缸内直喷汽油机多环芳烃排放特性的试验研究

在一台缸内直喷(GDI)汽油机上,分别用玻璃纤维滤膜和“聚氨基甲酸乙酯泡沫(PUF)+XAD-2”对尾气中的颗粒相和气相多环芳烃(PAHs)进行了采集,并用色谱-质谱联用仪(GC-MS)对PAHs进行了定性定量分析,研究了点火时刻和废气再循环(EGR)对PAHs排放的影响.结果表明:在缸内直喷汽油机尾气中,气相PAHs浓度远高于颗粒相PAHs浓度,在气相PAHs中主要是2环和3环等小环PAHs,而在颗粒相PAHs中则主要是4环及以上的大环PAHs.随着点火时刻的提前,尾气中PAHs总浓度呈现先减小后增加再减小的变化趋势,气相和颗粒相PAHs浓度也呈现相似的变化趋势.随着EGR率的增大,气相PAHs所占比例先减小后增大,颗粒相PAHs所占比例则先增大后减小,总PAHs的排放在整体上呈现逐渐减小的变化趋势.加入EGR后,GDI汽油机尾气的毒性显著增大.

PAHs emission characteristics of a gasoline direct injection engine

The particulate-phase and vapour-phase polycyclic aromatic hydrocarbons (PAHs) were collected by a fiberglass filter and a "polyurethane foam (PUF)+XAD-2" respectively on an airflow guided gasoline direct injection (GDI) engine. The collected PAHs were analyzed by Gas Chromatography-Mass Spectrometer (GC-MS) quantitatively and the effects of spark timing and EGR rate on the PAHs emission were investigated in this study. The results showed that the concentration of vapour-phase PAHs, which was composed mainly by 2 and 3 rings PAHs, was much higher than that of particulate-phase PAHs composed by larger PAHs (4~6 rings). Concentration of total PAHs in exhaust first decreased slightly, and then increased and decreased finally with the advance of spark timing, and the concentrations of particulate-phase and vapour-phase PAHs also had the similar trends. With the increase of EGR rate, the percentage of vapour-phase PAHs first decreased and then increased, whereas the percentage of particulate-phase PAHs had opposite tendency. And the total emission of PAHs showed a decreasing trend in the overall. The exhaust toxicity of GDI engine increased significantly after addition of EGR.