wltp-dtp-ap validation of n 2 o measurement wltp-dtp-ap subgroup additional pollutants validation of...

WLTP-DTP-AP Validation of N2O measurement

WLTP-DTP-AP

WLTP-DTP-AP

Subgroup Additional Pollutants

Validation of N2O measurement


WLTP-DTP-AP

4.1.4.9.1. A gas chromatograph with an electron-capture detector (GC–ECD) may be used to measure N2O concentrations of diluted exhaust by batch sampling from exhaust and ambient bags. Refer to §7.2. in this Annex. 4.1.4.10. Nitrous oxide (N2O) analysis with IR-absorption spectrometry (where applicable)The analyser shall be a laser infrared spectrometer defined as modulated high resolution narrow band infrared analyser. An NDIR or FTIR may also be used but water, CO and CO2 interference must be taken into consideration.

Methods for Measurement of N2O in GTR draft

• GC-ECD• Laser infrared spectrometer• NDIR• FTIR


WLTP-DTP-AP

Instrument availability and availability of data for evaluation

Instrument manufacturers

Data for validation

GC-ECD several VP2/industry

laser infrared spectrometer QCL Lasar Cavity ring down

several11

industrynonenone

NDIR several industry

FTIR several none


WLTP-DTP-AP

Pollutant Range of emission level to be measured

bag

dil

ute

d

raw

Cold start

[ppm]

stabi-lized

[ppm]hot start[ppm]

back-ground[ppm]

relevant net conc.

[ppm]

LoQrequired[ppm]

LoDrequired[ppm]

N2O 10 mg/mi x 0,6 0,6 0,6 0,3 0,3 0,1 0,03

sample from

typical bag concentration9 m³/min CVS Flow assumed

LoQ required (30 % of net conc.)LoD = 1/3 LoQ

Performance criteria for N2O measurement

4.1.4.10.1. If the analyser shows interference to compounds present in the sample, this interference can be corrected. Analysers must have combined interference that is within 0.0 ± 0.1 ppm.

Established by AP working group, not contained in GTR

Interference correctioncontained in GTR


WLTP-DTP-AP

N2O vehicle emission results from VP2

Analyser: GC-ECDLab: AECC

Source: WLTP VP2


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GC-ECD


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maincolumn

precolumn

sampleloop

valve 2

valve 1

totalflow

backflushflow

make upgas flow

carrier gas filtration

sample

pump

bachflush valve

ECD

Argon/Methan (95/5)

N2

O2-doting

Flow schematic of GC-ECD


WLTP-DTP-AP

LOD and LOQ of GC-ECD-Measurement

Assuming background is constant the LOD can be estimated as equal or better 3 * STDand LOQ as 10 * STD

STD = 0,00164 ppmLOD = 0,0049 ppmLOQ = 0,0164 ppm

• LOD and LOQ meet the requirements

Source: Daimler


WLTP-DTP-AP

Conclusions GC-ECD

• Systems are commercially available

• With proper application method is free of interferences (base line separation of N2O peak

• LOD and LOQ meet the requirements

• GC-ECD has proven to be a reliable method• Results from VP2• Results from industry

• Chemistry lab and well trained personal required

• Complicated and time consuming sampling and analysis


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laser infrared spectrometer (QCL)


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Correlation of GC-ECD and QCL

• GC-ECD and QCL show perfect correlation• QCL measures approx. 3 % less

Source: Daimler


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• LOD and LOQ exceed the requirements by far

• Measurement of pure N2 for 30 s

• LOD and LOQ derived from standard deviation

Determination of LOD and LOQ for QCL

1 2 3 RequiredMean 0,0006 0,0015 0,0015

Std 0,0001 0,0003 0,0003LOD (Mean + 3 * Std) 0,001 0,002 0,002 0,03

LOQ (Mean + 10 * Std) 0,0019 0,0041 0,0045 0,1

Source: Daimler


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Interference QCL

• there is no interference from CO but a slight interference from CO2 (or water) can be observed

• no interference correction is applied• the maximum interference requirement of +/- 0,1 ppm is met in all cases

Source: DaimlerSource: Daimler


Scatter of mass emission results (NEDC)

• results from all 6 correlation vehicles where within +/- 0,8 mg/km

data pool:•128 emission test (NEDC)•performed on 6 different vehicles (Euro 3/4/5)•results from 3 different test cells•test period: 6 month

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Korr02 Korr03 Korr04 Korr05 Korr06 Korr07 Korr08

devi

ation

to m

ean

N2O

[mg/

km ]

vehicle

N2OGes.[mg/km]

Source: Volkswagen


ambient N2O concentration

0.3000

0.3050

0.3100

0.3150

0.3200

0.3250

0.3300

0.3350

0.3400

0.3450

10 11 12 13 14 15 16 17 18 19 20

N2O

[ppm

]

test cell#

N2O ambient 1[ppm]

N2O ambient 2[ppm]

test cell#

N2O ambient 1

[ppm]

N2O ambient 2

[ppm]mean 0.3261 0.3264

std. dev. 0.0045 0.0052rsd 1% 2%

n 43 43mean 0.3239 0.3233

std. dev. 0.0024 0.0023rsd 1% 1%

n 43 43mean 0.3206 0.3195

std. dev. 0.0023 0.0022rsd 1% 1%

n 42 42

11

15

19

• ambient N2O concentration is about 0,330 ppm• on average all analysers are in excellent agreement (± 0,003 ppm)• All mesrements are within +/- 0,015 ppm

Source: Volkswagen


WLTP-DTP-AP

Conclusions QCL


• Perfect correlation to GC-ECD

• LOD and LOQ exceed the requirements

• Slight interference from CO2/water but well within limits

• QCL has proven to be a reliable method• various installations running without major problems• stable operation over more than one year


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laser infrared spectrometer (LASAR)


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Linearisation results LASAR

• The instrument is highly linear

Source: SEMTECH


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Accuracy, repeatability and noise testing results LASAR

Source: SEMTECH


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Interference LASAR

Source: SEMTECH

• no interference from CO2, CO or water• no inteference correction applied


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Conclusions LASAR

• System commercially available

• Perfect correlation to calibration gas

• LOD and LOQ exceed the requirements

• No interference from CO2/water or CO


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NDIR


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• Correlation not entirely satisfactory• Deviation of NDIR to GC of up to 25 %• Interference correction has large influence on NDIR results

Correlation of GC-ECD and NDIR

Source: Daimler


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• Even with interference correction in place the maximum interference requirement of +/- 0,1 ppm is not met in all cases

Interference correction NDIR

Source: DaimlerSource: Daimler


WLTP-DTP-AP

Conclusions NDIR


• correlation to GC-ECD not entirely satisfactory

• Pronounced interferences from CO2/water and CO require interference correction. For the NDIR investigated the combined interference did not fulfill the requirements, even when interference correction was applied with great care.

• NDIR is a comparatively inexpensive analyser. For the analysis of N2O it has to be operated at its limits.


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FTIR


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Linearity FTIR

• Linearity requirements are met

Source: BMW


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Conclusions FTIR

• Systems are commercially available• LOQ ~ 300ppb ambient air level with typically 30 sec integration time• Cross interference CO within LOD 100ppb (optimized spectral method)• Cross interference CO2/H2O (optimized spectral method): N2O in 3rd bag FTP

diluted exhaust typically at ambient air level for petrol vehicles with CO2 ~ 1Vol% and H2O ~1Vol% cross interference below LOD

• Linearity requirements comparable to otheranalyzers are met

Analyzer capable to meet legal requirements with increased integration time


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• The California ARB has published a procedure for N2O emission measurement with FTIR


WLTP-DTP-AP

• The methods to measure N2O as described in GTR draft have proven to be sufficiently accurate and robust

• Systems are commercially available from several instrument manufacturers

General conclusions

wltp-dtp-ap validation of n 2 o measurement wltp-dtp-ap subgroup additional pollutants validation of...

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