Report - DCE - Nationalt Center for Miljø og Energi

(2009), for the corresponding layer. A cut-off mileage of 120.000 km (pers.
comm. Ntziachristos, 2007) is behind the calculation of the modified emission
factors, and for the Danish situation the low sulphur level interval is assumed
to be most representative.
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Emissions and fuel-use results for operationally hot engines are calculated
for each year and for layer and road type. The procedure is to combine fuel
consumption and emission factors (and deterioration factors for catalyst vehicles),
number of vehicles, annual mileage levels and the relevant road-type
shares given in Table 3.27. For non-catalyst vehicles this yields:
( ,
, = () ,
, ⋅ 6 ⋅ 1 ,
⋅ 0 ,
Here E = fuel consumption/emission, EF = fuel consumption/emission factor,
S = road type share and k = road type.
For catalyst vehicles the calculation becomes:
( ,
, = ') ,
, ⋅ () ,
,
⋅ 6 ⋅ 1 ,
⋅ 0 ,
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Extra emissions of NOX, VOC, CH4, CO, PM, NH3 and fuel consumption
from cold start are simulated separately. For SO2, the extra emissions are derived
from the cold start fuel consumption results.
Each trip is associated with a certain cold-start emission level and is assumed
to take place under urban driving conditions. The number of trips is
distributed evenly across the months. First, cold emission factors are calculated
as the hot emission factor times the cold:hot emission ratio. Secondly,
the extra emission factor during cold start is found by subtracting the hot
emission factor from the cold emission factor. Finally, this extra factor is applied
on the fraction of the total mileage driven with a cold engine (the βfactor)
for all vehicles in the specific layer.
The cold:hot ratios depend on the average trip length and the monthly ambient
temperature distribution. The Danish temperatures for 2010 are given
in Cappelen et al. (2011). For previous years, temperature data are taken
from similar reports available from The Danish Meteorological Institute
(www.dmi.dk). The cold:hot ratios are equivalent for gasoline fuelled conventional
passenger cars and vans and for diesel passenger cars and vans,
respectively, see EMEP/EEA (2009). For conventional gasoline and all diesel
vehicles the extra emissions become:
&( = β ⋅ 1 ⋅ 0 ⋅ () ⋅ ( &(U −1)
,
,
,
, ,
Where CE is the cold extra emissions, β = cold driven fraction, CEr =
Cold:Hot ratio.
For catalyst cars, the cold:hot ratio is also trip speed dependent. The ratio is,
however, unaffected by catalyst wear. The Euro I cold:hot ratio is used for all
future catalyst technologies. However, in order to comply with gradually
stricter emission standards, the catalyst light-off temperature must be
reached in even shorter periods of time for future EURO standards. Correspondingly,
the β-factor for gasoline vehicles is reduced step-wise for Euro II
vehicles and their successors.