Study On Cooling And Thermo-mechanical Coupling Of Marine Low-speed Diesel Engine

As one of the important moving parts of the diesel engine,the piston is subjected to extremely high mechanical load and thermal load during the whole machine work.Good cooling of the piston is an important aspect to reduce the thermal load of the piston.More scholars have studied and broken the oscillation cooling of the annular cooling chamber piston.However,there are few studies on the cooling problem of the complex cooling chamber of the low speed diesel engine piston.In order to get more reasonable design and improvement of the piston,we must make a comprehensive analysis of its cooling characteristics and structural features.In this paper,the CFD software is used to analyze the conditions of the oscillation cooling and the flow distribution of cooling oil about a low speed diesel engine piston.Also,the transient convective heat transfer coefficient of the cooling chamber wall is calculated.The finite element analysis software is used to calculate the transient temperature field of the piston,and the finite element contact analysis is carried out for the worst condition.The specific research contents are as follows:(1)The cooling method and cooling characteristics of all kinds of marine low speed diesel engine pistons are analyzed by referring to foreign literatures.(2)Fluent as the CFD software was used to simulate and analyze the cooling chamber of the piston.The transient state of two-dimensional fluid region is simulated by the model of VOF and k-?.The oscillation of the piston cooling medium is simulated by the two methods of loading the momentum source term and the dynamic grid of Fluent,which proves the correctness of the simulation about the medium oscillation.The two-phase flow model of VOF and the turbulence model of k-? are used to simulate the transient flow state of the three-dimensional flow area,and the conditions of oscillation cooling are analyzed.The inlet velocity condition of the cooling chamber is simulated and loaded into the cooling chamber inlet boundary condition by means of UDF.The characteristics of the medium flow in the cooling chamber are analyzed for one period of the crankshaft rotation.The model of VOF two-phase flow and the turbulence model of SST k-? are used to simulate three different inlet velocity conditions of the cooling chamber,and the transient average convective heat transfer coefficient of the cooling wall was quantitatively calculated.Through the above calculation,the cooling characteristics of a low speed diesel engine piston are analyzed.(3)The thermo-mechanical model of the piston is established,and the finite element method is used to analyze the temperature field and the stress field of a low-speed diesel engine piston.The stress distribution of the piston assembly is analyzed by the method of finite element contact analysis.The worst state of the piston was selected to analyze the thermal stress,mechanical stress and thermo-mechanical coupling stress of the piston by the methods of finite element contact analysis.Finally,the conclusion is drawn that thermal load cause stress concentration of piston and the mechanical load cause the piston to fatigue.The analysis of the deformation of the piston shows that the piston thermal load mainly causes radial deformation of the piston,and the pressure of the cylinder mainly causes the piston to deform axially.