Mechanism Of Combustion Noise Of Turbocharged Direct Injection Diesel Engine In Transient Conditions

The combustion noise plays an important role in the whole noise of the direct injection diesel engine. The transient change of conditions firstly reflects the change of the in-cylinder process of the internal combustion engine. In order to study the phenomena that the noise changes acutely in transient conditions, it is necessary to find out the effect mechanism of the transient conditions on combustion noise.This dissertation takes a turbocharged direct injection diesel engine as its research object, applying testing technology and testing method to the research on the combustion noise in transient conditions. It measures the noise through the method of near-field sound pressure and obtains combustion noise by way of designing time window. Meanwhile it measures the cylinder pressure, the pressure of nozzle end and the vibration signal. It analyzes the cause of the differences in combustion noise in transient conditions and stable conditions respectively through two direct factors which influence the combustion noise: the Aerodynamic load and the high-frequency oscillation of cylinder pressure. It shows that the rate of pressure rise and the high-frequency oscillation of cylinder pressure are the main factors which influence the combustion noise.The combustion delay period, the quantity of fuel injected, and so on are indirect influencing factors of the combustion noise. This dissertation analyzes that how these factors vary in transient condition and stable condition respectively. Thought that, this dissertation then researches how these factors influence the stimulus property of the cylinder pressure and the high-frequency oscillation of the cylinder pressure, and how they further influence the combustion noise in transient and stable condition respectively.The research shows that differences in parameter such as the combustion delay period, the quantity of fuel injected, the temperature of chamber wall in transient and stable conditions in the same load and rotation speed respectively result in the change of combustion pressure, the rate of pressure rise, the frequency and amplitude of the high-frequency oscillation of cylinder pressure, therefore result in different combustion noise in transient and stable conditions respectively.