Study On Turbocharger Noise Control And Design Of Intake Silencers

The induction noise is a major noise source of turbocharged engine. This thesis introduced the situation and methods of turbocharged engine intake system noise study, explained the source characteristics and generation mechanisms as well as the control method of intake noise. The present works design two kinds of intake silencers according to the source characteristics of intake system noise. The perforated elements are commonly used in dissipative silencers to improve the acoustic attenuation and protect the absorbing material from running. To predict the acoustic attenuation performance of silencers, the acoustic characteristics of perforated elements in contact with fibrous material need to be determined first. Therefore, the present thesis will investigate in detail the calculation methods of acoustic attenuation performance of silencers and the acoustic characteristics of perforated elements in contact with fibrous material.The acoustic characteristics of perforated elements in contact with fibrous material are studied by using finite element methods. The finite element model for determination of the acoustic impedance of perforation is first built, and then the effect of various structure factors on the acoustic thickness correction coefficient of perforated element is investigated. A curve-fitting expression for the end correction coefficient is obtained based on the numerical results.According to the principle of Two-Load method, the fiber glass was used to verify the methods of measuring the acoustic characteristic parameters of absorptive material, and then the characteristic impedance and complex wavenumber of aluminium silicate had also been measured.The finite element models of intake silencer were created based on the physical model of the two mufflers. The models for the acoustic impedance of perforation in contact with fibrous material and the acoustic characteristic parameters of aluminium silicate were imported to software SYSNOISE. The transmission loss of intake silencer had been calculated and compared with the measured results. The results indicated that the model created for intake silencer was reasonable. The effects of various structure factors on the intake silencer are studied. The results indicated that the desired acoustic attenuation performance of intake silencer can be obtained by accommodating porosity, the density of sound-absorbing material, thickness of sound-absorbing material and so on.