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Institute for Powertrains
& Automotive Technology
Institute for Powertrains & Automotive Technology
Urea Injection and Preparation in
Diesel ApplicationsMultiphase Multicomponent Modeling using Star-CD
STAR European Conference 2010, London
Dipl.-Phys. Simon Fischer
Dr. Thomas Lauer
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 2
Contents
The SCR-Process: Problem Introduction
Methodology and Analysis Setup
Thermodynamic Multicomponent Model of a Urea-Water-Solution
Droplet-Wall-Interaction and Liquid Film Dynamics
Conjugate Heat Transfer and Liquid Film Boiling
Ammonia Homogenization
Conclusion and Outlook
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 3
Contents
The SCR-Process: Problem Introduction
Methodology and Analysis Setup
Thermodynamic Multicomponent Model of a Urea-Water-Solution
Droplet-Wall-Interaction and Liquid Film Dynamics
Conjugate Heat Transfer and Liquid Film Boiling
Ammonia Homogenization
Conclusion and Outlook
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 4
Problem Introduction: Future Diesel Emission Limits
exhaust aftertreatment of NOx is a major requirement for future Diesel engines
[1]
NOx- Emissions [g/km]
Pa
rtic
leE
mis
sio
ns
[g/k
m]
SC
R
source: Auto News
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 5
Principle of Selective Catalytic Reduction (SCR)
exhaust gas flow (NOx)
injection of a
water-urea mixture
32.5 mass-% urea
67.5 mass-% water
timescales of ammonia preparation
ammonia uniformity at catalyst frontal area
exhaust pipe
impingement film transport
heat transfer
ammonia (NH3) vapour
homogenization
preparation process
1) water evaporation
2) chemo-physical urea
decomposition to ammonia
(thermo-/hydrolysis)
CFD-simulation for efficient SCR-system designSCR-catalyst:„NOx+NH3 →N2 + H2O“
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 6
Contents
The SCR-Process: Problem Introduction
Methodology and Analysis Setup
Thermodynamic Multicomponent Model of a Urea-Water-Solution
Droplet-Wall-Interaction and Liquid Film Dynamics
Conjugate Heat Transfer and Liquid Film Boiling
Ammonia Homogenization
Conclusion and Outlook
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 7
Methodology and Validation Setup
straight exhaust pipe
urea-water-
solution-injection
from engine
exhaust gas flow
SC
R-C
ata
lyst
CFD mesh according to
experimental setup
OP 3 - high temperature / mass flow / NOx raw emission
OP2 - intermediate temperature / mass flow / NOx raw emission
OP1 - low temperature / mass flow / NOx raw emission
Analysis of Representative Operating Points (OP):
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 8
Contents
The SCR-Process: Problem Introduction
Methodology and Analysis Setup
Thermodynamic Multicomponent Model of a Urea-Water-Solution
Droplet-Wall-Interaction and Liquid Film Dynamics
Conjugate Heat Transfer and Liquid Film Boiling
Ammonia Homogenization
Conclusion and Outlook
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 9
Thermodynamic Multicomponent Model (Liquid Film, Droplets)
TBoil(Yurea)
Partial Pressures
(Raoult`s law):
AdBlue:
32.5 Mass.-% Urea,
67.5 Mass.-% Water
pure water:
Antoine
equation
implemented in
dropro.f, lqfpro.f
pure urea:
saturation
pressure curve
implemented in
dropro.f, lqfpro.f
)()( , TpxTp ipure
si
i
s
i
i
stot TpTp )()(
Total Pressure
(Dalton`s law):
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 10
Decomposition of a Single Urea-Water-Solution-Droplet
water evaporation urea thermolysis
two-step preparation process modeled
[1]
[1] Wang, Baek,Lee: Experimental Investigation on Evaporation of Urea-Water-Solution Droplet for SCR Applications, AICE 2009
heat flux
through fibre,
fine tuning of
urea-psat-curve
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 11
Contents
The SCR-Process: Problem Introduction
Methodology and Analysis Setup
Thermodynamic Multicomponent Model of a Urea-Water-Solution
Droplet-Wall-Interaction and Liquid Film Dynamics
Conjugate Heat Transfer and Liquid Film Boiling
Ammonia Homogenization
Conclusion and Outlook
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 12
Multiphase Modeling: Challenge Of Timescales
Small Time Scales:
turbulent flow field
droplet dynamics
species (ammonia) transport
Steady-State Calculation (PISO)
fluid flow field
temperature field
no spray injection (liquid phase)
Large Time Scales:
liquid film formation and -dynamics
ammonia formation from film
wall cooling (CHT)
Transient Calculation (Simple)
thermodynamics (enthalpy)
droplets and liquid film
species (ammonia, water vap.)
time steps: 0.1 ms (droplets present)
1 ms (otherwise)
Solution Strategy:
Restart with
flow field
solvers
switched off
simulated interval of several minutes incl. spray dynamics and species transport
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 13
Droplet Dynamics: Injection
three hole nozzle
diameter
distribution
from
measurement
timescale miliseconds
droico.f
no primary break-up modelled
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 14
Droplet Impingement Regimes
depending on liquid properties, droplet dynamics, wall temperature,…
OP 3 – high temp.
OP2- medium temp.
OP1 - low temp
…complex behaviour
Bai-M
odel (S
w30)
Sp
rea
d-M
ode
l
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 15
Liquid Film Formation: Validation
Experiment
(Videoanalysis)
Simulation Spread-
Model
Simulation Bai-
Model- Switch 30
OP 1
(„cold“)
extensive liquid
film, flow to pipe
bottom x
OP 2
(„medium“)
thin film after
some delay, no
remarkable flowx
OP 3
(„hot“) no permanent film x
impingement model not yet predictive across whole temperature range
not observed
in simulation
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 16
Simulated Liquid Film Formation
OP3-Bai-Sw30
OP2-BaiSw30
OP1- Spread
…
OP1-BaiSw30massive liquid film with spread model in OP1
small extent liquid film with Bai model in OP1
no permanent film in OP3
transient behaviour in OP2
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 17
Droplet Impingement and Liquid Film Dynamics
timescale millisecondstimescale minutesliquid film spread after 120 s
high
Droplet
Diameter
low
Film
Thickness
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 18
Liquid Film Dynamics Validation
180°
90°
180°
90°
Expe
rim
ent
Sim
ula
tio
nV
ideo-A
naly
sis
[2]
Sim
ula
tion
Distribution of Liquid Film after 120 Seconds
OP1- Spread
exce
llen
td
escri
ptio
no
f film
dyn
am
ics
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 19
Contents
The SCR-Process: Problem Introduction
Methodology and Analysis Setup
Thermodynamic Multicomponent Model of a Urea-Water-Solution
Droplet-Wall-Interaction and Liquid Film Dynamics
Conjugate Heat Transfer and Liquid Film Boiling
Ammonia Homogenization
Conclusion and Outlook
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 20
Thermal Wall Boundary Conditions In Star-CD
Adia
batic
Fix
ed
Tem
pera
ture
Fix
ed
with
Resis
tance
Conju
gate
Heat T
ransfe
r
Rele
vance
in
SC
R-M
odelin
g
wall as a heat source !!!cooling of wall due to
evaporation !!!
thermal inertia of wall !!
wall parallel heat conduction !!
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 21
Meshing For Conjugate Heat Transfer Approach
boundary Layer
extruded solid cells for CHT
single layer approach
fluid cells
trimmed from custom-grid
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 22
The Nukiyama Film Boiling Model (Star-CD 4.10)
OP 3
OP2
OP1
regime positions
from experiment
(IR-thermography)
Burnout Point
Leidenfrost Point
Film-boilingTransition-
Nucleate-Convection
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 23
Local Wall Spray CoolingOP 1-Spread
Temperature T[ C]
primary
impingement
position (water
evaporation)
Flow direction
IR-Thermography
Star-CD 4.10good qualitative representation
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 24
Wall Spray Cooling
OP3-Bai Sw30OP2-BaiSw30
Steady State Wall CoolingDynamics of Cooling Process
OP1-Spread
IR-Themography
Star-CD 4.06
Star-CD 4.10
numerical instability
in v4.10 Bai model
for thermal break-
up-regime
(currently fixed by
Switch 30 and
NOTHBREAK
in *.prob)
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 25
Contents
The SCR-Process: Problem Introduction
Methodology and Analysis Setup
Thermodynamic Multicomponent Model of a Urea-Water-Solution
Droplet-Wall-Interaction and Liquid Film Dynamics
Conjugate Heat Transfer and Liquid Film Boiling
Ammonia Homogenization
Conclusion and Outlook
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 26
Film
Thickness
OP 1
Ammonia Vapour Homogenization
Ammonia-
Concentration
high
low
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 27
Ammonia Vapour Homogenization: Validation
FTIR- measurement [2]
Ammonia-
Concentration
OP 1
Simulation
high
low
concentrations
scaled by
mean value
STAR European Conference 2010
Urea Injection and Preparation in Diesel Applications
March 23rd 2010 | London | Simon Fischer | Slide 28
Contents
The SCR-Process: Problem Introduction
Methodology and Analysis Setup
Thermodynamic Multicomponent Model of a Urea-Water-Solution
Droplet-Wall-Interaction and Liquid Film Dynamics
Conjugate Heat Transfer and Liquid Film Boiling
Ammonia Homogenization
Conclusion and Outlook
STAR European Conference 2010
Urea-injection and -preparation in Diesel applications
March 23rd 2010 | London | Simon Fischer | Slide 29
Conclusion
validated Star-CD-Model of the urea-water-solution preparation process:
simulation of several injection events and long time liquid film behaviour
via separated (steady) flow field and liquid-phase/thermodynamic calc.
two step ammonia preparation process modeled properly with Raoults` law
predictive impingement model for whole temperature range missing
→ massive film formation (OP1) currently forced by spread-model
→ break-up model in v4.10 (for high temp. impingement) not stable
liquid film dynamics well represented in simulation
implementation of Conjugate Heat Transfer for a correct prediction of liquid
film formation and preparation timescales (validated by IR-themography)
promising liquid film boiling model improvements from v4.06 to v4.10
STAR European Conference 2010
Urea-injection and -preparation in Diesel applications
March 23rd 2010 | London | Simon Fischer | Slide 30
Outlook
check and adaption of improved Star-CDs` physical models (4.10/4.12)
NIST approach (internal calculation) for multicomp. thermodynamics properties
fix of Break-Up regime numerical instabilities of extended Bai-model (v4.10)
(currently NOTHBREAK in *.prob and Switch 30 → support)
underestimation of liquid film at low temperatures (OP1): tuning of critical
Regime Weber-Numbers to realize „one-fits-all“ Bai-impingement-model
adaption of liquid film boiling model (Nukiyama-curve) for urea-water solution
(currently standard Star-CD parameter set for pure water)
(thermography data available)
evaluation of post impingement droplet properties (e.g. size distribution)
laser-diffraction data available
towards a fully predictive SCR-process Star-CD-model
Institute for Powertrains
& Automotive Technology
Institute for Powertrains & Automotive Technology
Thank you for your attention!
Dipl.-Phys. Simon Fischer
simon.fischer@ifa.tuwien.ac.at
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