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Urea SCR and DPF System for Tier 2 Diesel Light-Duty Trucks
Christine Lambert, Giovanni Cavataio, Yisun Cheng, Douglas Dobson, James Girard, Paul Laing,
Joseph Patterson, Scott WilliamsDiesel Exhaust Aftertreatment
Ford Research & Adv Engineering
August 24, 2006
DEER 2006 8/24/2006
2
Presentation Overview
1.Department of Energy Program Overview
2.Final System Durability and Results 3.Post Mortem Phase 4.On-going Catalyst Development 5.Conclusions
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3
1. DOE Program Overview
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4
Tier 2 Emission Standards
• Tier 2 Bin 5 / LEVII standards represent 90-95% NOx and PM reduction from Tier 1 standards for diesels.
Standard NOx (g/mi) PM (g/mi) Tier 1 (100k mi) 1.25 0.10 Tier 2 Bin 5 (120k mi) 0.07 0.01
• NOx and PM control remain a challenge for diesels.
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5
Program Objectives (2001)
• 0.07 g/mi NOx
• 0.01 g/mi PM
• 120,000 miles of durability
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6
Aftertreatment Selection
• Particulate Control – catalyzed DPF (CDPF)
• NOx Control 1 – HC SCR using diesel fuel
• NOx Control 2 – Lean NOx Trap (LNT)
• NOx Control 3 – SCR with ammonia-based reductant
(SCR = Selective Catalytic Reduction)
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7
Typical Performance Curves of Slightly Aged Catalysts
NO
x C
onve
rsio
n (%
)
100Urea SCR 90
80HD Dyno
Cert 120k Std.
70
60LNT
50
40
HC SCR30
20 LD FTP LD US0650k and10 4k Std.120k Stds.
0
0 100 200 300 400 500 600 700
Catalyst Temperature (°C)
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Simulated FTP NOx Conversion vs. FTP-75 Fuel Economy Penalty
0.0% 2.0% 4.0% 6.0% 8.0% 10.0% FTP Fuel Economy Penalty
0 10 20 30 40 50 60 70 80 90
100
FTP
N O
x C
onv e
rs io
n (%
)
LNT + filter
HC SCR + filter
Urea SCR + filter
3% due to filter
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9
Urea SCR Chemistry urea decomposition:
O
heat HNCO + NH3C
heatH2N NH2 H2Ourea CO2 + NH3
NO reduction: x
4NO + 4NH3 + O2 4N2 + 6H2O 6NO2+ 8NH3 7N2 + 12H2O 2NH3 + NO + NO2 2N2 + 3H2O “fast SCR”
SCR Catalyst Types: 1) vanadia and 2) base metal/zeolite
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NOx Activity Profiles for Cu, Fe, and V Based SCR FormulationsHTA 64hrs @ 670°C, 30,000/h
300 350 400 450 500 550 600 650
Inlet Gas Temperature (ºC)
• Cu/zeolites are best at low temperatures
• Fe/zeolites perform well at high temperatures
• Vanadium based SCRs are not appropriate for North America
100
90
80
70
60
50
40
30
20
10
0
100 150 200 250
Cu-Based SCR
Fe- Based SCR
Vanadium Based SCR
FTP US06
Gro
ss N
Ox
conv
ersi
on (%
)
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LDT Exhaust System (NOx)90% FTP NOx conversion, 0.07 g/mi TP NOx
urea
DOC
NOx sensor
SCR
DOC DOC
CDPF
Spray Target
exhaust flow Base Metal/
Zeolite
to engine intake
• Engine-out NOx lowered by 40% with increased EGR • Low tailpipe NOx achieved with rapid warm-up strategy
• lower thermal mass upstream of catalyst system • engine calibration changes during cold start (post injection & inc. idle speed)
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12
Diesel Fuel Properties
• ExxonMobil blended 14,000 gallon batch to represent typical 2007 ULSD
Est. Avg. Proposed Program Proposed ‘06 Diesel DOE Prog. Fuel 2007
Fuel Property Properties Min/Max Delivered Cert. Fuel Sulfur, ppm 15* 10 / 15 12.5 7 / 15 Density, kg/m3 850 820 / 850 841.1 839 / 865 Aromatics, vol. % 32 25 / 32 29.5 27 min Polyaromatics, wt. % 10 6 / 11 11.0 no spec Cetane number 46 44 / 48 44.9 40 / 50 T50, C 267 250 / 280 249 243 / 282 T90, C 306 300 / 320 307 293 / 332
* As delivered to the vehicle
DEER 2006 8/24/2006
EPA
-75
Wei
ghte
d (g
/mile
)
13
Weighted Tailpipe Emissionswith Low-mileage Catalysts on LDT
0.055
0.60
0.83
0.45
0.76
0.17
0.062
0.85
0.015
0.16 0.14
0.047 0.042
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
NMHC CO NOX
System 1
3' Injector to SCR
Deflector/mixer, long inlet cone
Larger DOC, upstream injection with spray target Turbo & EGR modifications, post injection
2.01
Reduced tailpipe
NOx
PM: 2-5 mg/mi
Increased distance to SCR
Baseline system FT
P-75
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14
Low-mileage FTP-75 Emissions with 6000 lb LDT gr
ams/
mile
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
0.129 (92%)
0.055
0.024
1.99
0.019 (81%)
0.051
0.013 (94%)
.022
0.015 (86%)
0.042 (97%)
0.014
THC
4.2 2.00 (78%)
CO
Bag 3 Bag 2 Bag 1
Tier 2 - Bin 5 Standard, 120k
(Catalyst efficiency)0.047 (89%)
PM ~ 2 mg/mi
NOX NMHC
• Emissions were below 120k mi Tier 2 Bin 5 standards
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2. Final System Durability and Results
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Durability Test Definition (Dyno Aging) • Full-size Urea SCR – CDPF system was aged for 120k mi on
engine dyno with a total of 643 CDPF regenerations.
vehi
cle
spee
d (m
ph)
Ford High Speed Cycle (HSC)90
80
70
60
50
40
30
20
10
0 0 250 500 750 1000
time (s)
• Typical time at high temperature in SCR ~ 6 min per regen
• 643 regens x 6 min/regen xh/60min = 64 h
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0
0.02
0.04
0.06
0.08
0.1
0.12
0.14 Ta
ilpip
e N
Ox
(g/m
i)
Increase due to loss of post injection control
4K 4K 50K 120K
4K DOC, 120K SCR
Improvement with fresh DOC
Aging Summary: FTP-75 Weighted NOx
• Loss of DOC activity resulted in higher NOx emissions at 120k mi
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Emissions With 120k mi Catalystson 6000 lb LDT (No Warmup)
4.2 2.50 (78%)
THC NMHC CO NOX
• Emissions were below 120k mi Tier 2 Bin 5 standards except for NOx
0.058
0.023
0.059 (61%)
0.055 0.042 (81%)
.027
0.027 (77%)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
gram
s/m
ile Bag 3 Bag 2 Bag 1
Tier 2 - Bin 5 Standard, 120k
(Catalyst efficiency)
0.141 (82%) 0.128 (74%)
0.029 (96%) Tailpipe NH3: 0 N2O selectivity: 15% PM: 1.2 mg/mile
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Emissions With 120k mi DOC and Lab Aged Improved SCR on 6000 lb LDT (No Warmup)
gram
s/m
ile0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
0.092 (87%)
0.051 (68%)
0.015 0.036 (78%)
0.013 (95%) 0.037 (91%)
0.017 (88%) 0.018 (87%)
0.018 (97%)
THC NMHC
4.2 1.67 (81%)
CO
Bag 3 Bag 2 Bag 1
0.081 (85%)
Tier 2 - Bin 5 Standard, 120k
(Catalyst efficiency)
NOX
• Improved SCR catalyst was less sensitive to NO2/NOx ratio
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3. Post Mortem Phase
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21
DOC HC and CO OxidationHC/CO Light-Off Conversion
DOC ABDOE Vehicle 120K Miles
100% T80:HC: ~70oC shift
75%
50% NMHC Conv - Inlet
T50: NMHC Conv - OutletCO Conv - Inlet
HC: ~65oC CO Conv - Outlet
shift 25%
0% 100 150 200 250 300 350 400 450 500
Temperature (Deg C)
• Key deactivation of inlet is chemical poisoning due to phosphorous deposition. • Key deactivation of outlet is due to fuel combustion required for DPF regen.
Con
vers
ion
Effic
ienc
y
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DOC NO OxidationNO2:NOx
DOC AB : 120K Miles
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% N
O2 o
f Tot
al N
Ox
Inlet Core Outlet Core
Better
100 200 300 400 500 600 700
Temperature (C)
• NO oxidation is more deactivated at the outlet of the 120k mi engine aged DOC
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DOC Fuel Quench Temperature FQT Results
DOC AB : 120K Miles
0
50
100
150
200
250
300
350
400
450 M
inim
um S
afe
FQT
Tem
pera
ture
(deg
C)
DOC AB Inlet 1 DOC AB Outlet 1
Better
• DOC outlet requires an inlet of 425°C to maintain DPF regeneration conditions.
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24 Post Mortem of 120k mi SCR – Core#1 NO only and SV=30,000/hr
-40
-20
0
20
40
60
80
100
Gro
ss N
Ox
conv
ersi
on (%
)
Inlet
Mid1
OutletFresh Mid2
100 150 200 250 300 350 400 450 500 550 600 650
Inlet Gas Temperature (ºC)
• 120k mi engine aging of SCR catalyst upstream of filter was non-uniform • Outlet of engine aged SCR correlates well to the 64hr/670°C hydrothermal aging • Inlet was most severely aged – work ongoing to understand
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25
-40
-20
0
20
40
60
80
100 G
ross
NO
x co
nver
sion
(%)
Core #1 Core #2
Core #3
Deactivation of Inlet of 120k mi SCR NO only and SV=30,000/hr
100 150 200 250 300 350 400 450 500 550 600 650
Inlet Gas Temperature (ºC)
• Severe deactivation is observed at inlet and across the radius
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Next Steps for DOC and SCR Post Mortem
• Investigate possible deactivation mechanisms: • Thermal deactivation due to DPF regeneration events
• Chemical poisoning from oil contamination
• Washcoat adhesion
• Contamination from urea by-products (SCR only)
• Develop new formulations that are more robust
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4. On-going Catalyst Development
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28
DOC DevelopmentC
onve
rsio
n Ef
ficie
ncy
HC/CO Light-Off Conversion NO2:NOxComparison of DOC Improvements Comparison of DOC Improvements 100%
CO 100%
90% DOE Program DOC AB New Formulation DOC AV
75% 80%
50%
25%
HC
% N
O2 o
f Tot
al N
Ox 70%
60%
50%
40%
30%
20% 0% CO DOE Formulation AB
CO New Formulation AV 10%100 150 200 250 300 350 400 450 500 HC DOE Formulation AB
HC New Formulation AV 0%
-25% 100 200 300 400 500 600
Temperature (Deg C) Temperature (C)
• HC and CO light-off has • NO2 generation has improved by ~ 20°C improved by ~10%.
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29
SCR Development: Importance of NH3 Storage
0
10
20
30
40
50
60
70
80
90
100 %
NO
x C
onve
rsio
n
Increasing NH3 exposure
0 100 200 300 400 500 600
Inlet Temperature, °C
• NOx Conversion of SCRs is strongly related to NH3 storage
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30
40
30
SCR Development: Benefits of Over-Dosing NH3 at High Temperature Low Temperature SCRSteady State Performance
Aged 64hrs@ 670°C, SV=30,000/hr, NO only
NOx Conversion - All FG NOx as NO - Varied Alpha, 350 ppm NO NH3 Slip - All FG NOx as NO - Varied Alpha, 350 ppm NO NOx Conversion NH3 Slip 100 800
Alpha = 0.7Alpha = 0.9Alpha = 1.0Alpha = 1.1Alpha = 1.2Alpha = 1.5Alpha = 2.0
SV=30k
No NH3 Slip
90 700
80 600
70
NO
x co
nver
sion
(%)
60
50
NH
3 Slip
(ppm
) 500
400
Alpha = 0.7Alpha = 0.9Alpha = 1.0
300 SV=30k
Alpha = 1.1 200 20 Alpha = 1.2
Alpha = 1.510 100Alpha = 2.0
0 0 100 150 200 250 300 350 400 450 500 550 600 650 100 150 200 250 300 350 400 450 500 550 600 650
Catalyst Temperature (ºC) Catalyst Temperature (ºC)
• Excess gas phase NH3 helps high • NH3 slip is controlled when over-temperature but no improvement is dosing above 450°C possible below 200°C
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31
SCR Development - Never-to-Exceed Temperature1hr Aging - SV = 30,000/hr - NO only
0
10
20
30
40
50
60
70
80
90
100 G
ross
NO
x co
nver
sion
(%)
NTE = 800°C 650C
750C
800C
850C
900C
950C
100 150 200 250 300 350 400 450 500 550 600 650
Inlet Gas Temperature (ºC)
• Robustness to occasional high temperatures during DPF regeneration is required
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32
Conclusions• Urea SCR has most potential to reach Tier 2 for light-duty trucks. Base metal
zeolites are superior to vanadia for NA applications.
• After 120k mi of engine aging, a DOC-SCR-DPF system met Tier 2 standards except for NOx. A new SCR formulation that was less sensitive to inlet NO2/NOx ratio resulted in tailpipe NOx that approached the standard.
• Post-mortem testing of the 120k mi catalysts revealed non-uniform activity. The outlet of the DOC and inlet of SCR were most severely deactivated.
• Improvements were made in DOC formulation for HC, CO and NO oxidation.
• Pre-stored NH3 and overdosing of NH3 increased overall activity of base metal/zeolite SCR catalysts.
• Base metal/zeolites are robust enough to handle DPF regeneration temperatures.
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Acknowledgements
DOE DE-FC26-01NT41103
Ford Brendan Carberry, Dick Chase, Bob Hammerle, Dave Kubinski, Santhoji Katare, Jeong Kim, Cliff Montreuil, Rick Soltis, Devesh Upadhyay, Michiel van Nieuwstadt, and many others
FEV Erik Koehler, Dean Tomazic
Exxon Mobil Rich Grosser, Marcus Moore, Mike Noorman, Charlie Schleyer
DEER 2006 8/24/2006