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Short communication

Impact of altitude on fuel consumption of a gasoline passenger car

Efthimios Zervas

School of Science and Technology, Hellenic Open University, Riga Feraiou 167, 26222 Patra, Greece

a r t i c l e i n f o

Article history:

Received 5 October 2009

Received in revised form 12 November 2010Accepted 3 February 2011

Available online 17 February 2011

Keywords:

Altitude

Fuel consumption

Gasoline

Passenger cars

Aerodynamics

a b s t r a c t

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 the-oretically leads to lower fuel consumption due to lower throttle frictions due to the wider throttle open-

ing. 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, on three regulated driving cycles, the

impact of high altitude on the fuel consumption of a gasoline passenger car. The impact of changed vehi-

cle aerodynamics of higher altitudes, through the change of deceleration times, on fuel consumption is

also analyzed.

2011 Elsevier Ltd. All rights reserved.

1. Introduction

Engines of new passenger cars are tuned to operate with the

lowest possible fuel consumption having the same time the high-

est output power and torque and respecting the regulations for ex-

haust 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 le-

vel. This has a significant impact on the local atmosphere quality

of many cities, as for example Mexico City which is found at an alti-

tude of 2200 m 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 en-

gine is less evident. From the other side, as the air is less dense

at higher altitudes, the vehicle aerodynamic is changed. For thisreason 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 con-

sumption 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 mea-

sured here and the fuel consumption of the higher altitude is

analyzed.

2. Experimental section

A Renault Clio equipped with a Euro3 gasoline engine of

1400 cm3 was used for these tests. The inertia of this vehicle is

2250 lbs and its SCx of 0.685. Two kinds of tests were performed

for the fuel consumption measurements: onealmost at the sealevel

(altitude of 70 m) and one atan altitude of 2200 m which is the alti-

tude of Mexico City. The above tests were performed using an alti-

metric test bench located at an altitude of 70 m. This altimetric test

bench has the ability to decrease atmospheric pressure to simulate

high altitude. 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 driving cycle. Fig. 1 shows

the driving profiles of those cycles andTable 1shows their main

characteristics. More details about the above driving cycles can be

found elsewhere[3]. The deceleration times were also measured

at the altitude of 70 m, but due to technical reasons, it was not pos-

sible to measure them at Mexico City altitude level (2200 m). Forthese reason, the deceleration times were measured at the altimet-

ric vehicle test bench, using the altitude of 700 m. Every test is re-

peated three times and average values are used. All tests used

here are validatedafter theprinciple that thecar/driver must follow

the driving profile with a difference less than 1 km/h.

3. Results and discussion

3.1. Driving cycle results

Fig. 2 shows the CO2 emissions on the three driving cycles

tested at the sea level altitude (70 m) and the altitude of 2200 m,

0016-2361/$ - see front matter 2011 Elsevier Ltd. All rights reserved.doi:10.1016/j.fuel.2011.02.004

Tel.: +30 2610 367 566.

E-mail address:zervas@eap.gr

Fuel 90 (2011) 23402342

Contents lists available at ScienceDirect

Fuel

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / f u e l

http://dx.doi.org/10.1016/j.fuel.2011.02.004mailto:zervas@eap.grhttp://dx.doi.org/10.1016/j.fuel.2011.02.004http://www.sciencedirect.com/science/journal/00162361http://www.elsevier.com/locate/fuelhttp://www.elsevier.com/locate/fuelhttp://www.sciencedirect.com/science/journal/00162361http://dx.doi.org/10.1016/j.fuel.2011.02.004mailto:zervas@eap.grhttp://dx.doi.org/10.1016/j.fuel.2011.02.004

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which corresponds to the altitude of Mexico City. This figure showsthat there is a decrease of 3.5% in the case of NEDC, when the vehi-

cle is used at the altitude of 2200 m instead of the sea level alti-

tude. However, this trend is not confirmed from the two US

cycles. The decrease on the FTP driving cycle on the 2200 m com-

paring 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. It must be noticed that the

repeatability of the tests is very high as the standard deviation is

less than 2.5% in the worst case. We cannot find an obvious reason

why the results of Highway driving cycle are opposite to the other

two driving cycles and no other researcher worked on this subject.

The only reason can be the higher average speed of this cycle.

The above results show that the impact of higher altitude thanthat of sea level on fuel consumption is not evident and there is not

always a decrease of fuel consumption according to theory. Fig. 2shows that the impact of the driving cycle used, and consequently

of the driving profile used, on fuel consumption is quite significant.

3.2. Deceleration tests results

As shown before, the lower air density at higher altitude

changes aerodynamics of the vehicle and thus changes the deceler-

ation times. Due to technical reasons, the measure of deceleration

times was not possible at the altitude of 2200 m above sea level.

These times were measured in the altimetric vehicle test bench

using an altitude of 700 m. Fig. 3 shows the difference between

the deceleration times as a function of the vehicle speed for the

two altitudes of 70 and 700 m. This figure shows that there is a sig-nificant difference on deceleration times between the two alti-

tudes. Our results are according to theory, as the altitude of

700 m has higher deceleration times. This difference depends on

vehicle speed: it is quite small at low speeds (less than 1%), but in-

creases significantly with speed to reach 6% at the speed of

120 km/h.

Time (s)

0

40

80

12

Speed(km/h)

ECE

EUDCNEDC

Time (s)

0

20

40

60

80

100

Speed(km/h)

FTP-75

Phase-1 Phase-2 Phase-3

0 400 800 1200

0 500 1000 1500 2000 2500

0 200 400 600 800

Time (s)

0

20

40

60

80

100

Speed(km/h)

Highway

Fig. 1. The three driving cycles used in this study.

Table 1

Some characteristics of the three driving cycles used in this study.

D uration ( s) Dist ance

(km)

Max speed

(km/h)

Average speed

(km/h)

NEDC 1180 11.07 120 33.6

ECE 780 4.052

EUDC 300 6.955

FTP-75 2477 (with stop) 17.86 91.2 34.2 (without stop)

Phase-1 505 5.8

Phase-2 867 6.3

Highway 765 16.5 96.4 77.4

NEDC FTP Highway

0

40

80

120

CO2emissio

ns(g/km)

70m

2200m

Fig. 2. CO2emissions on the three driving cycles tested at the sea level altitude and

at the altitude of 2200 m. Error bars correspond to one standard deviation.

0 40 80 120

Vehicle speed (km/h)

-8

-6

-4

-2

0

Diff.onthedeceleration

time(%)

Fig. 3. Difference of the deceleration times between the sea level altitude and thealtitude of 700 m.

E. Zervas/ Fuel 90 (2011) 23402342 2341

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The deceleration times of the altitude of 700 m were used on

the vehicle test bench to measure CO2 emissions on the NEDC.

Fig. 4 shows the fuel consumption (expressed as CO2 emissions)

of the two altitudes using the deceleration times of the altitude

of 700 m. The NEDC on the sea level emits 126.7 g of CO2/km, while

the altitude of 700 m gives an emission rate of 124.85 g of CO 2/km.

This difference is about 1.5%. It is evident that this gain will be

higher at the altitude of 2200 m above sea level.

4. Conclusions

This work studies the impact of high altitude on the fuel con-

sumption of a gasoline passenger car on three regulated driving cy-

cles. Even if there is a gain on fuel consumption of 3.5% in the caseof NEDC in the case of higher altitude, other regulated driving cy-

cles do not show the same tendencies. The gain on the FTP is only

2.6% on the 2200 m, 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 700 m increases deceleration times of the vehi-

cle. This increase is a function of speed and can reach up to 6% at

the speed of 120 km/h, leading to a decrease in fuel consumption

on the NEDC of about 1.5%.

References

[1] Schifter I, Daz L, Lpez-Salinas E, Ramos F, Avalos S, Lpez-Vidal G, et al.Estimation of motor vehicle toxic emissions in the metropolitan area of MexicoCity. Environ Sci Technol 2000;34(17):360610.

[2] Gamas ED, Diaz L, Rodriguez R, Lpez-Salinas E, Schifter I, Ontiveros L. Exhaustemissions from gasoline- and LPG-powered vehicles operating at the altitude ofMexico City. J Air Waste Manage Assoc 1999;49(10):117989.

[3] Zervas E, Bikas G. Impact of the driving cycle on the NOx and PM exhaustemissions of diesel passenger cars. Energy Fuels 2008;22(3):170713.

Altitude

110

115

120

125

130

CO2emissio

ns(g/km)

70m

2200m

Fig. 4. CO2emissions on NEDC at the sea level altitude and at the altitude of 700 m

for the two different deceleration times.

2342 E. Zervas / Fuel 90 (2011) 23402342