The Research Of A SCR Catalyst Control Strategy For Diesel Engines Based On NO_x Sensor

In recent years,the emission limits for vehicle emissions are becoming more stringent.In order to meet the increasingly stringent emission regulations and get better SCR control effect,the closed-loop SCR system based on NO_x sensor is adopted in this paper.The main contents of this paper are as follows:(1)Study on the Control Strategy of Urea Injection in SCR System.Firstly,the release condition of the urea injection control strategy of the SCR system is studied.When the working conditions are satisfied,the urea control strategy module is started.According to the engine fuel injection and speed,the engine NO_x emissions is determined,and on this basis NH3 demand is acquired.According to the operating conditions of the engine,such as steady-state conditions or transient condition,the external environment and the aging state of the SCR catalyst,correction factor are obtained,based on SCR closed-loop control algorithm quantity of urea injection is corrected by feedback control factor,so the final amount of urea injection is obtained.(2)Study on control-oriented temperature model for the SCR catalytic converter.According to the energy conservation and mass conservation equations and considering different heat transfer processes involved in thermal balance,four types of the mathematical models of SCR catalyst's temperature were built and graphical calculation models were constructed using MATLAB/Simulink.The models were checked based on the measured data on a diesel engine at a test bench under the condition of European steady-state cycle(ESC)and European transient cycle(ETC).Based on the model of the maximum degree of dispersion,fit and calculation time,the model is evaluated under three indicators.The result shows that the temperature model 1 has good prediction accuracy and real-time,and it is more suitable for the SCR control strategy.(3)Elimination of Cross Sensitivity of NO_x Sensor and Design of Feedback Controller.The signal of the NO_x sensor is processed by Unscented Kalman filter(UKF)to eliminate the cross sensitivity of the NO_x sensor.The processed NO_x sensor signal is used as the input of the feedback controller.According to the principle of the feedback controller,the feedback control model is built by software Simunlink,and the feedback of the urea injection quantity is corrected by the feedback factor.(4)Verification of SCR control strategy.The offline simulation is carried out usingthe test data of the ESC cycle and the ETC cycle,the ESC cycle and ETC cycle NO_x emissions and NH3 leakage can be obtained.Comparing to the bench results and regulatory objectives,the results show that the closed-loop control strategy based on NO_x sensor has reached the State V emission regulation.