1. Weighting Factors impact on WLTP CO2 emissions
L. Orofino (Italy)
2013 October 24th

2. Background information
WLTP cycle seems acceptable in its representativeness in terms of driving dynamics (databases have been developed for this purpose) and its modular design, identifying different driving phases and different categories of vehicles.
However WLTC cycle, in its whole, seems globally not representative of uses of vehicles, notably in France, by the relative weight of urban conditions, rural and motorway, and by the average speeds resulting.
This is also confirmed in the FIAT EcoDrive Data.

3. Speed Distribution Comparison
WLTP v5.3
Weigthed WLTP French proposal (L/M 75%; H/ExH 25%)
Weigthed WLTP H. Steven based on Ecodrive data proposal (L/M 65%; H/ExH 35%)
Eco:Drive data
WLTP v5.3
Weigthed WLTP French proposal
Weigthed WLTP eco:Drive proposal
Weigthed WLTP Steven proposal
Eco:Drive data
NEDC

4. Impact of Weighting Factors (W.F.) on WLTC CO2 emissions
Analysis based on WLTP measured data from EC Data Base.
Results show significant differences in terms of CO2 (g/km) emission figures.

5. Impact of W.F. on CO2 emission % variation as a function of engine power

6. Impact of W.F. on CO2 emission % variation as a function of engine displacement

7. Impact of W.F. on CO2 emission % variation as a function of vehicle curb mass

8. Impact of W.F. on CO2 emission % variation as a function of WLTP (no W.F.) CO2 emissions (g/km)

9. Impact of W.F. on CO2 emission (g/km) as a function of engine power

10. Impact of W.F. on CO2 emission (g/km) as a function of engine displacement

11. Impact of W.F. on CO2 emission (g/km) as a function of vehicle curb mass

12. Impact of W. F. on CO2 emission (g/km) as a function of WLTP (no W. F
Impact of W.F. on CO2 emission (g/km) as a function of WLTP (no W.F.) CO2 emissions (g/km)

13. Impact on fuel consumption
(Manufacturer data)
Border conditions :
Gasoline engines : 1,2 – 1,6 l with and without turbocharger
Diesel engines : 1,4 – 2 l
Vehicles : class A – C SUV
Gearbox : manual and automatic
With and without stop and start
WLTP
Concerning WLTP fuel consumptions, we still observe differences with real-life conditions and higher for the highest fuel consumptions (up to -1,5 l/100 km)  in an ideal situation, the slope should be flat and nearest to zero.
In terms of CO2 emissions these differences range between 10 and 35 g/km

14. Conclusions
French data state that real life CO2 emissions differ from measured WLTP CO2 emission from 10 to 35 g/km and that this difference increases with increasing fuel consumption (i.e. from small to large vehicles).
Analysis of EU Com measured CO2 emission data on WLTP cycle shows that Weighting Factors have a significant impact on CO2 emission figures. Applying Weighting Factors causes CO2 emission to increase from small to large vehicles.
Both proposed Weighting Factors (French proposal and H. Steven based on Ecodrive data proposal) will improve the coherence between real life CO2 emission and WLTP measured ones even if the gap cannot be totally filled.
In this respect French Weighting Factors proposal (L/M 75%; H/ExH 25%) improves the above mentioned coherence between real life CO2 emission and WLTP more than H. Steven based on Ecodrive data proposal (L/M 65%; H/ExH 35%).