Thermo-mechanical Fatigue Analysis Of A Diesel Engine Cylinder Head Based On Two-way Fluid-structure Interaction

The cylinder head is one of the parts working in the most severe condition in diesel engine.It bears high mechanical loads and high thermal loads.With the continuous enhancement of the diesel engine,the thermal load borne by the cylinder head has been greatly improved,and its thermal fatigue has been the focus of engineering development.In the design stage,considering the requirements of time cost and calculation precision,establishing an effective calculation method of diesel engine cylinder head fatigue analysis has become one of the key issues in the development of diesel engine.It is important in ensuring the trial production of diesel engine and avoiding the delay of the project period due to the reliability issue of the diesel engine.In this paper,a high strengthened four cylinder turbocharged diesel engine cylinder head is the research object.First,the fatigue of the cylinder head is analyzed by the one-way fluid solid coupling method with low time cost.The heat transfer boundaries of the gas and the cooling jacket are respectively obtained by the three-dimensional combustion calculation and the separate cooling jacket CFD analysis.The above boundary is loaded together in the solid model to obtain the temperature distribution of the cylinder head,whichis the boundary of the heat load.The mechanical stress is applied to obtain the stress results and the high cycle fatigue life is analyzed.Secondly,due to the high temperature of the initial cylinder head,the safety coefficient of the high cycle fatigue of the cylinder head does not meet the design requirements.Optimization of the fluid side structure of the cylinder head is done,and the final safety factor of the cylinder head satisfies the design requirements.It is found that the temperature distribution of the cylinder head is more reasonable after the structure optimization,the temperature deviation reduces from 78? to 20?,the consistency of each cylinder greatly improves,the stress of the fatigue failure position reduces from 245 Mpa to 200 Mpa,the high cycle fatigue life of the cylinder head increases from 0.6 to 1.3,and the low cycle fatigue life increases from 2100 cycle to more than 10000 cycle.Then,the final optimization scheme is studied by the two-way flow solid coupling method with the higher precision temperature field distribution.The test results of the cylinder head temperature field of the prototype show that the average error of the two-way flow solid coupling temperature field is only 4.9%,which is far lower than the error of the one-way fluid solid coupling,the temperature field based on the two-way fluid solid coupling is more accurate.The minimum safety factor of the high cycle fatigue is 1.14,which is located at the corner of the cooling jacket between the intake and exhaust port and the limit of the safety factor is more than 1.10.The low cycle fatigue danger point of the cylinder head is located at the hole of the third cylinder injector,and the fatigue life is 6720 cycle,which meets the design requirements.Finally,the diesel engine test prototype has passed the cold and heat shock test.It is proved that scheme select can be done by the one-way fluid solid coupling methodand the fatigue analysis can be determined by the two-way fluid solid coupling method.The time cost and the calculation precision can get better compromise in the process of the engineering development.