Research Of The Thermal-mechanical Stress And Fatigue In Diesel Engine Cylinder Head And Block

This paper proposed a complete set of multi-field coupling method for strength andfatigue analysis of cylinder head and block which combined CFD and FEA simulation.This method not only can accurately predict the temperature and stress of the cylinderhead and block, but also can get the distribution of the fatigue life, and finally predict thedanger area of the engine parts, which can help us make reasonable and improvementoptimization program.Aiming at a4-cylinder turbocharged diesel engine, this paper carried out simulationand experiment study for structure reliability of the cylinder-head and block which underthe conditions of maximum explosion pressure. The simulation study included severalsimulating explorations such as3-dimensional CFD of in-cylinder combustion and enginecooling jacket, simulation of cylinder head temperature field which use fluid-structureinteraction，stress and strain analysis under thermal-mechanical coupling conditions, andlow/high cycle fatigue analysis of the cylinder head. The experiment included thermalbalance test of engine cooling system and temperature measurement test of cylinder head.The analysis showed that computed temperatures were consistent with experimentalmeasurements, and the danger region predicted by calculating is matching the crack inactual experiment. In order to solve the problem of cracks, the simulation designed twooptimization schemes for problems of original head. The results showed that the stress atthe crack decreased from245MPa to230MPa and safety factor increased to1.21from1.02after increased wall thickness. On the other hand the stress dropped significantly afterchanged the cylinder material from gray iron to vermicular iron．Both by increasing thewall thickness and by replacing the material can solve the crack problem. In order to findout the load capacity of the nose area of the cylinder head, the simulation increased thecombustion pressure from19MPa to21MPa. Then the maximum temperature increasedfrom331℃to354℃and the low cycle fatigue life had declined24~32%. The resultsshow that21MPa is closing the extremely load capacity of the cylinder head.