Study On The Acoustic And Resistance Characteristics Of Engine Exhaust Purified Silencer

Diesel exhaust and noise pollutions are always urgent issues to be solved in world,now more effective measures are the use of catalytic converter (CC), diesel particulate filter (DPF)for purifying gas and the use of silencer for controlling noise. Given the limitation of space,an integrated device which not only can purify exhaust, but also eliminate noise may be preferred. Acoustic and resistance characteristics are important basis for evaluating and optimizing exhaust purified silencer, but acoustic and fluid filed calculation of catalytic converter or diesel particulate filter which can clean exhaust and reduce noise is complicated.So this paper firstly discusses the methods for calculating transmission loss and flow field, then studies the influencing factors in detail. The pressure drop of catalytic substrate and filter are calculated by using the porous media model in Fluent software. The solutions for viscous and inertial resistance coefficients can be obtained by contrasting the formula calculating pressure loss of the catalytic converter and diesel particulate filters with the mathematical model of porous media. Then, accuracy of the present models can be validated through comparing simulation results and experimental data in existing literature.Subsequently, the influences of the flow velocity, temperature, substrate density on the resistance characteristics of catalytic converter and the influences of the filter diameter, wall thickness, and length to diameter ratio on the resistance characteristics of diesel particulate filter are studied. Meanwhile, the paramedical studies of the coupling gap and coupling substrates with different length are also implemented.In this paper, to find an accurate and efficient method to calculate the transmission loss of catalytic converter and diesel particulate filter, the finite element method, the transfer matrix method and the transfer impedance method respectively are used to calculated the transmission loss of catalytic converter, then, the characteristics and accuracies of those methods are investigated by comparing the present results with the experimental data. The conclusion is that the results of the finite element method agree with the experimental data mostly. Finally, the effect of substrate density, length, and temperature on the acoustic characteristics of catalytic converter and the effect of channel width and temperature on acoustic characteristics of diesel particulate filter are investigated.Through calculating the transmission loss and resistance characteristics of exhaust purified silencer designed preliminary,then one can know that the resonance frequency is beyond the scope of fundamental frequency and the pressure loss is too large. Therefore this article analyzes other structures how to influence the acoustic and resistance characteristics,such as chamber length, resonance tube parameters, inlet and outlet perforated tube parameters and guiding annuluses, then an optimized scheme was given. The recalculated results show that the optimized scheme can meet not only the acoustic needs of different frequency, but also pressure drop limitation under different rotate speed, and have a good uniformity.