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Atmospheric Environment 55 (2012) 144e153

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Atmospheric Environment

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Emission consequences of introducing bio ethanol as a fuel for gasoline cars

Morten Winther a,*, Flemming Møller a, Thomas C. Jensen b

aDepartment of Environmental Science, Aarhus University, Frederiksborgvej 399, 4000 Roskilde, Denmarkb Technical University of Denmark, DTU Transport, DK-2800 Lyngby, Denmark

a r t i c l e i n f o

Article history:Received 31 October 2011Received in revised form8 February 2012Accepted 15 March 2012

Keywords:Bio ethanol emissionsCO2

NOx

VOCCOE5E85Road transportDenmark

* Corresponding author. Tel.: þ45 8715 8578; fax:E-mail address: mwi@dmu.dk (M. Winther).

1352-2310/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.atmosenv.2012.03.045

a b s t r a c t

This article describes the direct vehicle emission impact of the future use of bio ethanol as a fuel forgasoline cars in Denmark arising from the vehicle specific fuel consumption and emission differencesbetween neat gasoline (E0) and E5/E85 gasoline-ethanol fuel blends derived from emission tests usingprimarily the European NEDC and ARTEMIS driving cycles. The E0-E5 test vehicles (nine cars) representtoday’s gasoline car traffic well where most of the driving is being made with cars certified as Euro 3þ.The FFV test cars (25 cars) are all certified according to the Euro 4 emission standard introduced inEurope from the mid-2000s. This matches well with the propagation of the FFV technology in Europe.

For vehicles using E5 rather than E0, the average fuel consumption and emission differences are small.For CO, VOC and NOx the derived average differences are 0.5%, �5% and 7%, respectively. For FFVs usingE85 rather than E5, the emission differences become even smaller for VOC and NOx, but greater for CO.The derived average emission differences are in this case 18%, �1% and 5% for CO, VOC and NOx,respectively. In both comparative cases there is a large variation in the emission difference valuescalculated for the individual cars. The large standard deviations introduce some uncertainties in the finalaverages computed for each emission component.

The vehicle based emissions are made up for two fossil fuel baseline scenarios (FS), characterised byhigh and low traffic growth rates. For each FS, two biofuel scenarios (BS1, BS2) are presented. BS1 reachesthe Danish policy targets (10% biofuel share in 2020). BS2 is more ambitious (25% in 2030). By definitionthe biofuel part of the combusted fuel is CO2 neutral and the maximum CO2 emission difference betweenFS and BS2 becomes 27% in 2030. As predicted by the vehicle specific emission differences the calculatedemission impacts of using bio ethanol are small for NOx, VOC and CO. Instead, for FS, BS1 and BS2 largeemission reductions are due to the gradually cleaner new sold gasoline cars and the decline in totalmileage until the mid-2010s.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

The introduction of biofuels is seen as a very important measureto reduce the emissions of greenhouse gases from road transport;first of all CO2 emissions because biofuels are regarded as CO2neutral fuels (EU Directive 2009/28/EC). The CO2 emission conse-quences of introducing biofuels depend on the amount of transport.This, together with fuel effectiveness of vehicles, total vehicle fleetand composition with regard to age and size and decisions aboutthe biofuel share of fuel consumption determines the CO2 reductionpotential.

In Denmark the biofuel target for the transport sector inDenmark is 5.75% in 2010 (phased in until 2012). In 2020,10% of the

þ45 8715 5021.

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energy consumption in the transport sector is to be covered byrenewable energy, including biofuel. This is the background for themulti-disciplinary integrated impact assessment project ‘Renew-able Energy in the transport sector using Biofuels as an EnergyCarrier’ (REBECa), which was finalised recently. The aims of REBECawas to assess the impact on emissions, air quality and humanhealth as well as resource and land-use change, and to considereconomic and sociological aspects of the future use of biodiesel andbio ethanol in Danish road transport. The project period was2007e2010.

This paper has a strict focus on the direct vehicle emissionimpacts of using bio ethanol as a fuel for gasoline cars in Denmarkbased on the bio ethanol penetration rates defined in REBECa andthe vehicle fleet and mileage forecast made available to the projectcalculations. The emissions examined are CO2, NOx, VOC and CO. Animportant goal is also to explain the fundamental fuel consumptionand emission differences between neat gasoline (E0) and E5/E85

Total mileage - gasoline cars

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Fig. 1. Total mileage figures from 2004 to 2030 for gasoline passenger cars (100$ and 65 $ scenario) and layer specific mileage (65 $ scenario only) aggregated by engine size.

1 LHV: Danish Energy Authority (DEA, 2008); Neat gasoline: r¼ 0.75; Ethanol:r¼ 0.79.

M. Winther et al. / Atmospheric Environment 55 (2012) 144e153 145

behind the inventory calculations; these differences being based onthe literature review for traditional cars using E0 and E5 and FFVsusing E5 and E85.

Increased consumption of biofuels also has indirect emissionconsequences related to the full chain of production, distributionand combustion of biofuels. The indirect consequences of re-allocating society’s scarce resources are best analysed within anintegrated Life Cycle and Well-to-Wheel (LCA/W-t-W) framework(e.g. Menichetti and Otto, 2008; UNEP, 2009; Hoefnagels et al.,2010; Londo et al., 2010; Whitaker et al., 2010). In another part ofREBECA, aW-t-Wassessment of the total emission consequences ofproducing and using biofuels is made, where it is combined withawelfare economic cost benefit analysis to assess the consequencesfor society’s welfare of the different biofuel scenarios (Slentø et al.,2010). The results from this study regard to CO2 emissions arepresented in the discussion part of this paper.

The mileage forecast behind the calculations is presented inSection 2 as well as bio ethanol energy data and scenario specificbio fuel share of total fuels for road transport. Section 3 explains thefossil fuel baseline emission factors for gasoline cars, the E5 and E85dependent fuel consumption and emission differences and theresulting fuel consumption and emission factors for E5 and E85.Section 4 documents the fuel consumption and emission calcula-tion methodology. The calculated FS, BS1 and BS2 scenario resultsfor fuel consumption and emissions of CO2, NOx, VOC and CO areshown in Section 5 as totals for the basis year 2004, and also thescenario years 2010, 2015, 2020, 2025 and 2030. Further discus-sions and paper conclusions are given in Section 6.

2. Activity data

2.1. Total mileage data

Two mileage forecasts have been set up by DTU Transport,Technical University of Denmark, based on different assumptionson oil prices. The first mileage forecast is identical to the “lowgrowth” scenario produced for The Danish InfrastructureCommission (2008). It is based on a GDP growth of 1.2 % onaverage (according to a projection from The Danish Ministry ofFinance from 2005) and an oil price assumption of 65 $ per barrel ofoil (Fosgerau et al., 2007). In the second “alternative” scenario,somewhat lower mileage growth rates are expected due to anincreased oil price of 100 $ per barrel of oil. For cars the estimatedannual growth in the total mileage from 2005e2030 for the 65 $and 100 $ scenarios are 1.38% and 0.76%, respectively. A thoroughdocumentation of the mileage forecast is given by Jensen andWinther (2009).

In order to make sufficiently detailed fuel consumption andemission calculations, the car mileage figures from DTU Transportare further split into groups of vehicles with the same average fuelconsumption and emission behaviour; the so-called layers. Aninternal model developed by NERI (former National Environ-mental Research Institute of Denmark e now Department ofEnvironmental Science, Aarhus University) uses a detailed layerstructure and calculation methodology similar to the modelstructure of the European road transport emission calculationmodel COPERT. Relevant for cars the layer splits are madeaccording to fuel type, engine size and EU emission legislationlevels.

For more information regarding input data in the 2004e2006historical years and the 2007þ forecast period, please refer toNielsen et al. (2009, 2010). The historical and forecasted fleet andmileage data are for cars summed up in the NERI model in order toimplement the total DTU mileage levels by simple scaling acrosslayers.

For the two mileage forecasts, Fig. 1 shows the resulting totalmileage figures from 2004 to 2030 for gasoline passenger cars, aswell as layer specific mileage (65 $ only) aggregated by engine size.The significant decrease in total mileage for gasoline cars until themid-2010s is due to the dieselification of the Danish car fleet. Theswitch from gasoline to diesel vehicles has taken place for morethan a decade now and is envisaged to continue in the future.

2.2. Energy input data

The scenario bio ethanol energy share percentages, B%E, areshown in Fig. 2. The BS1 scenario assumes a bio ethanol energyshare of 5.75% in 2010, followed by a linear growth to 10% in 2020and constant levels in the following years. In BS2, the bio ethanolshare grows linearly from 5.75% in 2010 to 25% in 2030. For bioethanol, in REBECA the scenario definition is to use a five percentmix by volume of bio ethanol in gasoline fuels (E5) by all gasolinevehicles and then gradually increase the number of FFVs runningon E85 (85 vol % ethanolþ 15% gasoline) in the passenger carsegment of the fleet, as the share of bioethanol increases in thescenario period.

By taking into account the differences in fuel density, r, andlower heating values (LHV) between neat gasoline and bio ethanol(Table 11) by simple transformation (Winther, 2010) the energy

Table 1Fuel density and lower heating values for gasoline bioethanol.

Gasoline Bio ethanol E5 E85

LHV (MJ kg�1) 43.8 26.7 42.0 29.2B%V 0 100 5 85B%E 0 100 3.27 78.4

Energy based bio ethanol % in biofuel scenarios

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Fig. 2. Bio ethanol share by energy of road transport gasoline used in REBECa for BS1and BS2.

M. Winther et al. / Atmospheric Environment 55 (2012) 144e153146

based bio ethanol percentage, B%E, and the resulting LHV’s can bederived separately for E5/E85.

3. Fuel consumption and emission factors

Section 3.1 provides a brief explanation of the fossil fuel baselineemission factors for gasoline cars. An in-depth documentation ofthe E5 and E85 dependent fuel consumption and emission differ-ences is given in Section 3.2, based on data from the literaturereview. The data presented in the Sections 3.1 and 3.2 and the bioethanol fuel specific energy data explained in Section 2.2 lead to thefuel consumption and emission factors for E5 and E85 formulatedin Section 3.3.

3.1. Basis fuel consumption and emission factors

The fuel consumption and emission factors used in the baselinescenarios come from the COPERT model version IV (EMEP/EEA,2009). Fig. 3 shows the fuel consumption and emission factors ofNOx, VOC and CO for gasoline passenger cars. The layer specificfactors correspond with the mileage data presented in Section 2.1.The fuel consumption and emission factors presented in Fig. 3 areweighted according to mileage driven per road type and theemission effects of cold start and catalyst wear are also beingincluded.2

3.2. Differences for fuel consumption and emissions for neatgasoline vs. E5 and E5 vs. E85

An extensive literature review has been made in order toexamine the fuel consumption and emission differences betweenneat gasoline/E5 and E5/E85. Having primarily a European scopethe decision in this study has been to include E0/E5 and E5/E85emission data for cars certified according to EU emission legislationand experiments based on driving cycles relevant for Europe.Consequently, test results from studies using gasoline-ethanol fuelblends other than E5 or E85 (e.g. Karlsson, 2006) and experimentaldata obtained using constant engine loads, which do not representreal driving by driving cycle (e.g. Yüksel and Yüksel, 2004;Poulopoulus et al., 2001) are excluded from the emission databasis. Also, measurement results from test engine sizes unrealistic

2 Cold start and catalyst wear emission effects deviate to some extent from yearto year. However, in order to limit the data shown, the factors from Fig. 3 arederived for the inventory year 2015.

to cars (e.g. Koc et al., 2009; Yücesu et al., 2006; Topgül et al., 2006;Zervas et al., 2003) or data reported for test vehicles less modernthan new European FFVs (Graham et al., 2008) are disregarded inthe following.

The driving cycles behind the emission measurements areprimarily the European NEDC and ARTEMIS driving cycles. Foreach car and fuel consumption/emission component included inthe database average figures for the E0/E5 and E5/E85 differ-ences has been calculated. Subsequently total averages havebeen derived for fuel consumption and each emission compo-nent based on the number of cars represented bymeasurements.3

3.2.1. Neat gasoline vs. E5For neat gasoline and E5, CO, VOC and NOx emission results

were obtained by Martini et al. (2007) for seven cars. Single carmeasurements of the same emission components were made byDelgado (2003) and Hull et al. (2005). In all three cases theEU NEDC was used as a test cycle during the emissionmeasurements.

In Martini et al. (2007) one Euro 3 and six Euro 4 cars weretested and the emission components considered were CO, VOC,NOx, CO2 as well as fuel consumption (l/100 km) and energyconsumption (MJ/100 km). Delgado (2003) measured the emis-sions components of among others VOC (NMVOC and CH4), CO,NOx, NO, CO2 and fuel consumption (l/100 km) for a Renault Meg-ane 1.6 l, certified according to the Euro 3 engine emission stan-dard. Hull et al. (2005) measured the emissions of CO, VOC, NOx,CO2 and fuel consumption from a Volvo 245 (1987 model).

Fig. 4 shows the average percentage differences of CO, VOC andNOx emissions and energy consumption (MJ) derived from thereported measurement figures for the nine cars present from thethree above mentioned studies. As appears from Fig. 4, the averageemission differences between neat gasoline and E5 fuels are closeto zero. There is a tendency, though, towards smaller emissions forVOC and higher levels of energy consumption and CO and NOxemissions.

The average E0eE5 measurement differences display a largevariation in the emission difference values calculated for the indi-vidual cars. This is expressed by the large standard deviation of thetotal average emission difference computed for each emissioncomponent shown in Fig. 4. The large standard deviations influencethe precision of the derived average figures and it is important tokeep these uncertainties in mind when data are used as input forthe total emission calculations.

The very low average emission differences between neat gaso-line and E5 fuels found are supported by the findings from Egebäcket al. (2005). In this study no significant differences can be seenbetween neat gasoline and low gasoline bio ethanol blends(E10eE15) assessing emission test results from Australia, Canada,USA, Sweden and UK.

3 The decision has been to produce average figures from all measurements,regardless of driving cycle, in order to have as many as possible experimental databehind the final emission ratios.

Fuel consumption factor - gasoline cars

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Fig. 3. Layer specific fuel consumption and NOx, VOC and CO emission factors for gasoline cars.

6 Many future cars certified as Euro 6 will be equipped with direct fuel injection(DI) systems in order to improve fuel efficiency. By that time it is expected that fuelinjection equipment suppliers will have DI systems available that can handle E85during normal operation (Westerholm et al., 2008 and ExIS AB (pers. comm.. PeterAhlvik, 2012)), and are able to switch between E85 and lower blend ratio fuelsE70eE75 (low ambient temperature fuels) without technical difficulties (ExIS AB(pers. comm.. Peter Ahlvik, 2012)). Also according to ExIS AB there is no reason tobelieve that the degradation of exhaust after treatment systems installed in Euro 6FFV cars will be different due to primary use of E85 instead of E5. Hence, based on

M. Winther et al. / Atmospheric Environment 55 (2012) 144e153 147

3.2.2. E5 vs. E85In order to assess the fuel consumption and emission differences

between E5 and E85, this study has considered measurementsmade by de Serves (2005), Westerholm et al. (2008), Martini et al.(2009), Pelkmans et al. (2010) and AVL MTC (2011). In total, thetested vehicles comprise 25 FFVs, all certified as Euro 4. All five testprogrammes use E5 as the neat gasoline fuel basis.4 The emissionmeasurements were obtained from chassis dynamometer testsusing the driving cycles EU NEDC, ARTEMIS AU, AR and AH, US06(only Martini et al., 2009) and MOL30 (only Pelkmans et al., 2010).

In de Serves (2005), three Ford Focus 1.6 cars were tested. Emis-sions of CO, VOC, CH4, NOx, NO, NO2, particulates as well as fuelconsumption (l/100 km) and energy consumption (MJ/100 km)weremeasured. The same emission and fuel consumptionmeasurements,as well as measurements of several other unregulated pollutantswere measured by Westerholm et al. (2008). The tested FFVs werea Saab 9-5 Biopower (2.0 l.) and a Volvo V50 1.8 F (1.8 l.).

Martini et al. (2009) measured the emissions of CO, VOC, NOx,particulate matter (PM), CO2 as well as a number of differentunregulated VOC emission species. The single test vehicle wasa Ford Focus 1.8. Pelkmans et al. (2010) obtained fuel consumption(l/km and MJ/km) and CO, VOC and NOx and CO2 emissionmeasurements for a Saab 9.5 Biopower 2.3 and a Volvo V50 (1.8 l).

From AVL/MTC (2011) emission test data were provided fromthe Swedish in-use vehicle emissions programme. The measure-ments included fuel consumption (l/100 km)5 and CO, VOC and NOx

4 The baseline fuel quality for petrol in Sweden is predominantly E5. From 2010,E5 is also the baseline fuel quality in Denmark.

5 l/100 km was transformed into MJ/100 km for E5 and E85 by using LHV (MJ/kgfuel) and r (kg/l) for neat gasoline and ethanol. Neat gasoline: LHV¼ 43.8, r¼ 0.75;Ethanol: LHV¼ 26.7, r¼ 0.79.

emissions for 17 cars: five Ford Focus (1.8 l.), five Renault Megane(1.6 l.), five Saab 9.5 Biopower (2.0 l.), one Volvo (1.8 l.) and one Saab(1.6 l.).

Based on the above mentioned measurement results for Euro 4FFV cars, average figures for the E5/E85 differences have beencalculated for fuel consumption and CO, VOC and NOx emissions.The percentage differences are used for Euro 5 and 6 FFV cars also,6

and are shown in Fig. 5. PM emissions are excluded from thepresent study due to minor emission importance and due to thesmaller amount of experimental data reported in the literaturefor PM compared to the other emission components, CO, VOCand NOx.7

As shown in Fig. 5, there is a tendency towards lower fuelconsumption and smaller VOC emissions, and higher CO and NOxemissions for FFVs using E85 compared to E5. In rounded figuresthe average percentage reductions of energy consumption and VOC

the above technical explanations and due to absence of experimental data for Euro6 cars, the E5eE85 emission differences examined for Euro 4 FFV cars are used forEuro 5 and 6 FFV cars also.

7 In 2009, the total TSP emissions for gasoline cars are less than 10% and 4%,respectively, compared to the total emissions for cars and the grand emission totalfor road transport in Denmark. TSP data are reported for eight FFVs. Data for fuelconsumption, CO, VOC and NOx are reported for 25 FFVs.

E5 vs. neat gasoline

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Fig. 4. Average energy consumption (MJ), CO, VOC and NOx emission differences for E5versus neat gasoline.

M. Winther et al. / Atmospheric Environment 55 (2012) 144e153148

are 3% and 1%, respectively. For CO and NOx, the average percentageincreases are 18% and 5%, respectively, for E85 compared to E5.

Also for E85 compared toE5, large variations exist in the emissiondifference values calculated for the individual cars, being expressedby the large standard variations shown in Fig. 5. As previouslymentioned for the E5 versus E0 emission comparisons, the largestandard deviations influence the precision of the derived averagefigures and this potential impact has to be taken into account whendata are used as input for the total emission calculations.

The E5/E85 emission differences are used in the present study todescribe the emission differences between neat gasoline and E85 aswell, by adjustment of the well established COPERT emissionfactors (Section 3.1) for neat gasoline. This adjustment of emissionfactors is explained in Section 3.3. It is regarded to be too uncertainto transform the COPERT inventory values into new E5 baselinefactors in an intermediate step by using the E0/E5 adjustmentvalues from Fig. 4, prior to emission adjustment for the usage ofE85. The E0/E5 adjustment values are derived from a relativelysparse experimental basis (nine cars) and have large standarddeviations of the individual car results as shown in Fig. 4.

3.3. Fuel consumption and emission factors for E5 and E85

3.3.1. Fuel consumption factor functionsThe kfc(E%) values from Figs. 3 and 4 predict the percentage

energy (joule) consumption change for E5 and E85, respectively, due

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Fig. 5. Average energy consumption (MJ), CO, VOC and NOx emission differences forE85 versus E5.

to changes in engine thermal efficiency. The results from kfc(E%) aretransformed into fuel consumption change by mass, by multiplica-tionwith the LHV ratio, LHVE0/¼ LHVE%, between neat gasoline andE5 and E85, respectively.

Hence, the mass based fuel consumption factor in g km�1, fcM,for E5/E85 is calculated by using the LHVE0/¼ LHVE% and kfc(E%)adjustment factors in combination with the fuel consumptionfactor for neat gasoline, fcM,E0:

fcMðE%Þ ¼ fcM;E0$LHVE0

LHVE%$�100þ kfcðE%Þ

�.100 (1)

where: E%¼ E5, E85; fcM(E%)¼ fuel consumption factor (g km�1)for E5/E85; fcM,E0¼ fuel consumption factor (g km�1) for neatgasoline; LHVE0¼ lower heating value for neat gasoline (MJ kg�1),Table 1; LHVE%¼ lower heating value for E5/E85 (MJ kg�1), Table 1;kfc(E%)¼ fuel consumption change (%) by energy for E5/E85compared to neat gasoline, Figs. 4 and 5.

Finally the energy based fuel consumption factor in MJ km�1,fcE(E%), for E5/E85 is found from:

fcEðE%Þ ¼ fcMðE%Þ$LHVðE%Þ (2)

where fcE(E%)¼ energy based fuel consumption factor (MJ km�1)for E5/E85.

3.3.2. Emission factor functions for CO, VOC and NOx

The km based emission factor, emfkm, in g/km for the emissioncomponent i (CO, VOC, NOx), is calculated by using the emissionchange ratio, ki(E%) for E5 and E85, respectively (Figs. 3 and 4), incombination with the km based emission factor for neat gasoline,emfkm,B0:

emfkm;iðE%Þ ¼ emfkm;i;B0$ð100þ kiðE%ÞÞ=100 (3)

where emfkm,i(E%)¼ emission factor (g km�1) for the emissioncomponent i, for E5/E85 ki(E%)¼ emission change (%) for E5/E85compared to neat gasoline, Figs. 4 and 5 emfkm,i,B0¼ emission factor(g km�1) for the emission component i, for neat gasoline;i¼ emission component, i¼ CO, VOC, NO.

3.3.3. Emission factor function for CO2

Bio ethanol is CO2 neutral, and hence, as a function of ethanolenergy percentage for E5/E85 fuels (3.27/78.4 %, Table 1), E%E, thefuel related emission factors, emfCO2,E(E%) become:

emfCO2 ;EðE%Þ ¼ emfCO2 ;EðE0Þ$ð100� E%EÞ (4)

where emfCO2,E(E%)¼ fuel related emission factor (gMJ�1) for E5/E85 emfCO2,E(E0)¼ fuel related emission factor (gMJ�1) for neatgasoline.

4. Calculation of total fuel consumption and emissions

For each inventory year and vehicle layer, fuel consumption andemissions of CO, VOC and NOx are calculated as the product of fuelconsumption/emission factors (Eqs. (2) and (3)) and total mileage(Fig. 1). The calculated fuel consumption multiplied with the fuelrelatedCO2 emission factors (Eq. (4)) yields the total emissions of CO2.

For bio ethanol special remarks must be made in order to fullyexplain the calculation procedure. As mentioned in Section 4, theREBECA scenario definition is to use a five percent volume mix ofbio ethanol in gasoline fuels (E5) by all gasoline vehicles, and let theincreasing surplus of ethanol available in the scenario years be usedby FFVs using E85.

In practical terms it is assumed that in 2010, FFVs belonging tothe most modern Euro layer for gasoline cars (Euro 4) use the

M. Winther et al. / Atmospheric Environment 55 (2012) 144e153 149

amount of ethanol not being used as E5 blends by gasoline vehiclesas such. In 2015, the share of Euro 4 vehicles being FFVs is main-tained, hence assuming approximately the same rate of scrappingof vehicles irrespective of technology. Further, the remainingethanol surplus is assumed to be used by the most modern Euroclasses in 2015 (Euro 5 and 6). This step wise ethanol allocationprinciple is used for the years 2020, 2025 and 2030 also.

The VOC emissions from gasoline evaporation are calculatedusing the COPERT calculation approach explained e.g. in Winther(2008).

In REBECa no attempts are made to estimate the difference inevaporative hydrocarbon emissions from the use of E5 and E85fuels instead of neat gasoline. However, it is well known thatevaporative emissions are bigger for vehicles using fuels with smallethanol blends (<10%) than for vehicles using neat gasoline. Thishas been explained by a decrease in the canister efficiency due toethanol absorption (e.g. Martini et al., 2009). Conversely, for highethanol blends the evaporative hydrocarbon emissions tend to besmaller than those coming from vehicles running on low ethanolblends, or even tend to reach the same levels as those evaporativehydrocarbon emissions coming from the use of neat gasoline(Martini et al., 2009; pers. comm. L. Erlandsson, AVL/MTC 2009,pers. comm. B. Larsen, JRC 2010).

Two specific characteristics for the use of low ethanol blends inDenmark tend to minimise the increase in evaporative emissionsfrom fuels with low ethanol blends compared to neat gasoline. Asa starting point, the Danish fuel vapour pressures are already highfor neat gasoline. Adding 5% ethanol to this fuel base will notchange the fuel vapour pressure, since such changes are compen-sated for in the blending process by removing high volatilityhydrocarbons from the fuel. Hence, the effect of elevated evapo-rative hydrocarbon emissions becomes smaller. Moreover,improved emission after treatment systems also reduces thisparticular emission problem in the future, due to the fact that forthe future Euro 5 standards, vehicles must be equipped with largercarbon canisters and tanks made with low permeation materials.

5. Fuel consumption and emission results

5.1. Total fuel consumption and emissions

The calculated totals for fuel consumption, CO2, NOx, CO andVOC are shown for gasoline passenger cars in Table 2 for thebaseline (FS) and biofuel (BS1, BS2) scenarios based on the 65 $ and100 $ mileage forecasts, respectively.

Table 2Fuel consumption and emission results for the baseline and biofuel scenarios calculated

Mileage forecast: 65 $ M

Scenario Year Energy, PJ NOx, Tonnes VOC, Tonnes CO, Tonnes CO2, kTonnes Sc

FS 2004 75.4 20,371 20,423 158,855 5502 FSFS 2010 59.0 8033 8768 81,380 4309 FSFS 2015 52.2 3402 4354 43,458 3809 FSFS 2020 51.5 1678 2812 26,856 3759 FSFS 2025 52.6 1217 2421 21,275 3841 FSFS 2030 54.4 1120 2373 20,276 3970 FSBS1 2010 59.0 8570 8408 81,919 4048 BSBS1 2015 52.1 3628 4179 43,895 3487 BSBS1 2020 51.3 1789 2708 27,308 3352 BSBS1 2025 52.5 1297 2334 21,705 3427 BSBS1 2030 54.2 1193 2288 20,712 3543 BSBS2 2010 59.0 8570 8408 81,919 4048 BSBS2 2015 52.0 3627 4182 44,021 3372 BSBS2 2020 51.2 1787 2713 27,560 3125 BSBS2 2025 52.2 1293 2344 22,194 2989 BSBS2 2030 53.9 1188 2303 21,453 2881 BS

Although the forecasted mileage level is highest for the low oilprice traffic scenario, both the 65 $ and the 100 $ traffic forecastsexpect a significant decrease in total mileage for gasoline carsuntil the mid-2010s due to the dieselification of the Danish carfleet (c.f. Section 2.1). This is directly reflected in the calculatedfuel consumption results for gasoline cars shown in Table 2. ForFS, the expected fuel consumption reduction between 2004 and2030 is 28 % and 38 % for the 65 $ and 100 $ mileage case,respectively.

Compared to the FS baseline, the CO2 emissions estimated forBS1 and BS2 become significantly smaller and most markedly forthe most ambitious BS2 case. This is clear from the relative emis-sion changes between 2004 and 2030; for FS, BS1 and BS2 (resultsin brackets) these figures become [�28%, �36%, �48%] and[�38%, �45%, �55%], for the 65 $ and 100 $ mileage forecast,respectively. According to conventional inventory guidelines, bio-fuels are regarded as CO2 neutral for exhaust emissions (vehiclebased emissions). Further comments relating to this issue are givenin the following Section 6. The W-t-W emission consequences ofintroducing biofuels in the road transport sector, including theentire chain from agricultural production to manufacturing,distribution and engine combustion of the biofuel are treated ina different part of the REBECA project (Slentø et al., 2010), c.f.Section 6.

In each mileage case and for each of the remaining emissioncomponents the calculated changes between 2004 and 2030become very similar for FS, BS1 and BS2. Hence, the emissionimpact from the gradual strengthened emission standards for newsold gasoline cars and the decline in total mileage until the mid-2010s are much greater than the emission impact from the intro-duction of E5 and E85. For FS, the following emission reductionsfrom 2004 to 2030 are calculated for NOx, VOC and CO in the 65$[100 $] mileage case; 95%[95%], 88%[90%] and 87%[89%].

The percentage differences between FS and the BS1/BS2scenarios are shown in Section 5.2 (Table 3) and more thoroughlydiscussed in this part of the paper.

5.2. Fuel consumption and emissions differences between baselineand biofuel scenarios

Some of the most important fuel consumption and emissiondifferences between the 65 $ baseline scenario and the mostambitious biofuel scenario, BS2, are explained in the following. Thetrend and emission difference explanations given for the 65 $forecast results are valid for the 100 $ forecast also. In the latter case

for gasoline passenger cars in the present study.

ileage forecast: 100 $

enario Year Energy, PJ NOx, Tonnes VOC, Tonnes CO, Tonnes CO2, kTonnes

2004 75.4 20,371 20,423 158,855 55022010 50.9 6929 7627 70,193 37182015 44.6 2905 3772 37,122 32572020 44.0 1432 2449 22,918 32142025 45.0 1038 2115 18,149 32842030 46.5 955 2075 17,295 3395

1 2010 50.9 7392 7317 70,657 34931 2015 44.5 3099 3623 37,494 29821 2020 43.9 1526 2360 23,304 28651 2025 44.9 1106 2040 18,516 29301 2030 46.4 1017 2002 17,666 30292 2010 50.9 7392 7317 70,657 34932 2015 44.5 3098 3626 37,602 28832 2020 43.8 1525 2364 23,518 26722 2025 44.7 1103 2048 18,933 25562 2030 46.1 1013 2015 18,298 2464

Table 3Fuel consumption and emission percentage differences between baseline and biofuel scenarios BS1 and BS2 for gasoline passenger cars.

Scenario Year Mileage forecast: 65 $ Mileage forecast: 100 $

Energy NOx VOC CO CO2 Energy NOx VOC CO CO2

BS1 2010 �0.1 6.7 �4.1 0.7 �6.0 �0.1 6.7 �4.1 0.7 �6.0BS1 2015 �0.2 6.7 �4.0 1.0 �8.4 �0.2 6.7 �4.0 1.0 �8.4BS1 2020 �0.3 6.6 �3.7 1.7 �10.8 �0.3 6.6 �3.6 1.7 �10.8BS1 2025 �0.3 6.5 �3.6 2.0 �10.8 �0.3 6.5 �3.5 2.0 �10.8BS1 2030 �0.3 6.5 �3.6 2.1 �10.8 �0.3 6.5 �3.5 2.1 �10.8BS2 2010 �0.1 6.7 �4.1 0.7 �6.0 �0.1 6.7 �4.1 0.7 �6.0BS2 2015 �0.3 6.6 �3.9 1.3 �11.5 �0.3 6.6 �3.9 1.3 �11.5BS2 2020 �0.5 6.5 �3.5 2.6 �16.9 �0.5 6.5 �3.5 2.6 �16.9BS2 2025 �0.7 6.3 �3.2 4.3 �22.2 �0.7 6.3 �3.1 4.3 �22.2BS2 2030 �0.9 6.1 �3.0 5.8 �27.4 �0.9 6.1 �2.9 5.8 �27.4

M. Winther et al. / Atmospheric Environment 55 (2012) 144e153150

the emission levels are only somewhat lower due to less mileage inthe underlying traffic forecast.

As shown in Fig. 6, the consumption of neat gasoline in FS andthe total consumption of E5 and E85 in BS2 decreases until 2020due to the envisaged dieselification of the car fleet in the future. Thefuel consumption for BS2 becomes a little smaller than for FS, c.f.percent changes in Table 3 below, due to the small improvement inthermal efficiency for the FFV engines using E85.

The CO2 emission differences between BS2 and FS increaseduring the forecast period. The maximum emission reduction of27.4% calculated between BS2 and FS in 2030 (c.f. Fig. 6, Table 3) issomewhat lower than 25%, which would be expected from the BS2bio ethanol share defined in REBECa. The explanation is that E85covers the residual amount of ethanol substituting up to 25% of allroad transport gasoline. Since E85 is excluded from usage bygasoline vans, mopeds and motorcycles in REBECa, the energyshare of (CO2 neutral) ethanol used by gasoline cars become largerthan the ethanol energy share for road transport gasoline asa whole.

For gasoline cars, the NOx, VOC and CO emissions are shown inFig. 7 for the baseline scenario and BS2. As mentioned in theprevious Section 5.1, the emissions shown in Fig. 7 decreasesignificantly throughout the forecast period primarily due togradually lower emission factors (Fig. 3) and total mileage reduc-tions until 2020 (Fig. 1). Being based on the emission factordifferences shown in Figs. 4 and 5, the emission differences due tothe use of E5 and E85 are expected to be small.

The summary Table 3 shows the percentage differencesbetween the baseline scenario and BS1 and BS2 for fuel

Energy consumption - gasoline cars

0

10

20

30

40

50

60

70

2010 2015 2020 2025 2030

PJ

FS BS2

Fig. 6. Baseline and BS2 energy consumption and CO2 em

consumption and emissions. For all years the emission differencesare between 6% and 7% for NOx and�3% to �4% for VOC. For CO thelargest emission difference of 6% occurs between the baselinescenario and BS2 in 2030, related to a bio ethanol share of 25%.

Also in absolute terms the estimated emission consequences ofusing E5 and E85 are small (Table 2). For NOx the largest emissionincrease is 537 tonnes calculated for 2010, whereas the smallestemission increase reaches 68 tonnes in 2030. In the case of VOC thelargest emission saving is 359 tonnes in 2010, and the VOC emissionsaving potential reduces to 70 tonnes in 2030. The smallest andlargest emission increases calculated for CO are 539 tonnes in 2010and 1 177 tonnes in 2030.

6. Summary and discussion

This article describes the direct vehicle emission impact of thefuture use of bio ethanol as a fuel for gasoline cars in Denmarkarising from the vehicle specific fuel consumption and emissiondifferences between neat gasoline (E0) and E5/E85 gasoline-ethanol fuel blends derived from emission tests using primarilythe European NEDC and ARTEMIS driving cycles. The E0-E5 testvehicles (nine cars) represent today’s gasoline car traffic well wheremost of the driving is being made with cars certified as Euro 3þ.The FFV test cars (25 cars) are all certified according to the Euro 4emission standard introduced in Europe from the mid-2000s. Thismatches well with the propagation of the FFV technology inEurope.

The literature review shows that for vehicles using E5 ratherthan E0 the average fuel consumption and emission differences are

2010 2015 2020 2025 2030

CO2 emissions - gasoline cars

0

1000

2000

3000

4000

5000

kto

ns

FS BS2

ission results for gasoline cars in the scenario years.

NOx emissions - gasoline cars

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

2005 2010 2020 2030

2005 2010 2020 2030

2005 2010 2020 2030

To

nn

es

E5 (BS2) E85 (BS2) E0 (FS)

VOC emissions - gasoline cars

0

1000

2000

3000

4000

5000

6000

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To

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es

E5 (BS2) E85 (BS2) E0 (FS)

CO emissions - gasoline cars

0

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20000

30000

40000

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70000

80000

90000

To

nn

es

E5 (BS2) E85 (BS2) E0 (FS)

Fig. 7. Baseline and BS2 NOx, VOC and CO emission results for gasoline cars in the scenario years (65 $ mileage forecast).

M. Winther et al. / Atmospheric Environment 55 (2012) 144e153 151

small based on measurements from nine cars. For CO, VOC and NOxthe derived average differences are 0.5%, �5% and 7%, respectively.For FFVs using E85 rather than E5, the emission differences becomeeven smaller, except for CO. The derived average emission differ-ences are in this case 18%, �1% and 5% for CO, VOC and NOx,respectively.

The literature based emission comparisons made in this studydisplay a large variation in the emission difference values calcu-lated for the individual cars. This is expressed by the large standarddeviation of the total average emission difference computed foreach emission component in both comparative cases. The largestandard deviations introduce some uncertainties in the totalemission calculations and it is important to keep these uncer-tainties in mind when data are used as input for the total emissioncalculations and during the assessment of the total emissionsresults.

With CO2 as an exception and bearing in mind the uncertaintiesdiscussed above, the calculated emission consequences of using bioethanol as a fuel for gasoline cars are small even at blend ratios upto 25%. This is predictable from the fundamental fuel consumptionand emission differences between neat gasoline (E0) and E5/E85used in the calculations. The significant emissions decrease for theFS and for the BS1 and BS2 scenarios from 2004 to 2030 are

primarily due to gradually lower fossil basis emission factors andtotal mileage reductions until 2020. In all years the emissiondifferences between FS and the biofuel scenarios are between 6 %and 7 % for NOx and �3% to �4% for VOC. For CO the largestemission difference of 6 % occurs between the FS scenario and BS2in 2030, related to a bio ethanol share of 25%.

For CO2 significant emission differences are calculated betweenFS and the biofuel scenarios for gasoline cars; the largest differenceof 27% occurs between FS and BS2 in 2030. The reason for thesedifferences is that the present inventory follows the calculationapproach prescribed by the United Nations Framework Conventionon Climate Change (UNFCCC) and the UNECE CLRTAP (Conventionon Long Range Transboundary Air Pollutants) conventions. For roadtransport, only the vehicle based emissions are made up, andfurther, the biofuel part of the combusted fuel are regarded as CO2neutral. Emissions associated with e.g. biofuel production andalternative use of biomass are treated in other relevant UNFCCC/UNECE inventory categories. The focus on direct vehicle emissionsfor road transport as a single sectormakes sense for the combustionrelated emissions (this study focuses on NOx, VOC and CO), whichhave important environmental impacts on local air quality andhealth. For CO2, however, the calculated emission differencescannot be assessed by regarding road transport alone.

M. Winther et al. / Atmospheric Environment 55 (2012) 144e153152

Being a greenhouse gas, the emission impacts of CO2 must beseen from a global warming and policy perspective. In thisconnection the consequences for direct CO2 emissions are onlya part of the story. So, to answer the question if bio ethanol shouldbe introduced from a society point of view an integrated W-t-Wanalysis and welfare economic Cost Benefit Analysis is necessary.Such an integrated analysis describes the emission and welfareeffects for the full chain of production, distribution and combustionof bio fuels, and especially all the indirect consequences of re-allocating society’s scarce resources (land, real capital and labour)for bio fuel production. The most important parts of the W-t-Wanalysis are agricultural land use change, decreasing use of biomassfor energy production and the actual production of the biofuel.

An integratedW-t-Wand welfare economic Cost Benefit AnalysisismadebySlentø et al. (2010) inadifferentpartof theREBECAproject.For 1. generation bio ethanol Slentø et al. (2010)find that even if fossilfuel is used in the production process there will still be a decrease intotal CO2 emissions. For 2. generation bio ethanol the result is evenbetter. The total decrease in CO2 emissions is bigger than the directdecrease because of by-products that cause large CO2 savings.

In the two scenarios BS1 and BS2 total CO2 emissions in 2030decrease with 11% and 30% respectively. These numbers can becompared with decreases of 11% and 27% if only direct CO2 emis-sions are taken into account. The results are due to BS1 havinga high share of 1. generation bio ethanol and a low overall use of bioethanol. The total use of bio ethanol is higher in BS2 and the shareof 2. generation bio ethanol is bigger.

Slentø et al. (2010) also analyses the welfare economic conse-quencesof producing andconsumingbio ethanol. The result is highlydependable on the oil price, the price of agricultural production thatis lost and the shadowprice of CO2. Under realistic price assumptions1. generation bio ethanol is not profitable to society while 2. gener-ation bio ethanol is. The result, however, will change if agriculturalproducts become more expensive relative to oil.

Emissions of aldehydes, which are known to have irritant effectsof exposure by inhalation and to the eyes, and are classified aspossibly carcinogenic to humans, are also a main concern associ-atedwith the use of bio ethanol. Manymeasurement results (e.g. deServes, 2005; Westerholm et al., 2008; Martini et al., 2009) showincreased emissions of especially acetaldehyde for E85 compared toE5, indicating that acetaldehyde is formed with ethanol asa precursor (e.g. de Serves, 2005). The assessment of E5eE85aldehyde emission differences derived from the literature andsubsequent estimation of the total emission consequences hashowever not been a part of the present study.

The calculationmethod related to biofuel usage in road transportis well established for vehicle based CO2 emissions alone and hencethe estimated emissions presented in this study are regarded as veryprecise based on the present forecast data for fleet composition andvehicle mileage. Conversely e as previously discussed emainly dueto the average emission differences being considerably smaller thanthe standard deviations of the results for the individual cars, theestimated emission differences for NOx, VOC and CO are associatedwith some uncertainties, and consequently caution must be takenprior to the assessment of these emission differences.

The fuel consumption and emission differences between neatgasoline (E0) and E5/E85 gasoline-ethanol fuel blends presented inthis study can be used as an input for environmental impactassessment studies or for research purposes as such, but bearing inmind the uncertainties in relation to the combustion specificemission components, it is important to carry out sensitivityanalyses that reflect these uncertainties.

The presented fuel consumption and emission difference dataare in particular very useful for application in Europe. As previouslyexplained in the beginning of this section and in Section 3.2, the

data are derived from European measurement programmes usingEuropean driving cycles and test vehicles certified according to theEU emission legislation standards, ensuring fine interrelationsbetween test vehicles/test conditions and the emission data formatfor European emission inventories.

Acknowledgements

The REBECA project was funded by the Programme Commissionon Energy and Environment under the Danish Strategic ResearchCouncil. Lennart Erlandsson and Charlotte Sandström-Dahl, AVL/MTC,Giorgio Martini, JRC, Peter Ahlvik, ExIS AB, Scacchi Costanza, ERSES.p.A and Bo Larsen, JRC, must be thanked for providingmeasurementdata and other information used for the present literature review.

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