Study On Mechanism And Optimization Of Combustion Noise For DI Diesel Engine

Due to the rude work process of diesel engine,its issues of vibration and noise are very serious.Combustion noise occupies a very large proportion of the total radiation noise of diesel engine in the total radiation noise of the diesel engine and has a dominant impact on the engine vibration and noise performance.In this paper,the mechanism,influencing factors and optimization methods of diesel engine combustion noise are systematically studied through experiment and theoretical analysis.Taking a direct injection diesel engine as an example,the combustion noise is optimized and significant achievements are obtained.The mechanism of the combustion noise generation mechanism of the diesel engine is established.The relationships between the in-cylinder pressure signal and the vibration and noise signals in the time domain and the frequency domain are studied,and the close relationship between the combustion excitation and the vibration and noise response is pointed out.The effects of fuel injection parameters(common rail pressure,main injection advance angle,pilot injection interval time and pilot injection quantity)on the combustion noise at different engine speed are studied from three aspects:vibration and noise,combustion process and pressure oscillation.The influence law and mechanism of the diesel engine combustion noise are revealed.The main components and key factors influencing the combustion noise of diesel engine are revealed,which provides theoretical support and reference for the optimal design of combustion noise of diesel engine.The calculation model of the pressure oscillation energy at different injection stages is established,and the signal processing technology is applied to the time-frequency characteristic study of the pressure oscillation.The energy and time-frequency characteristics of the pressure oscillation in the multi-injection diesel engine are investigated intensively.The importance of pilot injection in pressure oscillation is pointed out,and the influence of fuel injection parameters on the oscillation energy and time-frequency characteristics of pressure oscillation in each combustion stage are studied.The combustion noise online optimization for diesel engine considering the emission performance is carried out for the first time in China.The two rounds of on-line optimization test program for diesel engine combustion process optimization based on the noise priority principle are designed.The fuel injection parameters of diesel engine are optimized according to the noise and emission performance respectively.On the basis of effectively reducing the noise of the engine,the power,emission performance and fuel economy stay the original level or even better state.The index that can indicate combustion process of multi-injection diesel engine are established and the correlation between the index and the engine noise is systematically studied.The model that can predict the engine noise using both the tested and the calculated in-cylinder pressure is put forward.Based on this method and the 3-D CFD simulation of diesel engine combustion process,the engine noise is predicted and the influence of fuel injection parameters on engine noise and emissions is studied based on the prediction noise and emission calculation results.Based on the combustion process simulation and proxy model,the multi-objective optimization is conducted to the engine noise and emission performance for the first time and remarkable results are achieved.Finally,the transfer characteristics of different components of the diesel engine are studied by dynamic test,and the importance of reducing the combustion noise from the transmission path is pointed out.The response characteristics of the main structural components of the engine are analyzed using the method of multi-body dynamics method.The low noise structural optimization is carried out and the diesel engine noise is reduced the transmission path.