# Design and Testing of a Gasoline Engine Muffler Based on the Principle of Split-Stream Rushing
## 3 Results  
### Subsection  
Since the muffler design needed to account for both performance indicators, the combined scoring method was used as the result analysis method in the orthogonal test [23]. The scoring formula of the comprehensive scoring method is as follows:  
\[X_{i}=\ Ai1 Xi1+Ai2 Xi2+\ldots+AijXij \tag{6}\]  
where _Aij_ is the weighting of indicators; _Xij_ represents the indicators of the test; \(i\) denotes the test number \(i\); \(j\) denotes the indicator number \(j\). The orthogonal test totaled two evaluation indexes, i.e., Transmission Loss and Pressure Loss, and since the muffler was designed with acoustic performance as the main consideration, the Transmission Loss accounted for 0.7 and the Pressure Loss accounted for 0.3. In order to more intuitively represent the comprehensive score of the split-stream rushing muffler, the summing operation was carried out on the Transmission Loss of the main muffling frequency bands (300 Hz to 1000 Hz), which was used as the acoustic performance evaluation index. In addition, it should be noted that the value of the Transmission Loss had to be as large as possible; on the contrary, the value of the Pressure Loss had to be as small as possible, so the Pressure Loss term was set as a negative term [24]. Table 3 shows the results of orthogonal tests.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Factor** & \multicolumn{3}{c}{**Level**} \\ \cline{2-4}  & **1** & **2** & **3** \\ \hline (A) Perforation aperture of the perforated pipe (mm) & 6 & 8 & 10 \\ (B) Perforation rate of the perforated pipe (\%) & 5 & 10 & 15 \\ (C) Perforation rate of the perforated plate (\%) & 7 & 9 & 15 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Factors and levels of orthogonal tests.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Test Number** & **A** & **B** & **C** & **TL/dB** & **CV/\%** & **PL/Pa** & **CV/\%** & **Comprehensive Scoring** \\ \hline
1 & 1 & 1 & 1 & 2591.31 & 0.14 & 4948.29 & 0.11 & 329.43 \\
2 & 1 & 2 & 2 & 2700.17 & 0.13 & 4716.34 & 0.13 & 475.22 \\
3 & 1 & 3 & 3 & 2962.92 & 0.16 & 4832.70 & 0.18 & 624.23 \\
4  
From the table of orthogonal test results, it can be seen that the best score among the nine models was achieved by model No. 5, with a Transmission Loss of 2932.67 dB, a Pressure Loss of 4525.41 Pa, and a comprehensive score of 695.25. Moreover, the structural parameters of No. 5 (perforated pipe perforation aperture diameter of 8 mm, perforated pipe perforation rate of 10%, and perforation rate of the perforated plate perforation rate of 15%) were the same as the optimal parameter combinations. From the table, it can also be seen that the factors that had a greater impact on the overall performance of the split-stream rushing muffler were perforated plate perforation rate > perforated pipe perforation aperture > perforated pipe perforation rate, respectively, in descending order of influence.  
After the optimal model structural parameters were derived from the orthogonal tests, the model was analyzed in detail for acoustic and aerodynamic performance, including Transmission Loss, velocity field, pressure field, and turbulent kinetic energy field.