Separation And Prediction Studies Of Gasoline Engine Combustion Noise

Nowadays,noise pollution has been one of the four major pollutants.The amount of cars are keeping growing and the noise they made play a more and more important role in the noise pollution.Engine noise is the chief culprits of the problems.It is said that the noise produced by engine account for more than 55% of the car's total noise.Therefore,we have to take measures to control the engine noise to reduce the noise of our surroundings.Based on the difference of transmission pass,the engine noise can be divided into two parts: the aerodynamic noise and the structural radiation noise.The former can be reduced by improve the air intake and exhaust system and exhaust muffler because it is more independent than the structural noise.However,the latter is harder to reduce because it has many excitation sources,the transfer pass of them is very complicated and the radiation noises are overlapped.Thus,many engine manufacturers are very concerned about the control of engine noise.On this background,this paper pays attention to the identification of mechanical noise and prediction of combustion noise to provide method to control the engine noise well.There are many methods to identify and separate the exciting source of the engine noise,but most of them are remedies after the engine has been produced which can't control the engine fundamentally.This paper proposed a method to predict the combustion noise and control the combustion noise during the plan and design stage of the engine.First,collect the in-cylinder pressure and noise signal of an engine.Then separate the combustion noise and the combustion pressure which excite the combustion noise from the original signal.Finally,calculate the combustion transfer function by the model of combustion noise and the combustion pressure.For the development process of an engine is always based on the old engine,the transfer can be used to calculate and predict the combustion noise of the new engine when it is still in the stage of design.Also,the design of combustion chamber,the injection strategy and the angle of ignition advance affect the noise a lot.So,the transfer function can be used to get the optimized values of these parameters by simulation.Identifying the noise of different engine accessories is very important to reduce the mechanical noise of engine,because the mechanical noise is constituted by many kinds of vibration.In this paper,the vibration signals of different engine accessories and noise signal are measured and used in the coherence function analysis to calculate the correlation coefficient between the engine accessories and the noise.By this way,the frequency contributed by the engine accessories to the noise can be identified and then reduce the mechanical noise by specific means.Besides,the coherence function analysis method is verified reliably by the experiment method.