基于热机耦合的柴油机活塞热应力及疲劳寿命分析

Thermo-Mechanical Analysis of Piston Thermal Stress and Fatigue Life for Diesel Engine

通过建立活塞裙部型线、活塞优化后的燃烧室及内冷油道等的有限元模型,采用PERMAS软件计算了优化后的活塞在标定工况下的温度场和热机耦合应力,分析了活塞的疲劳寿命,并测量了800h热冲击试验后,活塞环槽、活塞外圆尺寸等尺寸和型线的变化情况。结果表明:活塞高温区域主要分布在活塞顶部,最高温度约为301℃,在活塞材料许用范围内;第一环槽的表面平均温度为194℃,低于润滑油结焦温度230℃;增加了20%喷油量时,活塞的表面温度仍可满足设计要求。在活塞受到热机耦合作用时,活塞向主推力面方向倾斜,主推力面受力较大,约为44N/mm2,活塞销座表面最大应力值区域主要分布在后端销孔上侧,约为98N/mm2,应力值均在许用范围内。活塞疲劳寿命最低的部位在活塞燃烧室底部及燃烧室喉口,理论寿命分别为6.9和7.7,800h热冲击试验后,活塞环槽、销孔、活塞环槽底径、活塞外援尺寸等尺寸变化均较小,活塞外圆型线和椭圆型线变化不大,能够满足使用要求。

A finite element model of a piston including its skirt profile, optimized combustion chamber and oil gallery was established to investigate its temperature field, thermal stress and fatigue life at the rated condition by means of the finite element software PERMAS. and skirt profile were measured after a thermal shock test temperature areas are mainly found at top of the piston, Besides that, the sizes of the piston ring grooves for 800 h. The analysis results show that high with the maximum temperature reaching about 301 ℃, and the mean temperature reaching 194 ℃ is found in the top ring insert, much lower than 230 ℃ for oil coking. So they are all acceptable even when the fuel injection quantity is increased by 20%. The piston inclines to the thrusting side under the coupled thermo-mechanical force, and the thrusting side bears a stress of 44 N/mm^2. The peak stress of about 98 N/mm^2 in piston pin bore is found at the rear end of the bore and they all are acceptable. The lowest piston fatigue life occurs at the bottom and bowl rim of the combustion chamber, and their theoretical service lives are 6.9 and 7.7 respectively, and the sizes of piston ring grooves and skirt profile have a little change after the 800 h test, satisfying the requirements of use.