排气歧管热应力模拟计算及缸盖边界条件影响的分析

针对某型号柴油机在热冲击试验过程中排气歧管出现裂纹的问题,利用软件仿真技术进行了排气歧管的热应力模拟计算,分析了产生裂纹的原因。探讨了缸盖建模方法及缸盖设定温度对排气歧管热应力计算的影响。计算结果表明,缸盖限制了排气歧管的自由变形,在排气歧管裂纹出现部位产生较大的应力;在发动机冷热冲击试验时,排气歧管温度的变化造成热应力随之发生变化,导致排气歧管因热疲劳产生裂纹失效;采用简化的缸盖模型与完整缸盖模型所得的排气歧管热应力分布趋势一致,可用于排气歧管的热应力计算。

Thermal Stress Simulation of Exhaust Manifold and the Influence of Cylinder Head Boundary Condition

In order to analyse the cracks on a 4-cylinder diesel engine exhaust manifold,thermal stress distribution was obtained from simulation.The reason of crack was illustrated in this paper,the influence of exhaust manifold cylinder-head modeling method and temperature were also discussed.The results show that：Heat deflection of exhaust manifold is restrained by cylinder-head,and the stress concentratedly appears on the area where crack occurs;During the thermal shock test experiment,the temperature of exhaust manifold alternates between hot and cold,thermal stress shifts between high and low following the temperature alteration,and the crack occurs.A simplified cylinder-head model was used to compare with the complete cylinder-head model,the tendency of thermal stress distribution is almost the same,so the simplified cylinder-head model can be used in the simulation of exhaust manifold thermal stress.