空燃比和EGR对GDI汽油机多环芳香烃排放的影响

Influence of Air-Fuel Ratio and EGR on PAHs Emissions of a Gasoline Direct-Injection Engine

使用色谱-质谱联用仪对GDI汽油机排气中颗粒相多环芳香烃(PAHs)进行分析,研究了空燃比及EGR对多环芳香烃排放的影响规律.结果表明,随空燃比增加,颗粒物(PM)、可溶性有机物(SOF)和PAHs排放量降低,颗粒中大分子量的PAHs所占比例降低,二环和三环等小分子量的PAHs所占比例增加;EGR率小于10%时,PM、SOF和PAHs的排放量增加趋势不明显;EGR率大于10%时,排放量显著增加,四、五、六环PAHs排放量在EGR率大于10%时远高于二环和三环PAHs排放量;GDI汽油机颗粒物毒性当量远高于柴油机,浓混合气和中等EGR率时,颗粒物的毒性最大.

The polycyclic aromatic hydrocarbons （PAHs） in exhaust particulate matter （PM） from a GDI engine under different air-fuel ratios （RAF） and exhaust gas recirculation （EGR） rates were analyzed by gas chromatogram-mass spectrometry（GC-MS）. The results show that the emissions of PM, soluble organic fraction（SOF）, and PAHs are reduced with the increase of RAF. At higher RAF, the percentage of high molecular weight PAHs decreases while that of low molecular weight PAHs increases. The emissions of PM, SOF and PAHs increase slightly when the EGR rate is lower than 10% but increase significantly when the EGR rate is larger than 10%. When the EGR rate is larger than 10%, the emissions of PAHs with four, five and six benzene rings are much higher than those of PAHs with two and three benzene rings. The exhaust toxicity of GDI engine is much higher than that of diesel engine. Under the conditions of mixture or middle EGR rates, the exhaust toxicity of GDI engine reaches the highest.