Long-Term Aging of NO x Sensors in Heavy-Duty Engine Exhaust

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1 Long-Term Aging of NO x Sensors in Heavy-Duty Engine Exhaust by John Orban David Wendt (Battelle) Presented at the 10 th Diesel Engine Emissions Reduction (DEER) Conference September 1, 2004 Coronado, CA

2 APBF-DEC Participants Automobile: DaimlerChrysler Ford GM Toyota Engines: Caterpillar Cummins Detroit Diesel EMA International Truck & Engine John Deere Mack Trucks Government: CARB/SCAQMD DOE EPA NREL ORNL Technology: Battelle 7/22/04 2 Emission Control: Argillon ArvinMeritor Benteler Clean Diesel Tech. Corning Delphi Donaldson Co. Engelhard Johnson Matthey MECA NGK Insulators Rhodia Robert Bosch Corp. STT Emtec AB Tenneco Automotive 3M Umicore Energy/ Additives: American Chemistry Council API BP Castrol Chevron Oronite ChevronTexaco Ciba Conoco-Phillips Crompton Ergon Ethyl ExxonMobil Infineum Lubrizol Marathon Ashland Motiva NPRA Pennzoil-Quaker State Shell Global Solutions Valvoline

3 Acknowledgements Project Monitor Ralph McGill (ORNL) Technical Working Group Eric Liang (Caterpillar), Co-Chair Testing Lab Project Leaders Magdi Khair (SwRI) Chris Sharp (SwRI) NO x Sensor Supplier NGK Insulators 7/22/04 3

4 Study Objectives Demonstrate the Performance and Durability of NO x Sensors During 6,000 Hours of Operation Engine-Out (up to 600 ppm) Post Catalyst (up to 250 ppm) Steady-State (13 ESC modes) 7/22/04 4

5 Study Questions (NO x Sensor Study) 1. How well do the NO x sensor voltages correlate with the NO x analyzer readings? 2. What is the relationship between NO x sensor voltages and NO x analyzer readings at a given location? Does it change over time or by mode? 3. Are there systematic changes in sensor performance (overall or at a given sensor location)? 4. How often do sensors need to be recalibrated? 5. What is the expected lifetime of the NO x sensors? 6. Does the variability of the NO x sensors change over time or by mode (after corrections for NO x analyzer readings)? 7/22/04 5

6 Study Questions (NO x Sensor Study) 1. How well do the NO x sensor voltages correlate with the NO x analyzer readings? 2. What is the relationship between NO x sensor voltages and NO x analyzer readings at a given location? Does it change over time or by mode? 3. Are there systematic changes in sensor performance (overall or at a given sensor location)? 4. How often do sensors need to be recalibrated? 5. What is the expected lifetime of the NO x sensors? 6. Does the variability of the NO x sensors change over time or by mode (after corrections for NO x analyzer readings)? 7/22/04 6

7 Methods 25 Sensors Engine-out (5 sensors) Post DPF, pre SCR (10 sensors 5 per leg) Post clean-up catalyst (6+4 sensors) 21 with lab-grade electronics, 4 w/ production-grade Periodic Comparisons with Analyzer Readings Measure at 13 ESC modes every 120 hours 8 sets of comparisons every 1000 hours Independent Calibration Every 2,000 hours 7/22/04 7

8 Exhaust NO x Instrumentation Layout Cleanup Catalyst NOx CLA * Probe A1 NOx CLA * Probe A3 SCR Catalysts (2) Urea Injection Systems (2) Left Right NOx CLA * Probe B3 NOx Sensor Position 2L (0-1500ppm) Catalyzed DPFs (2) NOx CLA * Probe B1 Turbo Engine C 3-8C 3-9C 3-10C NOx Sensor Position 1 (0-1500ppm) NOx CLA * Probe A2 NOx Sensor Position 2R NOx Sensor Position 3 NOx CLA * Probe B2 (0-1500ppm) (0-500ppm) 3-1 Detail for Positions 1, 2R, 2L n n n n = Location (see above) n Flow n-1 Flow Note: In each group of five, NO x sensors are spaced evenly around top of pipe between 10 o clock and 2 o clock positions 7/22/04 8 * CLA = Chemiluminescent Analyzer

9 Analysis Approach Preliminary Analysis Resolve data collection issues Fit Simple Linear Regression Model Sensor Voltage = a + b*(analyzer ppm) Evaluate deviations By sensor, by mode, versus time Fit Multiple Regression Model Volt = a + b*ppm + (time, sensor, mode effects & interactions) Estimate mode effects and rates of change by sensor Confirm Results by Comparing Initial and 2,000-Hour Calibration Data 7/22/04 9

10 Overview of Findings - Durability Results Voltages from Pre-Catalyst Sensors ( ppm) Most (12 of 15) degraded by 3% to 4% Three degraded by 5% to 7% Voltages from Post-Catalyst Sensors ( ppm) Most (8 of 10 sensors) had minimal degradation One sensor (3-10C) did not operate properly (data not shown) One (3-3) demonstrated low sensitivity at the start of testing and significant degradation (30%) over 2000 hours Cause of Failures and Degradation Unknown at This Time Sensor problem? Electronics? Misconnection? Installation? 7/22/04 10

11 Sensor Position 1: Sensor Voltage vs. Analyzer ppm By Sensor By Mode 7/22/04 11

12 Sensor Position 1: Residual (observed-predicted) vs. Time Residuals for Location 1 Observed - Predicted (volts) Hours Sensor All sensors appear to degrade linearly Approximately 4% change over 2,000 hours Slight variations in rates of change by sensor Sensor No. 2 changing more quickly 7/22/04 12

13 Sensor Position 1: 3% to 4% Change over 2000 hrs Estimated Change Location Over 20001Hours - By Sensor Location 1 Percent Change in Volts 0% -2% -4% -6% -8% Sensor 7/22/04 13

14 Sensor Positions 2L, 2R: Residual (observed-predicted) vs. Time Residuals for Location 2L Residuals for Location 2R Observed - Predicted (volts) Sens or 2L-1 2L-2 2L-3 2L-4 2L-5 Observed - Predicted (volts) Sens or 2R-1 2R-2 2R-3 2R-4 2R-5 Hours Hours Results generally similar to sensors in location 1 Approximately 4% change over 2,000 hours Three sensors in location 2L show higher degradation Between 5% and 7% change over 2,000 hours 7/22/04 14

15 Sensor Positions 2L, 2R: 3% to 7% Change over 2000 hrs Estimated Change Over 2000 Hours - By Sensor Location 2L Estimated Change Over 2000 Hours - By Sensor Location 2R Percent Change in Volts 0% -2% -4% -6% -8% Sensor Percent Change in Volts 0% -2% -4% -6% -8% Sensor 7/22/04 15

16 Initial vs hr. Calibrations (percent error from initial calibration) Relative Calibration Error at Locations 1, 2L and 2R (Initial versus Final Calbration Data) 10% 5% Calibration Error (%) 0% -5% -10% -15% -20% -25% Operating Range 2L- 2 2L Actual Concentrations (ppm) Initial Calibration Data 7/22/ Hour Calibration Data

17 Sensor Position 3: Residual (observed-predicted) vs. Time Residuals for Location 3 Residuals for Location 3C Observed - Predicted (Volts) Sens or Observed - Predicted (volts) Sens or 3-7c 3-8c 3-9c Hours Hours Most sensors in location 3 show no significant degradation One sensor (3-3) shows more variability and degradation 7/22/04 17

18 Sensor Position 3: No Change Except Sensor 3-3 Estimated Change Over 2000 Hours - By Sensor Location 3 Estimated Change Over 2000 Hours - By Sensor Location 3C 20% 20% Percent Change in Volts 10% 0% -10% -20% -30% -40% Percent Change in Volts 10% 0% -10% -20% -30% -40% -50% % Sensor Sensor 7/22/04 18

19 Initial vs hr. Calibrations (percent error from initial calibration) Relative Calibration Error at Locations 3 and 3C (Initial versus Final Calbration Data) Calibration Error (%) 20% 0% -20% -40% -60% -80% -100% Sensor 3-3 Operating 0 Range Actual Concentrations (ppm) Initial Calibration Data 2000 Hour Calibration Data 7/22/04 19

20 Overview of Findings - Effects of Operating Mode Effects of Operating Mode on Sensor Calibration Relative error due to operating mode is less than 4% at engine-out concentrations Relative errors as high as 12% at lower concentrations Possible adjustments based on speed and torque 7/22/04 20

21 Differences Among Modes Relative to Calibration Curve Location 1 Locations 2L and 2R 6% 6% Percent Deviation 4% 2% 0% -2% -4% 1 Percent Deviation 4% 2% 0% -2% -4% 2L 2R -6% % ESC Mode ESC Mode Locations 3 & 3C 15% Percent Deviation 10% 5% 0% -5% -10% 3 3C -15% ESC Mode 7/22/04 21

22 Effects of Speed and Torque on Sensor Calibration Percent Deviation 6% 4% 2% 0% -2% -4% -6% Speed (rpm) vs. Speed Location 2L Location 2R Percent Deviation 6% 4% 2% 0% -2% -4% -6% Torque (ft lb) 7/22/04 22 Location 2L Location 2R vs. Torque

23 Preliminary Conclusions (based on first 2000 hours of a 6000-hr test) On average, sensors used in pre-catalyst applications degrade linearly at a rate of 2% per 1,000 hours of operation Some degrade much faster Investigation of failures is ongoing Calibration depends somewhat on operating mode. 7/22/04 23

24 Contact Information John Orban, Ph.D. Battelle (614)

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