Performance Analysis And Improved Design Of A Gasoline Engine Exhaust System

The automobile exhaust system has a great influence on engine performance,which in turn affects the power and economy of the vehicle."The vehicle development model based on the existing power and the target vehicle for the target truck",there is the problem of bad matching between the chassis of the standard model and the existing engine.Therefore,it is necessary to adapt the engine exhaust system,suspension system and other subsystems according to the design.In order to ensure the power and economy and emission performance of the new development vehicle,it is of great engineering significance to analyze and improve the performance of the exhaust system of this kind of product.The paper,based on an SUV of the enterprise,initially equipped with the "A" engine,according to the series requirements,upgraded to "B" engine,"B" and "A" engine are the same platform,but different displacement.The desired exhaust pipeline of the whole vehicle is basically continued,so that the change of the whole vehicle is the smallest.The exhaust system is required to meet the engine performance requirements,that is,the exhaust backpressure should not be greater than the target value.Therefore,we use CFD and FEA method to analyze and design exhaust manifold.At last,we have solved the actual problems of enterprises by testing and verified,and provided a fast and effective optimization analysis method for enterprises.The main contents of this paper are as follows:1.Firstly,according to the 3D model of the exhaust system of "A" engine,the internal flow channel is extracted and the CFD analysis model matching the B engine is established.The CFD analysis value and the test value of the exhaust backpressure are 60.5kPa and 60.9kPa respectively.The data consistency is better,but both were higher than the design goal of 55 kPa,which shows that the CFD model is feasible,but can not simply transplant the exhaust system of "A" engine to the "B" engine.Then,the CFD model is used to analyze the steady internal flow field of the exhaust manifold in the STAR CCM+,and the internal flow field in the exhaust manifold and the inner surface temperature and heat transfer coefficient of the manifold are obtained.The results show that the velocity uniformity of the exhaust manifold is poor,the air flow overlay area is low,and the velocity difference of the oxygen sensor is large.Exhaust manifold to make use of ABQUAS fluid-structure coupling FEA thermal analysis,get the manifold temperature field,thermal stress,thermal deformation and thermal modal and the characteristics of thermoplastic,exhaust manifold maximum thermal stress exceed the material yield limit,shows that there is an optimization space for the exhaust manifold structure.2.CFD and FEA based on the results of the analysis,the exhaust system back pressure is higher than the design index of 55 kPa,combined with the requirements of the overall arrangement and design of the exhaust manifold was designed to improve the reasonable structure,and the manifold before and after improvement were analyzed,The results show that the performance index of the improved exhaust manifold is better than that of the original one,and the analysis result of exhaust system backpressure is 52.2 kPa.meet the design requirements of the theory.3.The actual engineering tests on the exhaust system after the structure improvement have been carried out,such as the bench test and the whole vehicle test.The test results showed that the exhaust back pressure was 53.2kPa,which decreased by 7-8 kPa compared with the original plan,and no crack or fracture occurred in the exhaust manifold.The correctness of the results of CFD analysis and FEA analysis is verified,which shows that the theoretical analysis method is feasible and can guide the practical engineering problems.