柴油机后处理系统对细颗粒物排放特性的影响研究

Influence of Diesel Engine Aftertreatment System on Fine Particulate Matter Emission Characteristics

为研究柴油机细颗粒物排放特性,选取一台搭配SCR(selective catalytic reduction)后处理系统的国六重型柴油发动机进行世界统一瞬态循环WHTC(word harmonized transient cycle)测试。为获取对比数据,分别在原排、DPF(diesel particulate filter)后、尾排3个位置获取PN_(10)和PN_(23)细颗粒物数据。基于PN_(10)和PN_(23)排放特性,搭建紧耦合ccSCR(close coupling selective catalytic reduction)后处理系统,探究后处理系统对PN_(10)和PN_(23)颗粒物排放的影响。试验结果表明:尾排细颗粒物排放量随着尿素喷射量和SCR入口温度的提升而增加,其中PN_(10)增加趋势比PN_(23)更明显。粒径为10~23 nm细颗粒物占比与温度同样为正向关系,温度为200℃时占总粒径的55%,240~280℃时占比达到75%,280℃以上时占比超过80%。ccSCR与SCR相比,稳态工况下PN_(10)与PN_(23)排放均下降50%~80%;瞬态WHTC循环下,ccSCR的PN_(10)和PN_(23)排放分别为1.61×10^(11),2.92×10^(10)个/(kW·h),对比SCR的PN_(10)和PN_(23)排放分别下降57.2%和62.3%。

Based on a China VI heavy-duty diesel engine equipped with selective catalytic reduction(SCR)aftertreatment system,the fine particulate matter emission characteristics of diesel engine were tested according to WHTC.To obtain comparative data,particle numbers PN_(10)and PN_(23)were obtained from the raw exhaust pipe,the rear pipe of diesel particulate filter(DPF),and the end pipe.Based on the results of PN_(10)and PN_(23)emissions,a close coupling selective catalytic reduction(ccSCR)aftertreatment system was constructed to investigate the influence of aftertreatment system on emission characteristics of PN_(10)and PN_(23).The test results show that the fine particulate matter emissions in end pipe increase with the urea injection volume and the SCR inlet temperature,and the increasing trend for PN_(10)is more obvious than that for PN_(23).The percentage for fine particulate matters of 10~23 nm size is also positively related to temperature,which accounts for 55%of total particle size at 200℃,75%at most between 240~280℃,and higher than 80%beyond 280℃.The comparison between the ccSCR route and the SCR route reveals that the ccSCR route can reduce PN_(10)and PN_(23)of steady state operating conditions by 50%~80%at each point.PN_(10)and PN_(23)emissions of transient WHTC cycle are 1.61×10^(11)and 2.92×10^(10)#/(kW·h)respectively,which reduce by 57.2%and 62.3%compared to the SCR route.