Flow Performance And Thermodynamic Performance Analysis Of An Engine Exhaust Manifold

With the continuous improvement of engine power and emission requirements,the rationality of exhaust manifold design has an important impact on the performance of the engine.In practical use,the flow performance of the exhaust manifold not only affects the dynamic performance of the engine,but also the exhaust manifold is prone to thermodynamic performance failure due to excessive temperature during exhaust.Aiming at these problems,this paper studies the exhaust manifold of a diesel engine,which has certain theoretical significance and engineering application value.In this paper,GT-POWER,FLUENT and ABAQUS software were used to simulate and analyze the flow performance and thermodynamic performance of the exhaust manifold,and the structure of the exhaust manifold is improved according to the calculation results.The main work is divided into three aspects:(1)GT-POWER and FLUENT software were coupled to study the transient internal flow field of the exhaust manifold,and the flow performance of the internal flow field is analyzed.(2)CFD and FEA methods were combined to simulate and analyze the temperature field,stress field,fatigue life and modal performance of the exhaust manifold based on the fluid-solid coupling method of surface mapping.(3)Improved the design of the structure of the exhaust manifold.The main findings are as follows:For the original model:(1)Although the uniformity of the velocity at the outlet end of the exhaust manifold meets the requirements,gas channeling and vortex phenomena appear in the branch pipe during exhaust.(2)The maximum thermal stress of the exhaust manifold is close to the tensile strength of the given material;the fatigue life of the exhaust manifold is 27630 cycles.(3)The minimum natural frequency of the working state is 991.09 Hz,which is much higher than the exhaust excitation and road load excitation,and the exhaust manifold will not appear resonance phenomenon.After the improvement of the exhaust manifold structure by increasing the outlet diameter and installing stiffeners between the branch pipes,it can be found that:(1)The improved uniformity of the outlet end face velocity meets the requirements,but the exhaust manifold gas channeling and vortex phenomena are improved,and the volume flow at the outlet of the manifold has increased by 1.64 times,which is conducive to the rapid exhaust gas discharge.(2)The maximum temperature of the exhaust manifold after the improvement is reduced by 3.4% compared with that before the improvement;the maximum thermal stress value is reduced by 42.6%;the exhaust manifold will not break due to fatigue damage.(3)The natural frequency of the improved exhaust manifold is further away from the excitation frequency range of the engine and road.In summary,by increasing the diameter of the manifold outlet and installing stiffeners on the manifold,the exhaust manifold can better meet the requirements of use,which can provide a reference for the optimization design of the exhaust manifold in engineering practice.