汽油机排气颗粒粒径分布特征试验研究

MEASUREMENTS OF PARTICLE SIZE DISTRIBUTION FROM A GASOLINE ENGINE

对汽油机排气中颗粒的数浓度和粒径分布特征进行了测试.在测试工况下,汽油机排气中的颗粒呈包含核模态粒子(10 nm<Dp<50 nm)和积聚模态粒子(50 nm<Dp<487 nm)的双峰分布,排气颗粒的总数和总质量浓度分别为4.2×105—7.9×106个.cm-3和0.02—0.27 mg.m-3.汽油机在开环控制状态下(车速不低于90 km.h-1时)的颗粒数量排放明显高于闭环控制状态(车速不高于70 km.h-1),总颗粒质量浓度随车速的增大显著增加.随车速增大,积聚模态粒子的平均粒径先减小后增大,核模态粒子的几何平均粒径先增大后减小,低车速时,有大量10—20 nm的核模态粒子生成.柴油机和汽油机排气颗粒中核模态粒子通常占有大的数量百分比,为75%—95%,而其质量百分比仅为5%—25%.汽油机的总颗粒、核模态粒子和积聚模态粒子的数量和质量排放均远低于柴油机.

Measurements of exhaust particle number concentration and size distribution of a gasoline engine were conducted.The exhaust particle number weighted size distributions of the gasoline engine show bimodal with a nuclei mode in the 10—50 nm and an accumulation mode in the 50—487 nm.The total exhaust particle number concentrations of the port fuel injected gasoline engine tested in this study range from 4.2×10^5 to 7.9×10^6 partices·cm^-3 under the different vehicle speeds,and the total exhaust particle mass concentrations range from 0.02 to 0.27 mg·m-3.The variation of the vehicle speed shows no significant effect on the total exhaust particle number concentration at the low vehicle speed（20—70 km·h^-1;closed-loop）,while great increase of the total exhaust particle number concentration was observed at the high vehicle speed（90 and 120 km·h^-1;opened-loop）.The total exhaust particle mass concentration significantly increases with the increase of the vehicle speed.the accumulation mode geometric mean diameter pass through a minimum in some vehicle speed range before increasing again,while the nuclei mode geometric mean diameter pass through a maximum in the medium vehicle speed range before decreasing again.A large number of nuclei mode ranging from 10 to 20 nm were founded under low vehicle speed.For gasoline and diesel engines,the exhaust particle in the nuclei mode usually accounts for most of the particle number（75%—95%）,although it usually accounts for few of the particle mass（5%—25%）.Compared with the diesel engine,the number and mass concentrations of the total particles,the nuclei and the accumulation modes of the gasoline engine are significantly low.