Study On Design Match And Acoustic Performance Of Diesel Engine Muffler

The muffler is mainly used to eliminate the exhaust noise of the car,but the addition of the muffler will inevitably affect the performance of the engine.In order to achieve the best coupling between the muffler and the engine,it is necessary to study the acoustic performance of the muffler and the matching of the muffler with the engine design.In this paper,the muffler device of a certain type of diesel engine has been optimized and improved,and the acoustic performance of the muffler device has been improved while ensuring the dynamic performance.The model of diesel engine is built by the software GT-Power,and the model is simulated and verified.The numerical results of the engine external characteristic are compared with the bench experiment results,And the error is less than 5%,which proves that the simulation model of the engine is established correctly.The coupling simulation model of the engine and the muffler is established,the acoustic performance of the muffler is calculated,and when the diesel engine speed is 2000/ min,the muffler amount of the muffler is 20 dB(A),it is need to improve the acoustic performance of the muffler.Due to the existence of three-dimensional flow in the muffler,when turbulence and back-flow noise are generated,the sound wave will generate high-order harmonics during the propagation process,the high-frequency acoustic performance of the muffler is simulated by the three-dimensional acoustic simulation software Virtual.Lab.The transmission loss curve and the Sound pressure distribution nephogram of the muffler are simulated and calculated by the Virtual.Lab.According to the sound pressure distribution nephogram of the muffler,the change of sound pressure at the perforated tube and perforated plate is relatively large,which is the main cause of eddy current and back-flow noise.In terms of flow field,the computational fluid dynamics(CFD)software Fluent is used to simulate the dynamic performance.In Fluent,the internal flow field of the muffler is simulated at 10m/s,30m/s and 60m/s,and the pressure loss curve is drawn,and the pressure distribution nephogram,turbulent kinetic energy and velocity streamline graph are obtained.Finally,analyze the results.Considering the influence of the engine muffler on the dynamic performance and the feasibility of the installation,the influence of different expansion ratios on the transmission loss of the muffler is obtained by simulation analysis of the expansion ratio,and the optimized muffler transmission ratio is determined to be 24.Through the simulation analysis of the number of expansion chambers,it can be seen that when the number of expansion chambers is two,the noise cancellation effect for intermediate frequency noise is better.Through the simulation analysis of the length of the expansion cavity,it is found that the maximum amount of noise reduction is improved when the length of the two expansion chambers is 150 mm and 100 mm.Through the simulation analysis of the length of the inner cannula,when the length of the inlet and outlet cannula is 25 mm,the maximum noise reduction is achieved.Finally,the noise reduction of the optimized muffler is increased by 7 dB on average in the range of 260-690 Hz,and the transmission loss in the range of 910-1000 Hz is increased by 6.4 dB on average.It can be seen from the internal sound pressure distribution cloud diagram that the acoustic pressure of the muffler is relatively small and the acoustic performance is improved.It can be seen from the analysis of the flow field that the acoustic pressure loss of the muffler is reduced by up to 3 kPa,which improves the dynamic performance of the engine.In this paper,the influence of exhaust parameters of diesel engine on muffler performance is analyzed by CAE simulation method,and the muffler device is optimized and improved,and a new structural design scheme is proposed.The simulation results show that,on the basis of ensuring the dynamic performance of diesel engine,the acoustic performance of the optimized muffler device is improved.