Long term emission degradation

2 vehicles were tested according to NEDC and Artemis driving cycles at mileage intervals of 20 000 km, before and after maintenance (see sections 2.3.1, 2.3.2.6 and 2.3.3). It allowed us to design a long term degradation scheme (Geivanidis & Samaras, 2004).

3.2.3.1. Degradation scheme

The correction factor by which the basic emission factor should be multiplied in order to take into account the degradation of emissions due to mileage which was kept in-line to the MEET / COPERT

III methodology (Ntziachristos & Samaras, 2000a) is given by the equation:

MC_C,i = a_M× M_mean + b_M where:

M_mean: the mean fleet mileage of vehicles for which correction is applied

MC_C,i: the mileage correction for a given mileage (Mav), pollutant i and a specific cycle a_M: the degradation of the emission performance per kilometre

b_M: the emission level of a fleet of brand new vehicles

b_M is lower than 1 because the correction factors are determined using vehicle fleets with mileages ranging from 16 000 to 50 000 km. Therefore, brand new vehicles are expected to emit less than the sample vehicles.

By lack of data, it is assumed that emissions do not further degrade above 120 000 km for Euro 1 and 2 vehicles and 160 000 km for Euro 3 and 4 vehicles.

The effect of average speed on emission degradation is taken into account by combining the observed degradation lines over the two driving modes (urban, rural). It is assumed that for speeds outside the region defined by the average speed of urban driving (19 km/h) and rural driving (63 km/h), the degradation is independent of speed. Linear interpolation between the two values provides the emission degradation in the intermediate speed region. Table 31 in Annex 11 presents the methodology parameters and the application of the scheme that are being discussed later.

As regards Euro 1 and Euro 2 vehicles, MEET data are proposed to be used as the majority of data covering these vehicle categories contained in the Artemis database originated from the same dataset used for the MEET estimations.

In order to estimate the degradation of modern Euro 3 and Euro 4 vehicles, an analysis was performed on the data derived from the Artemis database (version 1/12/2004). The mileage effect on CO, HC and NO_x emissions was examined as CO₂ emissions have been proven to be unaffected by mileage (Samaras & Ntziachristos, 1998; Ntziachristos & Samaras, 2000b, 2001): The analysis was performed in two driving mode regions: urban and rural. In order to increase the number of data and to achieve a more realistic result, UDC (hot start) and Artemis urban measurements were combined to produce the urban driving mode data while EUDC and Artemis rural measurements were combined to produce the rural driving mode data. Due to the low number of data as well as low mileage of Euro 4 vehicles, they were considered in the same category as Euro 3 vehicles and the hypothesis that both Euro 3 and 4 vehicles are expected to have the same degradation behaviour was accepted. The emissions of all vehicles were plotted against their mileage. Linear regression

lines were produced as representative of the mileage degradation for three engine capacity ranges:

<1.4 l, 1.4-2.0 l, >2.0 l. An example of results of this approach is presented in Figure 13. Table 31 in Annex 11 summarizes the results of the regressions, together with the average mileage and the size of the part of the fleet that was used for each subset of data.

Figure 13: NOx degradation in urban driving behaviour for petrol vehicles.

Then we decided the vehicles with engine capacity >2 l not to be considered as an individual class due to the small size of the sub sample. We propose:

- For CO in urban condition, a degradation is proposed for each driving mode and for 2 engine capacity categories.

- For CO in rural condition, a degradation is proposed for vehicles ≤1.4 l while no degradation is proposed for vehicles with engine capacity above 1.4 l.

- For HC in urban and rural condition, a considerable degradation is observed only in the case of vehicles ≤1.4 l in urban driving mode.

- For NOin urban and rural condition, a considerable degradation is observed only in the case of vehicles >1.4 l in urban driving mode.

In order to apply a degradation scheme, the above estimated regression lines should be dimensionless. This can be achieved by normalizing the equations given that the correction factor MC should not modify the average emission factor of the sample when applied to the average mileage of the sample (Samaras & Ntziachristos, 1998; Ntziachristos & Samaras, 2000b, 2001).

The initial regression lines have the form:

emission[g/km]=a"mileage+b

The mileage correction factor (MC) should yield 1 for the average mileage of the sample (av.sam.mil) thus the normalization parameter (norm_par) is given as follows:

MC(av.samp.mil)= a"av.samp.mil+b

norm_par =1 _=>

=> norm_ par=a!av.samp.mil⁺b

Following the above the proposed parameters for Euro 3 and Euro 4 vehicle are presented in Table 22 on page 85. They can be applied according to the Copert methodology presented above using the

Equation 1 on page 84. The stabilization mileage was assumed to be 160 000 km. The Copert III/MEET values for the speeds defining the urban and rural regions were not changed for consistency reasons as they are very close to the average speed of the new cycles used (legislative and Artemis).

In average the emissions of CO, HC and NOx are multiplied by a factor 3.6 from 0 to 100 000 km for Euro 1 and 2 cars, and increase by 18 % for Euro 3 and 4 vehicles. For Euro 1 and 2 vehicles, NOx is more influenced by the mileage than CO and HC (multiplied resp. by 5.3, 2.9 and 2.7), but no influenced for Euro 3 and 4 cars.

3.2.3.2. Validation of the degradation scheme

A set of measurements on two specific vehicles was performed in order to get an image of the influence of mileage and regular maintenance on emissions (see section 2.3.3). No effect of maintenance was observed on the level of emissions neither as a consistent before-after maintenance improvement nor as a function of mileage. The same methodology that was applied to produce the mileage correction factor from the Artemis database was applied on the two vehicle measurements as well in order to validate the proposed degradation scheme.

The in-use durability requirements of EU for Euro 3 and Euro 4 petrol vehicles allow a deterioration factor of up to 1.2 for all emission components at 80 000 km. Although this factor refers to cold start NEDC emissions it has also been included in the validation of the degradation scheme under the assumption that it is an indication of the general trend of emissions. Figure 14 present an example of the correction factor as a function of mileage for Euro 3 and Euro 4 vehicles as it is proposed by the new Artemis scheme compared to the MEET approach as well as the measurements of the two specific vehicles, and the EU in-use durability requirements.

Figure 14: NOx correction factor comparison (MEET, Artemis, 2 tested vehicles: left), and relative to 0 km (right) with in-use legislative requirements.

The new Artemis degradation scheme predicts lower emission degradation with mileage than MEET. This lays closer to the EU in-use emission durability requirements in most cases. MEET predicts higher degradation (significantly higher in most cases) than the in-use durability factor requires.

As regards CO, Lanos seems to be closer to the MEET approach thus showing higher degradation than the EU limits while Matiz shows contradictory performance between urban and rural driving mode. In the case of NOx, Lanos shows an improvement of emissions with mileage which lies under even the lowest of all Artemis prediction. Matiz performance is close to the MEET scheme.

HC emission performance of both Lanos and Matiz seems to deteriorate higher than any of the rest prediction scenarios under urban driving conditions. The improvement of Matiz emissions under

rural driving conditions can only be attributed to the low number of mileage intervals it was measured under and the high influence of the last measurement.

Both vehicles that were examined during their mileage evolution showed no obvious malfunction that could lead to higher emission levels. Their operation though seems to have been affected by the harsh use conditions they were both driven under as both cars accumulated mileage as part of a car rental fleet. The initial top mileage limit after which these cars were scheduled to be withdrawn from the car rental company fleet was exceeded especially in the case of Lanos in order to be able to obtain measurements at higher mileage points. This top limit is determined by the certain company in cooperation with the manufacturer as the point where the operation of the vehicle is significantly deteriorating under the specific use. The above along with the fact that Matiz was a low engine capacity vehicle with bad emission performance position both vehicles at an extreme position compared to the average European fleet as regards both their emission level and emission durability performance.