passive ammonia scr for lean burn sidi engines · deer conference 2009 10. nh. 3. storage capacity...
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DEER Conference 2009
Passive Ammonia SCR
For Lean Burn SIDI Engines
Wei Li, Kevin Perry, Kushal Narayanaswamy, Chang Kim, and Paul Najt
GM R&D Center
1
DEER Conference 2009
Outline
Background and Concept
NEDC Test Results
NH3
Formation
NOx Conversions
Issues and Summary
2
DEER Conference 2009
Lean NOx Aftertreatment
3
LNT
TWCMB CLS 350 CGI•
High PGM Cost
•
Narrow Operating Temperature Window
•
Sulfur Poisoning and Desulfation
•
Secondary urea tank with injection system
•
High urea consumption
•
Urea solution freezing
•
Need customer intervention
Lean NOx Trap (NOx Absorber Catalyst)
Urea SCR
Optional
DEER Conference 2009 4
New Concept: Passive NH3
SCR
Use rich pulses to generate NH3
on the TWC and store it on the SCRRich: NOx + CO/H2
NH3
Use the stored NH3
for subsequent lean NOx
conversionLean: NOx + NH3
N2
Rich AFR NOx must at least balance Lean AFR NOx
LSF
LSULSU
LSF
Flex
TWC
SCR
No PGM required
DEER Conference 2009
Goal of the Work
Proof of Concept
Ability to make NH3
Ability to store NH3
and convert NOx
Catalyst Durability
High temperature redox aging
Aftertreatment System Architecture
Thermal management
5
Engine
2.2L stratified-charge direct-injection engine
Controller: d-SPACE with micro-Autobox
Transient Dynamometer : simulated NEDC cycle
Experimental
DEER Conference 2009
NH3
Formation over TWC
6
NO + 1.5H2
+ CO NH3
+ CO2
NH3
TWC OutNOx
EO
H2
EO
NOx limitedCO/H2
limited
H2
Eng. OutNOX
Eng. Out
NH3
TWC Out
12.012.212.412.612.813.013.213.413.613.814.014.214.414.614.815.0
Engine Air/Fuel Ratio
ppm
H2
0
ppm
NO
x, pp
m N
H3
DEER Conference 2009
Maximize Lean Operations During NEDC
7
Lean
Operation
s
Stoich /rich
Operations
DEER Conference 2009 8
NH3
Formation on the TWC Catalysts
Rich operations (AFR =14-14.2) during accelerations lead to NH3
formation; minimum FE penalty (within test variability) based on test cell data
NH3 Co
ncen
tration
DEER Conference 20099
Typical Thermal Operating “Windows”
with Aged Catalysts
LNT & SCR NOx
Conversion Capability
0
20
40
60
80
100
0 100 200 300 400 500 600
Catalyst Temp, Deg C
NOx Eff, %
NEDCCatalystTemps
LNT Range
SCR Range (w/Urea)
Passive SCR Range
Passive SCR conversion window about as broad as LNT, but at lower temperatures
Lacking steady NH3
supply, passive SCR NOx
conversion limited at high temperature
Effective NOX
conversion only possible in reduced window of operation
DEER Conference 200910
NH3
Storage Capacity Limitations –
Why passive SCR has smaller conversion window
Passive SCR is a discontinuous approach –
must store NH3
for use in lean periods
Storage capacity of known catalysts is negligible beyond 400 C
Effective NOX
conversion limited by intrinsic storage capacity
Cu
SCR
Fe SCR
~Zero Storage
capacity beyond
~400C
100 200 300 500400
NH3Storage capacity
Catalyst Temperature / C
DEER Conference 2009
Multiple SCR Architecture
11
Operating temperature window can be expanded with a multiple-SCR architecture
SCR1
SCR1SCR2
SCR2
TWC
DEER Conference 2009
NOx
Conversion Efficiencies over SCR
12
TWC Out NOx
SCR Out NOx SCR1 Bed T
Passive SCR
Conversion
Window
DEER Conference 2009
NOx Conversion During EUDC
13
Multiple‐SCR architecture required to reduce NOx emissions during high speed
(>100km/h) lean cruise during EUDC
Post TWC
Post SCR1
Post
SCR2
NO
x C
once
ntra
tion
DEER Conference 200914
NEDC Test Results with NH3 SCR
Passive NH3
SCR has potential to meet Euro6 emission targets with aged converters
Minimum fuel economy penalty for NH3
formation during NEDC (within test variability)
No significant slip of secondary emissions (NH3
, N2
O)4‐1 exhaust manifoldPUP Converter (aged RAT H 50h)4L SCR (aged RAT 750 50 h)
NH3
formation and OBD control methodSulfur impact: sulfur is known to greatly inhibit NH3
formation on TWCHC emission reduction is challenging due to the low exhaust temperaturesFurther improvements in SCR catalyst technologies are required for high speed (≥100 km/h) lean operations.
Remaining Issues
DEER Conference 2009
Summary
Passive NH3
SCR has been demonstrated as a high efficiency and low cost alternative lean NOx
aftertreatment
technology for stratified gasoline engines.
Very high NOx
conversion efficiencies were achieved during NEDC transient cycles.
Multiple SCR architecture expands the operating temperature window of passive SCR
Plan to further develop the system for US applications (SULEV)
15
Passive NHPassive NH
33
SCR: key enabler for lean gasoline enginesSCR: key enabler for lean gasoline engines