| With the increasing of vehicle population, the internal-combustion engine noise problems seriously affect people’s lives and work. The exhaust system noise is the important component of internal-combustion engine noise. In order to reduce internal combustion engine noise and abate noise pollution, the optimum design of muffler is of great importance to society and economy. There are two main measures to control the exhaust noise of internal combustion:One is controlling the noise source, the other is installing exhaust muffler which has been become the most widely used method.Resistance muffler is the main device to control the exhausted noise of internal combustion engine presently. So the study about muffler theory and application technologies have been become the focus of reducing internal-combustion engine noise. On the basis of discrete method, the transmission loss of different kinds of mufflers are calculated,various factors impacting acoustic performance are researched.And also the problems what should be pay attention to are proposed in the design phase of muffler.Firstly,as the basis of conservation of mass and Newton’s classical mechanics principle, continuity and momentum equations about controlling body are derived. The transfer relationship of acoustic pressure about perforated pipe is studyed and discrete modeling method for perforated pipes group is proposed.Secondly,the discrete methods and boundary conditions of straight-through perforated pipe mufflers for calculating transmission loss are given,then compared the calculating results of acoustic finite element method with discreted method,getting the good agreement and verifying the validity and accuracy of discreted method. Based on discreted method, the acoustic performance about straight-through perforated pipe mufflers are studyed.Thirdly, the sound pressure transfer matrixes of basic muffler units such as cross section expansion,cross-section contraction,intubation expansion,intubation contraction are derived.The discrete methods of calculating complex structure mufflers are put forward. The impacts of structural parameters for transmission loss are researched. The main influencing factors are analysised on the frequency of the mufflers. |
