Researches On Influencing Mechanism And Control Of Combustion Noise Of Diesel Engine

As people's standard is improving constantly, the quantity of possession of automobiles is substantially increasing and people's requirement for comprehensive performance of automobiles is also enhanced continuously. The research for NVH technology has been one of the main subjects in the research area of cars. The noise of engine is one of the major noise sources of automobiles and also the basis on the generation of other noise. Therefore, the control for the noise of engine is very practically significant. Vehicles powered by diesel engines, which become a direction receiving attention with the domestic development of the technology of the diesel passenger cars. The contribution of the combustion noise of DI diesel engine to the whole noise of diesel engine takes up a mainly position in idle condition. The diesel engine for the vehicle is in the transient state frequently in the actual operation; combustion noise in transient condition is higher than that in steady condition in the same load and rotation speed. On the basis of the research for the influencing mechanism of the combustion noise and control of combustion noise of diesel engine in steady condition, this paper is developing the research on control of combustion noise of diesel engine in idle condition and transient condition and presents the feasible control policy.This article firstly takes DI diesel engine as a main research object to analyze the mechanism of impact of turbocharged condition on the combustion noise of a diesel engine by testing the combustion noise before and after turbocharged condition and the factors of the impact on the combustion noise. Turbocharged condition has a greater impact on the combustion noise in the condition of the middle-speed and appropriate load, making most of the conditional combustion noise reduce to 1dB. The impact of turbocharged condition on the combustion noise is mainly by changing the rate of pressure rise and high-frequency oscillation of combustion pressure in the cylinder, and the change of combustion chamber wall's temperature caused by turbocharged is also one of the factors of the impact of the combustion noise. Design the reasonable Exhaust Gas Recirculation (EGR) system and carry out the mechanism research for the impact of the combustion noise of the diesel engine. The research result shows that EGR makes the combustion noise reduce in the steady condition of the mid-low load by ensuring the power loss within the rate of 6%, and then as the rate of EGR(within 16%) is increasing, the combustion noise is generally reducing. EGR changes Air/Fuel ratio and intake temperature, causing the change of ignition delay, changing the peak numerical of heat release rate, the rate of pressure rise and high-frequency oscillation of combustion pressure in the cylinder, thus impressing the combustion noise.This paper is developing the research on combustion noise for the control by pilot injection. The result shows:in the different conditions, the reasonable pilot injection can efficiently reduce the maximum of the rate of pressure rise, the peak numerical of heat release rate and high-frequency oscillation of combustion pressure, reducing the combustion noise; The greater pilot injection amount can make up for disadvantages of cold condition making combustion chamber wall's temperature lower and narrow the effect difference between pilot injection's control for the combustion noise of cold condition and that of warmer condition.In the aspect of control of combustion noise in idle condition, considered compression temperature is low, the mixture air is non-uniform and ignition delay is long, this article carries out the research of control combustion noise in idle condition by EGR, lower pressure of injection and pilot injection. The results show that EGR, lower pressure of injection and pilot injection can effectively control combustion noise in idle condition. It provides the reference for the actual control of noise of diesel engine in idle condition.On the basis of the research for the influencing mechanism of the combustion noise in transient condition, this paper carries on the research of control combustion noise in transient condition, analyzed control difference between transient condition and steady condition; presents control policy for control of combustion noise in transient condition. On the basis of the control policy, this paper using pilot injection, EGR and turbocharged condition controls combustion noise in transient condition. The results show pilot injection, EGR and turbocharged condition cause combustion noise in transient condition to reduce. It provides the foundation for the project actual application to control combustion noise in transient condition.