State Estimation for the Automotive SCR Process

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Selective catalytic reduction (SCR) of NOx is a widely applied diesel engine exhaust gas aftertreatment technology. For advanced SCR process control, like model predictive control, full state information of the process is required. The ammonia coverage ratio inside the catalyst is difficult to measure. Therefore we design an ordinary Kalman filter as well as an extended Kalman filter to estimate the ammonia coverage. The filters are built over a first principle model with four states. Among the four states, NO, NO2 and NH3 concentration are measured by the sensors, while the ammonia coverage ratio is left to be unknown. The performance of the filters is shown by simulation with the World Harmonized transient cycle. In particular, during transient operations the extended Kalman filter performs significantly better than the ordinary Kalman filter. Since such operation regimes are always present for SCR in engine applications, we recommend to estimating the ammonia coverage using the extended Kalman filter.
Original languageEnglish
Title of host publicationProceedings of the 17th Nordic Process Control Workshop
EditorsJohn Bagterp Jørgensen, Jakob Kjøbsted Huusom, Gürkan Sin
Place of PublicationKogens Lyngby
PublisherTechnical University of Denmark
Publication date2012
ISBN (Print)978-87-643-0946-1
Publication statusPublished - 2012
Event17th Nordic Process Control Workshop - Kongens Lyngby, Denmark
Duration: 25 Jan 201227 Jan 2012
Conference number: 17


Conference17th Nordic Process Control Workshop
CityKongens Lyngby
Internet address


  • Extended Kalman filter
  • Kalman filter
  • Selective catalytic reduction


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