Research On Vibration Predicting Technology For New Medium-Speed Diesel Engine

Diesel engines have high thermal efficiency, and they are economical. Compared to petrol engines, they have lower rotating speed, yet larger torque. Diesel engines do not have ignition system, and are quite reliable. They are widely used in the fields of civilian ships, small and medium-sized marine vessels, automobiles and engineering machinery. As marine diesel engines are developed with higher speed, lower mass, more power, greater strength of the diesel engines’main components is required. At the same time, diesel engines suffer more and more vibration and noise problems. Therefore, there are theoretical significance and practical engineering applications in research on strength and reduction of vibration and noise of diesel engines.The6L21/31medium-speed diesel engine is considered as the research object. Because the research used in vibration and noise prediction of marine diesel engines is imperfect. So research on6L21/31medium-speed marine diesel engine is carried out by using modern test technology and CAE software, on the basis of theories of vibration, modal analysis and finite element (FE). The main work presents as follows:1. According to2D-drawing and3D-model of the diesel engine on hand, the engine’s model is improved by Pro/E. Both the experimental and theoretical modal analysis of cylinder head, piston and cylinder liner of6L16/24diesel engine, as well as cylinder head of6L21/31diesel engine are carried out. Experimental modal parameters are identified to verify the theoretical models. They are the preconditions of building the FE-model of the whole diesel engine.2. FE-model of6L21/31diesel engine is built by MSC.Patran/Nastran. The modal analysis of the whole engine is done. The vibration characteristics such as natural frequency and vibration mode are found. They are basis of the following vibration analysis.3. Vibration analysis of6L21/31diesel engine is carried out by MSC.Nastran. The distribution of vibration speed and acceleration among all the components are got. For example, the oil-pan and inlet duct of the cylinder head are thin-wall construction. They have low stiffness, yet cause large vibration. On the other hand, the engine block has thick walls. That means it has large stiffness, cause small vibration.4. Vibration test of6L21/31diesel engine under rated condition is carried out. Vibration acceleration on primary locations is measured, and compared with FEA (finite element analysis) results, so the FE-model is further improved. The research shows that:The peak frequencies of oil pan become slightly smaller after lubricating oil addition, but the peak amplitudes get a little bit larger.