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1 NOx Measurement Errors in Ammonia-Containing Exhaust August 22,2006 Diesel Engine Emissions Reduction Meeting Detroit, MI John Hoard, Rachel Snow, Lifeng Xu, Robert Hammerle, Cliff Montreuil Chemical Engineering Department Christine Gierczak Physical and Environmental Sciences Department S. Iskander Farooq Safety Methods Development Department DEER 2006

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Page 1: NOx Measurement Errors in Ammonia-Containing Exhaust · 2014-03-10 · NOx Measurement Errors in Ammonia-Containing Exhaust ... 2 reduced to NO in converter; typical compositions

1

NOx Measurement Errors inAmmonia-Containing Exhaust

August 22,2006Diesel Engine Emissions Reduction Meeting

Detroit, MI

John Hoard, Rachel Snow, Lifeng Xu, Robert Hammerle, Cliff Montreuil

Chemical Engineering DepartmentChristine Gierczak

Physical and Environmental Sciences Department S. Iskander Farooq

Safety Methods Development Department

DEER 2006

Page 2: NOx Measurement Errors in Ammonia-Containing Exhaust · 2014-03-10 · NOx Measurement Errors in Ammonia-Containing Exhaust ... 2 reduced to NO in converter; typical compositions

2

Introduction

z Diesel NOx aftertreatment can lead to ammonia (NH3) in exhaust – Urea-SCR systems

– LNT systems near end of rich regeneration

– LNT-SCR combinations

z NH3 can cause significant measurement errors with various NOx instruments

z Larger issue for engine-out and mid-bed samples

DEER 2006

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3

Conc

entra

tion

(ppm

) Example of Concern

NOx (Introduced as NO2) Measurement on Various Analyzers

120 NH3 off

100

Mass Spec NH380

add Mass Spec NOx

60 30 100 ppm FTIR NH3

ppm NH340 NO2 FTIR NOx

NH3 to Horiba NOx20 100 ppm

0 0 500 1000 1500 2000 2500

time (seconds)

DEER 2006

Page 4: NOx Measurement Errors in Ammonia-Containing Exhaust · 2014-03-10 · NOx Measurement Errors in Ammonia-Containing Exhaust ... 2 reduced to NO in converter; typical compositions

4

Experimental Set-upheated filter Mass Spec

heated filter FTIR

Empty Catalyst Can (5.66” dia. x 14” long)

DOC heated filter CLD3 (GC)

heated filter CLD2 (GC)

heated filter CLD1 (COM3)

10 lpm MFC 1% NH3 Heated Un-Heated 2.2L

10 lpm MFC 2% NO Diesel Exhaust Engine Analyzer 25 lpm MFC 2% NO2

exha

ust f

low

DEER 2006

Page 5: NOx Measurement Errors in Ammonia-Containing Exhaust · 2014-03-10 · NOx Measurement Errors in Ammonia-Containing Exhaust ... 2 reduced to NO in converter; typical compositions

5

Standard Addition Test Concept

Y

7

6

5

4 y = 1.0 *x + 3

3

2

1

0

0 0.5 1 1.5 2 2.5 3 3.5

X

DEER 2006

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6

Test DesignReplicate Three

MFC Settings Standard Addition to Exhaust Flow rates NO NO2 NH3 NO NO2 NOx NH3 Total NO NO2 NH3 % % % (ppm) (ppm) (ppm) (ppm) L/min L/min L/min L/min

1 100 100 0 75 226 301 0 1330 10 15 0 2 100 100 100 75 224 299 149 1340 10 15 10 3 50 100 100 37 225 262 150 1335 5 15 10 4 100 50 100 75 113 188 150 1332 10 7.5 10 5 50 50 100 38 113 151 151 1327 5 7.5 10 6 50 50 50 38 113 151 76 1322 5 7.5 5 7 50 50 0 38 114 152 0 1317 5 7.5 0 8 50 100 0 38 226 264 0 1325 5 15 0 9 50 100 50 38 226 263 75 1330 5 15 5

10 100 50 50 75 113 188 75 1327 10 7.5 5 11 100 50 0 76 113 189 0 1322 10 7.5 0 12 100 100 50 75 225 300 75 1335 10 15 5

DEER 2006

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7

Chemiluminescent Analyzer (CLD)

z Developed at Ford Research in early 1970’s z Most common NOx measurement z Actually measures NO

– NO + O3 Î NO2* + O2

– NO2* Î NO2 + photon

z NO2 reduced to NO in converter; typical compositions – Carbon-molybdenum

– Molybdenum

– Carbon

– Gold

– Ferrous sulfate

– Stainless steel

DEER 2006

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8

Carbon-Molybdenum Converter

0

10

20

30

40

50

60

70

80

90

100 C

onve

rsio

n NO2 NH3

300 350 400 450 500 550

Catalyst Temperature °C

Data from Breitenbach and Shelef

DEER 2006

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9

Ammonia Reactions

z NOx can be removed by reactions with ammonia – Ammonium nitrate:

• 3NO2 + H2O Î 2HNO3 + NO (1) • NH3 + HNO3 Î NH4NO3 (2)

– SCR reactions:

• 6NO2 + 8NH3 Î 7N2 + 12H2O (3)

z Must keep sample lines above 100°C to avoid ammonium nitrate

z Choose converter that does not promote these reactions

DEER 2006

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10

CLD w/ COM3 Converter Main Effect of NH3 on NOx Measurement

NO

x (p

pm)

600

500

400

300

200

100

0 0 25 50 75 100 125 150

NH3 Standard Addition (ppm)

Non-random Run Order:

Memory Effect

1st Replicate ­CLD1

2nd Replicate ­CLD1

3rd Replicate ­CLD1

DEER 2006

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11

CLA NOx Response

z Regression equation from second replicate

z CLA with COM3 catalyst

z NOx = 337 + 1.14 NOadd + 0.924 NO2add - 0.164 NH3add

z R2 = 0.978

z All three coefficients are not zero at 95% confidence

z NOadd and NO2add slopes could be 1.0 within experimental confidence limits

DEER 2006

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12

95% Confidence Interval for Regression Coefficient(CLD - COM3)

300

320

340

360

380

400

420

440

460

480

500

NO

x M

easu

red

(ppm

)

Regression (m = 1.14)

95% C.I. High (m = 1.47)

95% C.I. Low (m = 0.82)

Expected Value (m = 1.0)

0 20 40 60 80 100

NO Added (ppm)

DEER 2006

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13

CLD w/ Glassy Carbon ConverterMain Effect of NH3 on NOx Measurement

NO

x (p

pm)

600

500

400

300

200

100

0 0 25 50 75 100 125 150

NH3 Standard Addition (ppm)

NH3 Interference

but no Memory Effect

1st Replicate ­CLD2

1st Replicate ­CLD3

2nd Replicate ­CLD2

2nd Replicate ­CLD3

3rd Replicate ­CLD2

3rd Replicate ­CLD3

DEER 2006

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14

CLA NOx Response

z Regression equation from second replicate

z CLA with Glassy Carbon catalyst

z NOx = 269 + 1.08 NOadd + 0.982 NO2add - 0.728 NH3add

z R2 = 0.986

z All three coefficients are not zero at 90% confidence

z Within experimental error, NO and NO2 slopes could be 1.0

z Large NH3 interference

DEER 2006

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15

CLA Summary

z NOx measurement accuracy and repeatability when NH3 is present is poor for the base COM3 converter.

z NOx measurement repeatability is much better with the updated glassy carbon converter, however a large NH3 interference makes measurements inaccurate.

z CLA NOx measurements are not accurate when NH3 is present in large concentrations.

DEER 2006

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16

FTIR

z Fourier Transform Infrared Spectroscopy

z Commonly used gas analysis but potential issues – Interference from gases not included in the analysis set.

– Saturation

– Excessive Interference even with gases in the analysis set

DEER 2006

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17

Typical Exhaust Spectrum

A b s o r b a n c e

250 ppm NO

Expanded on next

208 ppm NO2 slide

117 ppm NH3

Exhaust

3500 3000 2500 2000 1500 1000

Wavenumbers

DEER 2006

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18

Expanded Scale

A b s o r b a n c e

250 ppm NO

208 ppm NO2

117 ppm NH3

Exhaust

1910 1900 1890 1880 1870

Wavenumbers

DEER 2006

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19

FTIR NO Response

z Regression equation from second and third replicates

z FTIR

z NO = 57.7 + 0.843 NOadd + 0.0156 NO2add - 0.0279 NH3add

z R2 = 0.943

z NO and NH3 coefficients are not zero at 90% confidence

z NO coefficient range includes 1; could give accurate NO

z NO2 coefficient is not nonzero at 90% confidence

z No spectral saturation was present in the data

DEER 2006

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20

FTIR NO2 Response

z Regression equation from second and third replicates

z FTIR

z NO2 = 172 + 0.187 NOadd + 0.522 NO2add - 0.0141 NH3add

z R2 = 0.839

z NO2 coefficient is not zero at 90% confidence

z NO2 coefficient range does not include 1; NO2 readings are inaccurate

z NO and NH3 coefficients are not nonzero at 90% confidence

DEER 2006

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21

95% Confidence Interval for Regression Coefficient(FTIR NO2)

0

20

40

60

80

100

120

140

160

180

NO

2 Mea

sure

d (p

pm)

Regression (m = 0.52)

95% C.I. High (m = 0.67)

95% C.I. Low (m = 0.37)

Expected Value (m = 1.0)

0 20 40 60 80 100

NO2 Added (ppm)

DEER 2006

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22

FTIR Summary

z NO measurements are not affected by NH3, but may not match the known addition levels accurately

z NO2 measurements are not affected by NH3 level, and also do not match the known addition levels accurately

z Careful modification of the analysis method may well reduce the error in measurement

z Accurate measurement should be possible but requires careful user interaction

DEER 2006

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23

Mass Spectrometer Main Effect of NH3 on NOx Measurement

600

500

400

300

200

100

0 0 25 50 75 100 125 150

NO

NO2

NH3 Standard Addition (ppm)

1st Replicate ­NO

1st Replicate ­NO2

2nd Replicate ­NO

2nd Replicate ­NO2

3rd Replicate ­NO

3rd Replicate ­NO2

ppm

Run order effect

DEER 2006

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24

Run Order Effects

3530252015105

50

0

-50

Observation Order

Res

idua

l

Residuals Versus the Order of the Data (response is VF_NO2)

non-random run order trend in

residuals

•10 micron orifice? •Other contamination? •Sample lines?

DEER 2006

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25

CIMS NO Response

z Regression equation from second replicate

z CIMS

z NO = 105 + 1.21 NOadd + 0.0143 NO2add - 0.0194 NH3add

z R2 = 0.953

z NO coefficient is not zero at 90% confidence

z NO coefficient range includes 1

z NO2 and NH3 coefficients are not nonzero at 90% confidence; small interferences exist

DEER 2006

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26

CIMS NO2 Response

z Regression equation from second replicate

z CIMS

z NO2 = 225 - 0.0682 NOadd + 1.13 NO2add - 0.131 NH3add

z R2 = 0.992

z NO2 and NH3 coefficients are not zero at 90% confidence; interferences exist

z NO2 coefficient range includes 1

z NO coefficient is not nonzero at 90% confidence

DEER 2006

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27

CIMS Summary

z Accurate measurements require regular instrument maintenance, apparently due to ammonium nitrate formation in the system

z NO measurements are not affected by NH3, but may not match the known addition levels accurately

z NO2 measurements are affected by NH3 level, and additionally may not match the known addition levels accurately

z Careful recalibration and regular cleaning of the unit may well reduce the error in measurement, but is unlikely to remove the NH3 effect.

DEER 2006

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28

Estimate of Engine NOxz From Standard Addition Test, regression gives “zero addition” as

estimate of engine out NOx

z Measurements do not agree!

z Note: CLAs are “dry” where FTIR and CIMS are wet; expect 7% higher reading when water is removed

Instrument NO NO2

CLA COM3

CLA GC

FTIR 58 172

CIMS 105 225 330

230

269

337

NOx

DEER 2006

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29

Experiment Summary

z Chemiluminescent analyzers do not provide accurate measurement of NOx when NH3 is present in engine exhaust gas.

z FTIR may provide accurate measurements if analysis methods are developed to provide adequately low interference.

z Chemical ionization mass spectroscopy may provide accurate measurements, although the unit tested appears to need significant cleaning and maintenance to do so.

z No presently available measurement provides accurate and robust measurement of NO, NO2, NOx, and NH3 when NH3 is present in large quantity.

z Recommend development of an NH3 scrubber

DEER 2006