Content uploaded by Fanourios E. Zannikos
Author content
All content in this area was uploaded by Fanourios E. Zannikos
Content may be subject to copyright.
Proceedings of the 10th International Conference on Environmental Science and Technology
Kos island, Greece, 5 – 7 September 2007
A-1497
IMPACT OF DRIVING STYLE ON FUEL CONSUMPTION AND EXHAUST
EMISSIONS: DEFENSIVE AND AGGRESSIVE DRIVING STYLE
E. TZIRAKIS, F. ZANNIKOS and S. STOURNAS
Laboratory of Fuels and Lubricants Technology, School of Chemical Engineering,
National Technical University of Athens, Iroon Polytechniou 9 15773 Zografou Athens.
E-mail: vtziraks@central.ntua.gr
EXTENDED ABSTRACT
In the present work two different driving styles defensive and aggressive where adopted
with the aim to compare fuel consumption and exhaust emission. 12 passenger cars of
different categories were used for this work, of which 10 were petrol powered and 2 were
diesel powered. The vehicles varied on age, mileage, size, engine displacement and
technology.
Emission measurements where conducted on real driving conditions with the aid of
portable on-board emission analyzer. At the same time, the driving characteristics as well
as the exact position of the vehicle where recorded using modern electronic equipment.
The test field was a closed cyclic route infrastructure. The route is characterized by
altitude differentiations and traffic calming measures (humps) which result in a special
and repeatable speed profile, different from that of the usual driving, with frequent
accelerations and decelerations. The speed profile of the defensive driving style was
aimed to be kept the same for all vehicles in order to be characterized by a common
driving cycle. The average speed of the profile is 27.71 and the duration the complete
cycle is 392s. The target average acceleration that the vehicles had to accomplish is
0.638ms-2. In order to be precise the cycle vehicles were driven several times according
to the defensive driving. The acceleration for the aggressive style was depending on the
vehicle’s performance as the throttle accelerator was fully pressed between the humps,
resulting on different speed profiles for each vehicle. When driving defensively, a specific
driving profile had to be followed. For aggressive driving, drivers were free to step on the
accelerator at free will.
The composition of the exhaust emissions varied greatly depending on the driving style.
Those variations were becoming larger when emissions were transformed in terms of
g/km in a degree that is difficult to plot on a normal scale graph. Mainly due to the
technology, the mileage and the mass/performance ratio as well as the drivers’ mood, the
differences were very large or smaller. More specifically, in terms of g/km, the biggest
increases when driving aggressively were observed on newer petrol vehicles’ carbon
monoxide (CO), unburned hydrocarbon (HC) and nitrogen oxides (NOx) emissions.
Carbon dioxide (CO2) showed the smallest increase. The composition of emissions was
changing greatly. For petrol vehicles, CO2 was mainly decreased, while the emitted
pollutants (CO, HC, NOx) were dramatically increased. NOx and CO2 emissions in diesel
vehicles were increased. The differences on HC and CO were of minor importance
compared to CO2 and NOx. The increase of fuel consumption due to aggressive driving
compared to defensive driving, varied from 78.5% to 137.3% for petrol vehicles and from
116.3% to 128.3% for diesel vehicles.
Keywords: Economy, consumption, emissions, driving cycles, defensive driving style,
aggressive driving style.
A-1498
1. INTRODUCTION
Emissions from vehicles constitute the main source of air pollution in the Attica Basin.
The rapid increase of the passenger car fleet as well as the problematic traffic conditions
in modern cities cause a composite movement of the vehicles resulting on driving profiles
consisting of a complicated series of accelerations, decelerations and frequent stops.
Those driving characteristics are responsible for increased fuel consumption and exhaust
emissions and limited efficiency of emission control systems in vehicles. Additionally,
when driving becomes more aggressive with more vigorous accelerations and
decelerations the efficiency of the emission control systems is further reduced, resulting
on excessive surcharge of atmosphere in pollutants.
In modern cities with wide boulevards the aggressive driving style is a common practice.
It seems that a significant amount of excessive emissions that are released in the
atmosphere of the city, which could be avoided, is due to that style of driving.
Driving styles can be categorized according to the age or the sex of the driver, the traffic
conditions, the driver’s mood or even the vehicle type. However, there are four major
categories of driving styles with significant differences between them as far as driving
dynamics, vehicle operation, fuel economy and exhaust emissions are concerned [1]. The
first one is the defensive driving style which can be considered as a reference driving
style for the comparison of other three. There two styles targeting fuel economy; the “egg
style” driving which is characterized by very slow acceleration and the economy driving
style which is also called “new style driving” and which combines defensive driving with a
special way of accelerating and shifting gears [2]. Finally the aggressive style is
characterized by vigorous accelerations and decelerations with high power demand from
the vehicle’s engine, resulting on the exact environmental opposite of the other three
styles.
Previous studies have shown the impact of aggressive driving on exhaust emissions
using vehicles that were driven on chassis dynamometers according to selected driving
cycles [2]. In the present study, the first approach on “on-board” emissions measurement
on real driving conditions showed even greater differences on emissions according to
defensive and aggressive driving styles as well as between different vehicle technologies.
2. METHODOLOGY
2.1. Vehicles used
12 passenger cars of different categories were used for this work, of which 10 were petrol
powered and 2 were diesel powered. The vehicles varied on age, mileage, size, engine
displacement and technology (from Euro1 to Euro5). This was appropriate in order to
correlate the impact of aggressive driving on emissions and fuel consumption on vehicles
of different characteristics.
All vehicles were using unleaded gasoline 95 RON and retail automotive diesel. All fuels
were checked in order to ensure that they comply with the European specification limits.
The differences in their characteristics were negligible.
Table 1 shows the characteristics of the vehicles used and the maximum acceleration
and speed that were accomplished during the aggressive driving.
A-1499
Table 1: Characteristics of the vehicles used.
Vehicle
Displace-
ment
(L)
Intake Technology Mileage
(km)
Weight
(kg)
Max acc.
(m/s2)
Max speed
(km/h)
Nissan
Primera 1,6 Electronic carburetor 225000 1080 0,318 81,30
Peugeot
307 Xsi 1,6 Electronic multipoint
indirect fuel injection 75000 1175 0,314 74,39
VW Golf
FSi 1,6 Electronic multipoint
direct fuel injection 700 1184 0,317 80,67
Peugeot
206 1,4 Electronic multipoint
indirect fuel injection 65400 950 0,287 79,52
Alfa
Romeo
145 1,6 Electronic multipoint
indirect fuel injection 70300 1165 0,316 79,45
Seat
Ibiza 1,4 Electronic multipoint
indirect fuel injection 45000 1050 0,319 83,91
Mazda 2 1,6 Electronic multipoint
indirect fuel injection 22600 1155 0,360 87,13
Mazda 3 1,6 Electronic multipoint
indirect fuel injection 7300 1165 0,333 86,77
Mazda 6 2,0 Electronic multipoint
indirect fuel injection 17800 1375 0,341 87,04
Mazda
Tribute 2,3 Electronic multipoint
indirect fuel injection 27000 1595 0,295 85,17
Audi A2
TDi 1,4 Electronic multipoint
direct fuel injection 15000 1320 0,351 76,22
Seat
Altea TDi 2,0 Electronic multipoint
direct fuel injection 22700 1430 0,551 97,60
2.2. Equipment
The equipment that was used to monitor vehicles exhaust emissions was comprised of a
portable emission analyser (Table 2) and a laptop computer. Exhaust emissions
composition was recorded every 2 seconds which is the maximum resolution of the
analyser.
Figure 1: An instrumented vehicle.
A-1500
Vehicle driving characteristics were recorded using modern electronic equipment that
combines a powerful Global Positioning System engine and a CAN Bus decoder. The
characteristics recorded were the following:
• Position in the route infrastructure (GPS)
• Vehicle speed (CAN Bus)
• RPM (CAN Bus)
• Throttle position (CAN Bus)
The purpose of recording the driving characteristics was to ensure the correct driving of
the defensive driving style.
Table 2: Specifications of the portable exhaust emission analyser.
TEI Inc.
NOx Analyzer KANE Auto 5-1-NOx, CO, HC, CO2 and O2
Analyzer
Emission NOx NOx HC CO CO2
Method Chemi-
luminescence Fuel cell Infrared Infrared Infrared
Operation Range 0-5000 0-5000 0-5000 0-10% 0-16%
Accuracy 0.050 ±5% ±5% ±5% ±5%
Repeat-ability ±1%
The portable analyzer was able to measure and log a number of emissions ingredients.
The pollutants, Carbon Monoxide (CO), Unburned Hydrocarbons (HC) and Nitrogen
monoxide (NO), the Carbon Dioxide (CO2), Oxygen content (O2) and λ.
2.2. Driving route and instructions to drivers
The driving route infrastructure includes altitude differentiation, humps, and various
alternations on driving conditions, such as frequent accelerations and decelerations.
The downhill driving of the route accounts to 2332 metres and only of 668 metres was
uphill driving. However, the steepest upward slope was 12.99 % and the steepest
downward 6.8 %.
Figure 2: The target driving speed profile for the defensive driving style with the altitude
as recorded from the GPS.
The defensive driving pattern is common for all the test vehicles. Drivers were given
specific instructions on this matter. When driving defensively they had to follow a specific
driving profile and finish the cycle within a specific time bracket. The target speed profiled
is illustrated on figure 2 and its basic characteristics on table 3. The speed limit within the
campus is 40 km/h. The vehicle accelerates from the starting point to 30 km/h before it
reaches the first hump which overtakes with 15 km/h. The top speed between the humps
A-1501
should not exceed the designated speed limit. 1st to 2nd gear change is done at 25 km/h
and 2nd to 3rd at 35 km/h or at 2500 rpm. Between specific humps the speed was kept to
25 km/h or 30 km/h due to either uphill driving or the small distance between the humps.
This driving cycle was developed for fuel comparison tests [3], as the driving conditions
were stable enough (i.e. no heavy traffic, traffic lights, etc). This real-world driving cycle is
characterized by frequent accelerations and decelerations and low driving speeds due to
the humps. Its characteristics (Table 3) represent urban driving conditions therefore it can
be considered as an urban driving cycle [4], [5]. In order to accomplish accurate results
for the defensive driving style each vehicle was driven around the peripheral route
several times (by the same driver), where its driving characteristics were monitored. The
measurements for every vehicle during defensive driving were completed until five test
runs were within the specification limits set for the target profile of the driving cycle
(duration ±5 s, average velocity of the cycle ± 0.5 km/h). The emission results were then
further analysed in order to keep the most representative.
Table 3: Basic characteristics of the defensive driving pattern.
Duration (s) 392
Distance (km) 3.01
Average Speed (km/h) 27.71
Maximum Speed (km/h) 39.04
Average Positive Acceleration (m/s) 0.638
Figure 3: Gear position throughout the defensive driving profile.
As far as the aggressive driving style is concerned, the drivers were advised to step on
the throttle accelerator at free will. Most of the drivers were pressing throttle progressively
to the end of its stroke. Aggressive runs were only performed twice per test vehicle as it
was very hard for the vehicles due to the vigorous braking before every hump of the
route.
Figure 4: Comparison of a defensive speed profile with an aggressive one.
A-1502
3. RESULTS
Figures 5 to 9 illustrate the emitted pollutants of CO (in %vol), NO (in ppm) and HC (in
ppm), the CO2 emissions (in %vol) and the fuel consumption (in L/100km) for both driving
styles performed and for all the vehicles used. CO emissions were increased for all
vehicles tested except the AR 145. The diesel vehicles emitted very low levels of the
specific pollutant in both driving styles. The Nissan, which is the oldest of the fleet,
emitted the most of all vehicles. It also appeared to have the largest increase between
the two driving styles.
Figure 5: CO Emissions for both driving styles and for all vehicles tested.
Figure 6: HC Emissions for both driving styles and for all vehicles tested.
Figure 7: NO Emissions for both driving styles and for all vehicles tested.
A-1503
Figure 8: CO2 Emissions for both driving styles and for all vehicles tested.
Figure 9: Fuel consumption for both driving styles and for all vehicles tested.
Table 4: Emissions (in g/km) and fuel consumption for both driving styles and for both
vehicles.
Defensive driving style Aggressive driving style
FC CO CO2 HC NO FC CO CO2 HC NO
Primera 9,1 9,7512 236,035 0,2696 0,6123 18,4 71,2292 384,29 4,4698 0,5626
307 Xsi 9,4 0,2942 258,324 0,0514 0,0648 17 7,7983 445,51 0,2010 0,7515
Golf FSi 9,3 0,0030 240,201 0,0127 0,2110 19 7,2199 421,74 0,0608 0,1813
206 8,6 0,0010 231,343 0,0457 0,3169 17,8 0,3092 473,04 0,1300 3,0888
AR 145 9,4 7,2261 243,773 0,2912 0,0125 19 11,9576 473,90 1,1902 0,5903
Ibiza 9,3 0,0247 264,530 0,0149 0,0357 16,6 12,8374 414,34 0,1255 0,4149
M2 8,7 0,1384 250,507 0,0589 0,0276 17,1 20,6775 427,23 0,4119 0,1638
M3 8,8 0,1892 240,754 0,1376 0,0100 17,6 11,7173 461,18 0,3919 0,1339
M6 10,2 0,1902 319,972 0,0413 0,0088 24,2 44,2498 470,46 0,1365 0,0270
Tribute 11,8 0,0102 262,218 0,1349 0,0081 23,9 4,2213 475,44 0,8080 0,0769
A2 TDi 6 0,0055 113,755 0 0,5430 13,7 0,0286 438,02 1,2241 3,2641
Altea TDi 8,6 0,0039 338,787 0 0,3279 18,6 2,1986 736,94 0 3,0443
The differences between the two driving styles as far as emissions are concerned, can be
observed on Table 4 where emissions are expressed in g/km.
A-1504
HC emissions appeared to have the same behavior as the CO emissions. In this
occasion all vehicles increased their emissions during the aggressive driving cycle. NO
emissions were also increased during aggressive driving with the exception of two
vehicles, the oldest Primera and the newest Golf. No significant difference was observed
on CO2 emissions as far as %vol measurement is concerned. The converted in g/km CO2
emissions are higher for the aggressive style due to fuel consumption increase. The
increase of fuel consumption due to aggressive driving compared to defensive driving,
varied from 78.5% to 137.3% for petrol vehicles and from 116.3% to 128.3% for diesel
vehicles.
4. CONCLUSIONS
This research was conducted in order to compare the exhaust emissions derived from
two different driving styles. It is more than obvious that the aggressive driving style is
environmental opposite of the defensive driving style. Vehicles of low mileage and of
latest technology emit relatively low levels for both driving styles. The difference between
the styles is also smaller than the vehicle of 60000 kilometers or more. More specifically
Primera, which is the oldest in technology and mileage, emits the largest quantities of
pollutants than the newest vehicles (technology and mileage) the Mazdas and the VW
Golf. Nissan’s strange behavior for NO emissions maybe due to the catalytic converter
which is “two way” catalyst and does not reduce the specific pollutant.
Engine technology and vehicle weight affects exhaust emissions more than the fuel
physicochemical properties due to EPEFE research [6]. This seems to be strengthened
when driving becomes aggressive. The differences from vehicle to vehicle are too large
to be justified by the fuel quality.
The great increase of exhaust emissions due to aggressive driving style must sensitize
the communities and the governments to inform the drivers on the extra pollution caused
by aggressive driving. Although the increase on fuel consumption is obvious for the
driver’s wallet, the impact on city air quality is an unknown quantity. Instructions from the
government should be provided to the drivers for a more efficient and environmental
driving style.
REFERENCES
1. Gense, N.L.J. (2000), ‘Driving Style, Fuel Consumption and Tail Pipe Emissions’, TNO
Automotive, March, Delft.
2. OECD, (2004), ‘Can Cars Come Clean? – Strategies for Low-Emission Vehicles’, OECD
Publications, 2, rue Andre Pascal, 75775 Paris Cedex 16, ISBN-92-64-10495-X
3. Karavalakis G., Tzirakis E., Stournas S., Zannikos F., Karonis D. (2006) ‘Emissions
measurement in a diesel vehicle operated with diesel/biodiesel blends on a specific driving
cycle’ 2nd conf. Environment & Transport incl. 15th Transport and Air Pollution, Reims France
12-14 June 2006, proceedings no 107 Vol. 2 Inrets ed., Arcuei, France 2006, p. 156-161
4. Pelkmans L., Debal P. (2006), ‘Comparison of On-Road Emission with Emissions Measured
on Chassis Dynamometer Test Cycles’ Transportation Research Part D, Transport and
Environment, Volume 11, Issue 4, July 2006, Pages 233-241
5. Tzirakis E., Pitsas K., Zannikos F., Stournas S. (2006) ‘Vehicle Emissions and Driving Cycles:
Comparison of the Athens Driving Cycle (ADC) with ECE-15 and European Driving Cycle
(EDC)’ Global NEST Journal, Vol 8, No 3, pp282-290
6. EPEFE (1995), European Programme on Emissions Fuels and Engine Technologies, EPEFE
Report on Behalf of ACEA and EUROPIA