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Towards Quantitative Prediction of Urea Thermo-Hydrolysis and Deposits Formation in Exhaust Selective Catalytic Reduction (SCR) Systems
ISSN: 0148-7191, e-ISSN: 2688-3627
Published April 02, 2019 by SAE International in United States
This content contains downloadable datasetsAnnotation ability available
In order to assist in fast design cycle of Diesel engines selective catalytic reduction (SCR) exhaust systems, significant endeavor is currently being made to improve numerical simulation accuracy of urea thermo-hydrolysis. In this article, the achievements of a recently developed urea semi-detailed decomposition chemical scheme are assessed using three available databases from the literature.
First, evaporation and thermo-hydrolysis of urea-water solution (UWS) single-droplets hanged on a thin thermocouple ring (127 μm) as well as on a thick quartz (275 μm), have been simulated at ambient temperature conditions ranging from 473K to 773K. It has been shown that the numerical results, in terms of evaporation rate and urea gasification, as well as droplet temperature history are very close to the experiments if the heat flux coming from the droplet support is properly accounted for. Indeed, an additional conduction flux has proved to be necessary in the evaporation model in order to account for the droplet heating coming from the support (i.e. thermocouple ring or quartz bead). This additional heat conduction flux has shown more critical for droplets suspended on a thick quartz. It is also argued that our detailed kinetic mechanism is able to ensure accurate thermal decompositions as long as the temperature inside the droplet is still nearly uniform. This assumption is shown to be true at low temperature and so, at low evaporation and thermo-hydrolysis rates. However, for high gas temperature, bubble nucleation near the support surface induces non-uniform temperature distribution.. This process makes accurate simulation of thermal decomposition extremely dependent on the local temperature inside such large suspended droplets. These results are also relevant and underline the modelling difficulties that we must tackle when it comes to studying the evaporation, boiling and thermolysis of liquid films and deposits on the exhaust walls.
Next verification of the models has been carried out using UWS sprays injected in 6-m long pipe under typical Diesel engine exhaust manifold conditions. In this case, good agreement with experiments in terms of urea to ammonia (NH3) conversion efficiencies has been obtained under different temperatures and residence times. In addition, it proved that by-products (like solid biuret, Cyanuric acid and even ammelide) can be formed in the spray parcels upon water evaporation is completed during their travel to the exhaust catalyst inlet. These solid by-product particles may clog the catalyst inlet section.
CitationHabchi, C., Quan, S., Drennan, S., and Bohbot, J., "Towards Quantitative Prediction of Urea Thermo-Hydrolysis and Deposits Formation in Exhaust Selective Catalytic Reduction (SCR) Systems," SAE Technical Paper 2019-01-0992, 2019, https://doi.org/10.4271/2019-01-0992.
Data Sets - Support Documents
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- Birkhold , F. , Meingast , U. , Wassermann , P. , and Deutschmann , O. Modeling and Simulation of the Injection of Urea-Water-Solution for Automotive SCR DeNOx-Systems Applied Catalysis B: Environmental 70 1-4 119 127 2007 10.1016/j.apcatb.2005.12.035
- Ström , H. , Lundström , A. , and Andersson , B. Choice of Urea-Spray Models in CFD Simulations of Urea-SCR Systems Chemical Engineering Journal and the Biochemical Engineering Journal 150 1 69 82 2009 10.1016/j.cej.2008.12.003
- Munnannur , A. and Liu , Z.G. 2010
- Yong , Y. Development of a 3D Numerical Model for Predicting Spray, Urea Decomposition and Mixing in SCR Systems SAE Technical Paper 2007-01-3985 2007 10.4271/10.4271/2007-01-3985
- Zheng , G. CFD Modeling of Urea Spray and Deposits for SCR Systems SAE Technical Paper 2016-01-8077 2016 10.4271/2016-01-8077
- Fischer , S. , Bitto , R. , Lauer , T. , Krenn , C. et al. Impact of the Turbulence Model and Numerical Approach on the Prediction of the Ammonia Homogenization in an Automotive SCR System SAE Int. J. Engines 5 3 1443 1458 2012 10.4271/2012-01-1291
- Quan , S. , Wang , M. , Drennan , S. , Strodtbeck , J. et al. A Molten Solid Approach for Simulating Urea-Water Solution Droplet Depletion ILASS Americas 27th Annual Conference on Liquid Atomization and Spray Systems Raleigh, NC 2015
- Ebrahimian , V. , Nicolle , A. , and Habchi , C. Detailed Modeling of the Evaporation and Thermal Decomposition of Urea-Water Solution in SCR Systems AICHE journal 58 7 1998 2009 2012 10.1002/aic.12736
- Brack , W. , Heine , B. , Birkhold , F. , Kruse , M. et al. Kinetic Modeling of Urea Decomposition Based on Systematic Thermogravimetric Analyses of Urea and Its Most Important by-Products Chemical Engineering Science 106 0 1 8 2014 10.1016/j.ces.2013.11.013
- Lauer , T. Preparation of Ammonia from Liquid AdBlue-Modeling Approaches and Future Challenges Chemie Ingenieur Technik 90 6 783 794 2018 10.1002/cite.201700107
- Sun , Y. , Sharma , S. , Vernham , B. , Shibata , K. et al. Urea Deposit Predictions on a Practical Mid/Heavy Duty Vehicle After-Treatment System SAE Technical Paper 2018-01-0960 2018 10.4271/2018-01-0960
- Habchi , C. , Nicolle , A. , and Gillet , N. Numerical-Study-of-Deposits-Formation-in-SCR-Systems-Using-Urea-Water-Solution-Injection J Mater Sci Nanotechnol 6 2 2018
- Brack , W. , Heine , B. , Birkhold , F. , Kruse , M. et al. Formation of Urea-Based Deposits in an Exhaust System: Numerical Predictions and Experimental Observations on a Hot Gas Test Bench Emiss. Control Sci. Technol. 2 3 115 123 2016 10.1007/s40825-016-0042-2
- Cordier , M. , Lecompte , M. , Raux , S. , Ricordeau , V. et al. Optical Characterization of Urea Water Solution along an Exhaust Pipe SIA Conference - Rouen 2016
- Richards , K.J. , Senecal , P.K. , and Pomraning , E. CONVERGE: CONVERGECFD MANUAL SERIES (2.4) Madison, WI Convergent Science 2018 https://convergecfd.com
- Wei , L. , Youtong , Z. , and Asif , M. Investigation on UWS Evaporation for Vehicle SCR Applications AIChE J. 62 3 880 890 2016 10.1002/aic.15078
- Wang , T.J. , Baek , S.W. , Lee , S.Y. , Kang , D.H. et al. Experimental Investigation on Evaporation of Urea-Water-Solution Droplet for SCR Applications AIChE J. 55 12 3267 3276 2009 10.1002/aic.11939
- Kim , J.Y. , Ryu , S.H. , and Ha , J.S. Numerical Prediction on the Characteristics of Spray-Induced Mixing and Thermal Decomposition of Urea Solution in SCR System: 2004 Fall Technical Conference of the ASME Internal Combustion Engine Division ICE2004-889, Proceedings of ICE04 165 170
- Schaber , P.M. , Colson , J. , Higgins , S. , Thielen , D. et al. Thermal Decomposition (Pyrolysis) of Urea in an Open Reaction Vessel Thermochimica Acta 424 1-2 131 142 2004 10.1016/j.tca.2004.05.018
- Chauveau , C. , Halter , F. , Lalonde , A. , and Gokalp , I. An Experimental Study on the Droplet Vaporization: Effect of Heat Conduction through the Support Fiber 22nd European Conference on Liquid Atomization and Spray Systems September, 8-10 2008 http://ilasseurope.org/events/22th-ilass-europe
- Chauveau , C. , Birouk , M. , Halter , F. , and Gökalp , I. An Analysis of the Droplet Support Fiber Effect on the Evaporation Process International Journal of Heat and Mass Transfer 128 885 891 2019 10.1016/j.ijheatmasstransfer.2018.09.029
- Ebrahimian , V. and Habchi , C. Towards a Predictive Evaporation Model for Multi-Component Hydrocarbon Droplets at all Pressure Conditions International Journal of Heat and Mass Transfer 54 15-16 3552 3565 2011 10.1016/j.ijheatmasstransfer.2011.03.031