.The time of ammonia storage will be shorten with the increase of NSR,then the improving speed of NO_x conversion efficiency is high.The NSR fix 2.2,the NO_x reduction efficiency increase from 0 to 4.3% within 15 s,and the NO_x reduction efficiency increase from 0 to 8.7% within 15 s when NSR set 3.0.The time of ammonia slip and ammonia storage are closely related,the time of ammonia slip will be shorten with the increase of NSR.The method of NSR from larger to the smaller can increase ammonia storage rate and optimize NO_x conversion efficiency.Using this injection method to carry out the European transient cycle(ETC) test,the brake specific emission of NO_x reduce from 8.26 g/(kW·h) to 1.91 g/(kW·h),and the average and peak value of ammonia are 5×10^-6 and 18×10^-6,the NO_x can reach the National V emission regulations.