The Thermal-mechanical Coupling Strength Analysis Of Exhaust Valve Housing In Marine Diesel Engine

The exhaust valve housing in a marine two-stroke diesel engine is an important part of the combustion chamber assembly and its stress is very complex.Its bottom part bears the gas explosion pressure from the fire surface of the cylinder head and its upper part is constrained by pretension bolts.At the same time,the exhaust valve housing is provided with exhaust flue which is in direct contact with high temperature gas and cooling water chamber which is in direct contact with high temperature cooling fresh water.That will cause the exhaust valve housing to bear thermal stress generated by temperature difference when it works.In addition,due to the thin-walled structure of exhaust valve housing,the thermal stress or mechanical stress is easily concentrated in its abrupt section when it is subjected to external force.Therefore,the strength analysis of exhaust valve housing under thermal-mechanical couple load is important to improve the reliability of marine two-stroke diesel engine.The main content of the paper is described as follows:(1)According to the design data of marine diesel engine,the geometric models of exhaust valve housing and related connecting parts are established.At the same time,the cooling water chamber and exhaust flue model in exhaust valve housing are extracted.After that the simulation calculation models are established in the finite element software.(2)The cooling water flow in the cooling water chamber is calculated,and the heat transfer boundary conditions between the wall of the valve housing and the cooling water are obtained,then the cooling performance is evaluated according to the parameters of velocity and pressure.The exhaust process in the exhaust flue is calculated,and the heat transfer boundary conditions between the flue wall and the gas are obtained.(3)Based on the results of flow field analysis,the steady、state thermal analysis of exhaust valve housing is carried out,and the distribution of temperature field and heat flux is obtained.The mechanical loads,such as gas burst pressure and bolt preloading,are considered to analyze the strength of exhaust valve housing under mechanical load,thermal load and thermal-mechanical coupling load,and the stress field distribution and deformation of exhaust valve housing under different loads are obtained.According to the analysis results,the temperature distribution of the exhaust valve housing is demarcated by the cooling water chamber,and the high temperature region is mainly distributed in the middle part of the exhaust flue in exhaust valve housing which is farthest from the cooling water.The stress distribution of valve housing is mainly affected by thermal load,the deformation and stress of the valve housing under the mechanical load is small,and the deformation of the upper edge of the outlet of exhaust flue in valve housing under the thermal load and the thermal-mechanical load is large.The stress distribution mainly concentrates around the bolt hole of valve housing and the bottom of valve housing which is near the inlet of exhaust flue.The strength analysis of the exhaust valve housing under different loads provides a certain theoretical basis for the structure optimization and the improvement of reliability of exhaust valve housing in marine two-stroke diesel engine.