Selective catalytic reduction (SCR) is a promising technology
for diesel aftertreatment used to reduce NOX emission
effectively. SCR can be used to meet Euro - and even stricter
emission standards. Dosing of urea must be controlled to lower
NOX emission and NH₃ slip synchronously under the emission
standard limits.
A type of closed-loop control strategy based on NOX sensors
for SCR system was presented in this paper. To detect NOX
emissions, two NOX sensors were installed before and after the
catalyst. Meanwhile, to examine the trade-off relationship between
NOX emission and NH₃ slip, influences of different control
parameters to the control purpose were explored. These influences
include space velocity, catalyst temperament, NOX 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
NOX sensor. Subsequently, correct dosage of urea was given based
on the NH₃ adsorption model, NOX conversion efficiency, delay
algorithm, NOX 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 NOX limit of Euro V emission standard.