轻型汽油车排放颗粒物数浓度和粒径分布特征

我国机动车颗粒物排放研究多集中于重型柴油车,对于轻型汽油车的研究相对较少.本研究对3辆缸内直喷(GDI)汽车和1辆进气道喷射(PFI)汽车排放颗粒物的数浓度与粒径分布进行测试,并利用两台不同检测下限的颗粒物冷凝生长计数器(CPC)对轻型汽油车颗粒物实际排放水平进行了探究.结果表明,GDI汽车排放的颗粒物数浓度高于PFI汽车一个数量级,冷启动下颗粒物主要在测试循环前200 s大量产生,GDI汽车排放颗粒物数浓度与工况速度变化关系密切,而PFI汽车变化相对较小.GDI与PFI汽车排放的颗粒物粒径分布均具有核模态和积聚模态两个特征峰,核模态颗粒物峰值粒径约为20~27 nm,积聚模态约为80~95 nm.粒径检测下限为2.5 nm的UCPC测得的颗粒物数浓度比法规使用的粒径测量下限为23 nm的CPC测量结果分别高出35.0%(GDI)和50.4%(PFI).表明喷油技术是影响颗粒物数量排放水平的关键因素,法规测试会低估轻型汽油车实际颗粒物排放水平.

Number Concentration and Size Distribution of Particles Emitted by Light-duty Gasoline Vehicles

In this study, three GDI (gasoline direct injection) and one PFI (port fuel injection) light-duty gasoline vehicles were characterized for their particle emission (number concentration and size distributions). Two condensation particle counters (CPC) with different activation efficiencies (50% cut off diameter) were used. It was found that the number concentration of particles emitted by GDI gasoline vehicle was approximately one order of magnitude higher than that from PFI gasoline vehicle. High emission of particles occurred within the first 200 s of cold start. The number concentration of particles emitted from GDI vehicle was largely influenced by the vehicle working condition, while that of PFI vehicle was relatively stable despite of varying working conditions. The size distributions of particles emitted from GDI and PFI vehicles had both nucleation mode and accumulation mode. The peak diameter of nucleation mode particles was in the range of 20-27 nm, while that of accumulation mode particle was in the range of 80-95 nm. The number concentrations measured by the UCPC (50% cut off diameter of 2.5 nm) were 35% (GDI) and 50.4% (PFI), respectively, higher than those measured by the CPC (50% cut off diameter of 23 nm) used by the regulation.