# Design and Testing of a Gasoline Engine Muffler Based on the Principle of Split-Stream Rushing
## 1 Introduction
In summary, the acoustic performance and aerodynamic performance of mufflers are the main indexes for evaluating mufflers, and the discussions and research on these two indexes are mainly centered on basic theories and structural influencing factors. Therefore, the research on parameter optimization of the complex structure of multi-cavity mufflers is still lacking. Aiming to address the existing problems, the muffler based on the principle of shunt gas hedge muffling is a new research object, and the optimization of multi-structure parameters of the coupled muffler is a useful attempt to improve the performance of the muffler. At present, the noise frequency of a gasoline engine was mainly concentrated in the low and medium frequency regions, and there was a small amount of high-frequency noise distribution. High-frequency noise was more hazardous to health, and it was more difficult for the human ear to endure. The traditional gasoline engine muffler usually adopted an impedance composite structure. Among them, the resistive muffler was excellent in controlling medium and high frequency noise. The muffling principle involved using fiber or porous acoustic material placed above the airflow channel. When the sound wave passed through the porous acoustic material, under the effect of friction and damping, the sound wave was converted into thermal energy, so as to achieve the purpose of muffling. However, one of the obvious disadvantages of sound-absorbing materials was their short service life, they were easily affected by high-temperature oxidation, high-speed airflowimpact, and water vapor infiltration, which led to the failure of sound-absorbing materials, thus causing frequent maintenance of the muffler, poor effect, and short service life, etc. The reactive muffler was produced through the use of fiber or porous sound-absorbing materials. The reactive muffler was a muffler that produced sound energy reflection and interference caused by impedance change in the process of sound propagation through the mutation of pipeline cross-section or side-branch resonance cavity, thus reducing the sound energy radiated outward by the muffler to achieve the purpose of muffling sound. The split-stream rushing muffler belonged to the reactive muffler, and the split-stream rushing muffler structure could reduce the speed of the gas flow inside the muffler, so as to improve its acoustic and aerodynamic performance. After experiment verification, the split-stream rushing muffler structure had certain low-frequency and medium-frequency muffling effects, and it had obvious advantages for the suppression of high frequency noise [11, 12, 13, 14]. Therefore, the scheme of the split-stream rushing muffler structure coupled with the traditional reactive muffler structure was a brand-new idea to solve the exhaust noise problem of gasoline engine, while also verifying the applicability of the split-stream rushing muffler on different engines. On the basis of this group's previous research, the KTM690 single-cylinder gasoline engine used in formula racing was selected as a test prototype, and a split-stream rushing muffler suitable for single-cylinder gasoline engines was designed, which ultimately achieved good muffling performance and low exhaust backpressure.