LABORATORY OF APPLIED THERMODYNAMICS

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LABORATORY OF APPLIED THERMODYNAMICS Dr. Grigorios C. Koltsakis Aristotle University Thessaloniki Tutorial DOC & DPF modeling

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Microsoft PowerPoint - MODEGAT 2009 - Koltsakis presentation.ppt Fundamentals, basic model equations
Transport-reaction coupling
“3-dimensional” effects
Channel model
( ) ( )jsjgj
Substrate Ts, ρs, vs Washcoat
O2, N2, CO, HC, NOx O2, N2, CO2, H2O
Gas Tg, ρg, vg
(convection, exothermy)
profile at catalyst inlet, as function of flow
resistance
S r
T r
O2, N2, CO, HC, NOx O2, N2, CO2, H2O
Gas Tg, ρg, vg
( )
Temperature [°C]
E ff
Temperature [°C]
E ff
Temperature [°C]
E ff
Hydrocarbon adsorption
Langmuir isotherm
D-R isotherm is applicable to multilayer adsorption in microporous solids (zeolites).
The equation of the DR isotherm gives the adsorbed mass as function of temperature and partial pressure.
A linear «driving force» is assummed to calculate the rates towards equilibrium.
Adjustable parameters:
β (affinity parameter)
k (rate constant)
The rate constant for desorption is an exponential function of temperature.
2
Not possible with a single HC species
Pontikakis et al. (2000) used 4 HC species
Decane: fast oxidizing, easily adsorbable
Toluene: fast oxidizing, less easily adsorbable
Propene: fast oxidizing, practically non-
adsorbable
adsorbable
100 150 200 250 300 350 400
Temperature [°C]
Temperature [°C]
Time [s]
0.00E+0
2.50E-4
5.00E-4
7.50E-4
1.00E-3
1.25E-3
1.50E-3
C o n c e n tr a ti o n
Inlet
Time [s]
a ti o n a
t o u tl e t
-1.0
0.0
1.0
e d H
Time[s]
H C
]
o C
0
50
100
150
200
250
300
350
400
450
Time[s]
H C
]
o C
Decane adsorption desorption
Decane adsorption desorption
Water condensation/evaporation effect on thermal response
0 100 200 300 400 500
Time [s]
Periphery, exp.
Periphery, cmp.
Pontikakis et al., CaPoC 5, 2000
Hysteresis (history) effect
0
10
20
30
40
50
60
70
80
90
100
60 100 140 180 220 260 300 340 380 420 460
T [°C]
io n e
ie n c y %
CO light off CO cool down NO light off NO cool down HC light off HC cool down
COCO
HCHC
NONO
Definitions
Random shape, segmentation
any flow distribution
“Mixed reactor”
( ) IvY
Extremely high species transfer rates inside the porous wall
Species equations
( ) IvY
Haralampous O. A., Koltsakis G. C.: Industrial & Engineering Chemistry Research, Vol.43, Issue 4, p. 875-883, 2004.
Inlet channel Wall Outlet channel
Species equations
IIfwIIadv YvN ,, =
inI YY =
IwIadv YvN =,
Neglecting the convective species transfer from channel gas to surface
(not justified, especially in catalyzed applications)
Species equations
IIfwIIadv YvN ,, =
inI YY =
IwIadv YvN =,
IfwfIadv YvN ,,, =
IIfwfIIadv YvN ,,, =
IfI YY ,=
Bissett E. J., Shadman F., AlChE Journal (Vol31, No5), p. 753, May 1985. ”0-d model”
Bissett E. J., Chemical Engineering Science Vol. 39, Nos 7/8, pp. 1233-1244 (1984). “1-d model”
Neglecting diffusion in the wall-flow direction
Energy equations
Energy equations
( ) Ip vTC ρ
( ) IIfpwIIadv TCvH ,, ρ=
( )− Ip vTC ρ
)(zTI
Haralampous O., Koltsakis G. C.: Chemical Engineering Science, Volume 57, Issue 13, July 2002, Pages 2345-2355.
Energy equations
( ) wpwIIadv TCvH ρ=, ( ) IpwIadv TCvH ρ=,
( ) IIconvIconvreactwconv w
*
,
Bissett E. J., Chemical Engineering Science Vol. 39, Nos 7/8, pp. 1233-1244 (1984). “1-d model”
Koltsakis G. C., Stamatelos A. M., Ind. Eng. Chem. Res., 1997 Vol. 36 p. 4155-4165. “catalytic 1-d model, modified energy balance”
wIIf TT =,
Summary of model equations
( ) ( )jjsj
w
jw
w
radreactwallconv HHHHS +++=
S z
T k
radreactwallconv HHHHS +++=
LABORATORY OF APPLIED THERMODYNAMICS
Clean filter filtration modeling
wu pd
Does the unit-cell approach apply to wall-flow filter structure?
Semi-empirical cake formation modeling
0%
20%
40%
60%
80%
100%
C a k e f il tr
a ti o n e
ff ic
a ti o n e
ff ic
ff ic
0
10
20
30
40
50
60
70
80
90
100
Time [s]
ff ic
a s s [ g ]
Estimation of soot in the wall
depending on the wall structure
High Flow Rate (300 kg/h)
0
10
20
30
40
50
60
70
80
90
100
Time [s]
ff ic
a s s [ g ]
0
10
20
30
40
50
60
70
80
90
100
Time [s]
ff ic
a s s [ g ]
Estimation of soot in the wall
depending on the flow rate
Soot cake properties
Effect of pressure drop on porosity
Compressible soot cake modeling
Velocity [cm/s]
e n s it y [ k g /m
³]
Soot Mass [g/l]
Initial loading
Depth filtration of soot in the wall contributes strongly to pressure drop.
Pressure drop “hysteresis”
Soot Mass [g/l]
Initial loading
Depth filtration of soot in the wall contributes strongly to pressure drop.
Pressure drop “hysteresis”
Soot Mass [g/l]
Initial loading
Depth filtration of soot in the wall contributes strongly to pressure drop.
Pressure drop “hysteresis”
Soot Mass [g/l]
generatio n
After partial regeneration, oxidation of soot in the wall reduces pressure drop for same
soot mass, compared to initial loading.
Pressure drop “hysteresis”
Soot Mass [g/l]
generatio n
After partial regeneration, oxidation of soot in the wall reduces pressure drop for same
soot mass, compared to initial loading.
Pressure drop “hysteresis”
Soot Mass [g/l]
Reloading
Incoming soot does not re-penetrate the wall. The correlation of pressure drop vs soot
loading is depends on partial regeneration history.
Pressure drop hysteresis effect
Soot Mass [g/l]
dots: measurement
lines: simulation
Following an incomplete regeneration, the cake soot does not allow the incoming soot to-
penetrate the wall. The pressure drop correlation with soot loading changes dramatically.
Uncatalyzed soot oxidation reactions
1000/T [1/K]
a te
E=122±4 kJ/mole
NO2 is produced in the catalyzed wall
NO2 diffuses back to the soot layer
Soot density NO2 concentration
( ) ( )jjsj
w
jw
w
∑=




∂ ∂
− ∂

∑=




∂ ∂
− ∂

Haralampous O. A., Koltsakis G. C.: Industrial & Engineering Chemistry Research, Vol.43, Issue 4, p. 875-883, 2004.
O2 transfer from channel gas to soot surface
O2
Length [mm ]
C o
n c
e n
tr a
ti o
Wall flow
Due to concentration gradient, O2 is transferred from the axial flow to the soot layer and
increases local availability and reaction rates Haralampous O. A., Koltsakis G. C.: AIChE Journal, Vol. 50, No. 9, p. 2008, 2004
Importance of O2 transfer for the prediction of filter temperature
Ignoring O2 mass-transfer effects (diffusive-convective) leads to serious under-prediction
of peak temperatures
Soot loading [g/l]
800
900
1000
1100
1200
1300
1400
Soot loading [g/l]
Importance of O2 transfer for the prediction of filter temperature
Ignoring O2 mass-transfer effects (diffusive-convective) leads to serious under-prediction
of peak temperatures
Soot loading [g/l]
800
900
1000
1100
1200
1300
1400
Soot loading [g/l]
Importance of O2 transfer for the prediction of filter temperature
800
900
1000
1100
1200
1300
1400
Soot loading [g/l]
Ignoring O2 mass-transfer effects (diffusive-convective) leads to serious under-prediction
of peak temperatures
Catalyzed DPF simulation
Uncoated DPF
“Axial” zoning
Better cold-start performance
Better passive regeneration
for catalyst zoning
65
70
75
80
85
90
95
100
105
Filter Length [mm]
]
F-DPF in F-DPF out R-DPF in R-DPF out Z-DPF in Z-DPF out
CO CO gradient
CO
zoned
high-PGM
low-PGM
high-PGM
low-PGM
zoned
Koltsakis, G. C., Dardiotis, C. K., Samaras, Z. C., Frey, M., Wenninger, G., Krutzsch, B., Haralampous, O. A., SAE 2008-01-0445, 2008
LABORATORY OF APPLIED THERMODYNAMICS
3-d DPF regeneration simulation Sources of “3-dimensionality”
t=50 s t=60 s t=70 s t=80 s t=90 s
S oo
t T
em pe
ra tu
re F
lo w
“3-d effects”
Heat losses, segmentation, asymmetric inlet temperature/flow, oval DPF geometry
Flow, soot and temperature distribution effects due to inlet cone shape
Temperature (°C)
t=48 s
t=100 s
t=140 s
t=180 s
t=500 s
Koltsakis, G. C., Samaras, Z. C., Echtle H., Chatterjee D.,Markou P., Haralampous O., SAE paper 2009-01-1280, 2009
Model validation – centerline channel
300
400
500
600
700
800
900
1000
Time [s]
Dots: Measurement, Lines: Model
Koltsakis G.C, Haralampous O. A, Margaritis N., Samaras Z. C., Vogt C.D., Ohara E., Watanabe Y., Mizutani T.:, SAE Transactions,, 2005
Stress analysis
Koltsakis et al., FAD Conference-2007 (LAT-IAV GmbH-Exothermia)
62
Time [s]
T e
m p
e ra
tu re
Full-load Idle
Test data for model input from IAV engine bench (SAE 2007-01-1127)
DOC CDPF SCR
LABORATORY OF APPLIED THERMODYNAMICS