Acoustic Performance Simulation Analysis And Experiment Study For Exhaust Muffler Of Four-Cylinder Diesel

The exhaust noise is the most main noise source of automobile and even its internal combustion engine, often is about 10 ~ 15dB (A) higher than entire noise of the internal combustion engine in which exhaust noise isn't included. At present, it is the most effective and direct method to install the exhaust silencer to reduce the exhaust noise.Therefore, the researched exhaust silencer have the vital significance to reduce the exhaust noise .The present paper, summarized and infered transition matrix of acoustic primary element of silencer.By method of transition matrix, computed and analyzed effect of structure paremeter in the simple expansion type silencer and insert tube expansion type silencer to acoustic performance; Computed and analysed effect of designed parameter in Helmholtz wave resonating silencer and perforated pipe resonating silencer to noise elimination performance; Computed and analysed stream velocity and temperature'effect to noise elimination performance. The analysed conclusions show: When the stream velocity is smaller than about 35m/s, the stream velocity is not big effect to noise elimination performance; When the stream velocity is bigger than about 35m/s, along with the stream velocity increasing noise elimination performance suddenly drop. In addition, the different design parameter has the important influence to the noise elimination performance as well.Further, in order to study the silencer'performance, based on the finite element method. taking the simple expansion type silencer and Helmholtz wave resonating silencer as example, built three-dimension models of FEM—Fluid with the Sysnoise acoustic software. contrasted and analysed the transmission loss of silencer with or without air current existence; and contrasted the computed results of one-dimension model based on transmission matrix method and three-dimension finite element model. Simulated and computed internal pressure distribution and velocity distribution in silencer,and studied interior sound field characteristic of silencer. The results indicate, the silencer below 1500Hz, computed result of one-dimension model and three-dimension model is nearly consistent, but during other frequency bands, both of models are more inconsistent.According to tested noise result of four- Cylinder diesel with or without original silencer, when it run at the demarcated rotational speed, between 100Hz and 500Hz frequency scopes, original silencer is still improved. According to the transmission matrix technique, proposed four kind of improved design proposals, while considered economical factors and processing feasibility. In the end,selected plan 3 and plan 4 and processed. the test results indicate: under about 400Hz frequency, noise of improved silencer by plan 3 is about 3 dB (A) lower than improved silencer by plan 4, about 7 dB (A)lower than original silencer's. The test results also indicate, by method of transition matrix, established the mathematical model to reduce noise is feasible, and there is the important instruction significance to the silencer design.