Transportation Research Part D 11 (2006) 233–241

www.elsevier.com/locate/trd

Comparison of on-road emissions with emissions measuredon chassis dynamometer test cycles

Luc Pelkmans *, Patrick Debal

VITO, Flemish Institute for Technological Research, Boeretang 200, B-2400 Mol, Belgium

Abstract

In the context of the DECADE project, carried out under the 5th Framework Programme of the European Commis-sion, a software package has been developed to predict vehicle fuel consumption and emissions for a given distance–speedprofile. In order to give input to the model, specific light duty vehicles have been subjected to intensive measurements onengine dynamometers, on chassis dynamometers, on proving ground and in real traffic. This paper gives an overview of theemissions measured on the road for two vehicles in Belgium and in Spain (in urban, rural and motorway traffic), and com-pares these with the results obtained on chassis dynamometers. The tests on chassis dynamometers focused mainly on theEuropean Drive Cycle, but a number of tests were performed using a cycle derived from real world speed profiles. Whencomparing emissions on a grams per kilometer basis, it was established that some of the emissions measured in the certi-fication cycle differed dramatically from the real traffic emissions.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Vehicle emission; On road measurements; Driving cycle; EURO limit

1. Introduction

Emission certification tests are a means of comparing the emissions of vehicles and checking whether theystay within certain limits. The test cycles used depend on the type of vehicle. For heavy-duty vehicles theengine is usually tested separately on an engine test bench. Light-duty vehicles are mostly tested on a chassisdynamometer according to a predefined test cycle. This test cycle should generate repeatable emission mea-surement conditions and at the same time simulate real driving conditions.

In Europe the ‘New European Driving Cycle’ (NEDC) is used for the certification of light-duty vehicles.The cycle consists of a phase representing urban driving (ECE15) and a phase representing extra-urban driving(EUDC) (Samuel et al., 2002). The speed profile is represented in Fig. 1(a).

Prior to the certification test the vehicle is allowed to soak for at least 6 h at a test temperature of 20–30 �C.Until recently the engine was allowed to remain idle for 40 s before starting the measurement. From the year

1361-9209/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.trd.2006.04.001

* Corresponding author.E-mail address: luc.pelkmans@vito.be (L. Pelkmans).

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Fig. 1. Speed profile (a) and acceleration levels as a function of speed (b) of the NEDC cycle.

234 L. Pelkmans, P. Debal / Transportation Research Part D 11 (2006) 233–241

2000 (Euro 3) onwards, this idling period has been eliminated, meaning that emission sampling begins once theengine starts up. Emissions are usually sampled according to the Constant Volume Sampling (CVS) technique,and the total emissions are expressed in g/km for each of the pollutants. Fuel consumption and emissionsobtained in this test are the official figures published by manufacturers.

The certification tests are associated to limit values for the various emission components. The limit valueshave become much more stringent over time. For Euro 4 regulations (applicable to all car models from 2005onwards), limits for Carbon Monoxide (CO), Particulate Matter (PM) and Nitrogen Oxides (NOx) combinedwith Hydrocarbons (HC) are 5–10 times lower than the pre-Euro levels (before 1990).

As car models had to comply with these regulations, the emissions of new vehicle models during the NEDCtest cycle have been seriously reduced compared to older models. The question arises whether these results alsoreflect the pollutants emitted in real traffic. The European Drive Cycle is often criticized because of its verysmooth acceleration profile. The engine uses only a very small area of its operating range, and to fulfil theemission test engine manufacturers only have to focus on these zones (Kageson, 1998).

2. Comparison of the European Drive Cycle with recorded speed profiles

Acceleration levels in the NEDC cycle are shown in Fig. 1(b). The cycle contains four ECE segments (sim-ulating urban driving) and one EUDC segment (simulating extra-urban driving). It is already clear from thisfigure that the test focuses on some fixed vehicle speeds and fixed acceleration levels.

2.1. Database of the biodiesel project

There are various databases with driving patterns based on actual driving cycles in real traffic. For the ‘Bio-diesel Demonstration in Belgium’ project, coordinated by Vito during 1996–1998 (Pelkmans and Lenaers,2000), a considerable number of the speed tracks was recorded in real traffic (emissions and fuel consumptionwere measured concurrently). A VW Golf III, with a 1.9D engine (max. power ratings 42 kW) was tested usingvarious blends of biodiesel and diesel. The car was driven by two different drivers: one with a relaxed drivingstyle, the other with an aggressive driving style. As the effect of the biodiesel concentration on power andacceleration was hardly noticeable, all the recordings on this vehicle were grouped. Table 1 gives an idea ofthe test area and the number of tests performed.

The tested vehicle was a low-power vehicle and the vehicle was loaded with emission measurement equip-ment (total equivalent load �4 persons), so it can be assumed that these recordings do not overestimate thetypical acceleration characteristics of other passenger cars. Fig. 2 shows the acceleration levels reached duringthese tests as a function of speed. In this diagram the acceleration levels are related to a certain gear, whichdiffers between the two driving styles. The relaxed driver clearly reaches lower acceleration levels and shiftsgears much earlier than the other, more aggressive driver.

It is also clear from Fig. 2 that, although the base vehicle was not very powerful, the accelerations in realtraffic are much higher than in the European Drive Cycle, especially in urban traffic (below 50 km/h).

Table 1Number of tests taken into account

Distance (km) Number of tests

Relaxed driving Aggressive driving

Urban traffica 8.1 22 25Rural trafficb 10.8 30 32Motorway trafficc 25.5 32 26

a Mol City Centre (North of Belgium).b Mol – Oud-Turnhout and back.c E34: Oud-Turnhout – Zoersel and back.

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Ι

ΙΙ

ΙΙΙΙV

V

Fig. 2. Acceleration levels and gear changing in the biodiesel tests in real traffic (recorded using a VW Golf III 1.9D).

L. Pelkmans, P. Debal / Transportation Research Part D 11 (2006) 233–241 235

The data recorded in the biodiesel project resulted in a cycle, commonly referred to as the ‘‘MOL’’ cycle(Pelkmans et al., 2002). The ‘‘MOL’’ cycle consists of three phases: urban, rural and motorway. The speedprofile and acceleration levels are shown in Fig. 3. This cycle was implemented on a chassis dynamometerin the DECADE project (see below) to compare the emissions of the NEDC cycle with a real traffic-basedcycle.

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Fig. 3. Speed profile (a) and acceleration levels as a function of speed (b) in the MOL cycle.

236 L. Pelkmans, P. Debal / Transportation Research Part D 11 (2006) 233–241

2.2. Relative positive acceleration

Typical driving situations can be grouped in categories (e.g. urban driving). However the variations aboundeven within these categories, as elaborated by Ericsson (2001). As a result it would be useful to group certaincharacteristics when characterising a test cycle or traffic situation. Apart from the instantaneous speed andacceleration, an important parameter to compare the load of the test cycle is ‘relative positive acceleration’(RPA). The relative positive acceleration is a speed-related average of acceleration of the vehicle. It is directlyrelated to the average acceleration power of a vehicle. The definition of relative positive acceleration is (Van deWeijer, 1997):

TableOvervi

Test fa

Engine

Chassi

Chassi

Chassi

Provin

Real t

Real t

RPA ¼R T

0ðvi � aþi Þ � dt

x

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(m/s

²) NEDC & FTP75

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ARTEMIS cycles

MOL - diesel car

MOL - gasoline car

BCN - diesel car

BCN - gasoline carECE

EUDC

FTP75

Fig. 4. Comparison of relative positive acceleration of test cycles vs. real traffic.

2ew of emission tests within the DECADE project

cility Place Test procedures

test bench VITO, Belgium Steady state and dynamic transitions

s dyno CLE, Germany NEDC, FTP75 and MOL cycleTests on impact of test cycle, vehicle weight and tyre pressure

s dyno IDIADA, Spain NEDC and MOL cycleTests on impact of gear shift, air filter condition and fuel quality

s dyno MIRA, United Kingdom NEDC and MOL cycleTests on impact of air humidity, temperature and the use of airconditioning

g ground IDIADA, Spain High-speed testsGradient testsNEDC and MOL cycle

raffic In and around Mol, Belgium Urban trafficRural trafficMotorway traffic

raffic In and around Barcelona, Spain Urban trafficRural trafficMotorway traffic

L. Pelkmans, P. Debal / Transportation Research Part D 11 (2006) 233–241 237

where, T is total cycle time (s); x is total distance (m); vi is momentary speed (m/s); ai is momentary acceler-ation (m/s2) and + indicates only positive values.

Fig. 4 and Table 2 compare the relative positive acceleration in the test cycles and in various measurementsin real world traffic. The characteristics of the ARTEMIS cycles are also taken into consideration in lieu ofcomparison. The ARTEMIS cycles are formulated based on a statistical analysis of a large set of real worldrecordings (Andre, 2001), used within the European ‘ARTEMIS’ project. It is obvious that the NEDC cycle isfar less taxing than the other cycles. The characteristics of the MOL and ARTEMIS cycles seem more realistic.The average speed and RPA of the US-FTP 75 cycle are also shown in Fig. 4 for comparative purposes andclearly show that this cycle too has a low load (see also Lin and Niemeier, 2002).

The European Drive Cycle is effectively often criticized because of its very smooth acceleration profile(Andre and Pronello, 1997), which is reflected in a low relative positive acceleration value. Thus it underesti-mates the vehicle load compared to real traffic, which has a direct effect on fuel consumption. Moreover, theengine only uses a very small area of its operating range. In order to comply with the emission test, enginemanufacturers only have to optimize emissions in these operating zones.

Depending on the technology, the difference in driving patterns will either have a serious or minor impacton fuel consumption and emissions. In the following section, the difference will be quantified for two moderncars, a diesel and a petrol car, based on test results obtained in the framework of the ‘DECADE’project.

3. The DECADE project

The ‘DECADE’ (2000–2003) project was carried out under the European 5th Framework Programme. Itsmain goal was to develop a method for predicting fuel consumption and regulated vehicle exhaust emissionsduring dynamic engine behaviour (Pelkmans et al., 2004). Its calculation methodologies have now beenemployed in a computer simulation tool called VeTESS (Vehicle Transient Emissions Simulation Software).Initially the project focused on three vehicles with different engine technologies, representing the typical Euro-pean light vehicles (all year 2000 models). The vehicles selected were:

• a EURO 4 gasoline passenger car (VW Polo 1.4 16 V, same platform as Skoda Fabia and Seat Ibiza),• a EURO 3 family-size diesel car (Skoda Octavia 1.9TDi, 90 HP, same platform as VW Golf, Audi A3 and

Seat Toledo),• a EURO 2 light commercial vehicle (Citroen Jumper 2.5D, also marketed as Citroen Relay in the UK, same

platform as Peugeot Boxer and Fiat Ducato).

The three vehicles and their components were tested under various conditions. Table 2 shows an overview.Vito’s VOEMLow system is used as a common measurement system for all emission tests (on engine dyno,

chassis dyno and on-board the driving vehicles). This is the second generation of a dedicated system for on-road measurements, which measures fuel consumption and emission concentrations (CO2, CO, THC, NOx

and PM), in combination with the total mass flow of the exhaust gases. The results are thus expressed in gramsof pollutant per second. This new system has a drastically increased sensitivity to measure low emission levelsof vehicles in order to comply with future emission levels. VOEMLow measurements are performed at 1 Hz,thereby allowing for an investigation of the influence of several vehicle and engine parameters on fuel con-sumption and emissions (Lenaers et al., 2003).

Where possible, state-of-the-art CVS equipment at the chassis dynamometers of IDIADA and MIRA per-formed parallel emission measurements for establishing the correlation between the VOEMLow system andCVS equipment.

All tests (both on the engine and on the vehicles) were performed with a minimum mileage of 5000 km inorder to avoid running-in effects of the engines and of catalysts. The engines were always tested under hot con-ditions, so the influence of start-up or engine warming-up was not included in the tests. The figures mentionedfor the NEDC cycle are therefore not the official certification figures (as the official test also includes a warm-ing-up phase of the engine).

238 L. Pelkmans, P. Debal / Transportation Research Part D 11 (2006) 233–241

4. Impact on fuel consumption and emissions

The results of the ECE part of the NEDC cycle can be compared to urban traffic; the results of the EUDCpart are compared to rural traffic. All results cited are thus an average of at least three measurements.

4.1. Diesel passenger car (EURO 3)

Tables 3 and 4 show an overview of the results obtained on a chassis dynamometer and in real traffic withthe Skoda Octavia diesel car.

The impact of the test cycle is important for this vehicle.CO2 emissions (and fuel consumption too), which are directly related to the load of the cycle, increase by

15–20% in the MOL cycle compared to the NEDC cycle. Fuel consumption in real traffic compares quite wellto the MOL cycle. The measurements registered in the city of Barcelona featured a higher fuel consumption,which is related to the specific (very busy) traffic situation in the test area.

There is a substantial increase of CO emissions in urban traffic (both in the MOL cycle and in real traffic),compared to the ECE part of the NEDC. A more detailed analysis of the measurement data has revealed thatthis is related to a limited number of CO peaks (up to 0.05 g/s), occurring at high load/low engine speed. Shift-ing gears had a crucial effect on this.

The most important effect for the diesel car is noticeable on NOx emissions levels. For current diesel vehi-cles NOx limits are quite difficult to meet as current diesel catalysts do not reduce NOx in the exhaust. ThusNOx levels in diesel engines are controlled with EGR or in-cylinder measures. For this vehicle NOx emissionsare about twice as high in the MOL cycle and in real traffic compared to the NEDC cycle. The reason lies inthe EGR strategy, which is mainly active in lower loads (since highest loads are not applied in the NEDC test).NOx emissions in real traffic are even higher than in the MOL cycle, which is probably related to the highertest weight of the vehicle. A remarkable effect is that NOx emissions on the motorway are 45% lower in thetests around Mol compared to the tests around Barcelona. A more in-depth analysis has shown that duringmotorway operation (�120 km/h) the EGR valve is on the verge of switching from entirely open (lower loads)to partly open (higher loads). Thus a very small difference in load (due to wind or gradients) may lead to a bigdifference in NOx emissions.

4.2. Small petrol passenger car (EURO 4)

Tables 5 and 6 show an overview of the results obtained on the chassis dynamometer and in real traffic withthe VW Polo petrol car.

The vehicle is specially designed to comply with the EURO 4 legislation (valid from 2005). So it comes as nosurprise that the emissions for the NEDC cycle are very low. However, substantially higher emission valuesare recorded with a more demanding cycle.

Table 3Chassis dynamometer measurements on Skoda Octavia TDi (simulated weight: 1350 kg)

Skoda Octavia 1.9TDi Diesel EDC cycle MOL cycle

ECE EUDC Urban Rural Motorway

Speed (km/h) 18.8 61.9 19.4 62.8 92.6RPA (m/s2) 0.16 0.10 0.38 0.25 0.14

Fuel cons. (l/100 km) 6.6 4.9 8.1 5.6 6.5CO2 (g/km) 173 129 211 147 170CO (g/km) 0.012 0.008 0.049 0.012 0.013NOx (g/km) 0.62 0.42 1.02 0.92 0.99THC (g/km) 0.027 0.010 0.021 0.008 0.006PM (g/km) 0.06 0.08 0.08 0.08 0.18

Table 4Real traffic measurements on Skoda Octavia TDi (test weight: 1700 kg)

Skoda Octavia 1.9TDi Diesel MOL BARCELONA

Urban Rural Motorway Urban Rural Motorway

Speed (km/h) 23.6 57.9 105.9 14.6 56.8 99.1RPA (m/s2) 0.36 0.21 0.09 0.29 0.26 0.10

Fuel cons. (l/100 km) 8.2 5.6 5.9 9.2 6.5 6.1CO2 (g/km) 217 147 154 241 169 160CO (g/km) 0.105 0.020 0.009 0.158 0.033 0.014NOx (g/km) 1.35 0.93 0.61 1.50 1.24 1.12THC (g/km) 0.022 0.013 0.007 0.045 0.010 0.006

Table 5Chassis dynamometer measurements on VW Polo (simulated weight: 1050 kg)

VW Polo 1.4 Petrol EDC cycle MOL cycle

ECE EUDC Urban Rural Motorway

Speed (km/h) 18.5 61.8 19.2 62.6 93.7RPA (m/s2) 0.16 0.10 0.40 0.26 0.14

Fuel cons. (l/100 km) 8.5 6.1 10.6 6.9 7.6CO2 (g/km) 202 143 250 163 179CO (g/km) 0.003 0.039 0.071 0.479 0.579NOx (g/km) 0.025 0.007 0.350 0.123 0.050THC (g/km) 0.004 0.002 0.005 0.008 0.010

Table 6Real world measurements on VW Polo (test weight: 1400 kg)

VW Polo 1.4 Petrol MOL BARCELONA

Urban Rural Motorway Urban Rural Motorway

Speed (km/h) 20.6 51.6 102.8 16.7 52.6 96.9RPA (m/s2) 0.35 0.18 0.12 0.32 0.22 0.09

Fuel cons. (l/100 km) 10.7 6.9 7.3 12.0 7.0 7.3CO2 (g/km) 254 162 172 283 165 172CO (g/km) 0.013 0.131 0.620 0.072 0.621 0.635NOx (g/km) 0.570 0.109 0.018 0.231 0.063 0.030THC (g/km) 0.006 0.006 0.013 0.006 0.006 0.007

L. Pelkmans, P. Debal / Transportation Research Part D 11 (2006) 233–241 239

As noted earlier, part of this is related to the characteristics of the NEDC cycle, which only focuses on spe-cific operating zones of the engine. This specific engine reaches elevated NOx emissions at low engine speed/high torque, and elevated CO emissions at high engine speed/high torque. Fig. 5(a) shows that the conditionsof elevated NOx emissions are never reached in the NEDC cycle and that the conditions for elevated CO emis-sions are only reached for a short period. In real traffic these conditions are all reached (Fig. 5(b)), whichresults in a big difference between the emissions measured on the NEDC cycle and in real traffic or a real trafficbased cycle.

In the case of the MOL cycle the petrol car shows an increase of CO2emissions (and fuel consumption) ofaround 25% for the urban component (compared to ECE) and 15% for the rural component (compared toEUDC). Fuel consumption in real traffic compares quite well to the MOL cycle.

CO emissions rise drastically in the high speed part of the cycle (more than 10 times higher than in theEUDC part). When looking at the speed-torque distribution in Fig. 5, it is obvious in the MOL cycle andin real traffic that the area with high CO emissions (related to fuel enrichment) is used far more frequently.

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Fig. 5. Speed–torque distribution in the NEDC cycle (a) and the MOL cycle (b) for the petrol car (compared to conditions for elevatedNOx and CO levels).

240 L. Pelkmans, P. Debal / Transportation Research Part D 11 (2006) 233–241

NOx emissions rise substantially in urban traffic (10–20 times higher than in the ECE part). This is relatedto low speed/high torque operation, which is hardly used in the NEDC cycle, but occurs more frequently inreal traffic and in the MOL cycle.

The results measured in the MOL cycle compare quite well with the measurements in real traffic. There aresome variations between the measurements of CO and NOx emissions (which are also highly dependent on theshift in gears) but the tendency of high NOx/low CO in urban traffic and high CO/low NOx in motorway traf-fic is still the same.

4.3. Comparison with real traffic measurements on earlier car models

In order to show that there has indeed been a positive evolution of emissions in new car models in real traf-fic operation, we have compared these measurements with real traffic measurements on previous car models(Debal et al., 2003).

Comparable Euro 1 cars have been measured in the same region (urban, rural and motorway traffic aroundMol) in the period between 1994–1996. These results were used for the purpose of this comparison: the SkodaOctavia diesel car (Euro 3) is compared to a VW Golf 1.9D, model year 1993. The VW Polo petrol car (Euro4) is compared to an Opel Corsa 1.3 (with three way catalyst), model year 1993.

In both cases the older vehicle model had lower mass and less engine power, but this is in accordance withthe change in market trend (cars are heavier and more powerful than 10 years ago).

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Fig. 6. Real traffic measurements around Mol (Belgium): comparison Euro 1 diesel vs. Euro 3 diesel (a) and Euro 1 petrol vs. Euro 4petrol vehicle (b).

L. Pelkmans, P. Debal / Transportation Research Part D 11 (2006) 233–241 241

Fig. 6 shows that there has been a spectacular decrease in CO and THC emissions, both for diesel and pet-rol vehicles. In the case of diesel vehicles this is related to the introduction of the oxidation catalyst; in petrolvehicles this is related to improved lambda control.

NOx emissions have remained at approximately the same levels for the diesel car. The NOx-reducing mea-sures, which were introduced to achieve recent Euro limits, seem to be compensated by the higher power of thenewer diesel car. In the case of the petrol car there used to be a clear correlation between average speed andNOx emissions (highest in motorway traffic). The more sophisticated lambda control in recent petrol car mod-els has however changed this relation (higher NOx in urban traffic, very low NOx in motorway traffic).

One should keep in mind that the differences in weight and engine power may have an important impact onthe comparison between older and newer vehicle models. Thus these figures are only used to illustrate a trend.

5. Conclusions

The paper shows that pollutant emissions have actually been reduced in past years. However the emissionlevels measured in the European Drive Cycle can be very different from the emissions produced in real traffic.The NEDC cycle seems too smooth to be realistic and vehicle manufacturers only have to focus on limitedengine operating zones in order to obtain low emissions for this cycle. In practice real world emissions canbe substantially higher. In this paper it turned out that a model year 2000 vehicle, which already compliedwith EURO 4 limits, may reach CO and NOx emissions that may be up to 10 times higher in real traffic com-pared to the NEDC cycle. Fuel consumption and CO2 emissions are generally underestimated by 10–20% inthe NEDC.

Acknowledgements

The authors wish to thank the members of the DECADE consortium for their co-operation in the workprogramme. DECADE is a project of the 5th Framework of the European Union in the programme Energy,Environment and Sustainable Development.

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