Methoden voor de berekening van de emissies door mobiele ... - CBS

Figure 1.3 Calculating emissions from road traffic, emissions of VOC and PAH components
caused by combustion of motor fuels
EMISSION VOC
per
per
- vehicle category
- fuel type
- road type
mln kg
EMISSIONS mln kg
- year of manufacture
- vehicle category
- fuel type
- road type
PROFILE of
VOC emission
per
fuel type
Evaporation of motor fuels; VOC and VOC components
Petrol evaporates to some extent from vehicles when they are parked, when they cool off after
travelling and while they are travelling. In the Netherlands the evaporative emissions are calculated
according to the methodology described in the European ‘Emission Inventory Guidebook 2007’ [Ref.
116: EEA, 2007]. This methodology distinguishes three mechanisms which are primarily responsible for
the evaporative emissions from petrol driven vehicles (in case of LPG, diurnal emissions only):
1. Diurnal emissions
Diurnal emissions are evaporative emissions caused by a daily variation in the outdoor air
temperature. A rise in temperature will cause an increase of the amount of petrol vapour in the fuel
system (tank, fuel pipes and fuel injection system). A part of this vapour is emitted (together with
air) from the system to prevent overpressure (tank breathing). Diurnal emission mainly originate
from the fuel tank and are not dependent on vehicle use. The amount of diurnal emissions is
expressed in grams per vehicle per day.
2. Running losses
The running losses are evaporative emissions which occur while driving. The heat of the engine
leads to warming up of the fuel in the fuel system and by that to evaporation of a fraction of the fuel.
In modern cars the extent of use has no influence on the fuel temperature in the tank. Due to this the
running loses (and also hot and warm soak emissions) of these cars are very low. Running loses are
expressed in grams per car kilometre.
3. Hot and warm soak emissions
Hot and warm soak evaporative emissions are also caused by the engine heat and occur when a
warm engine is turned off. The difference between hot soak and warm soak emissions is related to
the engine temperature: hot soak occurs when the engine is completely warmed up. The
evaporation of petrol is less when the engine is not yet entirely warmed up. This is this case with
warm soak. Hot and warm soak emissions are expressed in grams per vehicle per stop.
The amount of petrol vapour released from these three mechanisms strongly depends on outdoor
temperature (variations), the fuel volatility and the type of fuel injection. Furthermore running losses
depend on vehicle use. Due to the application of carbon cannisters in new cars since the early
nineties the evaporative emissions have been reduced strongly. These cannisters adsorb the majority
of the emitted petrol vapour and lead this back into the engine.
The Emission Inventory Guide Book includes a generic set of emission factors for each of the
mechanisms mentioned above. Within these sets a distinction is made into the cannister type, cylinder
capacity, and average outdoor temperatures. Each set contains separate emission factors for cars
with a carburator and cars with fuel injection. Based on these factors a set of basic emission factors
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