Simulation And Experiments On Noise Elimination Characteristics Of Dual-mode Mufflers

Exhaust noise accounts for a large proportion of the vehicle noise,which has a negative effect on the comfort of the people inside the vehicle.Muffler is an important component for controlling exhaust noise.However,muffler will cause pressure loss when it works,which has a negative effect on the fuel economy and instantaneous power of the engine.Compared with the traditional muffler,dual-mode muffler adds a butterfly valve controlled by torsion spring.The valve can be closed or opened at a certain angle under different engine conditions,make dual-mode muffler have better acoustic performance and lower pressure loss.But the performance of dual-mode muffler needs to be further studied.Based on the acoustic finite element method,the acoustic characteristics of expanding cavity,inserting expanding cavity,Helmholtz resonator,leaking resonator and two-neck resonator are analyzed.The relationship between the peak noise elimination frequency of two-neck resonator and the second neck's diameter is verified by experiment.On this basis,the low-frequency acoustic characteristics of dual-mode muffler are analyzed.The low-frequency peak noise elimination frequency of dual-mode muffler increases with the increase of valve opening angle.The total sound pressure level(SPL)of exhaust noise can be controlled at a lower level,while adjust the order proportion to obtain better sound quality.The ideal matching curve of engine speed and valve opening angle is established.The influences of structural parameters on the dual-mode muffler's low-frequency acoustic characteristics are also discussed.In this paper,the flow field characteristics of dual-mode muffler are simulated and analyzed.The flow situation and the source of pressure loss in dual-mode muffler are discussed.When the valve is opened,the mass flow rate from orifices decreases,so the head loss near the orifices decreases.Therefore,dual-mode muffler can reduce the pressure loss compared with the traditional muffler.By integrating the pressure difference between the two sides of the valve,the force acting on the valve is obtained.A torsion spring is designed to meet the opening requirements at different engine rotating speeds.The influences of structural parameters on dual-mode muffler's flow field characteristics are also discussed.Based on large eddy model(LES),the main sources of dual-mode muffler's airflow noise are simulated and analyzed.The results show that dual-mode muffler can reduce the eddy current shedding and breaking in the first chamber compared with the traditional muffler,so dual-mode muffler can reduce the airflow noise.The pressure fluctuations on the cavity wall and the inlet tube surface are introduced into the acoustic software to calculate the acoustic response in the far field which verify the above results.The characteristics of dual-mode muffler are studied by cold-flow experimental bench.The relationship between pressure loss,airflow noise and valve opening angle with inlet airflow velocities are obtained.The experimental results show that dual-mode muffler can reduce the pressure loss and airflow noise compared with the traditional muffler,and the reduction amplitude increases with the increase of airflow velocity.