# Design and Testing of a Gasoline Engine Muffler Based on the Principle of Split-Stream Rushing
## 3 Results
### Acoustic Performance Analysis of Split-Stream Rushing Muffler  
#### 3.2.1 Acoustic Performance Simulation Test Results and Analysis  
The simulation software used in this paper was LMS Virtual. Lab 13.6, which mainly adopted two methods: the acoustic finite element method and the acoustic boundary element method, as part of the acoustic numerical calculation approach. The acoustic finite element method was used to simulate the Transmission Loss of the split-stream rushing muffler.  
The acoustic mesh of the split-stream rushing muffler was drawn using Hypermesh, and the number of tetrahedral meshes totaled 811,777. The acoustic mesh schematic is shown in Figure 9.  
Figure 9: Acoustic mesh of split-stream rushing muffler. (**a**) Overall diagram of acoustic mesh; (**b**) internal diagram of the acoustic mesh.  
The mesh file, which had been drawn into the software, was imported, and the Acoustic Finite Element module was opened. Next, the imported mesh was redefined as an acoustic mesh, and the fluid properties of the mesh were set to air. The air density was set to 1.293 kg/m\({}^{3}\). The inlet and the outlet were defined, and then the acoustic boundary conditions were set, with the inlet set to the plate velocity and the outlet using Automatic Matched Layer boundary conditions. Finally, the solution setup was performed, with the solution frequency of 1-5000 Hz and the interval of 10 Hz. Figure 10 shows the interface for calculating the Transmission Loss.  
Figure 11 presents the comparison of the Transmission Loss between the split-stream rushing muffler and the original muffler. Based on the Transmission Loss comparison graph, it was observed that within the main muffling frequency range from 300 Hz to 1000 Hz, the split-stream rushing muffler exhibited a peak Transmission Loss value of 110 dB, whereas the peak Transmission Loss of the original muffler was merely 45 dB at that time. Simultaneously, in this frequency band, the average Transmission Loss of the split-stream rushing muffler was 41.91 dB, and that of the original muffler was 34.13 dB. Evidently, the average Transmission Loss of the split-stream rushing muffler surpassed that of the original muffler. Secondly, upon aggregating the Transmission Losses within the main muffling frequency bands, it could be deduced that the Transmission Loss of the split-stream rushing muffler was 22.9% higher than that of the original muffler. In addition to the discussion and analysis of the Transmission Loss within the main muffling frequency bands, it was also essential to take into account the high-frequency noise suppression capacity of the split-stream rushing muffler. In the high-frequency noise region beyond 1000 Hz, with the exception of a few isolated frequencies and frequency bands where the Transmission Loss of the original muffler was greater than that of the split-stream rushing muffler, the Transmission Loss of the split-stream rushing muffler was considerably larger than that of the original muffler in the majority of the other frequency bands. Thus, it was apparent that the split-stream rushing muffler also possessed a certain degree of high-frequency noise suppression ability.  
In summary, whether considering the full frequency band noise suppression effect or the 300-1000 Hz key muffling area, the split-stream rushing muffler met the acoustic performance design requirements, and the acoustic performance was better than that of the original muffler.  
Figure 10: The interface for calculating the Transmission Loss.