Research On Acoustic Performance Of Diesel Engine Exhaust System In CN V Standard

At present,the diesel engine exhaust system that meet the national five emission standard is being vigorously pursued.The exhaust system which not only satisfies the emission regulations but also has good noise attenuation performance has become an important research topic.Compared with national four standard exhaust system,the influence of the special structure of the national five standard exhaust system on the acoustic attenuation performance has become a research hotspot.Firstly,acoustic characteristics of the exhaust system is analyzed and studied by experiment,according to the characteristics of high contribution of low frequency order noise and flow noise generation,select the existing methods to fit engineering requirement,discusses the classification of noise and acoustic performance evaluation index,build the impedance tube measurement system.By using transfer method,finite volume method and experimental testing,multiple factors of acoustic characteristic of muffler components in CN 5 exhaust system are analyzed,including pipe element,area discontinuity element,tailpipe,sound-absorbing materials,catalytic converter and external conditions,especially for section mutation unit,tailpipe and catalytic converter in diesel engine system.Experimental result shows that the flow noise generation can not be ignored in the study of exhaust noise,summarizes the mechanism of flow noise generation,study the whistle problem of straight-through perforated tube muffler as it is a typical phenomenon in flow noise generation.Results shows the sound absorbing material,smaller diameter,smaller length of perforation and smaller perforation rate are all effective means to reduce flow noise generation.For china 5 standard diesel engine system,the special point is muffler integrated with catalyst,so it is necessary to design a simple muffler in the limited volume to meet the engineering requirements.For a 7L volume,design the inner structure,study the parameter sensibility based on orthogonal design method,validate the muffler by experiment.For the high contribution of exhaust system to vehicle noise,design a whole band high attenuation absolute muffler,and has been applied in engineering practice.