The Three-dimensional Finite Element Analysis Of Transient Temperature Field&Stress Field On Marine Diesel Engine Piston

With the continuous strengthening of the marine diesel engines, the strength and liferequirements of pistons are increasing. Temperature field and stress field of pistons wasanalyzed by use of finite element method to know the distribution of heat load and stress,which will provide the basis for the design, improvement and optimization of pistons. It is ofgreat importance to improve the reliability of pistons. The paper took the piston of620single-cylinder engine as an example and analyzed the steady-state temperature field transienttemperature field and transient stress field under the standard conditions. The details are asfollows:1)A three-dimensional finite element model of the piston was established. Boundaryconditions of steady-state analysis, periodic transient analysis and starting were donerespectively. Comparison between steady-state temperature field with experimental valueswas done to verify the correctness of the steady-state boundary conditions and analyticalmethod. Through the periodic transient thermal analysis, temperature fluctuations on thesurface of the piston were derived, which indicated that the surface contacted with gas was themain temperature fluctuation area. The max temperature fluctuation can be up to20°C andthe wild fluctuation occurred in a distance of2mm from the surface of the piston. The lawthat the change of temperature in the condition of starting is exponential was derived throughthe analysis of temperature field. Extreme temperature fluctuations will generate hugequasi-static thermal stress.2) Simulation of transient thermal stress field was done based on the accurate pistontransient temperature field. Periodical mechanical load was added to the model to get transientmechanical stress and the transient thermal stress and the transient mechanical stress wascoupled together to derive transient coupling stress. The figure of stress concentration and theamplitude of stress and strain was calculated and the course graph of fluctuation with timewas derived. The influence factors of stress at different locations and different time wereanalyzed. The analysis showed that larger thermal stress occurred in the place with greatertemperature gradient and mechanical stress was most greatly influenced by the explosion ofgas. The origin of coupling stress was different in different stages and it was the biggest at themoment of explosion. Transient analysis can better describe the dynamic characteristics of pistons in theworking circulation of diesel engines and it shows the true state of pistons at working stage,which provides a theoretical basis for analysis of the fatigue life of pistons and the reliabilitydesign.