||Control of Urea Injection for an Automotive SCR Application
||Jørgensen, John Bagterp (Scientific Computing, Department of Informatics and Mathematical Modeling, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Huusom, Jakob Kjøbsted (Computer Aided Process Engineering Center, Department of Chemical and Biochemical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
||Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
||In this project, a soft model predictive controller (MPC) used to control
the injection of urea in the urea-SCR system, has been investigated. The
control objectives have been specified in accordance with the emission limits
of the Euro VI emission standard. Furthermore, an optimization problem
reflecting the control requirements has been formulated.
An offset-free model predictive controller based on ARX models has been
implemented, and the implementation has been successfully validated. The
corrective actions qualitatively have been shown to be appropriate, thus indicating
that the control methodology is applicable for controlling the urea-
Tuning of the closed loop system has been carried out in simulations using
a dynamic model developed at Haldor Topsøe A/S to approximate the actual
physical system. The tuning has been complicated due to difficulties in
reaching steady state conditions, and besides, long computation times have
been limiting factor for the number of simulations conducted. Consequently,
an optimal tuning has not been achieved for the offset-free soft MPC. This
has been reflected in simulations of transient cycles, where a maximum NOx
conversion of 75.4% has been achieved which is dissatisfactory.
With the purpose of narrowing the problem, the optimization problem has
been reduced to nominal MPC, and the behavior of the closed loop system
has been investigated. This has revealed that the description of the dynamics
by the estimated offset-free ARX is deficient.
Despite the difficulties in meeting the control objectives, the qualitative
results from the presented design activities can be used as a basis of further
improvements and a number of possible future improvements is suggested.
||Technical University of Denmark (DTU) : Kgs. Lyngby, Denmark
Creation date: 2011-04-27
Update date: 2011-04-27