Analysis Of Thermal-mechanical Fatigue For Engine Exhaust Manifold Based On Fluid-solid Coupling

With the engine power demand increasing and emissions limits is much more strict, Accessories& Components like exhaust manifold which is working under high temperature are getting more and more focus on. In actual use, fatigue fracture and the sealing failure are the most common fatigue problems in exhaust manifold which could have seriously impact on the performance of the engine. About this problems above, this paper will focus on the exhaust manifold of a diesel engine which has six cylinders and high pressure common rail to make the following analysis and prediction.The mainly content of this paper are : calculating the combustion in cylinder and the flow field in exhaust manifold by CFD software, calculating the exhaust pipe's temperature distribution by fluid-solid coupling calculation, modal analysis and thermal-mechanical stress analysis of exhaust manifold under heat- mechanical conditions, calculation about low- cycle thermal fatigue and analysis of sealing performance of the exhaust pipe gasket.The result indicates that the temperature of the exhaust pipe can reach a high value of 680?. With the bounding of exhaust manifold by the mounting flange, the natural frequency of the exhaust manifold reduces. But it is still higher than the excitation frequency from the engine, so that the resonance phenomenon will not occur. With the Bolts and thermal loads, the stress distribution indicates that stress concentration occurs in the tube mounting flange of exhaust pipe,Effect of thermal loading on stress distribution is great. Thermal fatigue life analysis shows that the number of cycles in the region declines, it can reach 1688 times lowest. According to the analysis of exhaust pipe gasket contact pressure under the thermal-mechanical action, the contact pressure distribution is quite different on the exhaust pipe seal ring; but much higher than the design requirements, so the leakage phenomenon will not occur.