EGR废气组分和温度对柴油机颗粒力学特征的影响

Effect of EGR Exhaust Gas Composition and Temperature on Mechanical Characteristics of Diesel Engine Particles

围绕柴油机颗粒的微观力学性能,针对不同EGR废气组分和温度条件下产生的颗粒,采用颗粒粒径分析仪和原子力显微镜等分析手段,研究了颗粒粒径、数量和质量浓度的变化规律,探讨了EGR废气组分和温度对颗粒弹性模量、团聚力大小和主要作用形式等微观力学性能的影响。研究结果表明,随着EGR废气温度升高,核模态颗粒总数量浓度变化不大,积聚态颗粒总数量浓度有较大幅度增加,颗粒的弹性模量逐渐增大,结构刚性逐渐增强,颗粒间的团聚力逐渐增加,团聚力作用的主要形式由液桥力逐渐向范德华引力转变;与引入废气时相比,分别引入N2和CO2时,颗粒间的团聚力分别主要以范德华力和液桥力形式存在;废气中的N2是导致采用EGR后积聚态颗粒粒径增加、数量和质量浓度升高、结构刚性和团聚力增强的主要气体成分,废气中的CO2可以显著降低积聚态颗粒排放数量和质量浓度、降低颗粒的结构刚性和团聚力。

Focusing on micro-mechanical properties of diesel engine particles, the variation of particle size, number and mass concentration were studied by using particle size analyzer and atomic force microscope for different EGR exhaust gas composition and temperature. The effect of EGR exhaust gas composition and temperature on the micro-mechanical properties such as particle elastic modulus, agglomeration forces and main action forms were analyzed. The results show that the total number concentration of nucleation mode particles has little change with the exhaust gas temperature increasing, however the total number concentration of accumulation mode particles increases significantly, and the particle elastic modulus, structure rigidity and agglomeration forces all increase significantly, while the force action type changes from liquid bridge force to Van Der Waals force. Compared with the introduction of exhaust gas, when N 2 and CO 2 are introduced respectively, the agglomeration force between particles is mainly in the form of Van Der Waals force and liquid bridge force. The N 2 in exhaust gas is the main gas composition that leads to the increase of particle size, number concentration and mass concentration, structural rigidity and agglomeration force of accumulation mode particles with EGR introduced while the CO 2 can significantly reduce the number and mass concentration of accumulated particles and reduce the structural rigidity and agglomeration force.