Numerical Analysis And Experimental Study Of DOC/SCR System For Vehicle Diesel Engines

With the continuous growth of motor vehicle ownership,the total amount of motor vehicle emissions in China continues to rise.Almost 50%of the global emissions of carbon monoxide?CO?,hydrocarbons?HC?and nitrogen oxides?NO_x?from fossil fuel combustion come from gasoline and diesel engines.In addition to the main pollutants emitted by vehicles,CO,HC,NO_x and particulates,heavy metal pollutants and sulfur oxides are also included in the veh icle emissions.With the increasingly widespread application of diesel engines in automobiles and the increasingly stringent emission regulations,NO_x emission problems in diesel engines are gaining more and more attention.According to the basic situation of our country,urea selective catalytic reduction technology is selected as the most effective NO _x control technology,and catalytic oxidation technology is selected as CO,HC control technology.Commonly used DOC?Diesel Oxidation Catalyst?and SCR?Selective Catalytic Reduction?system research methods mostly use the existing commercial software:ANSYS,Fluent,Fire and other three-dimensional research methods need to establish the DOC and SCR systems,three-dimensional models,grid models,time-consuming longer,not suitable for post-processing system development of new products.The one dimensional numerical calculation model has the advantages of convenient operation and short calculation time,and is particularly suitable for the pre-treatment system development and design.Therefore,based on a horizontal project of a domestic diesel engine enterprise,this dissertation studies and constructs a one-dimensional numerical model of diesel engine DOC and SCR system by means of numerical simulation and expe rimental research,and its main research work as follows:1)The catalytic performances of DOC and SCR catalysts under different operating conditions were tested respectively:Oxidation of CO,HC and NO by DOC catalysts with different lengths and different coating amounts;NO_x conversion efficiencies of SCR catalysts at different space velocit ies and ammonia nitrogen ratios;Pressure drop of SCR catalyst at different space velocities;The anti-sulfur performance of SCR system was tested.2)Based on the mathematical models of DOC and SCR,one-dimensional numerical models of DOC and SCR post-processing systems are set up respectively in MATLAB/Simulink environment.The pre-exponential factor,activation energy and other related parameters of DOC and SCR internal chemical reactions were identified in Matlab by using nonlinear least-squares method.The experimental data verify the accuracy of the model.3)Using the built one-dimensional calculation model,the following aspects are studied:The influence of DOC catalyst geometric parameters?length,diameter,channels per square inch?on CO,HC and NO conversion efficiency;NO₂/NO_x ratio on the NO conversion efficiency;Effect of SCR catalyst geometric parameters?length,diameter,channels per square inch?on pressure drop;Effect of SCR catalyst geometric parameters?length,diameter?,NH₃/NO_x ratio and NO₂/NO_x ratio on NO_x conversion efficiency.