柴油机排气颗粒与DPF过滤壁面的碰撞力学特性分析

Mechanical Characteristics of Diesel Exhaust Particles Colliding with DPF Filter Wall

为了研究柴油机排气颗粒与DPF过滤壁面的碰撞力学特性,基于柴油机排气颗粒在DPF内过滤壁面的碰撞过程,建立颗粒与壁面的碰撞反弹模型,运用Fluent仿真软件与相似理论,模拟孔道内的速度场分布情况,分析了颗粒与壁面的黏附力与黏附能、最大接触半径等碰撞特性参数以及颗粒发生反弹时的法向恢复系数、临界黏附速度等评价指标。应用原子力显微镜与搭建的试验台架,测量了模型中颗粒在碰撞反弹中受到的黏附力,确定了表面粗糙度修正系数,并对颗粒在DPF过滤壁面上的沉积形貌进行分析,对计算得到的结果进行验证。结果表明:随着孔道轴向距离的增加,孔道过滤壁面内流场速度先减小后增大;随着颗粒的入射角增大与入射速度减小,最大接触半径减小;随着颗粒与壁面之间的压缩距离增大与颗粒粒径增大,颗粒与壁面之间的黏附力和黏附能增大;随着颗粒入射速度增加以及表面能减小,颗粒碰撞后的法向恢复系数增加,法向临界黏附速度减小;孔道前端与后端沉积的颗粒较少,平均粒径小而比表面积大的颗粒更容易被捕集。

In order to study the mechanical characteristics of diesel exhaust particles colliding with filter wall of DPF,a model of particle-wall collision and rebound was established based on the collision process of diesel exhaust particles with the filter wall of DPF.Using Fluent simulation software and approximate theory,the velocity field distribution in the channel was simulated,the particle-wall collision characteristics such as adhesion force and energy and maximum contact radius were analyzed,and the evaluation indexes such as normal recovery coefficient and critical adhesion speed of rebound were further discussed.The adhesion force of particles during the collision and rebound in the model was measured by using atomic force microscope and test bench,the surface roughness correction coefficient was determined,the deposition morphology of particles on DPF filter wall was also analyzed,and finally the calculated results were verified.The results show that the velocity of flow field in the filter wall decreases first and then increases with the increase of pore passage axial length.The maximum contact radius decreases with the increase of the incident angle and the decrease of velocity of particles.The adhesion force and energy between the particles and wall increase with the increase of particle size and compression distance between particles and wall.The normal recovery coefficient after the particle collision increases and the adhesive velocity decreases with the increase of incident velocity and the decrease of particle surface energy.Besides,the deposited particles at the front and back of channel become less and the particles with small average particle size and large specific surface area are more likely to be trapped.