Thermal Fatigue Simulation Analysis For The Double-layer Water Cooled Exhaust Manifold Of Engine

The exhaust manifold is one of the important parts of engine exhaust system, itsstructural strength directly affects the working dependability and use durability and theemission performance of the engine. To accord with the safety requirements of surfacetemperature that does not reach423K, explosion-proof diesel engine exhaust manifold usesthe double-layer water cooled exhaust manifold. Because the double-layer water cooledexhaust manifold contact with high temperature exhaust gas and cooling water in theprocess of working, the wall temperature distribution is very uneven and the thermal stressconcentrates on the wall to make the double-layer water cooled exhaust manifold have therisk of fatigue damage. So it is necessary to study the thermal stress distribution and thethermal fatigue life of the double-layer water cooled exhaust manifold in working process.)The simulation results are important for improving the working dependability and servicelife of the double-layer water cooled exhaust manifold, they also have the certain referencevalue on structure improvement and optimization aspects in the future.This paper studies the double-layer water cooled exhaust manifold about a certainengine and establishes the3D modeling by UG software. The3D assembling models of thedouble-layer wall, inner gas and inner cooling water of the double-layer water cooledexhaust manifold is treated as flow-solid geometry model of CFD analysis. The3Dassembling model containing a simplified body plate and the vortex shell plate and bolt etc.parts is treated as the analytic model of thermal stress and thermal fatigue study. The paperdivides mesh by using the Hypermesh software and separately establishes boundarycondition of flow field analysis and stress analysis. Use the FLUENT software to analyze the double-layer water exhaust manifoldfluid-solid for flow-solid coupling. Double-layer wall is treated as solid field and flue gasand cooling water is treated as fluid field of the coupling system. In order to obtain theinternal flow field and temperature field distribution, this article studies fluid flow and heattransfer and coupled heat transfer between fluid and pipe wall of the double-layer watercooled exhaust manifold through the entire discrete and the whole solving method. Analysisresults show that the double-layer water cooled exhaust manifold has good liquidity andconforms to the requirements of the exhaust, at the same time it meets the requirements ofsafe explosion-proof because surface temperature is not more than423k. It also proves that3D model of the double-layer water cooled exhaust manifold is reasonable and feasible.On the basis of fluid-solid coupling calculation, put the wall temperature of thedouble-layer water cooled exhaust manifold as temperature load by ANSYS software,preload on the bolt. Adopting the full constraint loading way for fixed end simulates realworking condition of the double water cooled exhaust manifold to inspect the stressdistribution and obtain thermal deformation, thermal stress and strain.On the basis of the plastic strain increment of the thermal stress analysis, the end of thearticle predicts its fatigue life by Manson-Coffin formula, the result conforms to therequirements of the design, it provides certain reference basis for structure designimprovement and fatigue analysis research of the double-layer water cooled exhaustmanifold.