35
May 1, 2012 1 Future Directions in Diesel SCR Systems Christine Lambert Ford Research and Advanced Engineering Dearborn, MI 2012 CLEERS Workshop
May 1, 2012 1
Future Directions in Diesel
SCR Systems
Christine Lambert
Ford Research and Advanced Engineering
Dearborn, MI
2012 CLEERS Workshop
May 1, 2012 22
Outline
• Background of a 2010 U.S. SCR system
• Catalyst development challenges
• Catalyst and filter structures
• LEVIII catalyst system predictions
• Greenhouse gases (N2O)
• Summary / Next steps
• Acknowledgements
May 1, 2012 3
2010 U.S. Super Duty Diesel Aftertreatment
• 2011 model year trucks >8500 lbs (MDV)
• Certified as complete vehicle on LD FTP-75
• LEVII emissions (0.2 g/mi NOx)
• 120,000 mi durability
aqueous urea
media.ford.com, 2011
May 1, 2012 4
Diesel Fraction of New U.S. Vehicle Sales
Year
1990 1995 2000 2005 2010
% D
iese
l M
ark
et
Sh
are
0.1
1
10
100
Cars
Class 1 + Class 2 trucks
Class 2b + Class 3 trucks
Class 2b trucks
Class 2b trucks (Ford+GM+Chrysler)
Class 3 trucks (Ford+GM+Chrysler)
Wallington et al., Energy Policy, in press
Trucks
Class 1: < 6,000 lbs
Class 2: 6,001-10,000 lbs
Trucks
Class 3: 10,001-14,000 lbs
Class 2b: 8,501-10,000 lbs
Cars
May 1, 2012 5
A Brief History of U.S. Diesel
Aftertreatment
Model Year
1990 1995 2000 2005 2010 2015
Em
issio
n s
tand
ard
s a
pp
licable
fo
r m
ediu
m-d
uty
die
sels
(g/[
bh
p h
r])
0.01
0.1
1
10
NOx
PM
Evolution of emissions standards for NOx and PM.
• mid-1990s: Diesel oxidation catalysts (DOCs) with ceria and alumina for PM oxidation
• 2007:
• ultra-low sulfur diesel,
• particulate filters for PM control
• high precious metal DOCs
• lean NOx control (NOx traps)
• 2010:
• lean NOx control (urea SCR)
Wallington et al., Energy Policy, in press.
May 1, 2012 66
Timeline for 2010 Diesel Aftertreatment7/01Ford’s
DOEContractstarts
4Q05
Urea SCRselected for2010 Diesel
1Q05Ford’s
2010 DieselProgramstarts
3Q07
DieselCatalystRFQ to
Suppliers2Q06
EnhancedCu/zeolitedurability
achieved
12/05Ford’s
DOEContractends
4/10Super
DutyJ1
11/10
SuperDutyJ2
“Advanced”“Research”“Forward
Model”
Ford
researchon SCR~1990-2001
“not exactly to scale”
Parallel Researchon SCR and LNTs
Decision to chassis certify 8500-14K lbs
May 1, 2012 77
Diesel Aftertreatment Layout
HC ���� CO2
CO ���� CO2 NO + NH3 ���� N2
PM ���� CO2
NH3 ���� N2
HC,CO ���� CO2
urea
DOC
NOxsensor
SCR
DOC*DOC*
CDPF
Spray Target
to engine intake
exhaustflow
HC ���� CO2
CO ���� CO2 NO + NH3 ���� N2
PM ���� CO2
NH3 ���� N2
HC,CO ���� CO2
urea
DOC
NOxsensor
SCR
DOC*DOC*
CDPF
Spray Target
to engine intake
exhaustflow
CDPF
Spray Target
to engine intake
exhaustflow
Spray Target
to engine intake
exhaustflow
DOE Program Truck
6000 lbs LDDT• Pt DOC
• Cu/beta SCR
• Pt CDPF
2011MY Super Duty
8,500 – 14,000 lbs• Pd-rich DOC
• Cu/CHA SCR
• Pt/Pd CDPF
Cu/beta
Cu/CHA
Pt
Pd-rich
Pt
Pt/Pd
May 1, 2012 8
A Few Challenges Faced During Commercial
Urea SCR System Development
• Low exhaust gas temperatures
• Catalyst thermal stability
• HC poisoning/coking of SCR
• Precious metal poisoning of SCR
• Catalyst deterioration by sulfur
• Catalyst system cost
May 1, 2012 99
Temperature Operating WindowsSCR Inlet Temperature on FTP-75
Diesel truck has very low exhaust gas temperatures.
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
0 200 400 600 800 1000 1200
Test Time (s)
Tem
pe
ratu
re (
C)
0
20
40
60
80
100
120
Ve
hic
le s
pee
d (
mp
h)
Ford 2011MY Diesel (9500 lbs)
Ford 3.5L GTDI (5250 lbs)
May 1, 2012 1010
Thermal Stability of DOC
0
0.2
0.4
0.6
0.8
1
100 150 200 250 300
Convers
ion E
ffic
iency
Temperature (Deg C)
HC Light-Off Conversion2-Mode 100 hrs / 300 ppm S + 20 mgP/gal
20:1
2:1
1:4
Pt only
0%
10%
20%
30%
40%
50%
150 200 250 300 350 400 450 500 550
% N
O2
of
To
tal N
Ox
Temperature (C)
NO2:NOx
Pt only20:1
2:1
1:4
• Addition of Pd to Pt has a
stabilizing effect for HC oxidation
during cold-start
• Pd also stabilizes Pt for NO
oxidation but has no inherent
activity itself
May 1, 2012 11
Thermal Stability of SCR Catalyst
11
• Thermal stability of Cu/zeolite recently improved from
750 to 900°C (Cu/beta � Cu/CHA)
• NO2 no longer needed for low temp conversion
• Lower cost aftertreatment now possible
Cavataio 2008-01-1025
4NH3 + 4NO + O2 ���� 4N2 + 6H2O
May 1, 2012 1212
HC Poisoning/Coking of Zeolitic SCR
SCR HC/coking issue resolved by transition from Beta to CHA.
DEER 2004
May 1, 2012 1313
Precious Metal Poisoning of SCR
SAE 2008-01-2488SAE 2009-01-0627
• Pt from upstream DOC can volatilize and interfere with SCR function
• Prime indicators are increased NH3 oxidation and N2O make
• Front section of catalyst most affected and can be regenerated
• Pt DOC may be stabilized with addition of Pd and lower exotherm Ts
EVALUATION of DYNAMOMETER AGED FeSCR CATALYST
Lab flow reactor Pt poisoning of Cu SCR by upstream DOC
-50
-25
0
25
50
75
100
100 150 200 250 300 350 400 450 500 550 600
Inlet Gas Temperature (ºC)
NO
x C
on
ve
rsio
n (
%)
Non - Contaminated
Contaminated
0
10
20
30
40
50
60
70
80
90
100
100 150 200 25 0 300 350 400 450 500 550 6 00
Catalyst Temperature (ºC )
NO
x C
on
vers
ion
(%
)
1st Inch (Inlet)
2nd Inch
3rd I nch
4th Inch
5th Inch
6th Inch (Outlet)
May 1, 2012 1414
Sulfur Effects on Cu/zeolite
0
10
20
30
40
50
60
70
80
90
100
150 200 250 300 350 400 450 500 550 600 650
Catalyst Temperature (°C)
NO
x c
on
ve
rsio
n (
%)
degreened
120k mi sulfated
after regen at 650°C
• Sulfur affects NOx activity below 300C
• Sulfur can be removed by lean filter regeneration conditions (>650C)
• Amount adsorbed between regens can be tolerated based on 15 ppm-
wt S in diesel fuel
Effect of 20ppm SO2 at 200°C
(Calculated miles based on 15ppm fuel sulfur)
0
10
20
30
40
50
60
70
80
90
100
160 180 200 220 240 260 280 300
Temperature(°C)%
NO
x C
on
ve
rsio
n
0 miles
500miles
Effect of 120K mi
at 15ppm fuel sulfur
DEER 2004
May 1, 2012 15
0
20
40
60
80
100
120
140
2004 2005 2006 2007 2008 2009 2010 2011 2012
PGM Content Pt Equivalence
15
Catalyst Cost Impact Precious Metal Usage in Super Duty DOCs
Pt rich �
Pd rich
2011MY J1DOC+SCR+CDPF
2011MY J2DOC+SCR+CDPF
DOC only
DOC +CDPF
May 1, 2012 16
2012 MDV Cert Data
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
TP NMHC (g/mi)
TP
NO
x (
g/m
i)
8501-10000 lbs GVW 10001-14000 lbs GVW www.arb.ca.gov
Ford, GM, Daimler, Isuzu use Urea SCR
Dodge uses LNT
May 1, 2012 17
Future Implications for Chassis Certified Diesel MDV
• All 8501 to 10K lbs must chassis certify (~2016MY)
• FUL increased to 150,000 mi (2016MY start)
• SFTP at FUL (all emissions level lower than ULEV340 or
ULEV570 require SFTP)
– 8501-10K lbs US06 + SC03
– 10,001 – 14K lbs: LA92 + SC03
• CO2 reporting (2012MY)
• Greenhouse gases (CH4, N2O - reporting in 2012MY,
regulated in 2013MY)
May 1, 2012 18
Accelerated Aging Conditions Equivalent to 150K mi
DOCs 900°C, 80hrs
SCR catalysts 800°C, 80hrs
SCR filter 800°C, 80hrs
Slip catalyst 750°C, 80hrs
• Hydrothermal Oven:
May 1, 2012 19
2012 Chassis Cert Data (8501-10,000 lbs GVW)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
TP NMHC (g/mi)
TP
NO
x (
g/m
i)
LEV395ULEV340ULEV200SULEV170
SULEV150
~75% less NOx
May 1, 2012 20
2012 Chassis Cert Data (10,001-14,000 lbs GVW)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
TP NMHC (g/mi)
TP
NO
x (
g/m
i)
LEV630ULEV570
ULEV400
ULEV270
SULEV230SULEV200
~75% less NOx
May 1, 2012 21
Potential SCR Technologies: SCR Filter
SCR DPF DOC
Urea
From Engine
To
Tailpipe
SCR
FilterDOC
Urea
From Engine
To
Tailpipe
SCR
FilterDOC
Urea
Engine Tailpipe
SCR
“Simplified”
“Higher Performance”
May 1, 2012 22
Modeling Implications of SCR Filter
Technology
• Wall flow vs channel flow
• Lower washcoat loading per volume
• Backpressure sensitive
Low Pore VolumeSmall Pore Size
High Pore VolumeLarger Pore Size
High Pore VolumeLarger Pore Size
Low Porosity
Flow Through
High Porosity
Flow Through
High Porosity
Wall Flow
May 1, 2012 23
4.4LPrototype Light Duty Diesel Test Cycle: US FTP-75
FilterSCR SCRurea
Turb
o
Mixer SlipDOC
FilterSCR SCRurea
Turb
o
Mixer SlipDOC
0.00
0.02
0.04
0.06
0.08
0.10
0.000 0.020 0.040 0.060 0.080 0.100
TP NMHC (g/mi)
TP
NO
x (
g/m
i)
case 1
case 2case 3
case 4
case 5
SULEV 30
(b)
SAE 2012-01-0371
• Engine calibration changes
• Urea calibration changes
• Heating strategies ~1.8% FE
• Increased PGM
• SCR filter helps at higher SV
SCR
May 1, 2012 24
Future SCR TechnologiesExtruded zeolite offers higher density of active material
SCR DPF DOC
Urea
From Engine
To
Tailpipe
• Replace one or more bricks for higher performance
• Downsize the SCR System
eSCRexSCR DPFDOC
Urea
From Engine
To
Tailpipe
May 1, 2012 25
Modeling Implications of Extruded SCR Technology
• Higher backpressure due to thicker walls
• Slower warmup due to greater mass
• Higher SV if downsizing
• Different cell geometry
αs
wαs
w
Washcoated Extruded
Washcoat collects in corners,
resulting in circular flow channels.
Flow channels are assumed to be square.
May 1, 2012 26
NOx Conversion vs. CuZ Content
0
10
20
30
40
50
60
70
80
90
100
0 0.5 1 1.5 2
Normalized CuZ content
NO
co
nvers
ion
(%
)
% NO conv at 200C
% NO conv at 300C
SCR Filter
1xSCR
2xSCR or1x exSCR 2xexSCR
May 1, 2012 27
Predicted FTP-75 NOx Efficiency (9500 lbs diesel truck at 150K mi)
75
80
85
90
95
100
ExSCR SCR+SCR
Filter
2xSCR ExSCR+SCR ExSCR+SCR
Filter
2xExSCR +
SCR Filter
System SCR Content
FT
P-7
5 N
Ox
co
nv
ers
ion
(%
)
SULEV150 NOx conversion
with an avg 2012 TP NMHC
May 1, 2012 28
Temperature Pre-SCR Bag 2
150
160
170
180
190
200
210
220
230
240
250
500 600 700 800 900 1000 1100 1200 1300 1400
Time (sec)
Te
mp
era
ture
(d
eg
C)
Blue Lines - Double Wall/Heat Wrap Through DPF
Red Line - Strategy changes for Heat ManagementGreen Line - Baseline
Passive and Active Heat Management: FTP-75 preSCR T
Goal: manage heat while not impacting fuel economy or HC
May 1, 2012 29
Greenhouse Gases (2013+)
• MDV standards
– 50 mg/mi CH4
– 50 mg/mi N2O
• Composite of FTP-75 (55%) and HWFET
(45%)
• N2O factor =298 for CO2 equivalence
May 1, 2012 30
N2O from Diesel SCR Systems on FTP-75
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30
Test number
FT
P-7
5 N
2O
as
me
as
ure
d (
mg
/mi)
engine out
post DOC
post SCR
post DPF
• Half of N2O from HC + NOx on DOC
• Other half of N2O from Urea SCR Submitted to IJPT
May 1, 2012 31
N2O from Diesel SCR Systems During
Filter Regeneration on FTP-75
0
10
20
30
40
50
60
70
80
1400 1600 1800 2000 2200 2400 2600
Test time (s)
N2O
(p
pm
)
-800
-600
-400
-200
0
200
400
600
800
Exh
au
st
tem
pera
ture
(C
)
& p
os
tSC
R N
H3 (
pp
m)
postDOC N2O postSCR N2O postSCR NH3
postDOC temperature postSCR temperature postDPF temperature
Submitted to IJPT
May 1, 2012 32
Composite N2O for 9500 lbs diesel truck
2%43295556N2O (mg/mi)
CO2
equivalence
Composite
Weighted
HWFETFTP-75 w/regen
FTP-75
Submitted to IJPT
N2O formation pathways found:
Engine out HC +NOx --> DOC N2O DOC NO --> SCR NO2 --> SCR N2O
N2O minimized by:
- low loaded, Pd-rich DOCs
- Cu/CHA SCR
May 1, 2012 3333
Summary
• Diesel catalyst system development has unique challenges that were overcome
• Potential SCR technologies such as extruded SCR and SCR filter may help meet future standards
• Calibration and heat management will also play an important role
• The sources of N2O within the diesel SCR system are understood
May 1, 2012 3434
Next Steps for Diesel MDV• Materials cost reductions continue
– PGM reductions
– substitution of Pt with Pd
• Assess future emission impacts– FTP-75
– filter regen penalty
– SFTP
– PM
– GHG
May 1, 2012 3535
Acknowledgments
DOE: DE-FC26-01NT41103 (2001-2005)
Ford: VERL team, Jeff Hepburn, Douglas Dobson, James Warner,Jeong Kim, Giovanni Cavataio, Kevin Guo, Yisun Cheng, Cliff Montreuil, James Girard, Hungwen Jen, Scott Williams, Dave Kubinski, Brendan Carberry, Rick Soltis, Devesh Upadhyay, Michielvan Nieuwstadt, Mike Levin and many others
Catalyst Suppliers: BASF, JMI, Umicore
And many, many more …
