The European Commission s science and knowledge service. Joint Research Centre

Transcription

1 The European Commission s science and knowledge service Joint Research Centre

2 2017 assessment of PEMS measurement uncertainty B. Giechaskiel, M. Clairotte, V. Valverde, P. Bonnel Brussels, LDV-RDE meeting, 8 Nov 2017

3 Overview Uncertainty equations background Uncertainty calculation framework Input values Estimated margins Conclusions and next steps

4 Background (Emissions equation) u NOx is the ratio of the density of NOx and the overall density of the exhaust (considered constant) c NOx,i is the NOx instantaneous measured concentration in the exhaust at time i [ppm] q mew,i is the measured instantaneous exhaust mass flow rate at time i [kg/s] d is the distance of the test [km]

5 Background (Uncertainty) ε ENOx is the uncertainty of E NOx (in %) Error propagation rule The errors are assumed uncorrelated to each other and random

6 Background (Additional uncertainties) Time mis-alignment Boundaries conditions Zero drift The additional uncertainties were added to the uncertainty estimation in order to find the maximum uncertainty. The reason is that there was no input regarding their contribution in real operation (e.g. how the drift evolves)

7 Uncertainties calculation framework/scheme Error propagation (+) = addition EFM Distance uncertainty Relative uncertainty Absolute uncertainty NOx analyzer Zero drift (+) (+) Time alignment Worst case drift Final uncertainty

8 EFM accuracy EFM drift ε qmew,acc [%] ε drift,qmew [%] Distance ε d [%] EFM linearity Analyser accuracy Gas accuracy ε qmew,lin [%] ε C,acc,NOx [%] ε gas,nox [%] x 2 analyzers NOx emissions ε E,NOx [%] Time alignment / dynamics (+) ε t [%] Analyser linearity Span drift ε C,lin,NOx [%] ε span,nox [%] Boundary conditions (p, T, dt, dp) (+) ε B [%] Zero drift δ drift [mg/km] (+) δ E,NOx [mg/km] NOx emission limit Worst case drift δ drift,2 [mg/km] (+) δ F,E,NOx [mg/km]

9 2017 input Margins subgroup input Monitoring data input (No JRC data) Detailed analysis of input in previous presentations Based only on received data

10 Additional Analyzers EFM RDE regulation (in lab checks) experiments (real conditions) Accuracy 3% 2% 10% Drift 2% 2% 2% Linearity 2% 2% 2% Accuracy 2% 5% 2% Linearity 1% 1% 1% Span drift 2% 2% 5% Gas accuracy 2% 2% (2%) Distance 4% 4% (4%) Dynamics - 3% 3% Boundaries - 0% 0% Zero drift (Analyzer) 5 ppm 20% mg/km Worst case drift - 20% 0-10 mg/km In brackets ( %) not studied in 2017

11 final used values Distance 4.0% 4.0% 2015 study EFM accuracy 3.0% 4.1% 4.1% 10.0% NOx emissions uncertainty EFM drift 2.0% Linearity 2.0% 3% Time alignment/dynamics 13% (RDE 2%) 0% Boundary conditions Analyzer 5.0% 5.8% Diesel Gas accuracy 2.0% 8.2% 8.2% 10.4 mg/km 80 mg/km Limit Span drift 2.0% two analyzers (NO+NO2) Linearity 1.0% 16 mg/km Zero drift 20.0% 16 mg/km Worst drift 20.0% 42.4 mg/km input Margin 53% Margin diesel calculated Final 50% minus CVS unce 3.1% emission limit CVS uncert. 2.5 mg/km

12 Validation tests (monitoring data)

13 Validation tests (summary) Received (margins sub-group) Monitoring Cycles Sub-phases Cycles All (with unknown equipment) Outside permissible tolerance 9 26 Not valid tests percentage 6.3% 8.6% All (with known equipment) Outside permissible tolerance Invalid tests percentage 5.4% 6.3% 1.5%

14 Zero drift

15 Received (margins sub-group) Monitoring ZERO Lab (validation) RDE Extended RDE All Known All Known All Known Known Labs [#] 1+ACEA 1 3+ACEA Tests [#] PEMS [#] Mean [ppm] Median [ppm] Min [ppm] * Max [ppm] Failed [#] Failed [%] 16.7% 0% 1.1% 0.8% 0% 0% 0.9%

16 Span drift

17 Received (margins sub-group) Monitoring SPAN Lab (validation) RDE Extended RDE All Known All Known All Known Known Labs [#] 1+ACEA 1 3+ACEA Tests [#] PEMS [#] Mean [%] 0.0% 0.3% -0.1% 0.1% -0.2% 0.0% -0.3% Median [%] 0.1% 0.3% 0.1% 0.1% -0.2% 0.0% 0.0% Min [%] -7.0% 0.3% -5.0% -0.7% -8.9% -0.3% -9.3% Max [%] 5.1% 0.3% 3.1% 0.9% 11.7% 1.5% 3.3% Failed [#] Failed [%] 25% 0% 4.2% 0% 39% 0% 10.5%

18 Zero drift STEP & LINEAR zero drift

19 Zero drift STEP zero drift LINEAR zero drift Worst case drift Linear drift Step drift

20 Analyzers (JAMA data) vs lab analyzers Real time detail <20 mg/km 200 mg/km At 80 mg/km 5% analyzer s uncertainty seems realistic

21 EFMs vs traceable Reference after 1 y vs other methods EFMs are better than 4% at steady conditions, higher (10%) uncertainty can be seen in transient operation

22 2017 STEP final used values Distance 4.0% 4.0% EFM accuracy 9.6% 10.0% 10.0% 11.9% NOx emissions uncertainty EFM drift 2.0% Linearity 2.0% 3% Time alignment/dynamics 15% 0% Boundary conditions Analyzer 2.0% 3.6% Diesel Gasoline Gas accuracy 2.0% 5.1% 5.1% 11.9 mg/km 80 mg/km Limit mg/km Span drift 2.0% two analyzers (NO+NO2) Linearity 1.0% 15 mg/km Zero drift 18.8% STEP 10 mg/km Worst drift 12.5% STEP 36.9 mg/km 34.0 input Margin 46% Margin diesel Margin 57% Margin gasoline calculated Final 43% minus CVS unce 3.1% Final 52% minus CVS uncert. emission limit CVS uncert. 2.5 mg/km

23 2017 LINEAR final used values Distance 4.0% 4.0% EFM accuracy 9.6% 10.0% 10.0% 11.9% NOx emissions uncertainty EFM drift 2.0% Linearity 2.0% 3% Time alignment/dynamics 15% 0% Boundary conditions Analyzer 2.0% 3.6% Diesel Gasoline Gas accuracy 2.0% 5.1% 5.1% 11.9 mg/km 80 mg/km Limit mg/km Span drift 2.0% two analyzers (NO+NO2) Linearity 1.0% 10 mg/km Zero drift 12.5% LINEAR 0 mg/km Worst drift 0.0% LINEAR 21.9 mg/km 19.0 input Margin 27% Margin diesel Margin 32% Margin gasoline calculated Final 24% minus CVS unce 3.1% Final 27% minus CVS uncert. emission limit CVS uncert. 2.5 mg/km

24 Margins at various emission levels Contribution of constant and relative uncertainty

25 Conclusions Framework of calculating PEMS uncertainty Experimental data or RDE requirements as input Concerns for EFM NOx analyzers real time uncertainty needs further evaluation More real time data are necessary Two basic assumptions for the zero drift (step and linear) Final calculated uncertainty 24% to 43% at 80 mg/km Uncertainty depends on emission levels measured. Equation was given

26 Next steps / discussion points Uncertainty of boundary conditions was assumed 0%. Needs PEMS additional testing at extended conditions CVS uncertainty (3%) needs further investigation Drift in RDE trips needs to be investigated (step, linear or none) Additive uncertainty components to be re-examined For example there was no indication of zero drift systematic error. If it is random then normal propagation of error equations should be used Technical requirements that could be improved in future

27 Review procedure in the following years Identification of technical requirements that could be improved in legislation. Collection of new data and/or creation of other data through dedicated experimental campaigns. Confirmation with experimental data that the technical requirements are fulfilled both in lab and on the road. Assessment of each uncertainty according to the framework described. Adjustment of the framework if necessary. Amendment of relevant RDE performance requirements for PEMS equipment and adapting the NOx conformity factor.

28 Recommendations for regulation Mandate the validation test for both the total and urban phases (WLTP Phase 1+2) Define the margins at lower RDE max

29 Thank you! Any questions?