Strategies to Introduce N-Butanol in Gasoline Blends

sustainability

Article Strategies to Introduce n-Butanol in Gasoline Blends

Magín Lapuerta *, Rosario Ballesteros and Javier Barba

Escuela Técnica Superior de Ingenieros Industriales, University of Castilla-La Mancha, Av. Camilo José Cela s/n, 13071 Ciudad Real, Spain; [email protected] (R.B.); [email protected] (J.B.) * Correspondence: [email protected]

Academic Editors: Gilles Lefebvre and Francisco J. Sáez-Martínez Received: 13 February 2017; Accepted: 7 April 2017; Published: 12 April 2017

Abstract: The use of oxygenated fuels in spark ignition engines (SIEs) has gained increasing attention in the last few years, especially when coming from renewable sources, due to the shortage of fossil fuels and global warming concern. Currently, the main substitute of gasoline is ethanol, which helps to reduce CO and HC emissions but presents a series of drawbacks such as a low heating value and a high hygroscopic tendency, which cause higher fuel consumption and corrosion problems, respectively. This paper shows the most relevant properties when replacing ethanol by renewable n-butanol, which presents a higher heating value and a lower hygroscopic tendency compared to the former. The test matrix carried out for this experimental study includes, on the one hand, ethanol substitution by n-butanol in commercial blends and, on the other hand, either ethanol or gasoline substitution by n-butanol in E85 blends (85% ethanol-15% gasoline by volume). The results show that the substitution of n-butanol by ethanol presents a series of beneﬁts such as a higher heating value and a greater interchangeability with gasoline compared to ethanol, which makes n-butanol a promising fuel for SIEs in commercial blends. However, the use of n-butanol in E85 blends substituting either gasoline or ethanol may cause cold-start problems due to the lower vapor pressure of n-butanol. For this reason, a combined substitution of n-butanol by both gasoline and ethanol is proposed so that n-butanol can be used without start problems.

Keywords: n-butanol; gasoline; E85; interchangeability; density; heating value; vapor pressure

1. Introduction The gradual depletion of fossil fuels along with concern about global warming have led to the use of biofuels in internal combustion engines (ICEs) [1] Among various biofuels, bio-alcohols have been investigated as alternative engine fuels because of their potential for improving engine performance and reducing pollutant emissions [2]. Bio-alcohols such as ethanol and butanol can reduce the life-cycle greenhouse emissions, due to their biological production processes. In fact, ethanol is normally used in spark ignition engines (SIEs) replacing gasoline [3–6]. Both of the aforementioned alcohols have also been used in compression ignition engine (CIEs) as a diesel partial substitute [7–10]. This paper focuses on the use of alcohols in SIEs, in which the most used bio-alcohol is ethanol, which is very common in many countries. The main advantage of this fuel is the reduction of CO and HC emissions when used in SIEs as a gasoline substitute [5,11]. Particularly, ethanol has been proved to reduce the extra emissions of CO and HC during cold-start conditions with respect to hot engine conditions [4]. In direct-injection SIEs, which have been gaining prominence in the last few years, ethanol has been shown to reduce NOx emissions slightly [3] and PM emissions considerably [6]. The lower heating value of ethanol is much lower than that of gasoline fuel, which causes higher fuel consumption. However, the thermal brake efﬁciency has been shown to slightly increase [12]. Ethanol could also present corrosion problems in the injection system due to its hydroscopic tendency. Ethanol also presents low lubricity [13], which can cause problems in gasoline direct-injection engines. Finally,

Sustainability 2017, 9, 589; doi:10.3390/su9040589 www.mdpi.com/journal/sustainability Sustainability 2017, 9, 589 2 of 10 according to Rodríguez-Antón et al. [14], the addition of ethanol increases the vapor pressure of the blend only up to 35% by volume. A higher ethanol content would reduce the vapor pressure that leads to start problems [4]. n-butanol is considered the most promising bio-alcohol because of its numerous advantages over short-chain alcohols (methanol and ethanol mainly), including a higher energy density (higher lower heating values and higher density), lower viscosity, and higher lubricity. Additionally, n-butanol is much less hygroscopic and corrosive than ethanol. Besides, n-butanol seems to have a very interesting potential because its properties are very similar to those of gasoline; therefore, it would be compatible with the current fuel distribution infrastructure. n-butanol is a second-generation biofuel since it can be produced from lignocellulosic or waste biomass, with lower lifecycle greenhouse emissions than ethanol [15]. Currently, it can be produced through either an acetone–n-butanol–ethanol (ABE) fermentation process or an isopropanol–n-butanol–ethanol (IBE) fermentation process [16]. However, n-butanol has lower vapor pressure compared to ethanol and obviously compared to gasoline, which is a very evaporative fuel. This drawback could cause cold-start problems in SIEs when n-butanol is used in high proportions. Some authors [3,17–19] have reported studies using gasoline-butanol blends in SIEs. Costagliola et al. [17] tested 10% n-butanol (as well as different ethanol contents) in a port-fuel injection (PFI) engine showing similar benefits in CO, HC, and PM emissions as with ethanol, but also similar increases in carbonyl emissions. Galloni et al. [18] tested gasoline and n-butanol (20% and 40% butanol mass percentage) also in PFI engine. When using a B40 blend, power delivered at same engine speed decreased about 13%, mainly due to the difference between heating values. HC and NOx emissions decreased slightly, whereas CO emissions did not suffer any significant change when using B40. Again in a PFI engine, Li et al. [19] also observed lower CO (4.2%), HC (18.9%), and NOx (5.5%) emissions when using B30 compared to gasoline as a baseline fuel keeping the engine load constant at 300 kPa of the brake mean effective pressure. Fournier et al. [3] tested gasoline blended with butanol, butanol–ethanol, and butanol–ethanol-acetone, with butanol contents up to 40% in volume, in both direct and port-fuel injection (PFI), showing that benefits in HC emissions in PFI engines turned into HC increases in direct-injection engines. In this study, ethanol is replaced by n-butanol in commercial ethanol–gasoline blends, as well as in E85 blends (85% ethanol-15% gasoline by volume). Some properties of the blends were measured in order to compare the use of n-butanol instead of ethanol in commercial blends for their use in SIEs. The values of the different properties measured must be within the limits considered in EN 228 and EN 15376 standards. In summary, this paper discusses the advantages and drawbacks of using n-butanol instead of ethanol in different percentages and blends considering current European regulations. Vapor pressure, limited in both the E85 standard (CEN/TS 15293) and the gasoline standard (EN 228) was revealed as the most restrictive property. Within this European legal framework, the use of oxygenated compounds such as methanol, ethanol, isopropyl, ter-butyl, isobutyl alcohols, and ethers (with five or more carbon atoms) is explicitly considered. However, n-butanol should be included within the group of “other oxygenated compounds” despite having a similar octane number than gasoline, and closer polarity to that of gasoline, and thus greater miscibility than ethanol.

2. Experimental Procedure and Fuels The whole test matrix (shown in Figure1) carried out in this experimental study is divided into three submatrices (red, blue, and green dots) in order to study the most appropriate strategy for the use of n-butanol in commercial blends. First, commercial gasoline–ethanol blends in which ethanol (up to 10% by volume) was replaced by n-butanol (up to 16% by volume) were studied, keeping the oxygen content (limited by 3.7% by mass) constant, as limited by the EN 228 standard. Moreover, similar tests were carried out limiting the oxygen content to 6 and 7.4% by mass, considering possible future regulations. This submatrix is marked with red dots in Figure1. Second, considering E85 as a baseline fuel (marked in yellow), ethanol was replaced by n-butanol up to 50% by volume of ethanol Sustainability 2017, 9, 589 3 of 10 Sustainability 2017, 9, 589 3 of 10 baseline fuel (marked in yellow), ethanol was replaced by n-butanol up to 50% by volume of ethanol (minimum(minimum value value regulated regulated by by EN EN 15376), 15376), leading leading to to a ablend blend of of 50% 50% ethanol, ethanol, 35% 35% n-butanol, n-butanol, and and 15% 15% gasolinegasoline by by volume. volume. This This submatrix submatrix is is marked marked with with blue blue dots dots in in Figure Figure 1.1. Third, Third, considering considering again again E85E85 as as a abaseline baseline fuel, fuel, gasoline gasoline was was progressively progressively re replacedplaced by by n-butanol n-butanol up up to to 15% 15% by by volume, volume, thus thus removingremoving gasoline gasoline from thethe blend.blend. ThisThis submatrix submatrix is is marked marked with with green green dots dots in Figurein Figure1. Finally, 1. Finally, some someextra extra dots dots were were carried carried out for out a for more a more detailed detailed study study of vapor of vapor pressure, pressure, which which will bewill explained be explained in the incorresponding the corresponding section. section. These These extra extra dots aredots marked are marked in purple. in purple.

Figure 1. Test matrix carried out in the experimental study. Figure 1. Test matrix carried out in the experimental study.

TheThe main main characteristics characteristics of of pure pure alcohols alcohols (ethanol (ethanol and and n-butanol) n-butanol) and and gasoline gasoline are are shown shown in in TableTable 1.1. These These selected selected results results are are in in agreement agreement wi withth those those obtained obtained in in the the literature. literature. For For instance, instance, thethe lower lower heating heating value, value, the the density, density, and and the the vapor vapor pressure pressure are are very very similar similar to to those those obtained obtained by by ElfasakhanyElfasakhany [20] [20 ]and and Aleiferis Aleiferis et et al. al. [21] [21 ]for for ethano ethanoll and and n-butanol n-butanol fuels. fuels. However, However, the the vapor vapor pressure pressure valuesvalues for for gasolines areare variable,variable, since since gasoline gasoline is ais seasonala seasonal fuel, fuel, so its so properties its properties depend depend on the on season the seasonof the year.of the The year. experimental The experimental procedure procedure and the and devices the useddevices in thisused study in this to measurestudy to themeasure properties the propertiesdescribed described in the results in the section results are section explained are explained below. Density below. wasDensity measured was measured following following EN ISO 3675EN ISOstandard 3675 standard at 15 ◦C usingat 15 °C a densimeter. using a densimeter. A higher heatingA higher value heating was value measured was measured with a bomb with calorimeter a bomb calorimeter(Parr 1351) (Parr according 1351) toaccording UNE 51123 to UNE standard. 51123 Finally, standard. vapor Finally, pressure vapor was pressure measured was at measured a temperature at a temperatureof 38 ◦C with of a 38 commercial °C with a device commercial (Eralytics, device model (Eralytics, Evarap EV01)model according Evarap EV01) to EN according 13016-1. Research to EN 13016-1.Octane NumberResearch (RON)Octane measurements Number (RON) for measurements gasoline, E10 (10%for gasoline, ethanol E10 by volume (10% ethanol in gasoline by volume blend), inand gasoline Bu16 (16%blend), n-butanol and Bu16 by (16% volume n-butanol in gasoline by volume blend) in were gasoline carried blend) out were in a CFR carried engine out followingin a CFR enginethe ASTM following D 2699-15a the ASTM standard. D 2699-15a However, standard. a CFR engine However, is out a ofCFR range engine when is operatingout of range either when with operatingpure alcohols either such with as pure ethanol alcohols or n-butanol such as orethano withl blends or n-butanol with high or with alcohol blends content. with For high this alcohol reason, content.ethanol For and this n-butanol reason, valuesethanol were and takenn-butanol from values the literature were taken [18]. from the literature [18]. WithWith regard regard to to fuels, fuels, the the gasoline gasoline used used in in this this study study was was supplied supplied by by the the Repsol Repsol company, company, and and itsits main main characteristic characteristic is is the the absence absence of of oxygenated oxygenated additives additives such such as as ETBE ETBE and and MTBE MTBE in in order order to to properlyproperly observe observe the the effect effect of of alcohol alcohol addition. addition. Bu Butanoltanol was was supplied supplied by by Green Green Biologics Biologics Ltd. Ltd. (Milton (Milton Park,Park, UK), UK), as as a amember member of of the the Co Consortiumnsortium of of Butanext Butanext Project Project (s (seeee Acknowledgments), Acknowledgments), and and ethanol ethanol waswas supplied supplied by by PanReac PanReac AppliChem. AppliChem.

Sustainability 2017, 9, 589 4 of 10

Sustainability 2017, 9, 589 Table 1. Specifications of tested fuels. 4 of 10

Properties Method Gasoline a Ethanol a n-Butanol a Purity (% v/v) Table 1. Specifications of tested fuels. - 99.5 99.5 Density at 15 °C (kg/m3) EN ISO 3675 726.0 793.0 808.7 ViscosityProperties at 40 °C (cSt) EN Method ISO 3104 0.40–0.80 Gasoline a 1.08Ethanol a 2.63n-Butanol a Higher heating value (MJ/kg) UNE 51123 44.01 26.71 34.17 Purity (% v/v) - 99.5 99.5 DensityHigher atheating 15 ◦C (kg/mvalue3 (MJ/L)) EN ISO 3675 31.95 726.0 21.18 793.0 27.63 808.7 Viscosity atC 40(%◦ wt)C (cSt) EN ISO 3104 86.00 0.40–0.80 52.14 1.08 64.86 2.63 Higher heatingH value(% wt) (MJ/kg) UNE 51123 14.00 44.01 13.13 26.71 13.51 34.17 Higher heatingO (% value wt) (MJ/L) 0.00 31.95 34.73 21.18 21.62 27.63 C (% wt) 86.00 52.14 64.86 b b WaterH solubility (% wt) (ppm wt) EN ISO 12937 <0.1 14.00 Fully miscible 13.13 <7.7 13.51 Standard enthalpyO (% wt)of vaporization (kJ/kg) 380–500 0.00 b 904 34.73b 716 b 21.62 WaterStochiometric solubility (ppmfuel/air wt) ratio EN ISO 12937 1/14.7<0.1 b Fully 1/9.0 miscible 1/11.2<7.7 b Standard enthalpyCFPP of vaporization (°C) (kJ/kg) EN116 380–500 - b <−51904 b <−51716 b StochiometricOctane fuel/air number ratio ASTM D-2699 95.8 1/14.7 c 107.0 1/9.0 d 96.01/11.2 d CFPP (◦C) EN116 - <−51 <−51 VaporOctane pressure number (kPa) ASTM EN 13016-1 D-2699 60 95.8 c 15107.0 d 2 96.0 d VaporFlash pressure point (kPa) (°C) EN ISO 13016-1 2719 −45.00 60 13.00 15 36.17 2 ◦ a data measuredFlash point at University ( C) of Castilla-La Mancha; ISO 2719 b taken from−45.00 reference [22]; c 13.00 data provided 36.17by aRepsoldata measured company, at Spain; University d taken of Castilla-La from Reference Mancha; [18].b taken from reference [22]; c data provided by Repsol company, Spain; d taken from Reference [18]. 3. Results and Discussion 3. Results and Discussion 3.1. Density and Lower Heating Value 3.1. Density and Lower Heating Value The density of blends is usually given by a volume-weighted average of the densities of the The density of blends is usually given by a volume-weighted average of the densities of the components (all measured at the same temperature). However, some exceptions to this behavior, components (all measured at the same temperature). However, some exceptions to this behavior, excess volume, can be found due to a large mismatch in the molecular/compositional structure of the excess volume, can be found due to a large mismatch in the molecular/compositional structure of components. the components. In this work, besides the test scheduled in the test matrices, some extra-blends were tested to In this work, besides the test scheduled in the test matrices, some extra-blends were tested to evaluate possible non-lineal tendencies when small quantities of oxygenated fuels were added with evaluate possible non-lineal tendencies when small quantities of oxygenated fuels were added with respect to the original test matrix. As observed in Figure 2, n-butanol has a higher density than respect to the original test matrix. As observed in Figure2, n-butanol has a higher density than ethanol, ethanol, and both alcohols have a higher density than gasoline. In European countries, gasolines are and both alcohols have a higher density than gasoline. In European countries, gasolines are usually usually made to have densities close to the lower limit (upper and lower limits established in EN 228 made to have densities close to the lower limit (upper and lower limits established in EN 228 standard standard are shown in Figure 2 with dashed lines) for two reasons: first, the strong dieselization of are shown in Figure2 with dashed lines) for two reasons: first, the strong dieselization of the vehicle the vehicle market, leading to an extension of the diesel distillation range (and thus to an extension market, leading to an extension of the diesel distillation range (and thus to an extension of the diesel of the diesel density range); second, such a density allows for the further blending with oxygenates, density range); second, such a density allows for the further blending with oxygenates, which usually which usually have higher densities. In any case, only lower butanol concentrations with respect to have higher densities. In any case, only lower butanol concentrations with respect to ethanol could be ethanol could be used in the blends to fulfill the above-mentioned standard. used in the blends to fulfill the above-mentioned standard.

Figure 2. Density versus alcohol content. Sustainability 2017, 9, 589 5 of 10 Sustainability 2017, 9, 589 5 of 10 Sustainability 2017, 9, 589 5 of 10 With regard to heating value, an almost linear trend with the alcohol content (Figure 3) can be With regard to heating value, an almost linear trend with the alcohol content (Figure 33)) cancan bebe observed when both ethanol and n-butanol are used. However, n-butanol has a higher heating value observed when both ethanol and n-butanol are used.used. However, n-butanol has a higher heating value than ethanol in both mass and volume basis, as observed in Figure 3. For this reason, n-butanol blends than ethanol in both mass and volume basis, as observed in Figure 3 3.. ForFor thisthis reason,reason, n-butanoln-butanol blendsblends are expected to reduce the fuel consumption in an SIE vehicle with respect to ethanol blends [3], and are expected to reduce the fuel consumption in an SIE vehicle with respect to ethanol blends [3], [3], and would therefore increase the vehicle´s mileage. The effect of alcohol as a fuel component on the would thereforetherefore increase increase the the vehicle vehicle´s´s mileage. mileage. The The effect effect of alcohol of alcohol as a fuelas a component fuel component on the on engine the engine efficiency has been reported to be minor [3,17,20] and is not expected to modify this trend. engineefﬁciency efficiency has been has reported been reported to be minor to be [ 3minor,17,20 ][3 and,17,20] is not and expected is not expected to modify to modify this trend. this trend.

Figure 3.3. Heating value versus alcohol content in mass basis and volume basis. Figure 3. Heating value versus alcohol content in mass basis and volume basis. As shown in Figure 4, when the ethanol content increases, the octane number of the blend also As shown in Figure 44,, whenwhen thethe ethanolethanol contentcontent increases,increases, thethe octaneoctane numbernumber ofof thethe blendblend alsoalso increases. This could derive into an advantage, either because the compression ratio of the engine increases. This This could could derive derive into into an advantage, either because the compression ratio of the engine could be increased in a modified engine design, leading to improved engine efficiency, or because could be increased in a modiﬁedmodified engine design, le leadingading to improved engine efficiency, efﬁciency, or because additives improving the octane number could be avoided. Differently to ethanol, butanol presents a additives improving the the octane octane number number could could be be avoi avoided.ded. Differently Differently to to ethanol, ethanol, butanol butanol presents presents a similar value of octane number compared to gasoline and, thus, modifying the butanol content in similara similar value value of of octane octane number number compared compared to to gaso gasolineline and, and, thus, thus, modifying modifying the the butanol content in gasoline blends would not require re-design nor a reformulation of additives. Consequently, butanol, gasoline blends would not require require re-design nor a a reformulation reformulation of of additives. additives. Consequently, Consequently, butanol, butanol, compared to ethanol, can be considered as more interchangeable with gasoline. compared to ethanol, can be considered asas moremore interchangeableinterchangeable withwith gasoline.gasoline.

Figure 4. Octane number of ethanol and butanol blends with gasoline. Figure 4. Octane number of ethanol and butanol blends with gasoline.

Sustainability 2017, 9, 589 6 of 10 Sustainability 2017, 9, 589 6 of 10 3.2. Vapor Pressure

3.2. VaporWith Pressureregard to vapor pressure, four standards were used for the vapor pressure tests. Specifically, two American standards (ASTM D5191 and ASTM D6378) and two European standards With regard to vapor pressure, four standards were used for the vapor pressure tests. Speciﬁcally, (EN 13016-1 and EN 13016-2) were followed. Standard EN 13016-1 was selected because gasoline two American standards (ASTM D5191 and ASTM D6378) and two European standards (EN 13016-1 standard EN 228 indicates that vapor pressure tests must be made at 37.8 °C. This standard allows and EN 13016-2) were followed. Standard EN 13016-1 was selected because gasoline standard EN 228 for a vapor pressure increase when gasoline is replaced by ethanol up to 10% by volume as shown in indicates that vapor pressure tests must be made at 37.8 ◦C. This standard allows for a vapor pressure Table 2. This increase is motivated by its azeotropic behavior. increase when gasoline is replaced by ethanol up to 10% by volume as shown in Table2. This increase With regard to Submatrix 1, a sharp decrease in vapor pressure is observed in Figure 5 when is motivated by its azeotropic behavior. ethanol is replaced by n-butanol keeping the oxygen concentration constant. This decrease is With regard to Submatrix 1, a sharp decrease in vapor pressure is observed in Figure5 when observed for all oxygen limitations. This drop is due mainly to the lower vapor pressure of n-butanol ethanol is replaced by n-butanol keeping the oxygen concentration constant. This decrease is observed compared to that of ethanol. It can be observed that such a decrease is more effective for lower oxygen for all oxygen limitations. This drop is due mainly to the lower vapor pressure of n-butanol compared content than for high oxygen content. Nevertheless, substantial decreases in vapor pressure would to that of ethanol. It can be observed that such a decrease is more effective for lower oxygen content require high n-butanol contents (and thereby O2 content). than for high oxygen content. Nevertheless, substantial decreases in vapor pressure would require highTable n-butanol 2. Vapor contents pressure (and overrun thereby author O2 content).ized by the EN 228 standard for different ethanol additions.

Table 2. VaporEthanol pressure Content overrun (% authorizedv/v) Authorized by the EN Vapor 228 standard Pressure for differentOverrun ethanol (kPa) additions. 0 0 Ethanol Content1 (% v/v) Authorized Vapor3.7 Pressure Overrun (kPa) 2 06 0 3 17.2 3.7 4 27.8 6 3 7.2 5 48 7.8 6 58 8 7 67.9 8 8 77.9 7.9 8 7.9 9 7.8 9 7.8 10 107.8 7.8

FigureFigure 5. 5. VaporVapor pressure pressure versus percentage of n-butanol in Submatrix 1.

FollowingFollowing EN 228 228 standard, standard, summer summer vapor limits limits were were defined deﬁned between 45 and 60 60 kPa, kPa, whereas whereas winter limits were established between 50 and 80 kPa (shown in Figure6 6 with with a a shaded shaded area). area). Sustainability 2017, 9, 589 7 of 10 Sustainability 2017, 9, 589 7 of 10 Sustainability 2017, 9, 589 7 of 10 All the gasoline–ethanol–butanol blends tested in Submatrix 1 fulfill the vapor pressure limits AllAll the the gasoline–ethanol–butanol gasoline–ethanol–butanol blendsblends testedtested in Submatrix 1 1 fulfill fulﬁll the the vapor vapor pressure pressure limits limits established in the EN 228 standard for the winter season (as shown in Figures 5 and 6), so cold-start establishedestablished in in the the EN EN 228 228 standard standard for for the thewinter winter seasonseason (as shown in in Figures Figures 55 andand 6),6), so so cold-start cold-start problems should not arise. problemsproblems should should not not arise. arise.

Figure 6. Vapor pressure range (shaded area) accepted by EN 228 in winter. FigureFigure 6. 6.Vapor Vapor pressure pressure range range(shaded (shaded area)area) accepted by by EN EN 228 228 in in winter. winter. On the other hand, vapor pressure limitation is more restrictive in summer, as shown in Figures On the other hand, vapor pressure limitation is more restrictive in summer, as shown in Figures 5 andOn 7. the None other of the hand, gasoline–ethanol vapor pressure blends limitation would fulfill is more EN 228 restrictive requirements in summer, unless the as vapor shown 5 and 7. None of the gasoline–ethanol blends would fulfill EN 228 requirements unless the vapor in Figurespressure5 andoverrun7 . None (shown of in the Table gasoline–ethanol 2) is considered. blends On the would contrary, fulﬁll gasoline–n-butanol EN 228 requirements blends unless fulfill the pressure overrun (shown in Table 2) is considered. On the contrary, gasoline–n-butanol blends fulfill vaporthe pressureEN 228 standard overrun (shownfor much in lower Table 2alcohol) is considered. concentrations On the compared contrary, to gasoline–n-butanol ethanol, so no overrun blends the EN 228 standard for much lower alcohol concentrations compared to ethanol, so no overrun fulﬁllauthorization the EN 228 would standard be needed. for much It loweris important alcohol to concentrations remark that the compared gasoline todonated ethanol, by so the no Repsol overrun authorization would be needed. It is important to remark that the gasoline donated by the Repsol authorizationcompany is woulda fuel commercialized be needed. It isin importantwinter and totherefore remark not that prepared the gasoline for use donated in the summer. by the Repsol company is a fuel commercialized in winter and therefore not prepared for use in the summer. company is a fuel commercialized in winter and therefore not prepared for use in the summer.

Figure 7. Vapor pressure range (shaded area) accepted by EN 228 in the summer. FigureFigure 7. 7.Vapor Vapor pressure pressure range range (shaded (shaded area)area) accepted by EN EN 228 228 in in the the summer. summer. Sustainability 2017, 9, 589 8 of 10

WithSustainabilitySustainability regard 20172017 to,, 99,, E85 589589 blends (Submatrices 2 and 3), when 15% (volume basis) of gasoline88 ofof is 1010 kept constant (Figure8, squared symbols and Figure9, blue dots), and butanol content is increased to WithWith regardregard toto E85E85 blendsblends (Submatrices(Submatrices 22 andand 3)3),, whenwhen 15%15% (volume(volume basis)basis) ofof gasolinegasoline isis keptkept replaceconstantconstant ethanol (Figure(Figure by up 8,8, to squaredsquared 50% (volume symbolssymbols basis) andand FigureFigure according 9,9, blueblue to dots),dots), the EN andand 15376 butanolbutanol limits, contentcontent lower isis increasedincreased vapor pressure toto valuesreplacereplace are obtained. ethanolethanol byby up Thisup toto 50% means50% (volume(volume that replacingbasis)basis) accordingaccording ethanol toto thethe by ENEN n-butanol 1537615376 limits,limits, in E85lowerlower blends vaporvapor pressurepressure could cause cold-startvaluesvalues problems areare obtained.obtained. despite ThisThis the meansmeans lower thatthat enthalpy replacingreplacing of ethanolethanol vaporization byby n-butanoln-butanol of butanol, inin E85E85 blends andblends due couldcould to the causecause lower cold-cold- vapor pressurestartstart of problemsproblems n-butanol despitedespite [4,23 the–the25 lower].lower When enthalpyenthalpy n-butanol ofof vapovapo substitutesrizationrization ofof gasoline butanol,butanol, (Figure andand duedue8 , toto triangle thethe lowerlower symbols vaporvapor and Figurepressurepressure9, green ofof dots),n-butanoln-butanol cold-start [4,23–25].[4,23–25]. problems WhWhenen n-butanoln-butanol are expected substitutesubstitute toss be gasolinegasoline even (Figure more(Figure relevant, 8,8, triangletriangle thus symbolssymbols requiring andand a secondFigureFigure fuel tank9,9, greengreen with dots),dots), a more cold-startcold-start volatile problemsproblems fuel for areare the expectedexpected start. This toto drawbackbebe eveneven moremore is expected relevant,relevant, tothusthus be requiringrequiring less relevant aa in direct-injectionsecondsecond fuelfuel enginestanktank withwith due aa moremore to the volatilevolatile increased fuelfuel forfor cylinder thethe start.start. pressure ThisThis drawbackdrawback and temperature isis expectedexpected toto conditions. bebe lessless relevantrelevant Indeed, inin direct-injectiondirect-injection enginesengines duedue toto thethe increasedincreased cycylinderlinder pressurepressure andand temperaturetemperature conditions.conditions. Indeed,Indeed, as can be observed in Figure9 (shaded area), the replacement of either gasoline or ethanol by n-butanol asas cancan bebe observedobserved inin FigureFigure 99 (shaded(shaded area),area), thethe replacementreplacement ofof eithereither gasolinegasoline oror ethanolethanol byby n-n- would move the blend out of the limits established by the EN 15376 standard. For this reason, some butanolbutanol wouldwould movemove thethe blendblend outout ofof thethe limitslimits establestablishedished byby thethe ENEN 1537615376 standard.standard. ForFor thisthis reason,reason, extrasomesome blends extraextra were blendsblends tested werewere using testedtested E70 usingusing (70% E70E70 ethanol (70%(70% ethanol andethanol 30% andand gasoline) 30%30% gasoline)gasoline) as a baseline asas aa baselinebaseline fuel. fuel. Infuel. this InIn case,thisthis the replacementcase,case, thethe ofreplacementreplacement ethanol (up ofof ethanolethanol to 50% (up(up by to volumeto 50%50% byby according voluvolumeme accordingaccording to the EN toto thethe 15376 ENEN 15376 standard15376 standardstandard limits) limits)limits) by butanol byby keepingbutanolbutanol the gasolinekeepingkeeping thethe content gasolinegasoline constant contentcontent allows constantconstant for allowsallows the fulﬁllment forfor thethe fulfillmentfulfillment of the EN ofof thethe 15376 ENEN standard1537615376 standardstandard (Figure 9) despite(Figure(Figure thedecrease 9)9) despitedespite in thethe vapor decreasedecrease pressure inin vapovapo (circlerr pressurepressure symbols, (circle(circle Figure symbols,symbols,8). FigureFigure 8).8).

FigureFigureFigure 8. Vapor 8.8. VaporVapor pressure pressurepressure versus versusversus percentage percentagepercentage of of n-butanoln-butanol inin in SubmatricesSubmatrices Submatrices 22 andand 2 and 3.3. 3.

FigureFigureFigure 9. Vapor 9.9. VaporVapor pressure pressurepressure range rangerange (shaded (shaded(shaded area) ararea)ea) accepted acceptedaccepted byby by CEN/TSCEN/TS CEN/TS 15293/2011.15293/2011. 15293/2011. Sustainability 2017, 9, 589 9 of 10

4. Conclusions The main properties established in standards EN228 (for gasoline fuels) and CEN/TS 15293/2011 (for E85 blends) were measured for n-butanol–ethanol–gasoline blends and butanol–E85 blends. Fuels used in SIEs can contain up to 3.7% O2 by mass to be commercialized. In this frame, the substitution of ethanol (up to 10% by volume) by n-butanol (up to 16% by volume) presents a series of benefits such as a higher heating value or a lower hygroscopic tendency compared to ethanol blends, which makes n-butanol a promising fuel for SIEs. The higher heating value for butanol–gasoline blends would reduce the engine fuel consumption. When butanol is blended with gasoline, the vapor pressure decreases, and consequently, the blends fulfill EN 228. However, the use of n-butanol in E85 blends substituting either gasoline or ethanol can cause cold-start problems despite the lower enthalpy of vaporization of n-butanol. To avoid these problems, ternary blends where both gasoline and ethanol are simultaneously replaced with n-butanol should be used. As an example, if the baseline fuel is E70 (70% ethanol and 30% gasoline by volume), any replacement of ethanol by n-butanol would fulfill EN 15376, and cold-start problems should therefore not arise.

Acknowledgments: This research was co-funded by the European Union Horizon 2020 Research and Innovation Programme under grant agreement No. 640462 (ButaNext project). Repsol and Green Biologics are gratefully acknowledged for the donation of diesel and n-butanol fuels, respectively. Author Contributions: Magín Lapuerta conceptualized the study and organized the manuscript, Rosario Ballesteros conducted and processed the experiments and revised the laboratory conditions, Javier Barba processed the experiments and wrote the manuscript. All authors edited and approved the manuscript. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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