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

time and is also caused by ageing of technical aspects of the motor in the form of, for example, wear
of piston rings and valves. In the case of a cold engine the change in emissions due to ageing is
caused by the fact that it takes longer for the exhaust gas treatment device to come up to temperature
(and its maximal conversion performance).
VERSIT+ air conditioner effects (ACCESSORIES and PERCac)
The percentage of new passenger cars that are equipped with air conditioners has increased rapidly in
recent years. The RAI 12 has calculated that this percentage was 45% in 1998 and in recent years a
large majority of (new) cars is equipped with such a device. For the determination of the correction
factors for the use of air conditioners, measurements performed by EMPA [Weilenmann, 2005] are
used. EMPA has measured vehicles under different circumstances (regarding temperature and time in
the sun). TNO EST has used these measurements to derive correction factors for the Dutch situation.
The only EMPA measurements used are the measurements where the vehicle had top be kept at a
certain temperature by the air conditioner.
In the TNO study conducted for NOVEM [ref 35: Gense, 2000], additional tests were performed on 5
vehicles, with and without the air conditioning turned on. During the measurements with the air
conditioning on, it was left turned on full during the entire test. This is an extreme situation that virtually
never occurs in practice. Under normal conditions of use, depending on the weather, the air
conditioning operates at full capacity for only a portion of the travel time. As a result, the
measurements reflect a "worst-case situation".
The most important reason for the ascertained negative effects resulting from the use of air
conditioners is that the engine management system is generally not adjusted to the use of an air
conditioner because during the vehicle type approval test, the air conditioner can remain turned off.
The use of an air conditioner affects the operation of the lambda control system, which causes the
conversion efficiency of the catalyst to decrease. In addition, even without deterioration of the lambda
control, the increase in the total energy being generated leads to increased emissions and fuel
consumption.
For diesel vehicles, an air conditioner operating at full capacity sometimes leads to a decrease in
emissions. The reason for this is that diesel engines emit more components resulting from incomplete
combustion (CO and VOC) when the motor has a relatively low load than with a higher load. In some
cases, the increased motor load that is linked with the use of the air conditioner therefore has a
beneficial effect on the emissions. The effect with a cold motor has not been ascertained by the TNO
EST, but it is expected that there will be a neutral emission behaviour because a small increase in
engine emissions (with a cold catalyst) will be compensated by a shorter warm-up time for the catalyst
(due to the higher load on the motor). The fuel consumption, in contrast, will increase in a similar
fashion as with a warm motor due to the increased load on the engine.
No data are known about the average use duration of vehicle air conditioners in the Netherlands.
Research from France has shown that vehicle air conditioners are used on average 200 hours per
year. TNO EST has calculated that the average passenger car is used for 570 hours per year. If is
assumed that air conditioners in vehicles in the Netherlands, due to the colder climate, are used for
only 100 hours per year, and that the average driving speed does not differ between driving with the
air conditioner on or off, then the percentage of kilometres that are travelled with the air conditioner on
is approximately 18%.
Emission factors for the combustion of motor fuels; N2O and NH3
N2O
The emission factors of passenger cars for each vehicle class, fuel type and road type are based on
recent research conducted by TNO [ref 34: Feijen-Jeurissen et al., 2001]. This research indicates that the
newest petrol-fuelled vehicles emit less N2O than the first generation of such vehicles with a three-way
catalyst. The extent to which this difference concerns technical advances or ageing cannot be derived
from the research results. Table 1.16 shows the basic emission factors as measured in the TNO study.
For other vehicle categories, the default values as given by the IPCC have been used [IPCC, 1996].
These factors are also shown in Table 1.16. It should be noted that the emission factors provided by
the IPCC for heavy diesel vehicles (including trucks) are significantly higher than those found in the
TNO study. In the TNO study, a single measurement was conducted on a heavy diesel engine, which
showed that the relevant diesel engine did not emit any measurable amounts of N2O. Nevertheless, in
12 Mobility sector organization
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