Study On Design And Simulation Of Compact SCR Purified Noise Reduction Devices

With the emission standards becoming stringent, purification inside the engine has already been unable to satisfy the demand, thus strengthening the purification outside the engine becomes the tendency of the diesel engine exhaust purification. Selective catalytic reduction (SCR) is considered as the most promising application of diesel engine after-treatment technology. Compact SCR purified noise reduction device integrating both SCR catalytic converter and exhaust silencer, has the double effects on the diesel engine exhaust purification and noise reduction, and saves the space.This thesis analyzes the factors which influence the flow distribution, flow resistance loss and acoustic attenuation performance of compact SCR purified noise reduction devices.The flow field within the SCR catalytic converter is a typical gas-liquid two-phase flow, the monolith is treated as a porous medium. Theκ-εtwo-equation turbulance model of Fluent software is used in the paper to calculate the continuous phase of steady-state flow, DPM model is used to simulate the movement of spray particles which were injected into the SCR catalytic converter, and gas-liquid two-phase is coupled to solve the flow field. The influences of injection position, inlet/outlet conical tube shape, monolith length, monolith location, the ratio of length to radius and inlet flow rate on flow field distribution and flow resistance loss of catalytic converter are studied.The acoustic model is built up by using finite element method, the SCR catalytic converter is divided into two parts: monolith and the inlet/outlet cavities. The monolith is modified as the equivalent fluid, which is based on the replacement of equivalent sound velocity and equivalent density. When using SYSNOISE acoustic software for calculation, the sound velocity and density in two different regions are given respectively, the boundary conditions of SCR catalytic converter are velocity inlet and impedance outlet, and then transmission loss is obtained by calculation. The theory is validated by comparing with the experimental date of reference. In addition, the effects of inlet-outlet conical angle, fluid temperature, monolith length and equivalent aperture of non-flow state SCR catalytic converter on the acoustic attenuation performance of catalytic converter are analyzed.Compact SCR purified noise reduction devices are designed and the influences of inlet orientation, internal connecting tubes and perforated duct on flow field distribution, flow resistance loss and transmission loss of compact SCR purified noise reduction devices are investigated.