1 Da Yu Wang, Sheng Yao, David Cabush, Dave Racine DEER 2007 Ammonia Sensor For SCR NOX Reduction
Agenda
NH3 Sensor Usage in SCR system Overview NH3 Sensing Technologies Functionality of NH3 Sensor NH3 Sensor Design Test Results
– Cross Sensitivity – Test results
Close Loop Control of the SCR System with aNH3 Sensor - System Advantages Summary
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3
Diesel SCR System
DOC
SCR
Urea tank
Urea Level switch
SCR out T°
Turbine Wide range O2 Delphi NH3 sensor
SCR control sensor SCR control actuator Standard control sensor
Air + urea
Urea Air
Urea pump on/off Compressor on/off
[NH3] out (Delphi) SCR in T°
Dosing Unit
Feedback for closed loop control
Source of Ammonia: Urea through hydrolysis reaction (NH2)2CO + H2O > 2NH3 + CO2
DeNOx Reaction: At favored temperature 4NH3 + 2NO2 + 2NO > 4N2 + 6H2O
•
4
Sensing principle Non-equilibrium electrochemical sensing principle
– Proprietary NH3 sensing electrode materials – Both sensing and reference electrodes exposed to the engine
exhaust – Solid oxide electrolyte used as the sensor body
)(2
)(4
)(3 223 OHONH PLn
e kTPLn
e kTPLn
e kTEMF −−≈
•(Heater circuit not shown)
O2-
O2 + 4e 2O2-
Porous Protection
Lean Exhaust
Lean Exhaust
TEMP SENSING CELL
NH3 SENSING CELL
Lean Exhaust
ZIMP
EMF 3O= + 2NH3 N2 + 3H2O + 6e
Theory Semi-log output of EMF versus NH3 concentration
180
60
0 0 20 40 60
NH3 [PPM]
)
EMF
[mV]
kT kT kT 120
EMF≈ Ln(PNH ) − Ln(PO ) − Ln(PH2O3e 4e 2e3 2
– Interference effect due to H2O and O2 concentrations changing due tocombustion can be self-compensating
– The concentration of H2O and O2 vary in opposite directions as functionof A/F ratio minimizing effect
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Sensor structure
Contact pads : signal
+
-
Contact pads : heater
Protective layer (porous and dense alumina)
Sensing electrode
Reference electrode
Exhaust chamber
Structural layer & Temp Sensor (dense alumina & Zirconia)
Heater circuit
Protective layer (dense alumina)
Zirconia layer
+
-
Planar structure – Co-fired zirconia and alumina
layers with NH3 sensing,platinum reference electrode andheater circuit
Key Features – Integrated heater provides fast
time to activity – Temperature sensor included – No air reference – Alumina layers provide electrical
isolation between heater and sensor circuits
– Porous protection provides excellent exhaust poisonresistance
– Small size
Sensing Element Finished sensing elements
– Monolithic thick film multi layer composite substrate
» Alumina / Zirconia composite
» Alumina provides toughness - Zirconia electrolyte – Integral Heater and Temperature Sensor for heater control – Compatible with existing sensor packaging technology
NH3 electrode material applied on substrate surface
A poison protective material is applied over the NH3 electrode
Finished sensing element looks like exhaust oxygen sensing element
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Sensor package
Based on proven robust production planarsensor packaging
Package has capability beyond dieselexhaust temperatures
Lower shielding can be modified accordingto customer application
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NH3 Sensor System Mechanization Mechanization – Early systems being developed for commercial vehicle applications – Stand-alone electronic interface with CAN link to vehicle – A-sample hardware shown below.
» A-Sample systems provide either Analog or CAN message output
Advanced Development Hardware
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NH3 Sensor Performance Targets Measurement range: 0 – 100ppm NH3
– Tolerance: ± 5ppm NH3 at 10 ppm NH3. – Acceptable gas content without interference: NO, HC, CO, N2O. – Acceptable gas content with cross sensitivity: O2, H2O.
Temperature range: – Functional: 200 ºC to 450 ºC – Non functional: - 40 ºC to 700 ºC
Durability target: 5.000hours / 250.000km
NOx Exhaust gas content: 0 to 500ppm (sensor performance within spec)
H2O exhaust gas content: 1% to 8% by mass (sensor performance within spec)
Response Time: T60 = 3 s T90 = 5 s
Thermal Shock – Two layers of protection
1. Double layer protective shield 2. System algorithm to disable sensor when liquid water is possible in the exhaust
– Heated ceramic sensors must be protected from contact with liquid water to prevent damage do to thermal shock
NH3 Sensor Interface Electronics
Environment – Ambient Temperature (electronics): - 40 ºC to 105 ºC
Electrical – Sensor system compatible with either a 12V or 24V vehicle electrical
system – Sensor system communicates to vehicle over a CAN bus
Mounting/Installation – Sensor mounts directly to exhaust pipe via a M18x1.5 threaded boss – Sensor must be mounted 10 º above horizontal to prevent pooling of
water in shield
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Water and oxygen interference effect
Water and oxygen have opposite interference effect Self compensation effect is possible in a narrow range as shown in following figure (confirmed by lab gas bench too) Climate air humidity difference is a main concern but can be handled by calibration Model based correction is also possible if A/F ratio and air humidityinformation is available
-15
-10
-5
0
5
10
15
15 25 35 45 55 65 AIR TO FUEL RATIO
D E
MF
[mV]
0
2
4
6
8
10
12
14
16
H2O
, O2
[%]
D EMF [mV]
H2O [%]
O2 [%]
Oxygen
Water
D EMF Δ
NH3 Output in the Presence of NOX
Basic function demonstrated in gas bench testing– NH3 signal free from NOX interference – Some interference below 10ppm set point
-160 160 NOX=0 ppm NO=400 ppm NO/NO2= 200/200 ppm NO2=400 ppmNOX=0 ppm NO=400 ppm NO/NO2=200/200 ppm NO2=400 ppm
NH3=100 ppm
50 ppm
-80 25 ppm 80
10 ppm 5 ppm
0 0
10 ppm Control Point NH3
80 -80 0 20 40 60 80 100
TIME (M)
OU
TPU
T [m
V]
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Sensor performancecross interference
NH3 sensing accords to the theory prediction (semi-logarithms equation)
– Data obtained at lab gas bench, 14% O2, 1.5% H2O Interference from NO, CO, and HC is negligent
#53 BiVO4 (5% Mg, 5% Ta) AFTER 570 H, 800C
0
40
80
120
160
0 20 40 60 80 100 120 NH3 CONCENTRATION (ppm)
OU
TPU
T (m
V)
NH3 ONLY
100 ppm NO
100 ppm NO +1000 ppm CO
100 ppm NO +1000 ppm CO +1000 ppm HC
500 ppm NO
1000 ppm NO
1000 ppm NO
1000 ppm HC
1000 ppm CO
Log. (NH3 ONLY) NH3 cell only
Engine Test Stand PerformanceSteady State Test
NH
3_Se
nsor
[ppm
]
NH3 Sensor Performance--Test 2a (steady-state) NH3 Sensor Performance--Test 2a (steady-state) Temp=200 C; 17-March-2006 Temp=400 C; 17-March-2006
50 50
Sensor C4 Sensor C4 40 Sensor C6 40 Sensor C6
30
20
10 NH
3_Se
nsor
[ppm
]
30
20
10
0 0 0 10 20 30 40 50 0 10 20 30 40 50
NH3_LDS [ppm] NH3_LDS [ppm] Sensor data
– Steady state performance on HD diesel engine – Test stand fitted with SCR aftertreatment system – Sensors tested at 200 C & 400 C steady-state exhaust gas conditions – Ammonia slip between 0 and 50 ppm – Chart shows sensor output plotted against LDS instrumentation NH3 output signal
Result – Sensor accuracy within specification limits (+/- 5ppm at 10 ppm control point)
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Engine Test Stand PerformanceESC Cycle
NH3 Sensor output during an ESC cycle on the engine test stand – NH3 sensor output tracks LDS instrumentation over a dynamic test cycle
NH3 Sensor Perfromance Test--Test 2b ESC Engine cycle; 17-March-2006
50
IDEAL 40 Sensor C4
Sensor C6
30
20
10
0 0 10 20 30 40 50
NH3_LDS [ppm]
NH
3_Se
nsor
[ppm
]
No poison effects after 700h test cycle without DPF16
Sample to Sample Variation
100 100
200C 300C
SEN
SOR
_NH
3_[P
PM]
10 S_1_DA_1 Final S_2_DA_2 S_3_DA_1 S_4_DA_1 S_5_DA_1 S_1_DA_1 S_2_DA_2 S_3_DA_1 SE
NSO
R_N
H3_
[PPM
]
10 S_1_DA_1 Final S_2_DA_2 S_3_DA_1 S_4_DA_1 S_5_DA_1 S_1_DA_1 S_2_DA_2 S_3_DA_1
S_4_DA_1 S_5_DA_1 S_4_DA_1 S_5_DA_1 S_1_DA_1 S_2_DA_2 S_1_DA_1 S_2_DA_2 S_3_DA_1 S_4_DA_1 S_3_DA_1 S_4_DA_1 S_5_DA_1 S_1_DA_1 S_5_DA_1 S_1_DA_1 S_2_DA_2 S_3_DA_1 S_2_DA_2 S_3_DA_1 S_4_DA_1 S_5_DA_1 S_4_DA_1 S_5_DA_1 S_1_DA_1 S_2_DA_2 S_1_DA_1 S_2_DA_2 S_3_DA_1 S_4_DA_1 S_3_DA_1 S_4_DA_1 S_5_DA_1 S_1_DA_1 S_5_DA_1 S_1_DA_1 S_2_DA_2 S_3_DA_1 S_2_DA_2 S_3_DA_1 S_4_DA_1 S_5_DA_1 S_4_DA_1 S_5_DA_1
1 1 1 10 100 1 10 100
LDS_NH3_[PPM] LDS_NH3_[PPM]
100 • 30 sensors
400C • Same conversion equation
SEN
SOR
_NH
3_[P
PM] • No water-oxygen adjustment
10 S_1_DA_1 Final S_2_DA_2
S_3_DA_1 S_4_DA_1 • No air humidity adjustment S_5_DA_1 S_1_DA_1
S_2_DA_2 S_3_DA_1
S_4_DA_1 S_5_DA_1
S_1_DA_1 S_2_DA_2
S_3_DA_1 S_4_DA_1
S_5_DA_1 S_1_DA_1 • Red lines mark ±50% at 10 PPM NH3 S_2_DA_2 S_3_DA_1
S_4_DA_1 S_5_DA_1
S_1_DA_1 S_2_DA_2
S_3_DA_1 S_4_DA_1
S_5_DA_1 S_1_DA_1
S_2_DA_2 S_3_DA_1
S_4_DA_1 S_5_DA_1
1 1 10 100
LDS_NH3_[PPM]
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Exhaust Ammonia (NH3) Sensor - Optimized Performance of an SCR Converter
Graphical Representation of Key Factors to SCR Control
NH
3 , N
OX
[ppm
]
Urea Dosing
SCR
Effi
cien
cy
Open Loop Control
Control with NOX Sensor
NOX – Sensor
NH3 – Sensor (NH3 Slip) Tailpipe
NOX Emissions
Euro 4 limits can be achieved by usingopen loop control urea dosing
– SCR efficiency approximately 65%
The realization of maximum NOx conversion (without using a postoxidation catalyst) is only possible withclosed loop controlled Urea dosing:
– A NOx based SCR control does not enable the use of the maximum NOx conversion because of NH3 cross sensitivity of NOx sensor.
– The NH3 based SCR control enables operation at the conversion limit of the catalyst:
– >90% NOx conversion possible for highwadriving conditions
– Minimal catalyst volume
Control with NH3 Sensor @ 10 ppm NH3 Slip
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Conclusion
Sensor demonstration has been done – NH3 sensing accords to concept
Interference with NO, HC, CO is not significant O2 and H2O have opposite interference effect (minimumcompensation through calibration) Air humidity and air to fuel ratio information is required for model based correction of the interference effects of O2 and H2O (only required if highest accuracy is demanded) Response time T60 < 3 second, T90 < 5 sec Sensors are built on existing Delphi exhaust oxygen sensor technology NH3 Sensor provides an opportunity for improved SCR dosing control and system diagnosis