This content is not included in
your SAE MOBILUS subscription, or you are not logged in.
Urea SCR System Development for Large Diesel Engines
Technical Paper
2014-01-2352
ISSN: 0148-7191, e-ISSN: 2688-3627
Annotation ability available
Sector:
Language:
English
Abstract
The introduction of stringent EPA 2015 regulations for locomotive / marine engines and IMO 2016 Tier III marine engines initiates the need to develop large diesel engine aftertreatment systems to drastically reduce emissions such as SOx, PM, NOx, unburned HC and CO. In essence, the aftertreatment systems must satisfy a comprehensive set of performance criteria with respect to back pressure, emission reduction efficiency, mixing, urea deposits, packaging, durability, cost and others.
For on-road and off-road vehicles, urea-based SCR has been the mainstream technology to reduce NOx emissions. For category II marine engines with single cylinder displacement volumes between 7 liters and 30 liters, IMO III (Tier IV) emission regulations dictate approximately 80% reduction of NOx emissions vs. Tier II emission regulations [1]. Urea / ammonia SCR is being considered as an enabling technology to achieve IMO III regulations without significant impacts on engine performance and fuel economy.
As always, engine OEMs attempt to develop technologies mostly via engine measures such as EGR and high pressure common rail, in effect minimizing the content of aftertreatment systems. For instance, one engine OEM announced that engine-only measures without aftertreatment devices can meet IMO III regulations [2]. However, the efforts taken in engine developments are often enormous, requiring long development duration to resolve major technical challenges.
Compared with land-based (including mobile) applications, large engine applications face multiple challenges. Due to high sulfur content in diesel fuel, sulfur reduction would be an important task, affecting fuel switching, sulfur scrubber choices, and aftertreatment layout designs. For instance, the wet / dry desulfurization with appropriate reheating mechanisms will affect SCR temperature window which typically operates between 250 °C and 450 °C [3].
The scope of this paper is confined to urea SCR technology applications, hence does not touch complexities in sulfur related design issues. A typical urea SCR system includes a urea / ammonia injector / nozzles, injector housing, mixer, and appropriate pipe configurations. In marine applications, urea mixing, urea deposits, catalyst poisoning, dust removal, and catalyst choices are quite different from those of land-based mobile applications, however in many ways similar to power plant emission controls.
Compared with land-based mobile applications, urea mixing is made more difficult because of large spatial size and mixing space; in addition, low flow rate and temperature tend to negatively affect urea evaporation and turbulence intensity. Urea deposits, as a result of incomplete evaporation of urea solution, can create concerns of backpressure, engine power loss and material deteriorations. Catalyst poisoning occurs due to solid chemical deposits (such as ammonium bisulfate) on catalyst surface as a result of the reactions between ammonia and sulfur. Both urea deposits and sulfates can be removed by higher temperature. Ash and dusts are much more severe in marine applications than in land-based mobile applications because of impurities (mostly sulfur) from marine diesel fuel (DFO, IFO, HFO), therefore care must be taken in selecting SCR catalysts.
A successful urea SCR system design needs to satisfy a comprehensive set of performance criteria as outlined below:
- 1Efficient catalyst usage (small size)
- 2High NOx conversion efficiency
- 3No ammonia slip
- 4No urea deposits
- 5Low backpressure
- 6Compact, low cost, and low weight
- 7High acoustic (noise reduction) performance
This paper briefly reviews existing SCR technology in marine applications. Then a specific case study is introduced with an initial design layout of urea SCR. CFD method was applied to simulate urea spray transport, evaporation, and droplet-wall phenomena. Engine dynamometer tests were performed to validate the initial design. The urea deposit locations from tests were compared with CFD predicted results. With gained insights, three geometrical configurations of urea SCR systems were studied to address the deposit concerns. Multiple influencing factors such as wall temperature and mixers are evaluated. The optimized design is summarized at the end. Future developmental directions on marine applications are recommended in the conclusion section.
Recommended Content
Technical Paper | Electronic Direct Fuel Injection System Applied to an 1100cc Two-Stroke Personal Watercraft Engine |
Technical Paper | Diesel Engine Design Concepts for the 1980s |
Technical Paper | Development of Diesel Combustion for Commercial Vehicles |
Authors
- Guanyu Zheng - Weichai Power Emission Solutions Technology Inc.
- Fengshuang Wang - Weichai Power Emission Solutions Technology Inc.
- Sheng Wang - Weichai Power Emission Solutions Technology Inc.
- Wei Gao - Weichai Power Emission Solutions Technology Inc.
- Zhiguo Zhao - Tenneco, Inc.
- Jian Liu - Tenneco, Inc.
- Lin Wang - Tenneco, Inc.
- Lin Wu - Tenneco, Inc.
- Hongyu Wang - Weichai Power New Energy Inc.
Topic
Citation
Zheng, G., Wang, F., Wang, S., Gao, W. et al., "Urea SCR System Development for Large Diesel Engines," SAE Technical Paper 2014-01-2352, 2014, https://doi.org/10.4271/2014-01-2352.Also In
References
- EPA Regulatory Standards http://epa.gov/diesel
- GE Marine's non-SCR diesel technology requires no after-treatment http://media.getransportation.com
- Zheng , G. , Kotrba , A. , Golin , M. , Gardner , T. et al. Overview of Large Diesel Engine Aftertreatment System Development SAE Technical Paper 2012-01-1960 2012 10.4271/2012-01-1960
- 2012 DEER conference, “3rd Generation SCR System Using Solid Ammonia Storage and Direct Gas Dosing - Expanding the SCR window for RDE” Tue Johannessen, Amminex
- Kock Fabian Aftertreatment Systems for Marine Applications: Practical Experience from the Perspective of a Classification Society Paper No. 7, CIMAC Congress 2013
- Oesterle , J. , Calvo , S. , Damson , B. , Neumann , F. et al. SCR Technology with Focus to Stringent Emissions Legislation SAE Technical Paper 2008-01-2640 2008 10.4271/2008-01-2640
- Way , P. , Viswanathan , K. , Preethi , P. , Gilb , A. et al. SCR Performance Optimization Through Advancements in Aftertreatment Packaging SAE Technical Paper 2009-01-0633 2009 10.4271/2009-01-0633
- Schaber , O. M. , Colson , J. , Higgins , S. , Thielen , D. , Anspach , B. , and Brauer , J. Thermal Decomposition (Pyrolysis) of Urea in an Open Reaction Vessel Thermochim Acta 424 131 142 2004
- Scott Sluder , C. , Storey , J. , Lewis , S. , and Lewis , L. Low Temperature Urea Decomposition and SCR Performance SAE Technical Paper 2005-01-1858 2005 10.4271/2005-01-1858
- Xu , L. , Watkins , W. , Snow , R. , Graham , G. et al. Laboratory and Engine Study of Urea-Related Deposits in Diesel Urea-SCR After-Treatment Systems SAE Technical Paper 2007-01-1582 2007 10.4271/2007-01-1582
- Zheng , G. , Fila , A. , Kotrba , A. , and Floyd , R. Investigation of Urea Deposits in Urea SCR Systems for Medium and Heavy Duty Trucks SAE Technical Paper 2010-01-1941 2010 10.4271/2010-01-1941
- Fluent methodology manual 2007
- Stiesch , G. Modeling Engine Spray and Combustion Processes Springer-Verlag Berlin 2003
- Zheng , G. , Palmer , G. , Salanta , G. , and Kotrba , A. Mixer Development for Urea SCR Applications SAE Technical Paper 2009-01-2879 2009 10.4271/2009-01-2879
- Zheng G. , Lacin F. and Kotrba A. Development of a light vehicle diesel aftertreatment system with DOC DPF and urea SCR International Journal of Powertrains 3 1 2014