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Weekly UpdatesOn-board emission measurements are performed with the mini-CVS on a sample of eight vehicles where kinematics and carbon dioxide (C[O.sub.2]), CO, THCs, and N[O.sub.x] measurements are recorded. The WSL mini-CVS is a simplified system of the CVS for sampling vehicle gas exhaust developed by WSL (United Kingdom). The device used in this study has been partially modified by adding on-board analyzers to measure instantaneous emissions. (50) The new system is to be validated against a full CVS in future work. The sampling system is on-board the vehicle and connected to the tailpipe. The exhaust gases emitted by the vehicle pass in a cone-shaped splitter system including 112 parallel tubes directly attached to the muffler. Only the gases of one tube are brought to the dilution chamber, the other beams are rejected outside. The mass flows of exhaust gas collected and air dilution vary according to the engine regime and are unknown, but the total diluted volume passing through the mini-CVS is measured. The fraction of gas taken is inversely proportional to the number of tubes. At this stage, the admitted assumption is that the primary flow is supposed to be equally divided into 112 flows tested by WSL in the laboratory. (32) The assumption is validated by injecting a steady flow of C[O.sub.2] into the flow splitter and concentrations measured at the end of each tube and related to the unit value can range from 0.92 to 1.03 as a function of the tube studied. Nevertheless, complex aerodynamic phenomena around a moving vehicle-like flow rate profile in a tube, resistant due to gas expansion in the atmosphere, could lead to a pressure variation if proportionality is not met. The crosswind effect on emissions is estimated to be 10-14% in case winds of 5 and 10 m/sec, but the other complex issues are not addressed. Figure 2 shows the experimental apparatus with all the equipment aboard.
Six small pumps assembled parallel to one another powered with a 12-V battery are used to guarantee a constant sampling flow with low energy consumption, the exhaust gas is sampled and diluted in a mixing tube. Air dilution is taken from the ambient air at the same height from the ground as the tailpipe but symmetrically opposite to the longitudinal axis of the vehicle, to avoid high-polluted air and any disturbance due to the difference of pressure or turbulence at the vehicle back. The air dilution flow varies and is not measured; only the diluted gas mixture flow is measured and maintained constant at 300 [min.sup.-1]. A fraction of the diluted mixture is taken by a seventh independent pump with an adjustable flow and divided again in three flows equivalent to 85 [min.sup.-1] each by a three-way distributor, which is directed toward analyzers of CO/C[O.sub.2], THC, and N[O.sub.x]. An eighth independent pump is used for taking a sample of the used air dilution in a Tedlar bag of 70 L at a flow of 1 [min.sup.-1] to be analyzed at the end of every test. All flows are specific to the mini-CVS system, and the operating flow range is defined by its developer according to the tube sizes. (32)
C[O.sub.2] and CO are measured by infrared (IR) absorption (Cristal 300), N[O.sub.x] are analyzed by a chemiluminescence method (Topaze 3010), and a heated flame-ionization detector (FID; Graphite 750) is used for THCs. All the apparatuses were supplied by Cosma-Environnement SA. Calibration of all analyzers was made every day preceding the first measurement with 99.5% pure calibrated gases supplied by Air Liquide Company. Vehicle speed was recorded during the trip with a precision of 0.1 km/hr using a calibrated Doppler speed sensor DRS-6/laa supplied by BS2 Multidata GmbH. Electricity was provided to analyzers by a power generator unit (2.2 kVA) and a 12-V portable battery (200 Ah) supplied continuous current to mini-CVS. To avoid any influence on the engine load, no electric cable was connected to the vehicle battery. Tests were conducted with all material on-board for final calibration (1) to find the ranges of instantaneous emissions, (2) to check the stability of different flows of gas circuit on-road in real traffic, and (3) to check the analyzer's stability by the injection of calibrated gases. The total load of the equipment and accessories aboard the vehicle was 460 kg.
Emission Factor Calculation
The mass of pollutant emitted during one trip is the mass of pollutant measured in the diluted gas minus the mass of pollutant brought in the air dilution picked from the ambient air (eq 2).
[M.sub.e.sup.i] = 112([M.sub.d.sup.i] - [M.sub.a.sup.i]) (2)
[M.sub.e.sup.i] is the total mass of gas pollutant i emitted by the engine, [M.sub.d.sup.i] is the mass of pollutant i measured in diluted gas volume, and [M.sub.a.sup.i] is the mass of pollutant i in the dilution air.
The concentration of each pollutant in the diluted gas and in dilution air were measured, all sampled gas volumes were corrected regarding temperature in the mini-CVS chamber and normal temperature. The mass of pollutant emitted was calculated for each trip using eq 3, considering the dilution factor and the number of tubes (112) to obtain the total mass emitted for each test. Then the emission factor was obtained by dividing the total mass by the distance traveled in g/km for each trip.
[M.sub.e.sup.i] = 112[[rho].sub.0.sup.i] [[T.sub.0]/[T.sub.d]] [V.sub.d][[C.sub.d.sup.i] - [C.sub.a.sup.i](1 - 1/DF)] (3)
where [C.sub.d.sup.i] (ppm) is the concentration of pollutant i in the diluted gas, [C.sub.a.sup.i] (ppm) is the concentration of pollutant i in the dilution air, [V.sub.d] ([m.sup.3]) is the total volume of diluted gas sample, [T.sub.o] (Kelvin) is the normal temperature, [T.sub.d] (Kelvin) is the temperature of diluted gas, [[rho].sub.o] (g/[m.sup.3]) is the i pollutant density at normal temperature and pressure, and DF is the dilution factor.
For each test conducted, air dilution was sampled on board in a Tedlar bag of 70 L and C[O.sub.2], CO, and THC were analyzed immediately after the end of the trip. DF was calculated for each instantaneous measurement considering the ratio of concentrations of equivalent carbon before and after dilution. It was assumed that the engine runs with a stoichiometric air to fuel ratio (r = 1); C[O.sub.2] content in exhaust gases was then 13.4% for a gasoline engine. The average concentration of pollutants in dilution air for each test was used according to eq 4. DF for all tests varied from 15 to 25.
[FIGURE 2 OMITTED]
DF = 13.4/(C[O.sub.2d] + (TH[C.sub.d] + C[O.sub.d])[10.sup.-4]) (4)
where C[O.sub.2d] (%), TH[C.sub.d] (ppm), and C[O.sub.d] (ppm) are concentrations of emitted pollutant of the diluted gas.
Vehicle Sample
A sample of eight LDVs, less than 1.2 t, of category NI-1, were selected within the private Algerian running fleet, including two gasoline vehicles of 1.4 L and six diesel vehicles between 1.6 and 1.9 L. The two vehicles from 1993 and 1996 underwent repairs of their engine by their owner just before the measurement campaign. The two gasoline vehicles are rather old because the new LDVs are rarely powered by gasoline and few are put on the market; there has been a strong tendency toward their dieselization during the last decade. This is due to the low cost of diesel fuel of 13.70 Algerian dinars (DA)/L (U.S. $0.19/L) compared with gasoline, which costs 23 DA/L (U.S. $0.32/L). The size of our vehicle sample is comparable with similar studies carried out in Europe, whose synthesis was made by the European ARTEMIS project. ARTEMIS mainly considered six research studies conducted in six European laboratories, gathering an emission database from 27 LDVs from category NI-1. (40,51) The vehicle sample size per laboratory was only around 3-11. However, Joumard et al. (52) observed that the minimum vehicle sample size to build-up a representative model of average emissions is 10 vehicles. The global load of 460 kg including the driver corresponds to loads of 60 and 49% respectively for the tested gasoline and diesel vehicles. These loads are relatively high compared with the published literature of emission measurements.
There is no exhaust emission homologation procedure for new vehicles sold in Algeria. Because there are no regulations to comply with any kind of standards, vehicle suppliers do not reveal the standards (car manufacturers currently escape from this question and do not reveal this information). This raises a real problem for any emission evaluation or data comparison. The only available reference is the year of setting in traffic, which does not give any information related to the vehicle standard. In any case, gasoline tested vehicles are not equipped with three-way catalysts and diesel vehicles are not equipped with oxidation catalysts or particle filters.
Measurement Campaign
The measurement campaign occurred in Blida between September and November 2005. The Wilaya of Blida accounts for 780,000 inhabitants and is located 50 km south of the capital, Algiers. The car fleet of Blida is the second most important in the country after that of Algiers, with 6.4% of the national fleet and 7.7% of the LDVs. (49) Blida constitutes an important agricultural, commercial, and industrial zone. It is also a crossing area from north to south and from east to west. The topography of the city presents an average slope of 1.5%. The route selection is based on more than 1000 km of recorded kinematics carried out by a shadowed vehicle that is surrounded by city traffic flow for 6 months. (53) The route length of 6.4 km represents arteries and streets existing in Blida and local urban environment and traffic. Moreover, each vehicle is also tested on suburban roads and highways where the speed limit is 80 km/hr on a trip length up to 15 km. Each vehicle submitted from 5 to 13 urban tests at the same period of the day, which gives a total number of 55 urban tests for all the measurements corresponding to more than 480 km (Table 1). Van Ruymbeke (16) concluded that five tests are the minimum required to obtain representative data for the emissions of a vehicle with a 10% tolerance.
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