Optimization And Test Of Muffler For Small High-speed Gasoline Engine Based On The Principle Of Split-gas Opposed Exhaust

In recent years,car noise has become the culprit for the destruction of quiet living environment.Among them,the engine noise accounts for a large proportion of the overall noise of the car.According to the different sources of noise,engine noise can be divided into combustion noise,mechanical noise and aerodynamic noise.Exhaust noise is the main source of engine noise.At present,the best way to reduce engine exhaust noise is to install exhaust muffler.An excellent muffler can greatly reduce exhaust noise and exhaust back pressure.Aiming at the problem of high noise of gasoline engine,this paper designs and studies a muffler that conforms to high speed,single cylinder and gasoline engine.The main research contents are as follows:1.According to the exhaust noise characteristics of gasoline engine,the initial model of muffler is determined.Taking the KTM690 high-speed,single-cylinder,gasoline engine as the test prototype,the noise spectrum analysis of the engine was carried out in the early stage of the design to determine the main muffler frequency band.2.Based on the orthogonal test,the main structural parameters of the new muffler are simulated and optimized,and the acoustic performance and aerodynamic performance of the new muffler are comprehensively evaluated to determine the better structural model.The new muffler adopts the form of coupling the split-gas counter-flow muffler unit with the traditional resistance muffler unit,namely the perforated pipe and the perforated plate.The influence of three structural factors,such as the perforation rate of the perforated pipe,the perforation rate of the baffle and the perforation aperture of the perforated pipe,on the performance of the new muffler is studied and discussed.It is found that the structural parameters of the better model are the perforation diameter of the perforated pipe of 8 mm,the perforation rate of the perforated pipe of 10%,and the perforation rate of the baffle of 15%.3.The acoustic performance and aerodynamic performance of the new muffler and the original muffler are compared and analyzed.From the comparison of the transmission loss of the two,it is found that the average transmission loss of the new muffler is 41.91 dB in the main muffler frequency band of 300 Hz～1000 Hz,and the average transmission loss of the original muffler is 34.13 dB.The average transmission loss of the new muffler is 7.78 dB higher than that of the original muffler.In addition,the transmission loss in the main muffler frequency band is calculated,and it is found that the transmission loss of the new muffler in this frequency band is 22.91%higher than that of the original muffler.The flow field of the new muffler under three different inlet velocities is simulated.From the comparison of pressure loss,it can be found that the pressure loss of the new muffler is smaller than that of the original muffler.From the perspective of simulation,it can be concluded that the acoustic performance and aerodynamic performance of the new muffler are better than those of the original muffler.4.The insertion loss and pressure loss of the new muffler were tested on the real vehicle and test bench.Through the real vehicle insertion loss test,it is found that the insertion loss of the new muffler performs well at idle speed,medium speed and rated speed.Among them,at the rated speed,the average insertion loss of the main muffler frequency band is 19.14 dB,which is the highest under three different speed conditions.Under this speed condition,the peak frequency of the insertion loss of the new muffler is the best corresponding to the peak frequency of the engine exhaust noise,and the peak insertion loss is 40 dB.The pressure loss of the new muffler was tested on the test bench,and the pressure loss of the new muffler at different inlet velocities was measured.The relative error between the test data and the simulation data was within 8%.The test proves again that the new muffler can solve the exhaust noise problem of high speed,single cylinder and gasoline engine under the condition of small pressure loss.