Thermal Analysis of Coupled Thermal Stress and Fatigue Life of a Diesel Engine Piston

基於熱機耦合的柴油機活塞熱應力與疲勞壽命分析

許廣舉(Guang-Ju Xu) ； 李銘迪(Ming-Di Li) ； 趙洋(Yang Zhao) ； 李廣華(Guang-Hua Li) ； 陳慶樟(Qing-Zhang Chen)

《中國機械工程學刊》 40卷1期 (2019/02) Pp. 47-53

摘要

Using PERMAS software, the temperature and thermal-mechanical coupled stress of a piston under calibration conditions were calculated using the finite element model for the piston skirt profile, the piston combustion chamber and the inner cooling oil path. The fatigue life of the piston was analyzed, and the changes in the piston ring groove and the outer diameter of the piston were measured. The results show that the high temperature region of the piston is mainly distributed at the top of the piston and that the maximum temperature is approximately 301 ℃, which is within the allowable range of the piston material; the average surface temperature of the first ring groove is 194 ℃, which is lower than the lubricating oil coking temperature. When the piston is coupled to a heat engine, the piston is tilted toward the main thrust surface, and the main thrust surface is larger, approximately 44 N / mm^2. The maximum stress value of the piston pin seat surface is mainly distributed in the back pin hole, and the stress values are within the allowable range. The lowest fatigue life of the piston occurs at the bottom part of the combustion chamber and the combustion chamber roar mouth, which have theoretical fatigue lives of 6.9 and 7.7, respectively. After 800 hours of thermal shock testing, the piston ring groove, pin hole, piston ring groove bottom diameter and the piston show little change in dimension. All of these piston elements meet the fatigue life requirements.

關鍵字

diesel engine ； piston ； heat load ； fatigue life ； finite element

並列摘要

本文通過建立活塞裙部型線、活塞優化後的燃燒室及內冷油道等的有限元模型，採用PERMAS軟體，計算了優化後的活塞在標定工況下的溫度場和熱機耦合應力，分析了活塞的疲勞壽命，並測量了800小時熱衝擊試驗後，活塞環槽、活塞外圓尺寸等尺寸和型線的變化情況。結果表明，活塞高溫區域主要分佈在活塞頂部，最高溫度約為301℃，在活塞材料許用範圍內；第一環槽的表面平均溫度為194℃，低於潤滑油結焦溫度230℃，增加20%噴油量時，活塞的表面溫度仍可滿足設計要求。在活塞受到熱機耦合作用時，活塞向主推力面方向傾斜，主推力面受力較大，約為44N/mm2，活塞銷座表面最大應力值區域主要分佈在後端銷孔上側，約為98N/mm2，應力值均在許用範圍內。活塞疲勞壽命最低的部位在活塞燃燒室底部及燃燒室吼口，理論壽命分別為6.9和7.7，800小時熱衝擊試驗後，活塞環槽、銷孔、活塞環槽底徑、活塞外援尺寸等尺寸變化均較小，活塞外圓型線和橢圓型線變化不大，能夠滿足使用要求。