基于流固耦合计算的柴油机缸盖热-机械疲劳分析研究

Analysis of Thermal-Mechanical Fatigue of Diesel Engine Cylinder Head Based on Fluid-Structure Interaction

以一台重载车用柴油机为研究对象进行了缸内燃烧和冷却水套的三维CFD计算、缸盖温度场流固耦合计算、缸体-缸盖耦合热-机械应力分析、缸盖低周和高周疲劳预测分析,提出了完整的多场耦合进行缸盖结构强度和疲劳寿命计算分析的方法。计算结果表明:缸盖温度场的计算值与缸盖底板温度场的测量值一致,缸盖计算预测的疲劳危险区与实际缸盖裂纹产生的位置一致。针对原机存在的排气道裂纹问题,提出了两种优化方案。研究结果表明:增加壁厚之后,裂纹处的应力从245MPa降至230MPa,而将缸盖材料从灰铁更换为蠕铁后,应力也得到明显下降。

Taking a heavy diesel engine as an research object, several simulations were carried out. 3- dimensional CFD of in-cylinder combustion and engine cooling jacket, simulation of cylinder head temperature field using fluid-structure interaction, stress and strain analysis under thermal-mechanical coupling conditions, and low/high cycle fatigue analysis of the cylinder head, and a complete set of multi- field coupling methods was proposed for analysis of cylinder head strength and fatigue. The analysis shows that computed temperatures are consistent with experimental measurements, and the danger region predicted by the calculation is the region where crack occurs in the actual experiment. In addition, the simulation also analyzed two optimization schemes to address the exhaust port crack problem of the base cylinder head. The results show that the stress at the crack location decreases from 245 MPa to 230 MPa after increasing the cylinder head wall thickness, and the stress drops significantly after changing the cylinder head material from gray iron to vermicular iron.