Study On The Effect Of Back Pressure On The Muffler Performance Of Automobile Exhaust Muffler

Installing a well performed muffler in the exhaust system is the main controlling of method for exhaust and noise. With the improvement of automobile engine exhaust flow rate, temperature and air displacement, the requirements for acoustic properties and aerodynamic performance of exhaust muffler become larger and larger. In the muffler design of the past,people just researched how to improve the amount of noise elimination or reduced exhaust back pressure,and did not consider connection between them.So the study of the influence of the changes exhaust back pressure on the performance of muffler noise elimination has important and practical value.On the basis of UG and Hypermesh modeling software,the paper uses the platform of ANSYS CFX to simulate the flow field so that it can analysis the Simple muffler (expandable、 inner tube、dual-chamber、perforated tube and complex type), to obtain the distribution of pressure field, velocity field and analyzes the main cause of back pressure. Discuss the transport method between the flow field grid data and acoustic grid, based on the theory of flow field and acoustic field coupling analysis, then apply the acoustic software LMS Virtual. Lab to explore the effects of different muffler exhaust back pressure changes in the structure of their performance muffler, to get their acoustic pressure contours, transmission loss curve and niose eliminate curve, and summarizes the regularity of the exhaust back pressure’s effect on the performance of noise elimination. By the numerical analysis of a muffler, it can be found that the muffler exhaust back pressure is high and the effect of noise elimination is poor. In the end of the paper,the author put forward some improvement advice and strategies.The results show that:(1) the main reason for the resistant muffler producing exhaust back pressure is the consumption of energy caused by the airflow distribution in structure mutation and inside the cavity of the eddy current or circumfluence of molecular collision, the greater the airflow velocity is, the higher the exhaust back pressure will be. (2) the influence of the exhaust back pressure on different mufflers varies,when the exhaust back pressure increases,noise elimination will becomes poor in low frequency, the noise elimination performance is improved in the middle or high frequency and the farther the more obvious at high frequency. In the whole frequency range to calculate the exhaust back pressure on the influence of different structural muffler noise elimination performance is different, with the increase of the exhaust back pressure, when the value of different structural muffler exhaust back pressure calculated from the lowest to the highest(such as the back pressure from 2.8 kPa to 337.6kPa of muffler with circular cross section), the increase amplitude of their average amount of noise elimination was:the muffler of circular cross section was 17.4%; the muffler of elliptical cross section was 14.52%; the muffler of square cross section was 13.62%; the muffler of interpolation offset was 7%; the muffler of interpolation contraposition was 12.3%; the muffler of double cavity plate was 8.6%; the muffler of double cavity even tube was 7.7%; the muffler of straight-through perforated pipe was 20.3%; the muffler of out of perforated tube was 14.6%; the muffler of HTO100-1 was 15.6%. (3) Through comparison and analysis, the aerodynamic performance of muffler and noise elimination performance are greatly improved.