The Research Of SCR Close-loop Control Algorithm Of Diesel Engine

For satisfying the stage 5 and stage 6 emission requirement,The SCR aftertreatment system is often used in Heavy-duty disel engine;with the ever-increasing demands of the emission regulation,the traditional open-loop control strategy will not satisify the more regorous emission and OBD requirement,so the SCR close-loop control strategy must be the most important part of control.Through theory analysis determine SCR control strategy about NH3 storage control,and PID model control and OBD efficiency close-loop control,to consider the NOx sensor cross-sensitivity with NH3,Adding NOx adaptation model to ensur the NOx emission value is real used for SCR close-loop control.Through the analysis of SCR reaction parameter ensure that the SCR reaction model is base on a main control model which contain the reaction delay,and reaction inertia parameter and static constants.In low catalyst temperature operation condition used NH3 storage control and PID model control can satisfy the requirements of NOx efficiency,while is good of control in NH3 slip;In high catalyst temperature operation condition used PID model control and OBD efficiency close-loop control,Dramatically improved urea injection control precision and the NOx adaptation model can eliminate NH3 slip in the high conversion efficiency operation condition;The ESC and ETC emission test result indicate that using the NH3 storage control and PID control strategy has a great improvement in NH3 slip control compare with the open-loop control strategy;The maximum NH3 slip is 12 ppm,reduced by 80 percent in ETC cycle test,and the average NH3 slip is 4.5ppm,the NOx efficiency increase 14 percent compare with the open-loop control.