重型柴油机WHTC循环低温冷起动排放特性研究

Cold Start Emission Characteristics of Heavy-Duty Diesel Engine under WHTC Cycle

基于满足国Ⅵb阶段排放标准的柴油发动机,在配备低温环境仓的发动机台架上开展WHTC循环排放测试。设置多个环境温度,对比CO,HC,NO_(x),PN及PM的比排放结果。分析环境温度、中冷后温度、排气温度与排气污染物的关系以及WHTC循环3个阶段不同环境温度下CO,HC,NO_(x)和PN排放特性的差异。结果发现:环境温度降低,NO_(x),CO和HC比排放值逐渐增加,PN比排放值总体减少,PM比排放值先减少后升高;环境温度分别为-10℃和-15℃,且尿素冻结的状态下,NO_(x)比排放是尿素未冻结状态的1.2倍和3.3倍;阶段1、阶段2工况下,NO_(x)排放控制主要以DOC和EGR为主,阶段3的大扭矩、大负荷工况则更依赖SCR;CO和HC比排放结果中环境温度引起的差异主要发生于阶段1工况。环境温度-15℃和-20℃条件下,阶段1至阶段3的PN平均浓度均低于100个/cm^(3)。

Based on a diesel engine that meets the ChinaⅥb emission standard,WHTC cycle emission testing was conducted on an engine bench equipped with a low-temperature climatic chamber.Different simulated temperatures were set and the specific emission results of CO,HC,NO_(x),PN,and PM were compared.Then the relationships of ambient temperature,intercooled temperature and exhaust temperature with exhaust pollutants were analyzed,and the differences in CO,HC,NO_(x),and PN emission characteristics at different ambient temperatures during the three stages of WHTC cycle were also analyzed.The results showed that the specific emissions of NO_(x),CO,and HC gradually increased,while the overall specific emissions of PN decreased,and the specific emissions of PM first decreased and then increased with the decrease of ambient temperature.The NO_(x) emissions under-10℃and-15℃in frozen urea state were 1.2 times and 3.3 times of those in unfrozen urea state.NO_(x) emission control mainly relied on DOC and EGR at stage 1 and stage 2 and was more dependent on SCR under the high torque and load conditions of stage 3.The differences caused by ambient temperatures in the CO and HC specific emission results mainly occurred in stage 1.At-15℃and-20℃conditions,the average concentration of PN in stage 1 to stage 3 was below 100 unit/cm^(3).