Acoustical Research And Design Of Diesel Engine Exhaust System In CN ? Standard

In order to meet the requirement of environmental friendliness,and reduce vehicle exhaust emissions,the national standard for vehicle emission became increasingly stringent.The CN?emission standard has come into effect in January 1^st,2017.Moreover,6th stage of national emission standard is being drawn up.Therefore,developing a set of exhausting system which not only meets the new emission standard,but also has a good acoustic performance is a hot topic at present.The after-treatment catalysts and basic structure of exhaust system need to be changed.This paper takes exhaust system which meet CN VI emission standard as research object,the acoustic model of hot side is established,the main muffler in cold side is designed.Acoustic model is verified by experimental method,and insertion loss of the whole exhaust system is measured.The exhaust acoustic characteristics of four cylinder diesel engine is studied in this paper,the exhaust noise is measured in a semi anechoic chamber,and compared with the fluctuation of exhaust pressure.The characteristics of engine sound source is obtained in frequency domain,and the risks of engine exhaust noise is analyzed.The noise attenuation performance of hot side of exhausting system which satisfies CN VI emission standard is studied.Based on plane wave theory,transfer matrix method was used to establish transfer matrix model of sub-units in hot side system.The transmission loss of three catalysts,DOC,SCR and DPF,were calculated,and the acoustic characteristics of catalyst in the frequency domain was analyzed.By using transfer matrix method,the transfer matrix of sub-unit are connected and the transfer matrix model of hot side is obtained,and the transmission loss was calculated,the noise attenuation performance of the hot end in frequency domain is analyzed.A test platform using to measure transfer loss is built,and the transmission loss of hot side system is measured,Theoretical acoustic model is verified.According to the analysis results of hot side,combining with sound source of diesel engine,the contribution of hot side in exhausting system and the frequency range that existed risk is analyzed,and the design target of muffler in cold side is obtained.A basic structure of muffler is designed,and GT-Power simulation software is used to build a muffler model.Combine with the DOE method,the main parameters of muffler are optimized,and the noise attenuation performance in target frequency range is achieved.Combine the hot side with the cold side,an exhaust system for four cylinder diesel engine satisfy CN VI emission standard is designed completely.Insertion loss was measured in semi anechoic chamber,and the test result showed that the insertion loss of exhaust system exceeds national standard under all engine rotational speed,and achieve the design goal.