二甲醚发动机活塞二阶运动-润滑耦合模型建立及数值分析

A Numerical Simulation of Piston Secondary Motion-Lubrication Coupling Model for Dimethyl Ether Engine

通过改造潍柴WP6发动机的供油、燃烧系统,开发出一台二甲醚发动机。试验采集二甲醚发动机燃烧参数,针对活塞运动和润滑分析,建立活塞裙部系统以及由曲轴、连杆、活塞组成的多体系统的耦合润滑模型。基于拉格朗日乘子法建立多体动力学方程,并采用有限单元法对润滑模型进行求解。将耦合计算结果与实验对比,验证模型准确性。根据现有二甲醚发动机活塞裙部的结构参数,研究不同活塞结构参数对敲缸及润滑的影响。结果表明,活塞间隙越小时,活塞二阶运动的空间越小,导致敲缸现象减弱,磨损降低,但较小的间隙会产生比较高的油膜剪切力,微凸体表面接触也会加剧,引起较大的摩擦力及摩擦功耗;活塞裙桶形面最高点的位置也会影响活塞裙-缸套系统的运动和润滑特性;桶形面与活塞销中心的距离越小越容易满足力与力矩平衡条件,有利于降低敲缸以及摩擦损耗。

A dimethyl ether（DME） engine was developed with a modified fuel supply and injection system based on a WEICHAI WP6 Diesel engine.The combustion parameter of DME engine was acquired by experiments, and a numerical model for piston dynamics and lubrication analysis was proposed by coupling the dynamics model of multi-body system consisting of piston, crank and connecting rod, and the lubrication model of piston skirt-liner system.The lubrication model was solved with finite element method （FEM）, while the muhi-body dynamics equations were established with Lagrange multipliers.The coupling calculation results were compared with experimental ones, and the accuracy of the model was verified. Based on the present piston skirt structure, some structure parameters of piston skirt were investigated so as to reveal their effect on the slap noise and lubrication performances of the piston.The results show that, the smaller the clearance of pis- ton, the smaller the space of secondary motion of piston, which will decrease the slap noise of piston and reduce the wear. However small piston clearance will produce higher shearing force of oil film, and aggravate surface contact of asperity, leading to larger friction force and power consumption.Barrel peak position of piston skirt will also affect the characteristics of lubrication and motion of the piston skirt-cylinder system.When the distance between barrel surface and piston pin center is smaller, the balance condition of force and torque is more easy to be satisfied, which is helpful for reducing slap noise and friction power consumption.