Research Of Engine Exhaust Noise And Designing Of Residual Heat Recovery Special Muffler

Engine exhaust noise is one of the main noise sources of vehicles.At present,it is mainly controlled by the transmission path of noise,that is,the way of installing exhaust muffler.Considering that the research on muffler design is quite mature,and the installation of muffler with complex structure will lead to high exhaust back pressure and poor exhaust,which will affect the economy and power performance of the engine.This paper starts from the exhaust noise sources and residual heat recovery,aiming at reducing the intensity of dipole and quadrupole noise of "combustion chamber-valve-exhaust passage",improving the acoustic performance,aerodynamic performance and residual heat recovery capacity of muffler.The effects of different structural parameters on engine exhaust noise sources and the performance of heat recovery of the special muffler with residual heat recovery capacity were studied by means of CFD and acoustic finite element methods.By using FLUENT to do aeroacoustic simulations,the principle of aerodynamic noise production of "combustion chamber-valve-exhaust passage" and the relationship between aerodynamic noise and the engine speed are analyzed,and the measure to reduce the aerodynamic noise source intensity by increasing the radius of the transition corner of the exhaust valve was put forward.By controlling the neck shape and cavity volume of Helmholtz resonator,the resonator was changed to cylindrical cavities with different shapes,through the acoustic finite element software Virtual.Lab,the principle of the production of Helmholtz resonance noise was studied,the relationship between the sound pressure level and the shape of the resonance cavity was discussed,and find out that the first-order natural frequency is the Helmholtz resonance frequency,the resonance of neck air column,resulting in high sound pressure level throughout the cavity.The correlation between the natural frequency of the gas column and the structural parameters(length,bending radius,bending angle)of the pipeline was studied,it is found that only the length of the pipe has a great influence on the natural frequency of each stage of the gas column,and the other factors have almost no influence.By changing the number of fins around the expansion cavity of the special muffler and by means of numerical simulation,the influence of expansion cavity shape on transmission loss and pressure loss was discussed,it is found that the expansion cavity with fins is helpful to improve the high-frequency silencing performance,when the number of fins is 36,the pressure loss is the smallest.A kind of special muffler with residual heat recovery capacity was designed,and the influence of cooling medium velocity on it's aerodynamic performance and residual heat recovery capacity was analyzed by simulation,it is found that the pressure loss of the muffler is much lower than that of the original one,increasing the air flow rate can improve the residual heat recovery capacity and aerodynamic performance of the special muffler.