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

With the development of the diesel engine facing high speed, light, high efficiency, its vibration and noise question is increasingly prominent. In order to improve the diesel engine product quality, and reduce its noise level, it is of the vital practical significance and the project application value to research on its vibration and noise reduction technology.This article researches on noise predicting technology for the new medium-speed diesel engine, including the theoretical calculation and the experiment measurement two aspects. The vibration response analysis is carried on by the application of Finite Element Method (FEM) and the radiant noise is calculated using Boundary Element Method (BEM). The cylinder press, vibration and noise of the diesel engine is measured and analyzed. The experiment has provided the primary data for theoretical calculation, and examined the accuracy of the computation model and the calculation result. The main research conclusions are obtained as follows:1. The new medium-speed diesel engine's dynamics model is established, and its vibration response calculation is carried on by FEM. The distributed rule of the diesel engine surface vibration response is analyzed. The vibration gradually reduces from the cylinder head to engine body; and the oil sump's rigidity is smaller, its vibration is bigger.2. The influence of the isolation mounting is studied to the vibration response analysis on the diesel engine. After contrastive analysis, the vibration energy distribution changes, and the vibration frequency moves ahead.3. The boundary element model of the new medium-speed diesel engine is established. The speed boundary condition, the fluid material attribute, the sound load and the field point are defined. The radiant noise calculation is carried on by BEM. The analysis indicates that the radiant noise of diesel engine is caused by its structure vibration.4. The radiant noise analysis is carried on with the pressure intensifier's noise loaded or not. The research indicates that the pressure intensifier's noise increases middle and high frequency ingredient of the diesel engine radiated noise.5. The analysis is carried on between vibration measurement result and computed result by FEM of the diesel engine. From vibration frequency spectrum distribution, the computed and the measurement result's energy distribution tendency is close, each chief frequency is obvious, and the partial frequency's peak value is closer. The computed and the measurement result exists error, but reflects basically diesel engine's main vibration characteristic. It is showed that the diesel engine's dynamics model is correct.6. The analysis is carried on between the noise measurement and the calculation result by BEM of diesel engine. From 1/3 octave spectrum chart, the maximum value of acoustic intensity between the calculation and the measurement result is quite close. But both exists error, the reason is that the measurement noise is each kind of radiated noise comprehensive result in the diesel engine work process, including the aerodynamic noise, the combustion noise and the mechanical noise; while the calculated noise includes the mechanical noise caused by its structure vibration and the noise caused by the pressure intensifier noise source.The study provides analysis method for noise predicting technology for the new medium-speed diesel engine, and confirmed the feasibility and efficiency of FEM and BEM in the design of new medium-speed diesel engine.