Research On Multi-physics Coupling Simulation Models And Acoustic Optimization Design For Diesel Engines

Highly strengthened diesel engine is the mainstream of the engine industry future development; however, with the increasing of the enhanced performance of the engine, the reliability problems and NVH problems of strengthened engines are increasingly prominent. Engine NVH problems will seriously affect the durability and comfort of the vehicle. Therefore, the noise and vibration reduction work of strengthening the engines is received more and more attention. How to solve these problems becomes the important responsibility of internal combustion engine workers. Based on digital simulation techniques and experimental analysis techniques, this paper carried out a detailed research on the reliability and NVH performance for diesel engines under multi-physics coupling conditions, and achieved remarkable results.Fluid-solid coupling calculation model of diesel engine parts and water jacket was established. Using boiling heat transfer model, a detailed analysis was earned out for the thermal performance of diesel engine at high load transfer model. The temperature field and stress field of diesel engine parts were calculated with water jacket heat transfer results as boundary conditions. After that, the engine cooling water jacket was optimized; the cooling system thermal performance and the state of the structure stress distribution were improved.A detailed research was earned out on engine crankshaft fatigue strength performance under complex multi-physics coupling conditions. The crankshaft multi-body dynamics model was established coupled with hydraulic lubricating bearings calculation model, and by comparing with the different bearing calculation model results, the importance of thermodynamic properties in bearing dynamic performance prediction was proved. Based on thermal elastic hydrodynamic lubrication model and crankshaft bearing multi-body dynamics model, the dynamic stress distribution and fatigue strength of crankshaft were studied. Combined with the fatigue strength experiments, the importance of crankshaft digital analysis model in the fatigue strength of the crankshaft design was proved.The beamforming method was firstly used on noise source identification; this method significantly improves the efficiency and accuracy of the noise source identification. Coupled with multi-body dynamics model and bearings hydrodynamic lubricating model, the whole engine calculation model was established. Based on this model, the engine noise performance was predicted and verified by engine bench tests. On the basis of noise prediction, track by modal method and shape optimization method were used to improve the noise performance of the engine parts, the structural radiation noise was significantly reduced.By measuring the in cylinder of diesel engine combustion state and surface vibration acceleration and radiated noise, traditional attenuation curve method is studied on the diesel engine noise prediction application, and its advantages and disadvantages were pointed out. By comprehensive and detailed research on diesel engine combustion noise influence factors, the key factors that affect the diesel engine combustion noise were found. An entirely new combustion noise optimization method based on the noise changes was proposed. By single-variable optimization, multivariable optimal combination verification method, the optimization design was carried out for the combustion noise performance of a diesel engine. The studies on engine noise reduction in this dissertation took the lead in the combustion noise and whole engine noise reduction, provided important theoretical basis and engineering application foundation for the future internal combustion engine noise control study.