WLTP-DTP-02-XX NO2 v3.doc 1/2

WLTP DTP subgroup

Date 11 June 2010

Title Draft Nitrogen Dioxide (NO2) measurement procedure

Working paper number

WLTP-DTP-02-XX

1.0. Introduction These guidelines were developed following in response to discussions at the 1st DTP (Develop Test Procedure) meeting held in Ann Arbor in April 2010. It was identified that a test procedure is required NO2.

Once this proposal concept has been accepted by the DTP team, OICA will draft a proposal for the legislative text.

2.0. Background

2.1. Reason for the requirement Revised and challenging air quality standards for NO2 are in force since the beginning of 2010 in the European Union. As road transport contributes around half of the ambient NO2, it is anticipated that a comparable means of determining the ratio of NO2 to the total NOx emissions will be required for the ongoing discussions. It is therefore proposed to develop such a procedure during the WLTP project in order to ensure worldwide harmonisation from the outset.

2.2. Existing legislation In developing this draft test procedure, it was appropriate to review existing legislation that measures NO2. Although no test procedure is known for the measurement of vehicle emissions, there is an existing practice for air quality measurements and this should form the basis for a proposal, at least to ensure possible correlation of results.

3.0. Measurement principle Two alternative analyser concepts are proposed, these being Chemi-Luminescent Analyser (CLA) or Ultra-Violet Resonance Absorption (UV-RAS).

Contrary to the majority of today’s light duty measurement procedures, and due to the uncertainty of NO to NO2 ratios over time and the solubility of NO2

WLTP-DTP-02-XX NO2 v3.doc 2/2

in water, it is proposed to measure NO2 directly rather than from CVS bags.

As NO2 is seen as a pollutant emission, and therefore is expected to have the same dimension as NOx (unit mass per unit of distance), it is recommended to adopt the modal measurement process that is currently applied to FID hydrocarbon measurements in ECE R83.

Slide 1

Draft proposal for the measurement of NO2 in the exhaust from passenger cars

June 2010

This work is intended to start discussions at the DTP work group level. Changes are likely as the technical experts review proposals made and then consolidate into agreed upon approaches."

WLTP

Slide 2

Measurement of NO, NO2 and NOx Mass Emissions in the Exhaust of Light Duty Vehicles (LDV)

Effects leading to measurement errors:

Conversion of NO to NO2 (NOx remains constant)In presence of oxygen at ambient conditions NO is oxidized to NO2. Half life of NO at a concentration of 25 ppmv is of approx. 160 min.

Conversion of NO2 to NO (NOx remains constant)At elevated temperatures (> 150 °C) NO2 is converted to NO. Conversion rate can be significantly increased in presence of soot (e.g. on filters).

Solution of NO2 in water condensate (NOx decreases)NO2 is water soluble and can go into solution in presence of water condensate in the exhaust.

Slide 3

CVSDilutionair

Dilution tunnel

Reduction of NO2 to NO

under presence of soot

NOx = const.

Oxidation of NO to NO2

NOx = const.

Modal measurement

Bag measurement

Influencing Factors on NO/NO2 Ratio

Solution of NO2 in water

condensate (NOx

decreases)

Analyzer

Analyzer

Analyzer

End of pipemeasurement

Slide 4

Oxidation of NO to NO2 in the CVS bagComparison of measurement and theoretical approach

The measured values show a fair to good agreement with the theoretical approach (calculation).

0%

10%

20%

30%

40%

50%

0 20 40 60 80 100 120

time [min]

NO

-oxi

datio

n [%

]

Span gas (20 ppm)

Gasoline exhaust EU4 (4 ppm)

Diesel exhaust EU4 (25 ppm)

Diesel exhaust EU4 (10 ppm)

Calculation

exhaust/span gas in air

with: k = 7,5 •10-10 ppm-2 min-1

]O[]NO[]NO[2]NO[

2

kt

source: Baumbach G., Luftreinhaltung, 3. Auflage,Springer-Verlag, 1993

25 ° C

15 min

Slide 5

Oxidation of NO to NO2 in CVS bag after 15 minInfluence of NO concentration

mit: k = 7,5 •10-10 ppm-2 min-1[O2] = 19,7 %

dt = 15 min

]O[]NO[]NO[2]NO[

2

kt

0%

4%

8%

12%

16%

20%

0 10 20 30 40NO-concentration [ppm]

NO

-oxi

datio

n af

ter

15 m

in [%

]

Diesel exhaust

Gasoline exhaust

Span gas

Calculation

d[NO] = - 2 k * [NO][NO][O2]*dtwith k = 7,5 •10-10 ppm-2 min-1

[O2] = 19,7 %dt = 15 min

Bag measurement yields increased NO2 value due to oxidation of NO.

Slide 6

Conclusions

In the diluted exhaust NO partly oxidizes to NO2.

The reaction rate depends on the NO concentration (for T = const).

To avoid systematic error, residence time has to be minimized

modal measurement of NO

Slide 7

Mass emissions of NO, NOx and NO2 in emission test cycle:

NO: CVS with modal measurement of NO in the diluted exhaust gas and integration over the cycle/phase -> NO concentration.NOx: Measurement of NOx-concentration from CVS bag (standard method) -> NOx concentration.NO2: Difference of NOx and NO concentration.

Analyzer: CLD or DUV-RAS (see SAE-Paper 2004-01-1830).

Working groups to recommend sampling technologies to avoid aqueous condensation in dilute modal sample streams.

For NOx, NO and NO2 gas density of NO2 = 1.913 g/cm³ at 20° C is applied.

Slide 8

CVSDilution air Tunnel

Measurement of NOx from bag

ModalMeasurement

Bag Measurement

Measurement of NO from diluted

exhaust

Proposed setup for NO2 determination

Mass emission during cycle

Analyzer

NO-mode NOx-mode

Slide 9

Text based on Reg. 83

Sampling System Requirements

The sampling system response time (from the probe to the analyser inlet) shall be no more than [TBD] seconds.

The modal NO analyser shall be used with a constant flow (criteria for constant flow TBD) system to ensure a representative sample, unless compensation for varying CFV or CFO flow is made.

Nitrogen oxide (NO) analysis:

The analyzer shall be either of the chemi-luminescent (CLA) ort the ultra-violet resonance absorption (UV-RAS) type.

The analyzers shall have a measuring range compatible with the accuracy required to measure the concentrations of the exhaust gas sample pollutants.

Measurement error shall not exceed 2 per cent (intrinsic error of analyzer) disregarding the true value for the calibration gases.

For concentrations of less than 100 ppm, the measurement error shall not exceed 2 ppm.

The ambient air sample shall be measured on the same analyzer with an appropriate range.

No gas drying device shall be used before the analyzer.

Slide 10

Text based on Reg. 83

NO concentrations shall be calculated from the integrated NO analyzer reading, corrected for varying flow if necessary.

Determination of NOThe average NO concentration is calculated as follows:

where:

= integral of the recording of the modal NO analyzer over the test (t2-t1)

Ce = concentration of NO measured in the diluted exhaust in ppm.

12

2

1

tt

dtCC

t

tNO

e

2

1

t

tNO dtC

Slide 11

Reg. 83 Figure 10: Gaseous Emissions Sampling Schematic (addition for modal NO measurement)

P

Dilution Tunnel (see Figures 6 & 7)

Air

from vehicle exhaust

S1 S2 / SV

S3

F

P

N

FL

V BEQ

N

FL

V BAQ

to vent or optional

continuous analyser

to vent

HFID

zero gas

span gas

R, I

Fh Q BA

Lh Vh

NO-Analyzer

Figure based on Reg. 83