Finite Element Analysis And Structural Optimization Of Diesel Engine After-treatment System

In recent years,the automobile industry in our country has made a rapid development which followed by air pollution,noise pollution and other issues have become increasingly serious.As an important part of automotive exhaust systems,the after-treatment system plays an essential role in reducing emissions and noise reduction.After-treatment system was affected not only by both engine and road excitation in the actual operation,but also by the impact of high temperature from the exhaust gas.Thus,the system is prone to failure.The finite element analysis and optimization has great significance for the engineering design of the after-treatment system and also provides a theoretical basis for the research and design of system's structure.Combined with a after-treatment of diesel engine,some FEM software is used to do modal analysis,simulation of fluid solid coupling,structural strength and analysis of fatigue which based on road spectrum test.The main contents of this paper are as follows:(1)Establish finite element analysis model and carry out the modal analysis of the after-treatment system.According to the simulation results,the cause of the failure is analyzed.The results show that the resonance of the after-treatment system under the 2nd and 3th modes is the cause of the structural failure.Then the method of average driving DOF displacement is used to predict the location of rack mounting.After that,carry out the static analysis and fully constrained modal analysis of different design proposal and obtain a rational design.(2)According to the actual location of the structure,build the CFD analysis model of after-treatment system.Boundary conditions are set by the data provided by the enterprise.Subsequently,analyze the simulation of fluid solid coupling and receive the wall temperature and heat convection coefficient.Through evaluating the temperature and flow velocity of the carrier,prove that the carrier meet the general operational requirement.From the results above,the coefficient of heat transfer and wall temperature are mapped to the finite element model.After the iterative computation,the structure's temperature field is received and analyze the thermal stress.(3)Considering the after-treatment system's practical work environment,combine the thermal modal analysis with temperature field calculated above.According to the difference between the results of cold and hot mode,determine an optimum structure which is more approach to physical truth.(4)Due to the loading that pavement transmit to the after-treatment system is random and structural stress is different under diverse operating conditions,and in order to ensure the authenticity of the acquisition signal,it's valuable to do road spectrum test and check the consistency of the experimental data.These steps can provide input for analysis of structural strength and fatigue calculation.(5)According to the results of road spectrum test,coupling analysis of thermal and mechanical loads on the after-treatment system is done.Meanwhile,the conclusion shows the displacement variation and stress distribution and can make the analysis of fatigue happen.This paper integrate finite element analysis with road spectrum test and make a research on structural strength calculation and optimization design of a diesel engine.Considering the effect of temperature field into the method of average driving DOF displacement makes it has a certain reference significance.