The Couping Analysis On Thermal Load And Mechanical Vibration Load Of Exhaust Manifold

As an important part of automotive exhaust systems, the exhaust manifold hasan important impact on the performance of the engine, including dynamicperformance, economic performance and emission performance. The exhaustmanifold is working under poor conditions, thus there being failure of the exhaustmanifold. And as we know the thermal load and the mechanical vibration loads arethe two main causes. Therefore, the research on the coupled analysis of thermal loadand mechanical vibration load of exhaust manifold has important significance.Taking a supercharged four-cylinder gasoline engine exhaust manifold for study,the thesis analysis the freed modal and constraint modal on the manifold, which isbased on the finite element method. The analysis revealed that the first naturalfrequency of constrained mode is1059.7Hz. By using the vibration responseanalysis method, the top ten natural frequencies of the constraint mode is verified.We found that the maximum error between the resonance frequency and the naturalfrequency is0.67%, indicating that the analysis of the constraints modal is accurate.In this paper, three-dimensional model of exhaust manifold is established byPROE and finite element simulation model of exhaust manifold established inABAQUS, as well as the mesh and the model. Then based on the engine designparameters provided, we can get the overall temperature distribution of the exhaustmanifold through the STAR-CCM+fluid dynamics (CFD) software. In order toverify the accuracy of the temperature field, the paper also carried out experiments totest the temperature field of the exhaust manifold. Via an internal thermocouple, wemeasure the temperature of the inner fluid temperature and the outer surfacetemperature the engine exhaust manifold under the same operating conditions. Theresults found that maximum error is only4.3%between the simulation andexperimental results, therefore it is within the error range. In this paper, we get the overall stress distribution of the exhaust manifold inthe finite element software ABAQUS, by using the calculated temperature field fromSTAR-CCM+. It was found that while without the mechanical vibration load, theoverall stress of the exhaust manifold is basically between300MPa~400Mpa. Butthis result can’t be the final judge of whether this is the very cause of the failure ofthe exhaust manifold. In order to further study the reasons for the failure of theexhaust manifold, the paper also carried out the coupling analysis on the thermalload and mechanical vibration loads of the exhaust manifold.By using the finite element method, the paper carries out the coupling analysison the thermal loads and mechanical vibration loads of the exhaust manifold. Themechanical vibration loads are applied by using the way of vibration acceleration.Then we get the overall stress distribution at different speeds, and found that theoverall stress distribution of the exhaust manifold is between20MPa~200Mpa,which does not reach the yield strength. This paper also analyzes the stressconditions at different locations with the engine at the same speed, founding that themaximum value of stress is at the inlet flange. As well, the paper also analyzes howthe stress changes at the same position during different speeds. The result shows thatas the engine speed increases, the stress of the exhaust manifold substantially rises,however, there is no failure occurs in the exhaust manifold under the coupling ofthermal load and mechanical vibration loads.