Trouble Shooting of Exhaust Manifold Crack
排气歧管开裂故障分析

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.