High-strength Diesel Engine Thermal-mechanical Stress Analysis Of Cylinder Head-exhaust Manifold

At present,the internal-combustion engine gradually develops towards low fuel consumption and high power density,which inevitably results in the increase of thermal load and mechanical load.Therefore,its reliability needs to meet higher requirements.The cylinder head and exhaust manifold are the most directly heated components in an internalcombustion engine,and they are also the components that withstand the greatest mechanical loads.Their reliability directly affects the overall reliability of the internal combustion engine.Therefore,the analysis of the thermos-mechanical coupling stress of the cylinder head-exhaust manifold can provide a valuable basis for the structural design and optimization of the cylinder head-exhaust manifold system,thereby improving the overall reliability of the internal combustion engine.Based on a high-strength six-cylinder electronically controlled high-pressure commonrail diesel engine,the reliability of its cylinder head,exhaust manifold,and corresponding connecting components under complex thermal-mechanical loads is studied in this paper.Firstly,based on the diesel engine data,a one-dimensional and three-dimensional coupling calculation model of the exhaust system,a three-dimensional calculation model of the cylinder working process,and a three-dimensional calculation model of the cooling water cavity of the cylinder are established,and the thermal boundary conditions of the heat exchange surfaces are obtained.Then,through time-averaged method and fluid-structure coupling,the temperature field results of the cylinder head-exhaust manifold are obtained.Finally the mechanical load and temperature load are applied to the calculation model of the cylinder head and exhaust manifold through step loading to obtain the thermal-mechanical coupling stress distribution,and the calculation results are analyzed.The calculation process shows that a more accurate thermal boundary condition of the exhaust port and the inner surface of the exhaust manifold can be obtained by a onedimensional and three-dimensional coupling calculation,and the combined analysis of cylinder head and exhaust manifold can get more accurate temperature field data,so as to evaluate the reliability of cylinder head and exhaust manifold more accurately.The calculation results show that under a load cycle,the cylinder head basically meets the strength requirements,a small amount of plastic deformation occurs in the exhaust manifold,and the gasket meets the airtight requirements.Their most dangerous conditions are when bolt preload and temperature loads are applied.And,the largest area of thermal mechanical stress are the nose bridge area between the intake and exhaust valves and the transition area between the flange and the straight pipe.Among them,the most important threat of cylinder head is temperature load,and the main threat of exhaust manifold is stress concentration.Therefore,their structural strength can be improved by reducing the thermal headload of the cylinder head and optimizing the exhaust manifold structure.