1 ©2017ConvergentScience.AllRightsReserved
Zhaoyu Luo*,Parvez Sukheswalla,ScottDrennan,Mingjie Wang,PeterKellySenecal
ConvergentScienceInc.
3DNUMERICALSIMULATIONSOFSELECTIVECATALYTICREDUCTIONOFNOXWITHDETAILEDSURFACECHEMISTRY
Preparedfor2017CLEERWorkshopPresentationOct4th 2017
2
GeneralPurposeCFDPackage:CONVERGE
3
Outline• Introduction• Methodologies
- CONVERGE’ssteadystatesolver- Adaptivemeshrefinement- Ureadecomposition:Moltensolidmodel- Surfacechemistrysolver
• ResultsandDiscussion- 3DSingleSCRblockvalidations- 3DUrea/SCRSystemvalidations
• Conclusion
4
Introduction
5
ModernUrea/SCRSystemDesignChallenges• Meetingemissionsregulationsincost-effectivemanner
- FastproductdesigntimelineswithcomplexATsystems
• Movetocompact,lowtemperatureUrea/SCRdesigns- Relyondynamicsplashing/filmingandpulsedinjectors(i.e.,transient)
• Needtoaddressdifferentflowandcatalysttime-scales- Spray,film,mixingversusSCRsurfacechemistry
6
ConventionalSCRSystemSimulationApproaches• Focuson1Dsurfacechemistrysimulations
- AccurateCFDcouplingtakestoolong• ReducedfidelityCFDandCatalystwithcoupled3D/1Dsimulations- Steady-stateCFDwithpulsedsprays,filmsandmixing- TransientCFDwithverylargetime-steps
• ManualCFDmeshgeneration- Time-consuming,limitingproductivityanddevelopmentofBestPractices
Fullycoupled3DsimulationsofUrea/SCRsystemwastimeconsumingandimpractical
7
CONVERGESpeedsUREA/SCRCFDSimulations• Automaticmeshing
- Nouser-meshing- Automaticgrid-scaling- AdaptiveMeshRefinement(AMR)- Meshdependentà Grid-converged
• Superfasttransientsolver- Time-accurate- Pseudosteadystatesolver
• Comprehensivesetofaccuratemodels- Spray/Film- Ureadecomposition- Surfacechemistrysolver
Fullycoupled3DsimulationsofUrea/SCRsystemisnowapplicableandcanprovidemorephysicaldetails
8
Methodologies
9
SteadyStateSolverinCONVERGE(1/2)
• Densitybased• Fast,andaccuracyalmostasgoodastransientsetup
• Automatedcontrolofsolversettings
• HigherCFLnumbersattainable(20-30fornon-Reactingflows;10-15forReactingflows)
10
SteadyStateSolverinCONVERGE(2/2)
11
AdaptiveMeshRefinement(AMR)
• BaseGridsize:(Δ𝑥,Δ𝑦,Δ𝑧)- BasegridisatLEVEL0- LEVELn=(𝒃𝒂𝒔𝒆_𝒈𝒓𝒊𝒅)/𝟐^𝒏 [1]- GridsizeatanyLEVELisrelativetobasegridsize- Example:(1mmbasemesh,3levelsofrefinement)- Levels0,1,2,3=1.0,0.5,0.25,0.125mm
• AdaptiveMeshRefinement(AMR)- Refinemeshbasedonvelocity,temperature,species,Y+,etc.gradients
12
UreaMolten-SolidModel• Birkhold,F.etal,2007
• ValidatedinKimetalICEF2004-889
WaterEvaporating
WaterEvaporatedOnlyUrealeft
Ureadecomposing(Solidtogas)Nozzle Hydrolysisof
HNCOAmmonia(NH3)
Ammonia(NH3)Iso-cyanicacid(HNCO)
Molten-SolidApproach
13
SurfaceChemistrySolver
• CONVERGEusesimplicitsolverforsurfacechemistry
• Coupledwithgasphase• Fastandaccurate DetailedsurfacemodelfromOlssonetal2008
14
ResultsandDiscussion
15
Validation1:3DSingleSCRblock
• Experiment:SAE2013-01-1575
• Inlet:Exhaustgaswith~422ppmNOx
• P=~0.9atm,T=666K
• Surfacemechanism:Olssonetal;2008
• NOxconversionoverCu-Zeolites
NOxconversion
CONVERGE 38.87%
exp 37.8%
16
Validation2:3DUreaSCRSystem:Geometry• SurfacechemistryisactivatedintheSCRblockregion(red)ofthegeometry
• Totalmeshsizeatsteadystate:~2000000
• SimulationwasterminatedwhentheNOxmassreachedsteady-stateThecasewasrunwithbothasteady-statesolverandatransientsolver
17
Validation2:3DUreaSCRSystem:BoundaryandInitialConditions
No. Speed[rpm] BMEP[bar] Temp[K] UWS flowrate[g/s]
1 1200 11.6 666 0.12172 1200 11.6 678 0.1916
TwoSCRsystemsaresimulatedinthecurrentstudy:
ExamplespecificationforSCR-1
Speciescomposition CO2,N2,O2,H2O,NO,NO2Pressure(bar) 0.96
Steadytime(s) 20.0
Mechanism Olssonetal2008
18
Validation2:3DUreaSCRSystem:PressureDropinSCR
PorousmediamodelisusedintheSCRsystem;largeuncertaintyexistsandparameteroptimizationisperformed
19
Validation2:3DUreaSCRSystem:NOxConversions
0
0.1
0.2
0.3
0.4
0.5
1 2
SCR-1NOxCo
nversion
Rate
Experiment Simulation
(a)
(b)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1 2
SCR-2NOxConversionRate
Experiment Simulation
(a)
(b)
SCR-1 SCR-2
20
Validation2:3DUreaSCRSystem:TransientvsSteadyStateSolver(1/2)
0.0 0.5 1.0 1.5 2.0
0.0
2.0x10-7
4.0x10-7
6.0x10-7
8.0x10-7
1.0x10-60 2000 4000 6000
Transcient Approach
NH3
Flow
Rat
e, kg
/s
Time, s
Steady State Approach
Pseudo Time Step
0.0 0.5 1.0 1.5 2.0
0.0
1.0x10-5
2.0x10-5
3.0x10-5
4.0x10-5
5.0x10-5
6.0x10-50 2000 4000 6000 8000
Flow
Rat
e, kg
/s
Time, s
NO
NO2
(a)
(b)
0.0 0.5 1.0 1.5 2.0
0.0
2.0x10-7
4.0x10-7
6.0x10-7
8.0x10-7
1.0x10-60 2000 4000 6000
Transcient Approach
NH3
Flow
Rat
e, kg
/s
Time, s
Steady State Approach
Pseudo Time Step
0.0 0.5 1.0 1.5 2.0
0.0
1.0x10-5
2.0x10-5
3.0x10-5
4.0x10-5
5.0x10-5
6.0x10-50 2000 4000 6000 8000
Flow
Rat
e, kg
/s
Time, s
NO
NO2
(a)
(b)
SteadystatesolverwellcapturethesteadyresultsofNOxconversion
21
Validation2:3DUreaSCRSystem:TransientvsSteadyStateSolver(2/2)
0
5
10
15
20
1 2Speedup
Factor,Transient/SteadyS
tate
SCR-1 SCR-2
NH3contourvalidations Steadystatesolverspeedupfactor
*steadystatesolverresultsin~15-20timesspeedupcomparedtothetransientsolver,whichrenditpossibleforover-night 3DfullycoupledUREA/SCRsystemsimulations
22
Summary
• Afull-scale3DmodelofUREA/SCRsystemwassetupusingCONVERGEandvalidatedagainsttheexperiments.
• SteadystatesolvercoupledwithsurfacechemistryinCONVERGEcouldhelpacceleratingthesimulationsbyfactorsof15-20 whileretaininggoodaccuracy.
• Futurework- Issuenotaddressed:uncertaintyofthecouplingofdifferentphysicalmodel->sensitivityanalysis
- Baselinetovalidatemorehighfidelitymodels
23
THANKYOU!CONVERGECFD.COM
©2017ConvergentScience.AllRightsReserved
24
SurfaceChemistry(Olssonetal;2008)
Usersareallowedtosupplyinhibitionfunctionthrough
UDFs
