EUROPEAN COMMISSION
ENTERPRISE AND INDUSTRY DIRECTORATE-GENERAL
Sustainable Growth and EU 2020
Sustainable Mobility and Automotive Industry
Brussels, 04/03/2013
ENTR.F1/KS
WLTP: correction of CO2 emissions obtained at WLTP test temperatures for
European average temperature
1.
BACKGROUND
During the development of the WLTP it was decided that the emission test would be
performed at a test temperature1 TWLTP of 22° C – 25° C with a variation of 2° - 3° C
(the final values will only be fixed after full evaluation of the validation 2 results).
These relatively high test temperatures were supported by contracting parties from
hotter areas (India) and vehicle manufacturers, who claimed test lab related
infrastructural reasons (i.e. the number of tests at temperatures < 20° C should be
kept as low as possible).
After this decision had been taken, the EU announced that it would correct the CO2
emissions measured at the WLTP test temperature for substantially lower European
average temperatures TEU, which is expected to be somewhere between 8° and 12° C
(still to be determined), to obtain the regulatory European CO2 emissions. Since the
conditions for determining the latter will define regulatory incentives for the
technical design of the vehicles, it is important that the correction is applied in a
vehicle specific manner and not just by a default factor. Obviously vehicle specific
corrections imply additional tests, which have to be balanced with the overall testing
costs.
2.
POSSIBLE CORRECTION PROCESSES
The general principle should be that a vehicle, which is representative for a "larger
EU temperature vehicle family", comprising several CO2 type approval vehicle
families, is tested at a lower temperature in addition to the standard WLTP test
temperature. From comparing CO2 emissions measured at both conditions a
correction factor should be developed that would be applied to CO2 emissions
determined at the standard WLTP test temperatures for all vehicles of the "larger EU
temperature vehicle family".
1
In the following by "test temperature" the temperature in the actual test cabin that should be identical to
the pre-test soaking temperature is understood.
Commission européenne, B-1049 Bruxelles / Europese Commissie, B-1049 Brussel - Belgium. Telephone: (32-2) 299 11 11.
Office: BREY 10/027. Telephone: direct line (32-2) 2958557. Fax: (32-2) 2969637.
E-mail: nikolaus.steininger@ec.europa.eu
Two concepts could be practically considered for obtaining CO2 emission values for
the representative vehicle at the average European temperature TEU:
(1)
Testing the representative vehicle directly at TEU. For this purpose possibly
heat-storage/insulation systems of the vehicles should be taken into account,
e.g. defining the vehicle soak such that the cooling down is performed with
closed bonnet during a fixed (limited, e.g 12 h) period without pre-set final
target temperatures of relevant parts like coolant, oil (according to the
outcome of the discussion at WLTP-DTP LabProcICE, open issues 18, 18b).
(2)
Testing the representative vehicle at the regulatory type 6 (low temperature)
test temperature of -7° C (using the full WLT test cycle) and interpolating
CO2 emissions obtained at this low temperature and the standard WLTP test
temperature TWLTP for obtaining a CO2 emissions at TEU. This method could
possibly minimize the need for additional tests (or avoid them altogether if
"larger EU temperature vehicle family" and type 6 vehicle families can be
made identical). However, the validity of such temperature interpolation
would have to be checked.
For both approaches it has to be considered how road load factors are being
corrected, e.g. currently NEDC road load factors are increased by 10% at the -7° C
low temperature test.
3.
RESEARCH TO BE PERFORMED
In order to address the correction of WLTP CO2 emission values for the average
European temperature the following tasks have to be performed:
(1)
Definition of "average European test temperature" TEU. It should be noted
that a simple model using generally available meteorological data should be
sufficient since a few degrees variation of TEU are unlikely to have a big
impact on the results of the correction (and the details on how to determine
TEU are scientifically debatable anyway…).
(2)
Assessment of the variation of road load factors with the temperature (- 7° C,
TEU, TWLTP) e.g. by performing tests or using a theoretical approach.
(3)
Identify technical criteria for constituting a "larger EU temperature vehicle
family". This would basically mean that from the constraints defining CO2
emission test vehicle families (as outlined in Regulation (EC) 692/2008)
those, which may have a significant influence on the test temperature
dependence of CO2 emissions (e.g. constraints on the variation of engine and
powertrain characteristics) are retained, while others (e.g. constraints on the
variation of the vehicle reference mass and body shape) are dropped. For
instance, a single additional test at a lower temperature for all vehicles
having a given engine/powetrain configuration but different reference masses
and body shapes could be sufficient.
(4)
Identify a set of different vehicles, covering different engine/powetrain
technologies. Test at -7° C, TEU and WLTP standard test temperature and
verify the possible application of concepts 2(1) and 2(2) using the technical
2
criteria for constituting the "larger EU temperature vehicle families"
identified in 3(2). Obviously the latter technical criteria may be corrected
according to the experimental results. Possibly other correction methods than
a simple correction factor could be examined.
3