国Ⅵ直喷汽油机颗粒数量及微观形貌排气输运演变特性

Transport Properties of Particle Number, Size Distribution, and Morphology Characteristics of Particulate Matter Emitted from a Ⅵ Gasoline Direct Injection Engine

摘要:

开展了某一国Ⅵ直喷汽油机三元催化转化器（TWC）前、TWC后、汽油机颗粒捕集器（GPF）后3个位置的颗粒物采样及微观形貌研究，分析了发动机工况、TWC、GPF对国Ⅵ直喷汽油机尾气颗粒数量、粒径分布、微观形貌的影响。结果表明，该直喷汽油机尾气颗粒数量排放整体上呈单峰分布，低转速小负荷工况下，粒径<23 nm的颗粒数量较高。随着发动机转速和负荷的增大，峰值粒径向大粒径方向移动。直喷汽油机尾气颗粒物由“核?壳”结构基本碳粒子堆积形成，呈链状、枝状、簇状等结构；负荷增大，颗粒物尺寸略有增大，基本碳粒子重叠度增强，分形维数增大；转速增大，颗粒物尺寸减小，基本碳粒子重叠度减弱，分形维数减小。随着排气输运的进行，颗粒数量逐渐降低；TWC不影响颗粒的粒径分布形态，颗粒数量净化效率41.6%~94.2%，对<23 nm的小粒径颗粒净化效果较好，低转速小负荷工况的颗粒数量净化效率较高；GPF的颗粒数量净化效率约80%，23~100 nm颗粒数量净化效率较高，对粒径<10 nm的颗粒净化作用不大。TWC和GPF不影响颗粒物结构形式， TWC和GPF后颗粒物基本碳粒子重叠度减弱，分形维数减小。

Abstract:

Particulate matter （PM） was sampled from three positions of a certain Ⅵ gasoline direct injection （GDI） engine before three-way catalyst （TWC）， after TWC， and after gasoline particle filter （GPF）. Particle morphology was investigated and influences of working conditions， TWC， GPF on particle number （PN）， particle size distribution （PSD）， morphology of particles emitted from engine were analyzed. The results show that the PSD of PN emitted from the engine is unimodal， the PN of particles with a diameter less than 23 nm is higher under lower load and engine speed operating condition. With the increase of engine speed and load， the peak particle diameter increases. The PM of the engine is formed by the accumulation of basic carbon particles with a “core-shell” structure and presents chain， branch， cluster， or other structures. With the increase of load， the particle size increases slightly， and both the overlap of basic carbon particles and the fractal dimension increase. While with the increase of engine speed， all these three parameters of size， overlap， and fractal dimension of PM decrease. With the transport processing of exhaust gas， PN is reduced. TWC does not affect PSD， and the purification efficiency of PN is 41.6%~94.2%. It has a good purification effect on small particles with a diameter less than 23 nm， and the purification efficiency at a lower engine speed and load is higher. The purification efficiency of GPF is about 80%. For particles with a diameter of 23~100 nm， the purification efficiency of GPF is high. However， it has little effect on the purification of particles with a diameter less than 10 nm. TWC and GPF do not change the structure of particles， after TWC and GPF， the overlap of basic carbon particles and the fractal dimension decrease.