ACEA measurement uncertainty analysis · Uncertainty PEMS vs CVS bag on lab (2) 60 50 Uncertainty PEMS vs CVS bag on lab (3) 25 to 40 20 to 30 Drift NOx analyzeron JRC data 20 to

ACEA

measurement uncertainty

analysis

1st October 2015

� ONLY NOx-Emissions are considered.

� Since there is no limitation foreseen so far on CO, no

investigation has been carried out, no feedback can be given.

� PN-Emissions are a completely different story.

� No clear definition of:

� evaluation procedure,

� boundary conditions,

� measurement equipment and

� measuring procedure.

� There does not even exist a solid calibration procedure for

PN-PEMS, as non of the existing systems is 100% PMP-

compliant and therefore can not be compared correctly to

legally compliant measurements.

IMPORTANT INFORMATION

ACEA measurement uncertainty analysis

2

� To identify possible sources of error

� Assessment of the impact, only major sources of error are

considered.

� To refer the error margin on to the level of the regulation limit

(final goal of car performance).

� And to get a feeling for the applicable measurement uncertainty.

� Since it is not possible to reproduce a PEMS-trip, it cannot be

challenged 1:1, therefore more than average error must be

considered

� comparably large imprecision

� but not

To identify the best possible

repeatability of a well trained team

with hand-picked equipment.

Goal of Investigation


3

� Differences between PEMS and CVS-Reference

� Gas Sensor / Concentration

Exhaust Mass-Flow

Velocity /Distance

� Time Alignment

� Unaccounted Change in Humidity

� Unaccounted Influence on PEMS dynamics

� Additional Weight / Aerodynamics

(Effect on CO2)

� Differences between PEM-Systems

� Evaluation Procedure / Emission Calculation

Possible Errors on ”NOx”


4

NOx-Concentration andMass Measurement


5

ACEA agrees with the general approach, but…

Source: JRC

Validation of the PEMS before the RDE trip :

� Permissible tolerances in test lab conditions on WLTC:

� Remarks :

� test is done on same vehicle, same driving, same emissions …

� WLTC is not average driving, it is only one potential trip, and not the worst.

� No drift, dispersion, vibration, T or P variation during real PEMS trip taken

into account

Uncertainty: PEMS vs. Bag-CVS


6

WLTC on Chassis Dyno

PEMS analysis

Bag + CVS analysisOfficial text : Appendix3:Validation of PEMS and non-traceable

exhaust mass flow rate

3.3. Permissible tolerances for PEMS validation (table 1)

NOx [mg/km] 15mg/km

1 StdDev. 19-25%What happens in the same test condition but with another cycle ?

Accounted as systematic measurement error within previous documents(no drift, time alignment etc.)

� Different vehicles and cycles (NEDC, WLTC, FTP75, US06, ACEA-

RDE).

� On average very good correlation: deviation <3.7%, high R2 of

0.94.

� But individual test deviation on average

49.8 mg/km => 62% of limit.

Uncertainty: PEMS vs. Bag-CVS II


7

� At high emission levels the relative error is small.

� But even under „optimum“ conditions:

� Absolute Error > 20-30mg/km

Relative error (CF) vs. Absolute Error


8

Ford EU5 and EU6Experience

20 EU5 / EU6 PEMS-Test Examples

At low emission1 StdDev. > 25-40%

Drift: JRC Worst-Case-Scenario (NOx)

9

1.4l Diesel

(EU5)

3l Diesel

(EU6)

Measured Value: mg/km 848,3 423,8

Emission Limit mg/km 180 80

Absolute Drift mg/km 6,7 14

Absolute Drift mg/km 13,4 28

Absolute Drift mg/km 26 54,3

Considering Diesel Limit 8% 18%

17% 35%

33% 68%

Since Drift is technology and limit independent

Considering Gasoline Limit 11% 23%

22% 47%

43% 91%

Source: JRC

� 1 StdDev approx. up to 80% of limit for large engines.

10-60mg/km (depending on Engine)

Time Alignment (only NOx)

10

-2s -1s 0s +1s +2s

Max.

relative

Error

Test 1 -6,0% -3,5% 0,0% 3,0% 4,3% 4,3%

Test 2 -11,3% -3,3% 0,0% 0,3% 0,2% 0,3%

Test 3 8,3% 5,6% 0,0% -6,1% -12,2% 8,3%

Real Time Alignment Experience (ACEA-Member, Gasoline)

26,02

14,55

5,21

0,00

-2,47

-0,86

2,82

-5,00

0,00

5,00

10,00

15,00

20,00

25,00

30,00

-3sec -2sec -1sec 0 +1sec +2sec +3sec

Nox

CO2

26,02

14,55

5,21

0,00

-2,47

-0,86

2,82

-5,00

0,00

5,00

10,00

15,00

20,00

25,00

30,00

-3sec -2sec -1sec 0 +1sec +2sec +3sec

Nox

CO2

Real Time Alignment Experience (Source: ACEA-Member)

Example (Source: JRC)Was the „drafted method“ applied correctly?

Within the reasonable range of +/-2s� 1 StdDev. 10-15%

Time alignment does not only go in one direction!It has larger impact with larger mass flow and high dynamic. Increased influence with GDI.

*mg/km dependingon exhaust mass flow

8-12 mg/km*

Mass Flow Measurement

11

y = 0.8804xR² = 0.9641

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

EF

M #

1 [g

/s]

EFM #2 [g/s]

WLTC - Exh. MassFlow

Vergleich zweier Abgasmassenstromsensoren

y = 0.8804xR² = 0.9641

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

EF

M #

1 [g

/s]

EFM #2 [g/s]

WLTC - Exh. MassFlow

Vergleich zweier Abgasmassenstromsensoren

EFM

vs.

EFM

(Audi)

Observed Errors within reasonable range: � 1 StdDev. 10-15%

Also observed: >70% of tests overestimation of CVS-mass flow

Example:Checked Exhaust-Flow-Meter right after Manufacturer’s Calibration(Provided by Partner of ACEA-Member)

8-12 mg/km


� Pressure compensation of equipment

� Additional Weight / Aerodynamics / CO2-Contribution

� Measuring Differences between 2 different PEMS

� Natural Humidity Influence (not corrected)

� Cross-Sensitivity NOx/CO, NOx/CO2

� Difference T90-Responses of Systems

Unaccounted Errors


12

Estimation1 StdDev. 10-15%

8-12 mg/km

Although humidity influence will not be corrected, it has to be taken into account for

CF-definition as a measurement uncertainty.

Although humidity influence will not be corrected, it has to be taken into account for

CF-definition as a measurement uncertainty.

� Due to different T90-rise/fall time an error is observed

(excl. time alignment error).

� The more dynamical the trip, the larger the error

Dynamics


13

-- CVS-- PEMS

NO

[ppm

]In

tegra

l N

O [

ppm

*s]

10% difference @ RCA

Time [s]

Source: ACEA-member

diffe

rence in

inte

rgra

l valu

e [

%]

Summary

14

SourceError margin (1

std. Dev) (%)

Total Mass

(mg/km)

Uncertainty PEMS vs CVS bag on lab (1) 19 15

Uncertainty PEMS vs CVS bag on lab (2) 60 50

Uncertainty PEMS vs CVS bag on lab (3) 25 to 40 20 to 30

Drift NOx analyzer on JRC data 20 to 80 10 to 60

Time alignment 10 to 15 8 to 10

Mass Flow Measurement 10 to 15 8 to 10

Distance 4

Unaccounted errors 10 to 15 8 to 10

total tolerance min 33 23

total tolerance average 60 43

total tolerance max 86 64

CF min 1,3

CF average value 1,6

CF max 1,9

ACEA proposal 1,7

APPLYING:

(1) Allowed tolerance during validation@ WLTC // (2, 3) @ other cycles

% mg/km

Grey lines are not taken into account for calculation

� Even if a car is performing below or close to the

limit, PEMS may lead to significantly different

results.

� Gasoline and Diesel face the same absolute

uncertainties.

� Due to existing experience the following

uncertainties must be expected:

� 80mg/km limit and 40mg/km error = 1,5

� 60mg/km limit and 40mg/km error = 1,67

� CF Conclusion: a CF around 1,7 or 40mg/km of

uncertainty are justified with moderate conditions.

Conclusion


15

Documents

ACEA measurement uncertainty analysis · Uncertainty PEMS vs CVS bag on lab (2) 60 50 Uncertainty PEMS vs CVS bag on lab (3) 25 to 40 20 to 30 Drift NOx analyzeron JRC data 20 to