通过在重型车底盘测功机上模拟夏季柴油车在不同载荷状态下冷、热机启动过程,重点分析了柴油车在冷、热启动条件下的NOx与NH3排放特性及影响因素.结果表明,冷启动时排气温度与冷却液温度上升较慢,NOx传感器延迟工作,82%以上的NOx排放发生在传感器启用前;热启动因系统温度较高,SCR与传感器快速投入运行,NOx排放明显降低.NH3排放受启动状态与模拟载荷影响显著,冷启动初期因SCR温度低排放因子高于平均水平;热启动时尿素快速水解且未与NOx充分反应,导致NH3排放增加.微观运行模态分析表明,NOx排放差异主要由发动机与SCR温度决定,NH3排放差异则与SCR温度及尿素喷射量相关.需要重视夏季柴油车冷机启动过程的污染物排放,协同优化启动过程的温度控制和SCR尿素喷射策略,进一步降低夏季柴油车排放对大气污染的影响.
Abstract
This study investigated cold and hot start processes of diesel vehicles under different load conditions in summer using a heavy-duty chassis dynamometer, with a focus on analyzing NOx and NH3 emission characteristics and influencing factors. The results showed that during cold starts, the exhaust gas temperature and coolant temperature rose slowly, and the NOx sensor was delayed in activation, with over 82% of NOx emissions occurring before the sensor became operational. During hot starts, the SCR system and sensor entered operation rapidly due to higher system temperatures, leading to significantly lower NOx emissions. NH3 emissions were significantly affected by the start condition and simulated load. In the initial phase of cold starts, the NH3 emission factor was higher than average because of low SCR temperatures. During hot starts, rapid urea hydrolysis without sufficient reaction with NOx resulted in increased NH3 emissions. Micro-scale operational modal analysis revealed that the difference in NOx emissions was mainly determined by engine and SCR temperatures, whereas the difference in NH3 emissions was associated with SCR temperature and urea injection quantity. The study emphasizes the need to address pollutant emissions during summer cold-start processes and proposes synergistic optimization of temperature control and SCR urea injection strategies to reduce the environmental impact.
关键词
柴油车 /
夏季排放 /
冷热启动 /
NOx /
NH3
Key words
diesel vehicles /
summer emissions /
cold start and hot start /
NOx /
NH3
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基金
国家重点研发计划(2022YFC3703602)
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