Theoretical Research And Analysis On Acoustic Characteristics Of Muffler Based On Multi-layer Sound Absorbing Material

Muffler is an important device in automobile exhaust system.It can not only greatly improve the noise propagation in the exhaust pipe during the operation of the automobile,but also play the role of transmitting engine exhaust gas and reducing the vibration of the vehicle caused by these exhaust gases.One of the important evaluation indexes to evaluate the sound absorption ability of sound absorbing materials or structures is the sound absorption coefficient.Under the same frequency range,different sound absorbing structures,sound absorbing materials and their different combinations will have different sound absorption coefficients,showing different sound absorption effects.Therefore,the sound absorption coefficient and noise attenuation amount can be used as the main theoretical targets to evaluate the sound absorption capacity of the muffler body structure.Transmission loss is one of the two indicators usually used to study the acoustic characteristics of automobile noise.Its principle is the same as that of resistance.What it feedback is is the difference of sound power level of noise energy from the input end of the muffler to the output end of the noise.Its measurement results are basically the same as the actual noise attenuation deviation.In addition,compared with the measurement of the transmission loss,the insertion loss is more convenient and more suitable for laboratory research.Therefore,in the research on the muffler of multi-layer sound absorbing material,the paper selects the transmission loss to evaluate its index.In view of the narrow frequency bandwidth and low noise attenuation of traditional resistant muffler and resistant muffler,two kinds of body structure combination of multi-layer sound absorbing materials through perforated pipe muffler were designed first.Then,the combination of multi-layer sound absorbing materials was calculated by using acoustoelectric analogy method and MATLAB software.From the aspects of the width of the sound absorption band,resonance peak,resonance frequency and so on,the influence of different structural parameters on the sound absorption coefficient of low and high frequency and the noise reduction is studied and analyzed,which shows that the design scheme of the muffler based on the multi-layer sound absorption material is feasible.Then,a direct micro-perforated tube muffler with a cross section of annular runway was designed.The muffler was divided into regions,and the interpolation function was selected to approximate the acoustic variables of each regional unit.The finite element equation was established by Galerkin weighted parameter method.The sound pressure level,total sound pressure field,velocity flow line and pressure are obtained.Then,the transmission loss gap under different parameters can be obtained by changing the structural parameters of the muffler.Through the experiment,it can be seen that the simulation results are not different from the experimental results.The research shows that compared with the traditional resistant muffler,the transmission loss of each frequency band of this new type of perforated tube muffler based on multilayer sound absorbing material is much larger,and its muffler effect is significantly improved,which provides a new direction for the design and research of the muffler in the future,and has a strong guiding significance and application value for the study of this type of muffler in the future.