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Weekly UpdatesThe average ambient temperature of all the tests is 22.8 [degrees]C, close to that of ARTEMIS, 23 [degrees]C. Without any preliminary maintenance, the first test of each vehicle stopped all night constituted a cold-start measurement that was conducted under the same conditions as the hot tests. The vehicle was surrounded by the traffic flow of the selected trip and was only driven by one driver to eliminate variability associated with driver behavior, which can be significant according to numerous authors. (26,54-56) Instructions were given to the driver to reproduce the shadowed vehicle kinematics as accurate as possible while in the flow, avoiding extreme behaviors.
RESULTS
For each vehicle test, mean values correspond to the average test results (Table 2). These averages are thus representative of the tests carried out and could be higher considering the underestimation of the gas sampling technique used by approximately 5% compared with CVS. The relative standard deviation is approximately 33% for all tests and all pollutants. These standard deviations are probably due to the kinematic differences between tests. Facing the lack of emission standards and former data of vehicle emissions in Algeria, we sought to compare our results with the emission levels of the European vehicles of the ARTEMIS model for equivalent vehicles. (40-41) For these vehicles, the average fuel consumption of ARTEMIS is calculated using consumption data of their database whereas their emissions are calculated using for the same speed and load as our tests.
Similar vehicle sample is taken from the ARTEMIS database for comparison where parameters are the vehicle model, engine capacity, fuel type, age, vehicle technology, vehicle load, and speed. The comparison with the emissions of the ARTEMIS model highlights that our gasoline vehicles are close to the European vehicles pre-Euro and are qualified as pseudo-pre-Euro. The diesel vehicles from the years 1993 and 1996 have emissions close to those of the European vehicles meeting the standard Euro I (Figure 3); the other diesel vehicles have emissions close to the standard Euro II. We thus qualify them respectively as pseudo-Euro I and pseudo-Euro II, which enables us to distribute our diesel vehicles sample in two groups. Our sample of vehicles tested can thus be divided into three subsamples: two gasoline LDVs pseudo-pre-Euro, two diesel LDVs pseudo-Euro I, and four diesel LDVs pseudo-Euro II.
Hot Emissions
The average emission factors rise for pseudo-pre-Euro, pseudo-Euro I, and pseudo-Euro II to 123.4, 143.5, and 167.4 g/km for C[O.sub.2]; 11.99, 0.68, and 0.49 g/km for CO; 1.42, 0.08, and 0.05 g/km for THC; and 1.14, 0.59, and 0.48 g/km for N[O.sub.x], respectively (Table 2). The N[O.sub.x] emissions vary from 0.19 to 1.6 g/km for all vehicles, gasoline and diesel, but remain low compared with ARTEMIS emissions Euro I and Euro II. These low emissions of N[O.sub.x] are probably due to the low acceleration observed during the tests because of the road environment and the high load rate, which does not facilitate high acceleration. Osses et al. (57) showed that N[O.sub.x] are better correlated with positive acceleration rather than speed for noncatalyzed vehicles and Joumard et al. (52) demonstrated that N[O.sub.x] and C[O.sub.2] LDV emissions are very sensitive to the acceleration frequency and high acceleration.
Gasoline Vehicles. The C[O.sub.2] emissions for gasoline vehicles are lower than 125 g/km with an average of 123.4 g/km, still lower than ARTEMIS pre-Euro, which is characterized by levels higher than 180 g/km for all speeds. The CO emissions have an average of 12 g/km, which decrease quickly with speed to a minimum of 6.5 g/km at the speed of 55 km/hr. The variation of these emissions according to the average speed is shown in Figure 4 and is similar to that of ARTEMIS, which has an average level of 10.4 g/km. The THC average emissions rise to 1.4 g/km and remain close to the ARTEMIS emissions. The N[O.sub.x] emissions grow proportionally with speed and vary from 0.55 to 1.6 g/km with a mean level of 1.1 g/km, but remain lower than the ARTEMIS values, which vary from 1 to 3.2 g/km according to speed. This variation is undoubtedly due to the weak accelerations practiced, with a maximum in the urban environment of 0.60 m/[sec.sup.2]. The positive average acceleration of urban cycles of loaded LDVs of ARTEMIS is 0.76 m/[sec.sup.2] (58) and thus much higher. Recorded accelerations are weak not only because of the high load but also traffic congestion and urban conditions. The emission factors obtained on the tested sample of vehicles show that CO and THC emissions of gasoline LDVs are comparable with the ARTEMIS pre-Euro emissions, but there is a difference when considering N[O.sub.x] emissions.
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Diesel Vehicles. The C[O.sub.2] diesel emission average is 155.4 g/km, which is much lower than ARTEMIS Euro I and Euro II. The low emission levels of the pseudo-Euro I group vehicles is undoubtedly due to the recent replacement of engine parts made on these vehicles. The emissions of the pseudo-Euro II group remain close to ARTEMIS Euro II. These last vehicles did not undergo modification of their engine. The average CO emission is 0.58 g/km, which lies between the ARTEMIS Euro I and Euro II values. The pseudo-Euro I group shows emission levels appreciably lower than ARTEMIS Euro I levels whereas those of the group pseudo-Euro II coincide with ARTEMIS Euro II, as illustrated in Figures 5 and 6. The average THC emissions is 0.06 g/km for the entire sample and remain included between ARTEMIS Euro I and Euro II. The average of the pseudo-Euro I group is 0.08 g/km and that of pseudo-Euro II is 0.05 g/km. The average N[O.sub.x] emission is 0.53 g/km with tendencies similar to the variations of the ARTEMIS emissions for the two groups pseudo-Euro I and pseudo-Euro II. The diesel vehicle emissions are broadly comparable with the ARTEMIS emissions, which supports the assumption formulated with respect to the standards of the vehicles tested. The existing differences could be due to the environment and conditions of use in which these vehicles evolve.
Ratios. The ratios of CO/C[O.sub.2] and THC/C[O.sub.2] are indicators of the state of maintenance of vehicles; (59) low ratios reveal good maintenance of the vehicle. To compare the level of maintenance of our tested vehicles, the ratio was calculated for all vehicles in our sample and that of ARTEMIS. Obtained ratios are reported as intervals in Table 3. In general, ratios are from 2 to 5 times higher than those for the ARTEMIS data, which indicates poor maintenance of the tested vehicles. This constitutes an issue for vehicles older than 3 yr in Algeria after the guarantee period. This is mainly due to a weak technical capacity for vehicle engine repair and also a lack of material. The high cost of original spare parts regarding the average income leads people to a large use of imported counterfeit products because there is no local product. We observed that the vehicle from 1996 had been repaired and thereafter presented a ratio (THC/C[O.sub.2]) of 0.016%, close to the ratio of the vehicle from 2004 (0.013%). This highlights the importance of maintenance for the reduction of pollutant emissions.
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Cold-Start Excess Emission
The mass difference of pollutant emitted by cold and hot-start tests for a given trip with a same average speed represents absolute cold excess emission (Table 4). Rated by the unit hot emission, this absolute emission is expressed in an equivalent distance run with a hot engine. In other words, it is the distance necessary for a hot engine to emit the same mass of pollutant as the cold-start excess emission. This distance is not related to the cold distance, which explains the distance necessary to reach a hot engine. On the other hand, it expresses the weight of cold emission compared with hot emission. This equivalent distance is variable according to the pollutant and the vehicle: the maximum value reached is 83 and 90 km for the cold emission of CO and THC, respectively, for a diesel engine. The C[O.sub.2] emission is equivalent to 6.2 km for a gasoline engine and to 4.5 km for a diesel engine; for CO it is 28.2 km for a gasoline engine and 23.7 km for a diesel engine; for THC it is 22.7 km for a gasoline engine and 27.7 km for a diesel engine; and for the N[O.sub.x] it is -1.7 km for the gasoline and 4.1 km for a diesel engine. A negative distance suggests an underemission. The cold-start emission is thus particularly important for CO and THC, moderately important for C[O.sub.2], and of little importance for N[O.sub.x]. On average for all pollutants, the cold emission represents the equivalent of 13.8 km for the gasoline engine and 15.4 km for the diesel engine, which is thus of comparable relative importance for the two engines.
Fuel Consumption
The average fuel consumption of gasoline and diesel vehicles pseudo-Euro I and pseudo-Euro II are reported in Table 2. The consumption of gasoline vehicles remains lower than that of ARTEMIS, which is 68.9 g/km. On the other hand, the consumption of the diesel vehicles in the pseudo-Euro I group is comparable with ARTEMIS, which is 54.5 g/km whereas the pseudo-Euro II group has a higher consumption. These consumption variations can be due to weak acceleration but also to the repair of the pseudo-Euro I vehicles. Fuel consumption comparison for cold and hot-starts reported in Table 4 shows an average excess of consumption of 67 and 49% for gasoline and diesel engines, respectively. For comparison purposes, an extracted subsample from the ARTEMIS database (51,60,61) of eight LDVs vehicles from category N1-I that have been tested at both cold and hot-starts were used: three gasoline pre-Euro vehicles, one diesel pre-Euro vehicle, three diesel Euro I vehicles, and one diesel Euro II vehicle. Only data from cold starts with similar parameters to our sample such as load rate, ambient temperature, and speed were used to calculate the percentage of excess of fuel consumption at cold start to hot start during tests conducted on different urban cycles in Europe. The excess obtained varied in the range of 25.7-31.5% for an average speed of 18 km/hr and an ambient temperature of 18.4 [degrees]C and a load rate of 16% for all technologies of diesel vehicles. The range of excess for pre-Euro gasoline vehicles was 27.5-29.4% for an average speed of 41.5 km/hr, a load rate of 10.4%, and an ambient temperature of 18 [degrees]C. Our results compared with ARTEMIS data show a fuel consumption excess 20.4% higher for diesel engines, which could be attributed to the difference in load rate of 33%. In the case of gasoline vehicles, the excess is approximately 38.2% higher for a difference in load rate of 49.6%. According to these results, it seems that high load rate has an important influence on fuel consumption at cold start for diesel and gasoline LDVs. Further investigation should be conducted to explore the influence of the driving conditions, the ambient temperature, and high load on cold-start emissions and fuel consumption.
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