The Research Of Adjusted Dosing Strategy Based On Ammonia Surface Coverage Of The Catalyst

With the implementation of China IV emission regulation in January 1,2015,after-treatment system should be installed on the diesel engine to meet the emissions requirements.Urea_SCR system is more and more widely used on the diesel engine as the best choice.The main control strategy of SCR system is the open-loop control strategy based on map currently,which don't control the ammonia surface coverage of the catalyst.The ammonia surface coverage of the catalyst directly influences the conversion efficiency of NOX and the amount of NH3 slip.Therefore,it is urgent to develop a suitable control strategy to achieve high conversion efficiency and low NH₃slip.The main contents of the paper are as follows.?1?The calculation model of the ammonia surface coverage of the catalyst is established,which is used to calculate the ammonia surface coverage of the catalyst.The optimum control range of the ammonia surface coverage of the catalyst is obtained by simulation analysis.The model contains the engine-out NO_X model and the catalyst model.The engine-out NO_X model modifies the value of NO_Xmap in order to obtain more accurate engine-out NO_X than NO_Xmap.The catalyst model that simulate the chemical reaction in the catalyst could output the ammonia surface coverage for control strategy.The parameters of the model are automatically calculated by the Parameter estimation toolbox of Matlab/Simulink.The optimum control range of the ammonia surface coverage of the catalyst is obtained by simulation analysis.When the real ammonia surface coverage of the catalyst is in the range,the post-NO_X emission of the steady state condition is under 3.5 g/?kW·h?and the amount of NH₃ slip is under 10 ppm.?2?The adjusted urea-dosing strategy based on the ammonia surface coverage of the catalyst is put forward.The control map is automatically calculated by the Response Optimization toolbox of Matlab/Simulink.The control strategy controls the ammonia surface coverage of the catalyst in the target value.The ammonia surface coverage of the catalyst is obtained through the calculation model of the ammonia surface coverage of the catalyst,while the target value is obtained by the map.The control map is automatically calculated by the Response Optimization toolbox of Matlab/Simulink.Computing and simulation in Matlab/Simulink,we can see that the control effect of the control strategy is good.The actual ammonia surface coverage is always maintained in the vicinity of target coverage in ESC/ETC cycle.The post-SCR NO_X is also controlled in the vicinity of the target value in ESC/ETC cycle.The amount of NH₃ slip is very low in ESC/ETC cycle.?3?The adjusted urea-dosing strategy that is automatic calibration is verified by the bench test.The post-SCR NO_X in ESC/ETC/WHTC cycle are all able to meet the Beijing V emission regulation.Test results of the adjusted urea-dosing strategy based on the ammonia surface coverage of the catalyst are compared with test results of he adjusted urea-dosing strategy based on map,the former is better.In this paper,the adjusted urea-dosing strategy based on the ammonia surface coverage of the catalyst is proposed,which could be automatically calibrated by simulation platform.The workload of calibration is reduced,and the control effect is verified by bench test.