Establishment And Application Of Ammonia Storage Model Of Urea-SCR Catalyst For Diesel Engine

With the wide application of the diesel engine,the impact on the environment caused by the diesel engine emissions can not be ignored.As a kind of aftertreatment technology of diesel engine,Urea-SCR can effectively reduce the NOx of emission from diesel engine.The core of Urea-SCR technology is to control the injection amount of urea solution to meet the NOx conversion efficiency and to meet the requirements of ammonia slip.The ammonia storage model of Urea-SCR catalytic converter was established and the application research of the ammonia storage model was carried out in this paper,The detailed tasks of this paper are expressed as follows.First of all,the dynamic parameters associated with the ammonia storage model were given definition in this paper,and control significance and change regularity of these dynamic parameters were discussed in this paper.The influence of the engine speed,torque and the amount of urea injection on the dynamic parameters is analyzed through the test data obtained from the bench test,which provided the basis for the development of a reasonable control strategy of urea injection.Secondly,the main reaction and the reaction rate in the SCR catalytic converter were analysed,and established ammonia storage model based on the SCR reaction mechanism,which considering the adsorption / desorption reaction of ammonia,the redox reaction of NOx and the oxidation reaction of ammonia.A method based on the change of NOx concentration in the catalytic converter downstream was proposed to calculate the amount of ammonia adsorbed on the surface of the catalyst.And compared with the mass conservation method,the method based on the change of NOx concentration in the catalytic converter downstream excluded the effect on the calculation results caused by the incomplete decomposition of urea solution and the reduction reaction between HC of the emissions and NOx,which make sure that the ammonia storage amount calculated by the method based on the change of NOx concentration in the catalytic converter downstream is more closer to the true value.The method based on the change of NOx concentration in the catalytic converter downstream was used to calculate the ammonia storage capacity under different conditions,to provide the basis for parameters identification.Again,the exhaust gas quality flow,exhaust temperature,exhaust gas composition concentration and other datas in different conditions were obtained through the bench test,and the genetic algorithm was used to identify the parameters of ammonia storage model.Compared the experimental data with the simulation results,and the results showed that the model could accurately predict the value and change trend of the ammonia coverage of the catalyst.Finally,the control target of ammonia storage model was determined by the dynamic parameters,and the ammonia coverage was controlled in the range of 0.6-0.8.Urea injection control strategy under steady-state conditions based on the ammonia storage model was proposed to improve the engine emissions.Controlled the ammonia coverage at about 0.7 with PID control.Made correction on the temperature,and the Urea injection control strategy under transient-state conditions based on the ammonia storage model was proposed.The ammonia storage model of Urea-SCR catalytic converter was established and applied in this paper,which had important significance on the research of the control strategy of the urea injection,and made foundation for the closed-loop control strategy of Urea-SCR system.