Applied Energy 86 (2009) 610–615

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Applied Energy

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Comparison of GHG emissions from diesel, biodiesel and natural gas refuse trucksof the City of Madrid

José Ma López *, Álvaro Gómez, Francisco Aparicio, Fco. Javier SánchezPolytechnic University of Madrid (UPM), Automobile Research Institute (INSIA), Carretera de Valencia, km 7, Madrid 28031, Spain

a r t i c l e i n f o a b s t r a c t

Article history:Received 8 November 2007Received in revised form 11 August 2008Accepted 14 August 2008Available online 23 October 2008

Keywords:Well-to-wheelRefuse truckBiodieselNatural gasGreenhouse gas

0306-2619/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.apenergy.2008.08.018

* Corresponding author. Tel.: +34 91 336 53 06; faxE-mail address: josemaria.lopez@upm.es (J.Ma. Lóp

The aim of this paper is to carry out a comparative study with regard to energy consumption and green-house gas emissions, in respect of two types of engines with three different fuels. The fuels analysed arediesel, biodiesel 30% (B30) and compressed natural gas (CNG). The engines tested were a spark ignitionengine (Otto cycle) and two compression ignition engines (Diesel cycle), the first fed with CNG and thelast two with B30 and diesel. What is new about this study is its scope of application concerning refusecollection services in the city of Madrid. The tests were carried out on refuse trucks of the FCC Companyalong actual urban routes in the city of Madrid. Also taken into account were the energy input and thegreenhouse gases emitted for each of the paths taken by the fuels analysed, from resource recovery todelivery to the vehicle tank.

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

The technological improvements that have been implementedin vehicles during the last decades have greatly reduced the emis-sions of some pollutants as CO, NOx and NMVOC. However, energyconsumption and CO2 emissions have experienced a sustainedgrowth. Available forecasts show that, under a business-as-usualscenario, this growth will continue in the near future [1,2].

A diversification of automotive fuels and powertrain technolo-gies will be needed if national and international targets on green-house gas emissions are to be met. Following this diversification,advanced technology vehicles such as hybrid electric vehicles withgasoline and diesel, and various fuel cell based vehicles, are cur-rently under extensive research and development [3]. Recently, lifecycle assessment (LCA) has been garnering increased interest frompolicy analyst and decision-makers. LAC can be used effectively toanalyze transportation fuel pathways. Many quality and compre-hensive studies have been conducted for transportation fuels, bothin North America [4] and non-North America [5,6] contexts.Against this background, in order to evaluate the greenhouse gasemissions reduction potentials, we focus on estimating well-to-tank (considerating fuel from resource recovery to delivery to thevehicle tank) greenhouse gas emissions of automotive fuels to beused in these refuse trucks for the present and near future. Further,by adding these to well-to-tank results, we show well-to-wheel(integration of the well-to-tank and tank-to-wheel components)

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: +34 91 336 53 02.ez).

greenhouse gas emissions under specific condition of driving a re-fuse truck.

A number of studies with comparisons of diesel, natural gas anddiesel/biodiesel blends bus emissions have been published previ-ously [7–9]. The basis for these comparisons, the choice of vehiclesand even the outcome vary significantly. Other researches havebeen conducted to develop a methodology for the generation ofdriving and duty cycles for refuse vehicles matching the statisticalmetrics and distributions of the generated cycles to the collecteddatabase [10,11]. These cycles will be utilized in the developmentand computer simulation of future refuse vehicle designs, specifi-cally energy-saving hybrid-electric vehicles. Other comparisons in-clude a chassis-based testing program to document emissionreduction (NOx, HC, CO and PM) performance from a fleet of vehi-cles accumulating mileage or applying standard driving cycles[12,13].

In this study, we have aimed to show the results of the testsmade on three refuse collection vehicles with regard to their en-ergy consumption. Each of the three vehicles was designated torun on a different fuel: diesel, biodiesel and natural gas.

The compaction process has a strong influence on the consump-tion and greenhouse gas emissions in this kind of vehicle. Compac-tion process and transfer to dump causes a relatively highconsumption and CO2 emission, comparing with other types of ur-ban fleet such as buses. Collections segment is a combination ofkinematic and hydraulic operation and also includes a significantnumber of stops per kilometre. The vehicle spends a large portionof this driving cycle idling (over 50%), mostly while the refuse isbeing collected. Due to frequent compactations, body hydraulics

J.Ma. López et al. / Applied Energy 86 (2009) 610–615 611

are engaged (power-take-off operation) for more than 19% of thewhole cycle.

The fact that three fuels were analysed is due, on the one hand,to the current state of activity in fleets of refuse trucks, and on theother hand, to the recommendations from the European Commis-sion regarding biofuels for this decade and the next.

NG is considered to be one of the alternative fuels with thegreatest potential for application to urban services [14]. The useof NG in transport is growing rapidly in Spain in public services,and in other countries even for general use in automobiles. In Eur-ope, the European Commission, in its Green Paper, has madereplacing 23% of conventional fuel with alternative fuel a goal for2020. With regard to NG, it was thought it should have a penetra-tion of 10% [15]. Recently, the EC has ratified this value [16].

The EU White Paper on transport warns of the need to reducedependency on oil-based fuels in order to have clean efficienttransport [17]. In many countries NG has been introduced for ur-ban service fleets, in urban bus services, for instance.

Urban buses operate on fixed routes and refuel in the bus de-pots. This same situation is now successfully applied to refuse col-lection vehicles in Madrid, Barcelona, Oviedo, Tarragona, Valencia,Reus, Vigo and other cities, with Spain alone reaching 800 indus-trial vehicles in urban applications with a daily service.

A detailed study of this kind of vehicles working in such specificconditions had never been performed, so it can be an importantcontribution to the state of art of these kind of studies.

2. Calculation methodologies

Energy Logistic Modelling (ELM) is a method developed at theDepartment for Transportation and Logistics at Chalmers Universityof Technology, Sweden, for the transportation sector [18]. ELM isbased on traditional logistics and on Life Cycle Assessment (LCA).

The ELM for motor fuel describes a method for analyzing energyand exergy utilization and emissions for a fuel that is made fromdefined raw materials, with defined production processes, locatedat specific places and used by specific users, e.g. vehicles, vehiclefleets and vehicle categories.

It is well known that the use of the exergetic method when awhole fuel and vehicle LCA is to be done. In this study it was notso necessary since we have started from the General Motors data,that have even been checked by manufacturer cars.

Several processes (e.g. oil or natural gas supply) can be com-bined to energy chains by input/output relation (energy, material).

In many LCAs all kinds of energy are treated in the same way,notwithstanding, the quality of the energy, i.e., the exergy. Thereis, indeed, a big difference in fields of application between 1 MJof electricity, 1 MJ of biomass and 1 MJ of surplus heat. Electricityis produced, oil is refined before use, biomass is cultivated, etc. Inour study these factors have been considered.

Effective decision-making about fuel vehicle policy and regula-tion requires a life cycle perspective. When LCA is applied to fuel/vehicle pathways it is often called well-to-wheel (WTW) analysis.The proposed methodology is based on a global knowledge of theenergies involved in the entire process. The methodology is dividedinto three segments:

(a) The well-to-tank (WTT) component accounts for the energyuse and the resulting GHG emissions associated withresource recovery through to delivery of the useable fuelto the tank of the vehicle.

(b) The tank-to-wheel (TTW) evaluation which accounts for theenergy use and GHG emissions from the use of the fuel invehicles.

(c) Well-to-wheel (WTW) global analysis, taking account of theabove combinations.

3. Well-to-tank emissions analysis

The well-to-tank assessment accounts for the energy consump-tion and GHG emissions associated with the production of the fuel,including the production of its feedstock, processing the feedstockand transportation of the fuel to the dispenser at the fuelling sta-tion. The following fuels will be analysed:

� Diesel.� Natural Gas.� B30 (biodiesel 30%, diesel 70%).

Much information can be found from technical literaturesources about well-to-tank analysis [19–21]. For this study, thewell-to-tank data have been selected from the General MotorsEuropean Well-to-Wheel Study [6], corrected in those particularcases where it has proved necessary.

3.1. Diesel

A representative European crude oil mix is delivered via mar-itime vessel from the point of origin to a European port. Nearthe port, the crude oil is refined, to obtain several compounds,one of which is diesel. The product is delivered via pipeline, in-land ship or railroad to a depot. Finally, it is assumed that distri-bution to the service stations will require about 150 km of roadtransport.

Table 1 shows GHG emissions and energy requirements of die-sel pathway.

The Fig. 1 illustrates the energy diagram blocks for the dieselpathway.

3.2. Natural gas

3.2.1. Description of the natural gas based pathway to CNG fuelEurope’s five largest natural gas suppliers are Russia, Algeria,

Holland, Norway and Great Britain. They supply 85% of Europe’snatural gas, which is called EU natural gas mix. NG from EuropeanNatural Gas Mix is delivered to the refuelling station supplied witha suction pressure of 0.1 MPa (a) or 4 MPa (b) and is dispensed intothe vehicle under an unload pressure of 25 MPa.

Table 2 shows GHG emission and energy requirements of theCNG pathway.

NG from the European network is supplied to service stationsunder different pressures:

(a) Low pressure network (domestic network): CNG is com-pressed at the station from its entry pressure of 0.1 MPa toa supply pressure of 25 MPa (the electric power consump-tion by the compressor is 0.011 kWhel/MJCNG).

(b) High pressure network (industrial network and powerplants): CNG is compressed at the station from its entrypressure of 4 MPa to a supply pressure of 25 MPa (the elec-tric power consumption by the compressor is 0.003 kW hel/MJCNG).

NG supply pressure in the city of Madrid is around 1.2 MPa,which means that the above table must be modified. For each MJof energy reaching the tank, 1.14 MJ have been input and 9.71 gCO2 equivalent have been emitted.

3.2.2. Compressed natural gas from liquid natural gas (CNG from LNG)Natural gas is liquefied in a remote area and transported by ship

more than 10,200 km, supplied to a European port and finally dis-tributed more than 500 km to the service stations. Turning CNGinto gas and the supply destined for vehicles is done at 25 MPa.

Table 1GHG emission and energy requirements of the selected crude oil pathways: DIESELsupply

Energy inputa,b

MJ/MJdiesel

Energy lossesb

MJ/MJdiesel

Greenhousegases(GHG)b g/MJdiesel

Crude oil extraction 1.027 0.027 3.6Crude oil transport 1.039 0.012 0.9Refining 1.099 0.060 4.7Distribution 1.119 0.020 1.1Total 1.119 0.119 10.2

a Cumulative, includes the energy delivered to the vehicle.b Per MJ delivered to the vehicle.

612 J.Ma. López et al. / Applied Energy 86 (2009) 610–615

In this case, for each MJ delivered to the tank, 1.23 MJ have beeninput and 16.2 g CO2 equivalent have been emitted.

3.3. Bio-ester from rapeseed (biodiesel)

Rapeseed or sunflower seed is cultivated, collected and trans-ported by truck 50 km to an oil processing plant. There the oil is ex-tracted, refined and esterified with methanol. The plant oil ester istransported 150 km for blending with diesel fuel.

Table 3 shows GHG emission and energy requirements of bio-diesel pathway using glycerine as a fuel in the process.

The CO2 emissions depends on energy inputs. Therefore, weneed a formula to calculate resulting CO2 emissions as a functionof a carbon content of energy inputs:

CO2 � emissions ¼ ðEnergy input

� CO2 content of energy carrier� CO2 content of product

Oil production and esterification process, the formula gives:

CO2 � emissions ¼ ð2;11� 0Þ � 76;7 ¼ �76;7 gCO2 � equiv=MJ

The glycerine from the biodiesel plant substitutes glycerinewhich is produced in conventional way in the chemical industry,for that reason, a credit is added to give –80 gCO2-equiv/MJ.

3.4. Fuel pathways comparison (well-to-tank)

Table 4 shows an overall summary of energy input and green-house gas emissions for the fuels analysed. The greenhouse gasemissions in order to obtain diesel and CNG are relatively similar.Most of the carbon is contained in the fuel and is given off as CO2

during combustion in the vehicle’s engine.With biomass, the CO2 is absorbed from the atmosphere during

the growth process and is not given off until used in the vehicle.This is why CO2 emissions are usually negative, but the use ofexternal fossil energy or fertilisers needed for their cultivation,transport and processing make the CO2 equivalent emissions lessnegative. In the case of methyl ester from rapeseed, the mostimportant emissions are N2O when it comes to the final count ofgreenhouse gas emissions (1 g N2O � 310 g CO2).

CRUDE OIL EXTRACTION

CRUDE OIL TRANSPORT

3,6 g CO2-equiv/MJ

0,9 g CO2-equiv/MJ 4,

0,027 MJ/MJ 0,012 M

1,027 MJ/MJ

Fig. 1. Connection of processes to e

Finally, biodiesel B30 (30% methyl ester and 70% diesel) offersadvantages in respect of diesel-related greenhouse gas (1.65 gCO2/MJ-obtained by calculation).

4. Tank-to-wheel analysis

For the tank-to-wheel analysis three routes were evaluated bymonitoring: average speeds, distances, times, and the fuel con-sumption. In consultation with FCC staff, it was determined thatthe most severe usage of a refuse vehicle in terms of physical harmto the vehicle is in residential settings. The vehicles specificationsare described below:

s IVECO 240 E 26 GNC Sel 25 m3 CE Double Polyvalent. IVECO8469.41.10 engine. Rear-loading. Turbo intercooling. Displace-ment: 9500 cm3. Multipoint injection. Stoichiometric air/fuelratio. Fuel: natural gas. Hereafter CNG.

s IVECO 240 E 25 Cross Sel 25 m3 CE Double Polyvalent. IVECO8460.41.320 engine. Rear-loading .Turbocharged intercoolingdirect injection. Displacement: 9500 cm3. Fuel: diesel. HereafterDiesel.

s IVECO 240 E 25 Cross Sel 25 m3 CE Double Polyvalent. IVECO8460.41.320 engine. Rear-loading.Turbocharged intercoolingdirect injection. Displacement: 9500 cm3. Fuel: biodiesel 30%.Hereafter B30.

Three real itineraries were selected as illustrated in Table 5. Thedaily data collection procedure requires shadowing of the testvehicle along its route during 5–7 h. Every vehicle repeated theitinerary seven times charging the refuse truck in the same se-quence. The EDM eco of SIEMENS VDO was used to measure thefuel consumption. EDM eco was connected to the electronic deviceof the truck. EDM eco is an interactive consumption measurementsystem that guarantees economical vehicle operation.

Some of the EDM specifications are presented in Table 6.Alongside current fuel consumption, average consumption and

accumulated running costs are also displayed on the Eco-Displayscreen. EDM eco was calibrated before starting individual itinerar-ies, in order to check the fuel consumption at stationary condition,accelerated idle–1500 rpm- to assure k = 1 on CNG vehicle. For thecalibration an external CO2 analyzer was used, connected to the Pi-tot tube installed at the end of the exhaust tailpipe (Fig. 2). Thevehicle mass was measured before and after each dump and theamount of a fuel to fill the tank at the end of the shift was mea-sured in order to provide fuel consumption metric. This valuewas used to recalibrate EDM eco parameters.

Table 7 shows the data parameters that were directly availableon the device. There is a download software available for furtherdata processing, allowing the data to be downloaded from the dis-play into a PC and evaluated and recorded as both driver-relatedand vehicle-related data.

Table 8 shows measured average consumptions for each route.It can be seen that engine consumption in g/km, with B30 is 13.4%

REFINING DISTRIBUTION

7 g CO2-equiv/MJ 3,6 g CO2-equiv/MJ

J/MJ 0,06 MJ/MJ 0,02 MJ/MJ

1,119 MJ/MJ

nergy chains by energy flows.

Table 2GHG emission and energy requirements for CNG from EU NG-Mix

EU NG-Mix at 4 MPa EU NG-Mix at 0.1 MPa

Energy inputa MJ/MJCNG

Energy losses MJ/MJCNG

GHG g/MJCNG

Energy input1 MJ/MJCNG

Energy losses MJ/MJCNG

GHG g/MJCNG

EU NG-Mix high pressure delivery 1.09 0.09 6.5 1.08 0.09 6.6Low pressure distribution – – – 1.09 0.01 2.9CNG Refuelling station (NG compression and

dispensing)1.12 0.03 1.4 1.20 0.11 4.9

Total 1.12 0.12 7.9 1.20 0.21 14.4

a Cumulative.

Table 3GHG emission (CO2 equivalent) and energy requirements for methyl ester

Glycerine used as a fuel in the process

Energy input[MJ/MJRME]

Energy losses[MJ/MJRME]

GHG[g/MJRME]

Rapeseed cultivation 1.26 0.26 60Drying rapeseed 1.27 0.01 0.7Transport 1.29 0.02 0.6Oil production and esterification 2.11 0.82 �80Distribution 2.12 0.01 0.4Total 2.12 1.12 �18.3

Cumulative.

Table 4GHG emission (CO2 equivalent) and energy requirements for the fuel paths analysed

Energy input[MJ/MJ]

Energy losses[MJ/MJ]

GHG emissions[g CO2-eq./MJ]

UE CNGa 1.141 0.14 9.71CNG from LNG 1.23 0.22 16.2Diesel 1.119 0.119 10.2Biodiesel 2.12 1.12 �18.3B30b 1.40 0.44 1.65

a Calculated for a 12 bar line pressure.b Calculated for a mix of 30% methyl ester and 70% diesel.

Table 5Type of service and average load, for each of the itineraries selected

Type of service Domestic waste-1strun (kg)

Domestic waste-2ndrun (kg)

Plastic waste(kg)

Itinerary 1(120 km)

6 380 3 607 1 095

Itinerary 2(130 km)

5 826 4 922 1 053

Itinerary 3(124 km)

6 766 5 621 817

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greater than for diesel; this is mainly due to its lower heat value.Diesel and CNG consumptions are approximately equal.

In order to calculate CO2 emissions in g/km, the carbon balancemethod through stoichiometry of the chemical reaction wasapplied:

CaHb þ aþ b4þ c

� �� ðO2 þ 3:773N2Þ

! a � CO2 þb2� H2Oþ 3:773 � aþ b

4þ c

� �� N2 þ c � O2

For diesel, the composition was C13.5H24.6. For B30 the followingcomposition was used: C18.7H34.9O2 and for NG, 85% of CH4 wasused and 15% of C2H6.

Table 9 shows the figures for CO2 emissions in kg/km. It can beseen that for the CNG engine with a catalytic converter and stoichi-ometric ratio, emissions are the lowest with 1.76 kg CO2/km.

In US legislation a differentiation between methane and non-methane hydrocarbons (NMHC) has been already applied de factofor many years, basically regulating non-methane hydrocarbons.The rationale for this is that methane is neither toxic nor reactive;it is, however, a relatively strong greenhouse gas, with an effectapproximately 20 times greater than CO2.

In diesel engines, the exhaust contains hydrocarbons (HC) de-rived from partly burned fuel. During the combustion process,some new types of hydrocarbons or components like aldehydesand ketones are also formed [22].

In a natural gas engine, typically more than 90% of the totalhydrocarbon value (THC) is methane, and only small portion isNMHC. For the time being, the European legislation for heavy-duty vehicles regulates total hydrocarbons (THC) for conventionaldiesel engines and both methane and NMHC for natural gasengines.

Measurements on modern buses, diesel and CNG vehicles, havebeen carried out in Finland by VTT Processes [23]. Two differentduty cycles were used, the European Braunschweig cycle and theUS Orange County cycle. It turned out to be that both cycles gavepractically identical results. As can be expected, the THC valueswith CNG were higher than with diesel. The THC values for CNGranged from 0.25 to 2.0 g/km. In the case of diesel, the THC valueswere within the range of 0.4 to 0.05 g/km.

The methane emission of the CNG vehicle was low. Even if themethane was multiplied by a factor of 20 and added to the CO2

emission value to quantify total greenhouse gas effect, this wouldnot change the outcome of the comparison. Estimated N2O emis-sion factors for diesel engines are about 0.0099 g/km and0.0087 g/km for CNG. Even considering a factor of 310, does notchange the outcome of the comparison.

The current heavy-duty CNG engines are spark-ignition enginesoperating on the Otto cycle. For this reason, the thermal efficiencyof these engines is lower than for diesels. For chemistry, less car-bon and more hydrogen in natural gas than diesel fuel compensatefor the lower efficiency resulting in tailpipe CO2 emissions lowerthan from diesels. As can be seen from the results (see Table 10),the vehicle with the CNG engine is the one that emits the lowestamount of greenhouse gases to the atmosphere during the selectedcycle, compared to diesel and B30 engines.

5. Well-to-wheel analysis

The total WTW energy use is calculated by multiplying the WTTenergy requirements by the fuel consumption of the vehicle. TheWTW emissions are calculated multiplying the WTT GHG emis-sions in gram per MJ by the energy consumption of the vehiclein MJ per km, to which the TTW GHG emissions were added (ingram per km, see Figs. 3 and 4).

From the well-to-wheel analysis, it may be deduced that thevehicle fed with CNG is the one that emits the lowest amount ofgreenhouse gases into the air, both per kilometre run and per MJof energy input. As for energy demands, that is, the number of

Table 6EDM technical information

Operating voltage UB = 12 / 24 VOperation temperature �30 �C to + 70 �CSignal inputs Speed, injection valve, EBC signal, CANTachograph interface Counter output (1–100 L) UBOn-board output interface Impulse output 5 V (1–1000 impulses/L)Measuring accuracy ± 3% depending on calibrationDownload interface PC standard COM part serial RS232

Fig. 2. Refuse collection vehicle calibration.

Table 7Basic functions

Overall consumption Liter (0–9999 L)Distance km (0–9999 km)Average consumption l/100 kmCurrent consumption l/100 kmAverage speed km/hDriving time h (0–9999 h)

Table 8Measured average consumptions for the routes run and its standard deviation

Vehicle Fuel consumption

[g/km] [l/km] [MJ/km] r

Diesel 646.68 0.77 27.39 0.040B30 756.5 0.89 31.00 0.037CNG 637.5 0.85 m3 N/km 28.56 0.047

Table 9Calculation of CO2 emissions

Diesel B30 CNG

Calculation of CO2 emissionsDensity [kg/l] 0.835 0.85 0.00075Fuel mass [kg] 532.57 557.54 515.1kg CO2/kg fuel 3.18 3.07 2.77Mass CO2 [kg] 1 693.57 1 711.74 1 426.82Mass CO2 [kg/km] 2.03 2.32 1.76

Table 10Tank to wheel analysis

GHG emissions[gCO2-eq./MJ]

GHG emissions[gCO2-eq./km]

Fuel consumption[MJ/km]

Tank-to-wheel (TTW)Diesel 73.37 2 009.77 27.39B30 74.13 2 298.20 31.00CNG 61.32 1 751.36 28.56

GHG g=kmð Þ=consumption l=kmð Þ � density kg=1ð Þ � LHV MJ=kgð Þ � gfuelCO2=MJ.

WELL-TO-WHEEL ENERGY REQUIREMENTS

0 10 20 30 40 50

B30

CNG

DIESEL

[MJ/km]

Fig. 3. Energy requirements in MJ/km of vehicles fed with B30, CNG and diesel forthe global well-to-wheel analysis (WtW).

Well-to-Wheel

0 500 1000 1500 2000 2500 3000

[gCO2-eq./km]

B30

CNG

Diesel

Fig. 4. Greenhouse gas emissions in g CO2 eq./km for the well-to-wheel analysis(WtW) for vehicles fed with B30, CNG and diesel.

614 J.Ma. López et al. / Applied Energy 86 (2009) 610–615

MJ needed to run a kilometre, it can be seen that the vehicle fedwith CNG is positioned between the diesel vehicle and the biodie-sel one, due basically to the performance of the Otto cycle.

6. Conclusions

The following basic conclusions can be extracted from this com-parative study:

� Well-to-tank analysis shows that B30 pathway fuel presents thebest conditions from the GHG point of view.

� The Tank to Wheel GHG emissions for CNG vehicle were thelowest.

� CNG refuse collection vehicles are those that emit the lowestemissions of CO2 during well-to-wheel, which means that theirglobal environmental impact (greenhouse effect) is lower.

In the t VTT study, the best available European diesel bus tech-nology was compared with the best available European CNG bustechnology. The average CO2 emissions were 1.224 g/km for dieselbuses and 1.077 g/km for EEV certified CNG buses [23].

Acknowledgements

Special thanks should be given to FCC for their collaborationwith this study, not only for making the vehicles available to runthe chosen routes but also for the drivers’ enthusiastic willingness

J.Ma. López et al. / Applied Energy 86 (2009) 610–615 615

to follow the instructions for carrying out the driving cycles withthe seriousness required by the replicate of these tests.

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