Thermal Structural Analysis Of Tight Coupling Exhaust Manifold For An Engine

Tight coupling exhaust manifold developed in recent years can well solve the problem of pollutant emission in vehicle cold start.It is because the three-way catalytic converter and exhaust manifold are assembled into one body,catalyst soon reaches the ignition temperature of the catalytic,which greatly reduces pollutant emissions.As a new developing exhaust manifold,currently,scholars analyze less the thermal structure properties of tight coupling exhaust manifold.Because the structure form and materials are different from the traditional ones,plus the cycled temperature that it bears in the high and normal temperature and the vibration excitation from surrounding parts,the work environment is very bad,so it is necessary to analyze the thermal structure property.Based on the above background,this dissertation analyzed the thermal structure property of a tight coupling exhaust manifold that is newly developed by an enterprise,so as to investigate whether it can meet the requirements of application.Computer numerical simulation method is used to calculate and analyzed the thermal structure property from the temperature field,structure mode,thermal stress,low-cycle thermal fatigue life and other aspects.The main contents are as follows:(1)According to the design parameters of engine and exhaust system provided by the enterprise,using GT power software builded the one-dimensional engine simulation model with exhaust system,the rationality of the model was verified based on engine external characteristic test data,and finally the boundary conditions required for the analysis and calculation in the next step are obtained.(2)Using STAR-CCM+ fluid simulation software and ABAQUS solid simulation software to simulate and analyze heat transfer of fluid-solid coupled,according to the HB5217-1982 low-cycle thermal fatigue test method of metals,the heat transfer of unsteady fluid-solid coupled of the exhaust manifold was analyzed,the temperature field of outside wall of fluid and convection heat exchange coefficient field were calculated as well as the temperature field of solid area.(3)Based on the above-obtained temperature field in the solid area,the thermal modal parameters of the exhaust manifold were calculated and analyzed,and the modal natural frequency was evaluated.The thermal modes of the structure under different temperature loads were calculated,and the influence rule of the temperature load on the structure mode was summarized.(4)Under influence of cycled temperature load,the thermal deformation,thermal stress and equivalent plastic strain of the exhaust manifold structure were simulated and analyzed,on the basis of Manson-Coffin formula,the low-cycle thermal fatigue life was estimated.The exhaust manifold was improved based on the above analysis result.The analysis result showed that elevated temperature can reduce the natural frequency of structure mode,and the higher the modal order,the larger the range is,so the exhaust manifold cannot have the resonance.The temperature of the junction of 4 tubes is higher and the temperature gradient in the region is large,the produced thermal stress exceeds the yield strength of the material,the low-cycle thermal fatigue life was calculated.It showed that the exhaust manifold can meet the use demand,and the improved thermal structure property is strengthened.