The connecting rod of high-power marine diesel engine fractured near the bolt hole before reaching the life expectancy, in which the typical fatigue fracture characteristics were found. The study improved the traditional simulation method of connecting rod to simulate the diesel engine more realistically. On the basis of the crank train model, various relevant boundary conditions are considered by introducing membrane mesh. The simulation results are consistent with the failure analysis of diesel engine, which verifies the correctness of simulation method proposed in this research. The material used for the connecting rod is 42CrMoA, which fatigue performance can only be obtained through fatigue testing. The yield limit of the material is 950MPa and an exact S-N curve is obtained by the fatigue test. This paper combined the material fatigue property with dynamics simulation, and found that the minimum safety factor of connecting rod occurs 5°CA after the TDC and is 1.33, which is satisfied but not sufficient. Meanwhile, the relationship between the bolt preload force and the stress level was investigated as the damage of connecting rod appears in the bolt hole region. Various preload forces were analyzed and the safety factor increased from 1.33 to 1.97 when the preload force is set to 80kN, which increased by 43%. In addition, the influence law between preload force and stress as well the empirical formula between them were summarized. This research not only provides a new method for the selection of preload force, but also allows rapid analysis of the connecting rod stress without complex finite element models in the conceptual design stage.

The piston of low speed diesel engine works in bad environment and bears large thermal and mechanical load, so it is necessary to study the piston. In this paper, a Marine low-speed diesel engine piston as the research object, builds the piston component - crosshead assembly - connecting rod - crankshaft model, simulation of the piston in the working process of the actual working condition, through professional simulation software for fluid-thermal-structure coupling calculation, the temperature field and coupling stress field of piston assembly are obtained. In this paper, the convective heat transfer coefficient and fluid temperature on the surface of the piston cooling oil chamber are obtained by CFD simulation, the temperature field of the piston assembly is obtained by fluid-thermal coupling, and the coupling stress field and deformation of the piston assembly are obtained by fluid-thermo-solid coupling. Finally, the maximum temperature of the piston is 313.9°C, the maximum deformation is 1.03mm, and the maximum stress is 347.4Mpa, which meet the requirements.

The connecting rod assembly of a high-power low-speed diesel engine has high quality and high cost. If the connecting rod component is damaged, the whole machine may be paralyzed, resulting in serious economic losses and safety problems, so it is necessary to carry out strength analysis and structure optimization, reduce the failure rate, and increase its life. This paper takes the connecting rod of a low-speed diesel engine as the research object, builds the crank connecting rod mechanism model, and carries on the strength simulation analysis through professional simulation software. During this period, the accurate S-N curve of connecting rod material is obtained through a fatigue test, and the static strength test of the connecting rod assembly is carried out by an electro-hydraulic servo universal testing machine. The numerical modeling is validated based on the test results. Therefore, the influence of the structural parameters of the cross-section and the large end transition fillet on the stress of the connecting rod is analyzed. The results show that optimizing matching between the large end fillet of the connecting rod and the long diameter of the rod section not only reduces the mass but also improves the safety factor. After optimizing the structure of the connecting rod, the mass of the connecting rod is reduced by 5.85%, the maximum stress is reduced by 13.7%, and the safety factor is increased by 16.0%. In addition, due to the low-speed diesel engine connecting rod assembly weight is big, and the simulation computation efficiency is low, this paper by studying the influence of the cross-section parameters of the rod body and the large end transition fillet on the stress of the connecting rod, fitted the empirical formula calculating the maximum stress of connecting rod, for this model and similar type in the conceptual design, technology design provides a new analysis method, improved the efficiency of structural optimization and strength analysis of connecting rod assembly, filled the research gap of strength analysis and structural optimization of low-speed diesel engine connecting rod.