WLTP-DTP-AP Validation of N2O measurement
WLTP-DTP-AP
WLTP-DTP-AP
Subgroup Additional Pollutants
Validation of N2O measurement
WLTP-DTP-AP 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 Validation of N2O measurement
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 Validation of N2O measurement
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 Validation of N2O measurement
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N2O vehicle emission results from VP2
Analyser: GC-ECDLab: AECC
Source: WLTP VP2
WLTP-DTP-AP Validation of N2O measurement
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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 Validation of N2O measurement
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 Validation of N2O measurement
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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
WLTP-DTP-AP Validation of N2O measurement
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Correlation of GC-ECD and QCL
• GC-ECD and QCL show perfect correlation• QCL measures approx. 3 % less
Source: Daimler
WLTP-DTP-AP Validation of N2O measurement
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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
WLTP-DTP-AP Validation of N2O measurement
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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
WLTP-DTP-AP Validation of N2O measurement
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
WLTP-DTP-AP Validation of N2O measurement
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 Validation of N2O measurement
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Conclusions QCL
• Systems are commercially available
• 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
WLTP-DTP-AP Validation of N2O measurement
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Linearisation results LASAR
• The instrument is highly linear
Source: SEMTECH
WLTP-DTP-AP Validation of N2O measurement
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Accuracy, repeatability and noise testing results LASAR
Source: SEMTECH
WLTP-DTP-AP Validation of N2O measurement
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Interference LASAR
Source: SEMTECH
• no interference from CO2, CO or water• no inteference correction applied
WLTP-DTP-AP Validation of N2O measurement
WLTP-DTP-AP
Conclusions LASAR
• System commercially available
• Perfect correlation to calibration gas
• LOD and LOQ exceed the requirements
• No interference from CO2/water or CO
WLTP-DTP-AP Validation of N2O measurement
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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
WLTP-DTP-AP Validation of N2O measurement
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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 Validation of N2O measurement
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Conclusions NDIR
• Systems are commercially available
• 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.
WLTP-DTP-AP Validation of N2O measurement
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Linearity FTIR
• Linearity requirements are met
Source: BMW
WLTP-DTP-AP Validation of N2O measurement
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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
WLTP-DTP-AP Validation of N2O measurement
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• The California ARB has published a procedure for N2O emission measurement with FTIR