Development of Closed-loop Control Strategy for Urea-SCR Based on NO _X Sensors 2011-01-1324

Selective catalytic reduction (SCR) is a promising technology for diesel aftertreatment used to reduce NO_X emission effectively. SCR can be used to meet Euro - and even stricter emission standards. Dosing of urea must be controlled to lower NO_X emission and NH₃ slip synchronously under the emission standard limits.

A type of closed-loop control strategy based on NO_X sensors for SCR system was presented in this paper. To detect NO_X emissions, two NO_X sensors were installed before and after the catalyst. Meanwhile, to examine the trade-off relationship between NO_X emission and NH₃ slip, influences of different control parameters to the control purpose were explored. These influences include space velocity, catalyst temperament, NO_X conversion efficiency, NH₃ adsorption and desorption characteristics, and so on. Results were used to optimize the dosing control strategy of urea. Base dosage of urea was confirmed based on the signals of NO_X sensor. Subsequently, correct dosage of urea was given based on the NH₃ adsorption model, NO_X conversion efficiency, delay algorithm, NO_X feedback correction, and so on. Actual dosage of urea is the sum of base and correction dosage.

Test results of the ETC and the ESC indicated that the SCR system with closed-loop control dosing strategy effectively meet the NO_X limit of Euro V emission standard.