This content is not included in
your SAE MOBILUS subscription, or you are not logged in.
A Switched, Controls-Oriented SCR Catalyst Model Using On-Line Eigenvalue Estimation
Technical Paper
2009-01-1284
ISSN: 0148-7191, e-ISSN: 2688-3627
Annotation ability available
Sector:
Language:
English
Abstract
Selective catalytic reduction (SCR) of NOx is coming into widespread use for diesel exhaust emissions control in passenger cars, light trucks, and commercial vehicles. Because of the transient nature of these applications, modeling is a critical element of the controls development process. For software-in-the-loop simulation, the model must run in real-time while still retaining first order accuracy. Furthermore, if used as an embedded system or nonlinear observer, the allowable time step must not be shorter than the control module clock rate. Unfortunately, the time scales for ammonia storage decrease exponentially with temperature. The end result is a trade-off between spatial resolution, real-time performance, and temperature range. If the SCR catalyst is placed downstream of a particulate filter, this issue is even more acute due to the high temperatures that occur during regeneration.
A switched catalyst model is proposed that breaks this trade-off. The model computes equilibrium ammonia coverage distribution and catalyst eigenvalues on-line. This is accomplished with a generalized approach that is amenable to a wide range of reaction mechanisms. In this particular case, the model includes ammonia adsorption-desorption with a coverage dependent activation energy. It also includes NO2/NOx ratio effects, NO to NO2 conversion, ammonia oxidation, and N2O formation. When the eigenvalue magnitude exceeds a threshold, the original state equations are replaced with pseudo-state equations. This preserves model order while enabling larger time steps. Model validation is achieved by comparing to published flow reactor measurements for a copper-zeolite coating on a 400/7 cordierite substrate. Model capability and robustness are demonstrated through simulation of an ESC test and a filter regeneration event.
Recommended Content
Authors
Topic
Citation
McKinley, T. and Alleyne, A., "A Switched, Controls-Oriented SCR Catalyst Model Using On-Line Eigenvalue Estimation," SAE Technical Paper 2009-01-1284, 2009, https://doi.org/10.4271/2009-01-1284.Also In
References
- Flynn, PF Durrett, RP Hunter, GL Akinyemi, WC Farrell, LA “Minimum Engine Flame Temperature Impacts on Diesel and Spark-Ignition Engine NOx Production,” SAE Paper 2000-01-1177 2000
- Johnson, TV “Diesel Emission Control in Review,” SAE Paper 2008-01-0069 2008
- Ericson, C Westerberg, B Odenbrand, I “A State-Space Simplified SCR Catalyst Model for Real Time Applications,” SAE Paper 2008-01-0616 2008
- McKinley, TL Alleyne, AG “Real-Time Modeling of Liquid Cooling Networks in Vehicle Thermal Management Systems,” SAE Paper 2008-01-0386 2008
- Kleeman, M Elsener, M Koebel, M Wokaun, A “Hydrolysis of Isocyanic Acid on SCR Catalysts,” Ind Eng Chem Res 39 4120 4126 2000
- McKinley, TL Alleyne, AG “A Urea Decomposition Modeling Framework for SCR Systems,” SAE Paper 2009-01-1269 2009
- Westerberg, B Kunkel, C Odenbrand, I “Transient Modelling of a HC-SCR Catalyst for Diesel Exhaust Aftertreatment,” Chemical Engineering Journal 92 27 39 2003
- Olsson, L Sjövall, H Blint, R “A Kinetic Model for Ammonia Selective Catalytic Reduction over Cu-ZSM-5,” Applied Catalysis B: Environmental 81 203 217 2008
- Shost, M Noetzel, JD Wu, M-C Sugiarto, T Bordewyck, T Fulks, G Fisher, GB “Monitoring, Feedback, and Control of Urea SCR Dosing Systems for NOx Reduction: Utilizing an Embedded Model and NH3 Sensing,” SAE Paper 2008-01-1325 2008
- Khalil, HK Nonlinear Systems Third Edition Prentice Hall Upper Saddle River, NJ 2002
- Boger, T Rose, D Tilgner, IC Heibel, AK “Regeneration Strategies for an Enhanced Thermal Management of Oxide Diesel Particulate Filters,” SAE Paper 2008-01-0328 2008