The Numerical Simulation And Structural Optimization For The Exhaust Port Flow Characteristics Of 4190Z_LC Diesel Engine

The gas flow in the intake and exhaust system of the engine is complex,which will affect the volumetric efficiency,the exhaust emission and the gas exchange loss of the engine directly;the gas exchange process decides the combustion either good or bad,and consequently affects the power output,economy and emission of the engine.When the structure design of the exhaust port is unreasonable,the cylinder pressure will drop slowly during the exhaust,and exhaust gas flows not smoothly,and the pumping loss will increase during the exhaust stroke.This paper takes the exhaust port of 4190 Z_LC diesel engine as the object,and the optimizing of flow characteristics of it as the research purpose;the methods of steady flow test and numerical simulation are adopted to analyze the exhaust gas flow so as to find out the unreasonable places of the flow passage structure and their improvements;the overall optimization is determined.First of all,the exhaust port is measured on the steady flow test bench by AVL constant pressure difference method,and the flow coefficient test data is obtained with different valve lifts;Secondly,the geometry model of exhaust port is obtained by using the reverse engineering method and the exhaust system model is established further;Then the exhaust port is simulated on the platform of AVL FIRE software,and the model is verified to be correct through comparing the simulation flow coefficients with the test data;and then through a detailed analysis of the three-dimensional flow fields,the unreasonable structure positions of the exhaust system are found out,which providing a basis of the structure optimization of the exhaust system of the engine;Finally,using the traditional optimization methods,the exhaust port is optimized depending on the results of the flow field analysis.Research shows that: for the original exhaust port there are unreasonable flow losses in the positions in the exhaust gas passage,the valve seat near the cylinder,the valve seat and the valve,etc.;among them the relative positions of the valve seats on the cylinder head and the exhaust gas passage affected the flow performances of the exhaust port greatly,but the structures of the valve seat and the valve affect less;After optimizing the whole exhaust system,the flow coefficients increase largely;the average flow coefficient is increased by 16.71%,and the flow performance is improved substantially.This paper provides a theoretical basis for the optimization of the real exhaust system of the engine.