Impact of altitude on the fuel consumption of a gasoline passenger car

Transcription

1 Impact of altitude on the fuel consumption of a gasoline passenger car EFTHIMIOS ZERVAS* Department of Environmental Engineering Democritus University of Thrace Vas. Sofias 12, 671 Xanthi GREECE ezervas@env.duth.gr Abstract: - Engines of new passenger cars are tuned at the sea level. However, in several countries, a significant part of the engine operation is performed at higher altitudes than that of the sea level. The different air density can have a significant impact on fuel consumption. In the case of gasoline engines, the higher altitude theoretically leads to lower fuel consumption due to lower throttle frictions due to the wider throttle opening. From the other side, as the air is less dense at higher altitudes, the vehicle aerodynamic is changed and this also leads to lower fuel consumption. This work studies the impact of high altitude on the fuel consumption of a gasoline passenger car. The impact of higher altitude is studied on three regulated driving cycles. The impact of changed vehicle aerodynamics of higher altitudes, through the change of deceleration times, on fuel consumption is also estimated. Key-Words: - Altitude, fuel consumption, gasoline, passenger cars 1 Introduction Engines of new passenger cars are tuned to operate with the lowest possible fuel consumption having the same time the highest output power and torque and respecting the regulations for exhaust emissions. This engine tuning is usually performed at the sea level. However, in several countries, a significant part of the engine operation is performed at higher altitudes than that of the sea level. This has a significant impact on the local atmosphere quality of many cities, as for example Mexico City which is found at an altitude of 22m above sea level, and on fuel consumption. Some authors study the impact of altitude on exhaust emissions [1, 2]; however no work studies the impact on fuel consumption. In the case of gasoline engines, the lower density of air at higher altitude leads theoretically to a decrease of fuel consumption due to the lower negative loop of engine operation due to the decreased frictions due to the wider throttle opening. The case of Diesel engine is less evident. From the other side, as the air is less dense at higher altitudes, the vehicle aerodynamic is changed. For this reason the deceleration times of the vehicle increase and that have also an impact on fuel consumption. This work studies the impact of high altitude on the fuel consumption of a gasoline passenger car. The impact of higher altitude is studied on three regulated driving cycles. Also, the change of aerodynamics through the change of deceleration times is measured here and the fuel consumption of the higher altitude is estimated. 2 Experimental section A Renault Clio equipped with a Euro3 gasoline engine of 14 cm 3 was used for these tests. The inertia of this vehicle is 225 lbs and its SCx of.685. Two kind of testes were performed for the fuel consumption measurements: one almost at the sea level (altitude of 7m) and one at an altitude of 22m which is the altitude of Mexico City. A commercial Euro3 fuels was used for these tests. The above tests were performed on three regulated driving cycles: the New European Driving Cycle (NEDC) and two driving cycles from USA, the FTP and the Highway one. Figures 1-3 show the profiles of those driving cycles. More details about those driving cycles can be found elsewhere [3]. The deceleration times were also measured at the altitude of 7m, but due to technical reasons, it was not possible to measure them at Mexico City. For these reason, the deceleration times were measured at an altimetric vehicle test bench, using the altitude of 7m. ISSN: ISBN:

2 Max. speed = 12 km/h Average speed = 33.6 km/h Duration = 1 18 s Distance = 11.7 km 1st part: urban (ECE): 4,52 km Elementary urban cycle NEDC Cycle 2nd part: extra-urban (EUDC): 6,955 km Fig 1. The New European Driving Cycle (NEDC) Phase 1: 55 s (5,8 km) Cold phase Phase 2: 866 s (6,3 km) Steady phase FTP 72 or LA4 cycle Cycle City or FTP 75 Engine stop closed hood 1 ± 1 min Max. speed = 91.2 km/h Average speed = 34.2 km/h (stop excluded) Duration = s (stop included) Distance = km Weighting factors: Phase 1 :,43 Phase 2 : 1, Phase 3 :,57 Phase 3: 55 s (5.8 km) Warm phase Fig 2. The FTP driving cycle. ISSN: ISBN:

3 12 1 Highway Cycle Max. speed = 96.4 km/h Average speed = 77.4 km/h Duration = 765 s Distance = 16.5 km Fig3. The Highway driving cycle. 3 Results and discussion 3.1 Driving cycle results Figure 4 shows the CO 2 emissions on the three driving cycles tested at the sea level altitude (7m) and the altitude of 22m, which corresponds to the altitude of Mexico City. Figure 4 shows that there is a gain of 3.5% in the case of NEDC, when the vehicle is used at the altitude of 22m instead of the seal level altitude. However, this trend is not confirmed from the two US cycles. The gain on the FTP driving cycle on the 22m comparing to the sea level altitude is lower than that of NEDC: only 2.6%, while the Highway driving cycle shows the opposite trend: an increase of 6.2% of fuel consumption at the altitude of Mexico City comparing to the sea level one. The above results show that the impact of higher altitude than that of sea level on fuel consumption is not evident and there is not always a decrease of fuel consumption according to theory. The impact of the driving cycle used, and consequently of the driving profile used, on fuel consumption is quite significant. More work is necessary to clarify this change. Our future, more detailed, work includes tests on each engine operating point and also on several transition points to analyze the impact of altitude on the complete engine operation cartography. CO 2 emissions (g/km) m 22m NEDC FTP Highway Fig4. CO 2 emissions on the three driving cycles tested at the sea level altitude and at the altitude of 22m. 3.2 Deceleration tests results As shown before, the lower air density at higher altitude changes aerodynamics of the vehicle and thus changes the deceleration times. Due to technical reasons, the measure of deceleration times was not possible at the altitude of ISSN: ISBN:

4 22m above sea level. These times were measured in an altimetric vehicle test bench at an altitude of 7m. Figure 5 shows the deceleration times as a function of the vehicle speed for the two altitudes of 7 and 7m and figure 6 the difference between these times. These figures show that there is a significant difference on deceleration times between the two altitudes. This difference depends on vehicle speed: it is quite small at low speeds (less than 1%), but increases significantly with speed to reach 6% at the speed of 12 km/h. Deceleration time (s) m 7m Vehicle speed (km/h) Fig5. Deceleration times at the sea level altitude and at the altitude of 7m. Diff. on the deceleration time (%) Vehicle speed (km/h) Fig6. Difference of the deceleration times between the sea level altitude and the altitude of 7m. The deceleration times of the altitude of 7m were used on the vehicle test bench and a new NEDC is performed. Figure 7 shows the fuel consumption (expressed as CO 2 emissions) of the two altitudes. The NEDC on the sea level emits g of CO 2 /km, while the altitude of 7m gives an emission rate of g of CO 2 /km. This difference is about 1.5%. It is evident that this gain will be higher a the altitude of 22m above sea level. CO 2 emissions (g/km) m 22m Altitude Fig7. CO 2 emissions on NEDC at the sea level altitude and at the altitude of 7m for the two different deceleration times. 4 Conclusion This work studies the impact of high altitude on the fuel consumption of a gasoline passenger car. The impact of higher altitude is studied on three regulated driving cycles. Also, the deceleration times are measured and the fuel consumption of the higher altitude is estimated. Even if there is a gain on fuel consumption of 3.5% in the case of NEDC in the case of higher altitude, other regulated driving cycles do not show the same tendencies. The gain on the FTP is only 2.6% on the 22m, while the Highway driving cycle shows the opposite trend: an increase of 6.2% of fuel consumption. The above results show that the impact of higher altitude is not evident and there is not always a decrease on fuel consumption and more work is necessary to clarify the impact of higher altitude. From the other hand, an altitude of 7m decreases deceleration times of the vehicle. This decrease is a function of speed and can reach up to 6% at the speed of 12 km/h, leading to a decrease in fuel consumption on the NEDC of about 1.5%. References: [1] Schifter I., Díaz L., López-Salinas E., Ramos F., Avalos S., López-Vidal G., and Castillo M., Estimation of Motor Vehicle Toxic Emissions in the ISSN: ISBN:

5 Metropolitan Area of Mexico City, Environonmental Science and Technology, 34 (17), 2, pp [2] Gamas, E.D., Diaz, L., Rodriguez, R., López- Salinas, E., Schifter, I., Ontiveros, L., Exhaust emissions from gasoline- and LPG-powered vehicles operating at the altitude of Mexico City, Journal of the Air and Waste Management Association, 49 (1), 1999, pp [3] Zervas E., Bikas G. (28), Impact of the driving cycle on the NOx and PM exhaust emissions of Diesel passenger cars, Energy and Fuels, 22 (3); ISSN: ISBN: