中文摘要：

采用DMS500快速颗粒取样分析仪对一台气道喷射国Ⅲ汽油机进行了颗粒物粒径分布特性的试验研究．结果表明，汽油机排气中颗粒物以核态为主，仅部分工况存在积聚态．怠速时呈现包括核态和积聚态的双峰分布；低转速时表现为核态的单峰分布；中等转速时粒径分布范围扩大，既存在核态颗粒物，也存在积聚态颗粒物．相同转速下，随负荷的增加核态颗粒物数密度峰值先降低后增加；相同负荷下，随转速的升高核态颗粒物数密度峰值和峰值粒径均降低，积聚态颗粒物数密度峰值有增加的趋势．催化器对核态颗粒物的净化效果较好，对积聚态颗粒物的净化效果较差，对低转速下的粒径分布有明显影响．

英文摘要：

A DMS 500 fast particulate spectrometer was employed to characterize the particle size distribution from a port fuel injection （PFI） gasoline engine which meets the regulations of China III standards. The results show that exhaust particulates from gasoline engine are dominated by nucleation mode particles, with accumulation mode particles generated only under some conditions. Under an idle condition, exhaust particles exhibit a bimodal size distribu- tion consisting of nucleation mode and accumulation mode. Particle number size distribution shows a unimodal nucleation mode at low engine speed and a large size distribution involving nucleation mode and accumulation mode at middle engine speed. At the constant speed, the peak value of number concentration for nucleation mode shows an increasing trend after an initial decrease with the increase of engine load. At the constant load, both the peak value of number concentration and the peak diameter for nucleation mode drop with the increase of engine speed, while the peak value of number concentration for accumulation mode shows an increasing trend with the increase of engine speed. Conversion efficiency of three-way catalyst （TWC）is high for nucleation mode particles, while it is low for accumulation mode particles. Furthermore, particle size distribution varies greatly between the upstream and down- stream of TWC when engine runs at low speed.