Study On Acoustic Performance Of Exhaust Muffler Of Portable Diesel Generator Set

Exhaust noise is the most important noise source of diesel engine generator set.Exhaust muffler as the most direct and simple control exhaust noise device,its muffling effect directly affects the overall noise level of the generator set.Therefore,studying the acoustic performance of exhaust mufflers has important theoretical and engineering application value for controlling exhaust noise and improving the performance of the whole machine.In this paper,aiming at the exhaust noise control problem of a portable diesel generator set,the muffling performance of the acoustic element of the resistant muffler based on the sound transfer matrix theory and the acoustic finite element method is studied,and on this basis,an exhaust muffler with double-layer perforated plate structure is designed,and this exhaust muffler is analyzed in an orthogonal test.The main research contents are as follows:Firstly,based on plane wave theory,the acoustic transfer matrix of the basic anechoic unit is analyzed and studied,and the calculation model of the resonance frequency of the double-layer perforated plate and the transfer matrix of the inlet and outlet pipe structure of the vertical cavity tube shaft are derived.Secondly,the acoustic finite element method is used to study the influence of each main muffling element on the acoustic performance of the muffler under different structural parameters,and the simulation results of the transmission loss of muffling components such as inner tube,partition and perforated plate at different frequencies are obtained.Among them,the secondary internal line muffler has a worse muffling effect in the 10 Hz ～ 300 Hz frequency band than the primary internal line muffler with the total length of the same cavity.The perforated plate structure muffler can ensure the sound attenuation effect in the frequency band of 10 Hz ～ 500 Hz,and the double-layer perforated plate improves the noise reduction amount of the single-layer perforated plate within1900 Hz ～ 2400 Hz,and improves the muffling performance of other frequency bands.Then,a bench test was carried out on a portable diesel generator set,the exhaust noise source signal of the unit was measured,the frequency characteristics of the exhaust noise source were analyzed,and the exhaust muffler of the generator set and the main frequency segment to be suppressed were determined.Finally,according to the results of the analysis of exhaust noise frequency characteristics,combined with the simulation analysis conclusions of the acoustic performance of the basic components of each muffler,considering the economy of the acoustic structure,a resistant exhaust muffler with a double-layer perforated plate structure is designed,and the optimal combination of the structural parameters of the acoustic elements of the exhaust muffler is further determined by orthogonal test method.The test results show that the insertion loss of this muffler reaches 23.1 d B(A),and compared with 27 sets of orthogonal tests,the noise reduction of the exhaust muffler under the optimal parameter combination is increased by 12% compared with the average value,and the fuel consumption rate is only increased by 0.5%.Finally,the test results are verified with the finite element simulation,and the experimental analysis results show that the muffling effect of the muffler with the optimal parameter combination on each frequency component of exhaust noise is basically matched with the simulation analysis results.