排气歧管开裂故障分析

某柴油机新设计的排气歧管在试验过程中出现开裂现象,通过全面分析该排气歧管的热应力和振动特性,应用AVL公司的FIRE软件,建立排气歧管的有限元模型并确定它的边界条件,对CFD分析计算出排气歧管内外表面的温度和热传递系数,然后用非线性结构分析软件ABAQUS软件计算排气歧管的温度场和热应力;同时也对排气歧管的振动特性进行了计算。结果表明排气管开裂不是由热应力引起的,而是共振的原因,建议更改排气歧管加强筋以提高它的刚度,提高排气系统的固有频率,避免与发动机产生共振。

Trouble Shooting of Exhaust Manifold Crack

A newly-designed exhaust manifold for a diesel engine had cracks in the course of the experiment.By analyzing the thermal stress and vibration characteristic of the exhaust manifold entirely and using AVL software FIRE to set the limited models of exhaust manifold and ascertain the edge conditions,the temperatures and heat transfer coefficients(HTC) on interior and exterior walls of exhaust manifold were calculated by computational fluid dynamics(CFD) analysis.Then,the fields of temperature and thermal stress were calculated by using non-structural software ABAQUS.At the mean time the exhaust manifold vibration characteristic was also calculated.The results showed that the cracks of the exhaust manifold were caused by resonance instead of the thermal stress.It was suggested that the reinforcing steel should be replaced by a stronger one to enhance its rigidity and to raise the innate frequency of the exhaust system to avoid the resonance in the engine.