# Design and Testing of a Gasoline Engine Muffler Based on the Principle of Split-Stream Rushing
## 1 Introduction  
With the continuous development and progress of the automobile industry, automobiles account for an increasing proportion of people's travel choices. By the end of June 2024, the total number of motor vehicles in China had reached 440 million, of which automobiles accounted for 345 million, representing 78% of the total number of motor vehicles. The increase in the number of automobiles provides people with greater convenience for traveling but also introduces new challenges; that is, the increase in the number of automobiles contributes to environmental pollution. Among these issues, the noise pollution caused by automobiles is particularly serious. Automobile noise can be classified according to the source, mainly including engine noise, transmission system noise, intake and exhaust system noise, tire noise, braking system noise, and wind noise. The impact of vehicle noise is primarily manifested in four aspects. (1) Human health: long-term exposure to noise canpotentially damage hearing and cause severe harm to the nervous system, cardiovascular system, and audiovisual function. Prolonged exposure to high levels of vehicle noise may lead to irreversible hearing impairment, and it can also disrupt normal physiological functions, triggering stress responses in the body. This might result in elevated blood pressure, an increased heart rate, and various cardiovascular disorders. Additionally, it can affect cognitive functions, cause sleep disturbances, and lead to psychological problems such as anxiety and irritability, thereby impacting the overall well-being of individuals. (2) Ecosystem: noise can significantly interfere with wildlife behavior, altering their natural routines and patterns. It can disrupt the communication, foraging, mating, and migration processes of wild animals. Moreover, it may have a negative impact on the endocrine and immune systems of wildlife, thereby reducing their reproductive success and survival rates. Some species may be forced to change their habitats or migration routes due to noise pollution, which could disrupt the ecological balance in the long term. (3) Urban acoustic environment: vehicle noise is a major source of urban noise pollution, which severely degrades the acoustic environment of cities. It creates a noisy and unpleasant atmosphere, exceeding acceptable noise levels in residential, educational, and commercial areas, thus significantly affecting residents' daily activities, including rest, study, and recreational pursuits. The continuous presence of vehicle noise can diminish the quality of life in urban areas and affect the overall comfort and tranquility of the living environment. (4) Buildings and facilities: in certain situations, especially on high-traffic, high-speed, and high-noise road sections, the vibration generated by vehicle noise can affect nearby buildings. Over time, this vibration may lead to the loosening of structural components, such as causing cracks in walls and compromising the stability and safety of buildings. Although the immediate impact may not be drastic, the cumulative effect of long-term exposure to such vibrations could pose risks to the structural integrity of buildings. The negative impact of vehicle noise spans across human, ecological, urban, and architectural domains. Consequently, its control and management play a crucial role in environmental protection and urban development [1; 2; 3]. Among these sources, engine noise is the most important source of noise in automobiles. The emission noise of the engine exhaust system without exhaust muffler treatment is the main source of engine noise, so it is crucial to design a muffler with excellent muffling performance. Regarding the calculation and analysis of the acoustic characteristics of the muffler and intake and exhaust systems, plane wave theory was proposed as the earliest method to calculate the acoustic characteristics of the muffler.