Marine diesel exhaust manifold failure and life prediction under high-temperature vibration

The working environment of the diesel exhaust manifold is harsh. On one hand, exhaust gas with high temperature continues to flush on the inner wall of the manifold, and on the other hand, the manifold is also affected by some complex factors, such as diesel engine vibration. If the design is unreasonable, air leakage, cracking, and other failure phenomena are easy to appear. In this article, aiming at the aforementioned problems in the exhaust manifold design process, a high-speed diesel exhaust manifold is taken as an example and analyzed by computational fluid dynamics and finite element method technology. The temperature field distribution of the exhaust manifold is simulated by the fluid-structure interaction method, and then the thermal stress distribution is simulated based on the temperature field of the exhaust manifold. According to the thermal stress of the exhaust manifold and the vibration stress in three directions (axial, transverse, and vertical), combined with the time domain acceleration signals, the high-cycle fatigue life of the exhaust manifold is obtained. The exhaust manifold structure is optimized based on the minimum high-cycle fatigue life position. Then, the high-cycle fatigue life analysis of the optimized structure shows that the optimized structure can significantly improve the life of the exhaust manifold. Then, the optimized structure is further analyzed for low-cycle fatigue life to check whether it meets the requirements of low-cycle fatigue life. After simulation, it can be known that the low-cycle fatigue life meets the design requirements. Finally, sensitivity analysis of the fatigue life under different loading conditions (thermal load and vibration intensity) shows that the thermal load has a significant influence on the fatigue life, so the thermal load should be paid attention to in the design process.