排气再循环对柴油机颗粒官能团的影响

Effect of Exhaust Gas Recirculation on C-Functional Groups in Particles Emitted from Diesel Engine

通过对不同EGR率、EGR废气组分以及EGR温度下产生的颗粒进行采集,采用X射线近边吸收光谱（NEXAFS）技术,研究了EGR对柴油机颗粒官能团的影响.通过分析颗粒的NEXAFS谱线特征,确定了颗粒中官能团的主要组分,采用分峰拟合方法,考察了EGR对官能团相对含量的影响规律.结果表明：柴油机颗粒中碳官能团主要分布在近边能量为284～292,e V范围内,呈典型石墨结构,主要包括不含氧的芳香基碳和石墨碳官能团,醌类、羧基、羰基和酚/酮类等含氧官能团以及脂肪族C—H官能团;随着EGR率增加,颗粒中不含氧官能团逐渐降低,含氧官能团以及脂肪族C—H官能团呈升高趋势,说明EGR对于提高颗粒的氧化活性具有一定促进作用.废气中的CO_2增加了颗粒中含氧和脂肪族C—H官能团,降低了不含氧官能团,N2对官能团的相对含量影响不大;EGR温度增加,颗粒中不含氧官能团增加明显,含氧官能团以及脂肪族C—H官能团均有所降低.

Particle samples under different EGR rates,EGR gas compositions and EGR temperatures were collected.X-ray absorption near edge structure（NEXAFS）was used to analyze the C-functional groups in particles.Characteristics of NEXAFS spectra of different particle samples were recorded and compared.Main composition of C-functional groups was determined and the regular pattern of content with the variation of EGR was examined.Results show that the C-functional groups in particles mainly distribute near the energy range of 284～292,ev,similar to the typical distribution of graphite structure and they mainly consist of aromatic-C,graphite-C,arboxylicC,carboxylic-C,phenol/ketone-C and aliphatic-C.These main compositions have little change under different EGR conditions.With the increase of EGR rate,the content of oxygen-free functional groups is decreased while the oxygen-containing functional groups and C—H group are increased.Carbon dioxide in the exhaust gases decreases the oxygen-free functional groups and increases the oxygen-containing functional groups and C—H group.However,nitrogen has little effect on the content.The oxygen-containing functional groups and C—H group decrease significantly and oxygen-free functional groups increase remarkably with the increase of EGR temperature.