This content is not included in your SAE MOBILUS subscription, or you are not logged in.
Development of a 3D Numerical Model for Predicting Spray, Urea Decomposition and Mixing in SCR Systems
ISSN: 0148-7191, e-ISSN: 2688-3627
Published October 29, 2007 by SAE International in United States
Annotation ability available
In a typical automotive SCR system, the urea-water solution is injected into the exhaust gas stream and breaks up into small droplets through the atomization process due to the interaction with the exhaust gas flow. The water vapor is released by vaporization and leaves the urea component in the droplets. The urea component is converted to ammonia and iso-cyanic acid and other species through thermal decomposition and hydrolysis processes. A multi-dimensional CFD model is developed in the present study to simulate injection and mixing in the automotive SCR systems. The urea-water solution is modeled as a bi-component liquid mixture with evaporation laws for each component. A Lagrangian method with spray sub-models is used to track the liquid droplets and the atomization process. The thermal decomposition and hydrolysis processes of the urea and iso-cyanic acid are simulated by simplified two-step reaction mechanisms.
The spray and mixture qualities are investigated in the paper for an exhaust system. A uniformity index is developed to evaluate the mixture quality at the inlet of the SCR catalyst, which could also serve as an indirect indication of the de-NOx efficiency of the SCR system. The effects of mixers on the spray and mixing are studied in this paper.
CitationYi, Y., "Development of a 3D Numerical Model for Predicting Spray, Urea Decomposition and Mixing in SCR Systems," SAE Technical Paper 2007-01-3985, 2007, https://doi.org/10.4271/2007-01-3985.
- Zhang X. Romzek M. “3-D Numerical Study of Flow Mixing in Front of SCR for Different Injection Systems” SAE paper 2007-01-1578 , SAE World Congress Detroit, USA 2007
- Reitz R.D. Bracco F.V. “Mechanism of Atomization of Liquid Jets” Physics of Fluids 25 1730 1982
- Yi Y. Reitz R.D. “High-Pressure Spray and Combustion Modeling Using Continuous Thermodynamics for Diesel Fuels” SAE paper 2001-01-0998 2001
- Taylor J.J. Hoyt J.W. “Water Jet Photography - Techniques and Methods” Exp. Fluids 1 113 120 1983
- Braun J. Lehnen R. “Modeling Urea Distribution in SCR-Exhaust Aftertreatment Systems - A Simple Approach” The 1 st European Automotive CFD Conference Bingen, Germany Jun 25-26 2003
- Wurzenberger J.C. Wanker R. “Multi-Scale SCR Modeling, 1D Kinetic Analysis and 3D System Simulation” SAE paper 2005-01-0948 2005
- Smith J. M. Van Ness H. C. “Introduction to Chemical Engineering Thermodynamics” McGraw Hill New Jersey 1986
- Jin J.D. Borman G.L. “A Model for Multi-component Droplet Vaporization at High Ambient Pressure” SAE paper 850264 1985
- Schaber P.M. Colson J. Higgins S. Dietz E. Thielen D. Anspach B. Brauer J. “Study of the Urea Thermal Decomposition (Pyrolysis) Reaction and Importance to Cyanuric Acid Production” American Laboratory 13 21 August 1999
- Koebel M. Strutz E.O. “Thermal and Hydrolytic Decomposition of Urea for Automotive Selective Catalytic Reduction Systems: Thermochemical and Practical Aspects” Ind. Eng. Chem. Res. 42 2093 2100 2003
- Yim S.D. Kim S.J. Baik J.H. Nam I.S. Mok Y.S. Lee J.H. Cho B.K. Oh S.H. “Decomposition of Urea into NH3 for the SCR Process” Ind. Eng. Chem. Res. 43 4856 4863 2004
- Rota R. Antos D. Zanoelo E.F. Morbidelli M. “Experimental and Modeling Analysis of the NOxOUT process” Chemical Engineering Science 57 27 38 2002
- Fluent User Manual 2007
- Lefebvre A.H. “Atomization and Sprays” Hemisphere Publishing Corporation 1989
- Amsden A.A. O'Rourke P.J. Bulter T.D. “KIVA-II - A Computer Program for Chemically Reactive Flows with Sprays” Los Alamos National Labs, LA-11560-MS 1989
- Liu A. B. Mather D. Reitz R. D. “Modeling the Effects of Drop Drag and Breakup on Fuel Sprays” SAE Technical Paper 930072 SAE 1993
- O'Rourke P. J. “Collective Drop Effects on Vaporizing Liquid Sprays” Princeton University Princeton, New Jersey 1981