the octane numbers of ethanol blended with gasoline and its surrogates

Fuel 115 (2014) 727–739

Contents lists available at ScienceDirect

Fuel

journal homepage: www.elsevier .com/locate / fuel

The octane numbers of ethanol blended with gasoline and its surrogates

0016-2361/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.fuel.2013.07.105

⇑ Corresponding author. Tel.:+ 61 383446722.E-mail address: [email protected] (M.J. Brear).

Tien Mun Foong a, Kai J. Morganti a, Michael J. Brear a,⇑, Gabriel da Silva b, Yi Yang a, Frederick L. Dryer c

a Department of Mechanical Engineering, The University of Melbourne, VIC 3010, Australiab Department of Chemical and Biomolecular Engineering, The University of Melbourne, VIC 3010, Australiac Department of Mechanical and Aerospace Engineering, Princeton University, NJ 08544, USA

h i g h l i g h t s

� The RONs and MONs of ethanol blended with gasoline and its surrogates are reported.� Ethanol blends synergistically with n-heptane and isooctane in octane numbers.� Ethanol blends antagonistically with toluene in octane numbers.� These observations appear to explain the varying reported trends in ethanol blending with gasoline, and have implications for fuel design.

a r t i c l e i n f o

Article history:Received 25 January 2013Received in revised form 25 July 2013Accepted 25 July 2013Available online 8 August 2013

Keywords:Research Octane Number (RON)Motor Octane Number (MON)EthanolGasolinePrimary Reference Fuels (PRFs)

a b s t r a c t

This paper reports the Research (RON) and Motor (MON) Octane Numbers of ethanol blended with pro-duction gasoline, four gasoline surrogates, n-heptane, isooctane and toluene. The ethanol concentrationwas varied from zero to 100%, resulting in a clear picture of the variations of the RONs and MONs inall cases. Of initial interest are the RONs and MONs of ethanol blended with an Australian production gas-oline and with several US production gasolines. The observed differences then prompt a systematic studyof the variation in the RONs and MONs of ethanol blended with four gasoline surrogates, as well as withn-heptane, isooctane and toluene. Both n-heptane, isooctane and their Primary Reference Fuels (PRFs) areshown to blend synergistically with ethanol, whilst toluene blends antagonistically. Consistent withthese trends, a progressive increase in the toluene content in Toluene Reference Fuels (TRFs) of a constantRON results in increasingly linear ethanol/TRF blending. Together, these results show that the antago-nism of ethanol’s blending with toluene acts against its synergism with isooctane and n-heptane, andmore broadly suggest that the antagonism of ethanol’s blending with aromatics may act against its syn-ergism with paraffins. If correct, this explains trends observed both in the literature and in this study, andhas implications for fuel design.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction a total of 36 billion gallons per year by 2022. Ethanol is expected

Ethanol use in liquid transportation fuels has grown signifi-cantly in recent years. The removal of tetra-ethyl lead (TEL) fromgasoline during the 1980s in the United States, and the possiblelink of its replacement methyl tert-butyl ether (MTBE) to drinkingwater contamination [1], have led to increased use of ethanol as anoxygenate and octane enhancer. These are of course in addition tothe potential greenhouse benefits of displacing gasoline with eth-anol. Whilst variable, and strongly dependent on both the feed-stock and production route, these benefits appear significant insome cases [2–4]. From 2007 to 2008, estimates show that the per-centage of ethanol blended with gasoline globally increased from3.8% to 5.5% [5]. In the United States, the 2007 Renewable FuelStandard further requires that the use of biofuels be increased to

to supply the majority of this mandated fuel volume, and could dis-place approximately 20% of gasoline demand in the United Statesby then [6]. These changes in energy policy imply a continuinggrowth in ethanol production and use as a fuel in the near future.

Ethanol shows significant potential for improving spark-igni-tion engine performance [7–10]. It is already well-known that, rel-ative to regular gasoline, ethanol has a significantly higher octanerating. Although different RONs and MONs of neat ethanol havebeen reported previously [11–15], the RON of ethanol was gener-ally reported to be approximately 109 and the MON approximately90 [12,15]. Gasoline, on the other hand, typically has a RON of atleast 90 for regular and up to 100 for premium gasoline. As onewould expect, blending ethanol with regular gasoline increasesthe RON of a given blend [12,15], although the extent of RONimprovement varies from one study to another. Hunwartzen [12]measured the RON of premium gasoline (RON = 99) blended withethanol in a 50:50 volumetric ratio, and reported an approximately

http://crossmark.crossref.org/dialog/?doi=10.1016/j.fuel.2013.07.105&domain=pdf

http://dx.doi.org/10.1016/j.fuel.2013.07.105

mailto:[email protected]


http://www.sciencedirect.com/science/journal/00162361

http://www.elsevier.com/locate/fuel

728 T.M. Foong et al. / Fuel 115 (2014) 727–739

linear increase in RONs with the volumetric concentration of etha-nol. Measurements reported by the American Petroleum Institute(API) [16] on various gasoline blendstocks blended with ethanolshowed a non-linear dependence of the RONs on the ethanol con-tent on a volume basis, but an almost linear relationship on a molebasis. However, non-linearity in RONs was observed both on amole and a volume basis in data from Anderson et al. [15], suggest-ing synergistic blending (i.e. an octane number that is higher thanthat obtained by linear interpolation from that of its pure constit-uents). With respect to MONs, antagonistic blending (i.e. an octanenumber that is lower than that obtained by linear interpolationfrom that of its pure constituents) has been reported [12] for eth-anol/gasoline blends. More recent studies [15,16], however,showed the opposite trend. Such differences in trends are likely aresult of different gasoline compositions, although it appears thatat present little is understood as to the causes of such effects.

Compounding the uncertainty around the octane numbers ofethanol fuel blends is that the standard RON test itself is sensitiveto the fuel’s charge cooling as well as its autoignition chemistry[17]. Indeed, the charge cooling effect of ethanol/gasoline blendsvaries considerably with ethanol content, due to the significantlyhigher enthalpy of vaporisation of ethanol [18]. Under the standardRON test conditions, a recent work by the authors showed that whilegasoline is fully vaporised, air–fuel mixtures entering the cylinderare saturated and likely two-phase at high ethanol content [17].

This paper builds on previous studies that consider the Research(RON) and Motor (MON) Octane Numbers of ethanol/gasolineblends. The blends considered range from zero ethanol contentto neat ethanol, with the other blend component being one of pro-duction gasoline, four gasoline surrogates, n-heptane, isooctane ortoluene. Further, this systematic study suggests that the RONs andMONs of ethanol blended with Primary Reference Fuels (PRFs) andToluene Reference Fuels (TRFs) are consistent with that of ethanolblended with n-heptane, isooctane and toluene. It also suggests anexplanation for trends observed both in the literature and in thisstudy for ethanol blending with production gasolines of differentcompositions, and has implications for fuel design.

2. Experimental methods

Defined in the ASTM D2699 and D2700 standards, the RON andMON test methods quantify the propensity of a fuel to knock in astandardised single-cylinder CFR engine [19,20]. One of the key dif-ferences between the two methods is the charge temperature. Inthe MON method, the intake air temperature (IAT), which is mon-itored upstream of the carburettor, is specified to be 38 �C, and theair–fuel mixture temperature entering the engine to be 149 �C [20].The RON method, however, specifies only the IAT to be 52 �C, leav-ing the air–fuel mixture temperature entering the engine to vary,particularly due to fuel evaporation [19].

Questions have been raised as to whether the RON and MONmethods are appropriate for rating fuel blends with high ethanolcontent. Originally developed for rating gasoline, use of the standardCFR engine may be problematic for fuels with drastically differentproperties [21,22]. The major hardware limitation is the fuel meter-ing jet and the air–fuel mixture heater. The stock fuel metering jet,while providing a sufficient fuel flow rate of gasoline or PRFs, maylimit the fuel supply when rating ethanol due to its low stoichiome-tric air–fuel ratio [12]. Hence, careful selection of an appropriate fuelmetering jet is required in order to deliver a sufficient fuel flow rate.As a result, the ASTM standards recommend that both test methodsmay not be applicable to fuels with high oxygenate concentration,although no information about the upper limit of the oxygenate con-centration that may be used is provided [19,20].

2.1. CFR engine and the test method

The RON and MON values were measured on a standard Wau-kesha CFR engine. Standard knock rating instruments, includingthe detonation meter, and the knock meter, were used. An airdehumidifier was installed upstream of the carburettor to controlthe humidity of the intake air. Critical engine parameters weremonitored and maintained within the accepted limits as definedin the standards [19,20] during the tests.

The RONs and MONs in this study were determined using theequilibrium fuel level bracketing procedure. This method involveslinear interpolation of the knock intensity of two PRFs of knownoctane number which ‘bracket’ the sample fuel. During the ratingof a fuel, the air–fuel ratio was adjusted such that maximum knockintensity could be attained, as measured by the knock meter. Asdefined in the Standard, the difference between two test resultsunder repeatable conditions would exceed an octane number(ON) of 0.2 only in one case out of twenty for fuels having RON val-ues between 90 and 100 [19], and MON values between 80 and 90[20]. Outside of these ON ranges less repeatability is expected dueto increasing experimental uncertainties.

2.2. Engine compliance tests

Toluene standardisation fuels were utilised to verify enginecompliance in accordance with the ‘Fit-for-Use Procedure’ in theASTM standards [19,20]. By this procedure, the engine was deemedfit for rating any sample fuel with a RON or MON between 40 and120 inclusive.

2.3. Fuel metering jet

Measurements showed that while the required air–fuel ratio formaximum knock intensity varies from fuel to fuel, overall it wasslightly rich in all cases. However, rating neat ethanol requires aconsiderably higher fuel flow rate, since its stoichiometric air–fuelratio (9:1) is significantly lower than that of gasoline (15:1). Hence,the stock fuel metering jet in the present CFR engine fails to pro-vide an adequate fuel flow rate in this case. In order to handlethe increased fuel flow, the original jet in the carburettor was re-placed by an adjustable orifice jet, following the recommendationsdetailed in the standards [19,20,23].

2.4. MON heater

While in a previous study [12] an auxiliary heater was requiredin the MON test to attain the mixture temperature of 149 �C whenrating fuels with high ethanol concentrations, it was found that thestock MON heater alone was sufficient to achieve that for all fuelsin this study. A similar observation was reported in a recent studyby Anderson et al. [15].

2.5. RON measurement drift

Neat ethanol was rated among the first tests of those reported,and the rating was repeated after all RON tests were completed(approximately 3 months later). A measurement drift was ob-served, where the average RON (out of five tests) of neat ethanolhad decreased from 108.5 to 108.0. It is believed that the measure-ment drift was a result of increasing combustion chamber deposits[24]. Deposit build-up in the engine hinders heat transfer and pro-motes the formation of hot spots [25], and hence more prone toautoignition, and consequently a lower ON. It is emphasised thatwhile measurement drift was present, the ‘Fit-for-Use Procedure’(see Section 2.2 ‘‘Engine compliance tests’’) that was performedfor each operating period confirmed that the CFR engine was com-

T.M. Foong et al. / Fuel 115 (2014) 727–739 729

pliant with the standard throughout the tests, and that all mea-surements were within rating tolerances [19].

2.6. Fuels

Regular unleaded gasoline was obtained from a service stationin Melbourne, Australia. The density of gasoline was determinedas 0.73 g/cm3 at 25 �C through simple volume-mass measure-ments, and its molecular weight was assumed to be 100 g/mol, atypical value for gasoline [15]. Isooctane (reference fuel grade)was obtained from Haltermann GmbH. Neat ethanol (anhydrous,not denatured) was at least 99.5% pure and obtained from Chem-Supply. The dilute tetraethyl-lead (TEL), required for rating fuelswith RONs and MONs above 100, was obtained from Innospec.All other chemicals used in the experiments were analytical gradeand at least 99% pure.

Blending of all fuels was done gravimetrically using a precisionbalance with a repeatability of 0.001 g. This is well within theblending tolerance limits of ±0.2% for a 500 ml sample [19,20].

2.7. Formulation of gasoline surrogates

Various gasoline surrogates have been proposed in the litera-ture. PRFs are a popular choice, given their well validated chemis-try [26,27] and defined octane numbers [19,20]. However, previousstudies [28,29] showed that the autoignition characteristics of PRFsare significantly different from those of full-boiling-range gasoline.Several recent studies instead propose the use of TRFs, which are aternary mixture of isooctane, n-heptane and toluene, as a gasolinesurrogate [30–32]. A fourth component, such as 2-pentene [29]and 1-hexene [33,34], has also been included in surrogates to rep-resent olefins. Surrogates with more than 4 components have alsobeen proposed [35], but are less common due to the complexity ofthe chemical model.

In this study, one PRF blend and three different TRF blends wereselected as the gasoline surrogate fuels. PRF91, a mixture of 91%isooctane and 9% n-heptane (v/v), was chosen as a surrogate, sinceit has a similar RON to that of the commercial gasoline (91.5 in thisstudy). The formulation of the TRF compositions, on the otherhand, was based on the following constraints, which were adaptedfrom other works [36,37],

1. RON � 91,2.Pn

i¼1xiHi=Pn

i¼1xiCi ¼ 1:85,

where n is the number of compounds in the surrogate, xi is themolar fraction of species i, Hi is the number of hydrogen atoms inspecies i and Ci is the number of carbon atoms in species i.

Matching both the RON and MON of commercial gasoline wouldbe preferable [37]. Implementing this approach, however, wouldover-constrain the formulation of a 3-component (TRF) surrogatebased on the RON-MON model of Morgan et al. [28]. While theRON test conditions differ considerably from the regime in whichmodern spark-ignition engines are usually operated, RON is stillarguably the better representative test method for determiningknock propensity compared to MON [38,39]. Hence, MON is not ta-ken into account in the formulation of gasoline surrogates in thisstudy, although the MONs of these fuels will be reported.

The hydrogen to carbon (H/C) ratio is an equally important cri-terion in formulating a gasoline surrogate. The H/C ratio deter-mines the stoichiometric air–fuel ratio, and affects the adiabaticflame temperature and the lower heating value of a fuel, and thusaffects flame propagation and the heat release during combustion[37]. An H/C ratio of 1.85 was chosen to be consistent with what isspecified in the Australian Standard AS2877 [40] for commercialgasoline in Australia.

The formulation of the TRF gasoline surrogates was done in twosteps. First, the composition of a TRF blend which satisfies theaforementioned constraints was determined using the modifiedlinear by volume model (RON) by Morgan et al. [28],

RON ¼ appþ atolv tol þ atol2 v2tol þ atol;pxtolp; ð1Þ

where v is the volume fraction, a are the model coefficients, and thesubscripts tol and p refer to toluene and any PRF blend respectively.The variable p is defined by,

p ¼ v iO

v iO þ vnH; ð2Þ

in which the subscripts iO and nH refer to isooctane and n-heptanerespectively. The values of these model coefficients can be found in[28]. Next, an octane rating test in accordance with the ASTM stan-dard [19] (the so-called ‘standard’ test) was performed to measurethe RON of that particular TRF blend. The model yielded good agree-ment (within ±1.0 ON) between the estimated (from Eq. 1) and themeasured RONs. The composition of the blend was then adjustedslightly such that the measured RON yielded approximately 91. Inorder to explore the effect of aromatic content on gasoline perfor-mance, TRFs were prepared with 15% (v/v), 30% (v/v) and 45% (v/v)toluene, which represent the range of total aromatics content typi-cally encountered in gasoline [41]. These TRF blends are referred toas ‘TRF91-15’, ‘TRF91-30’ and ‘TRF91-45’ respectively. Note that byvarying the toluene content in these TRFs, the H/C ratio (except forthat of TRF91-30) no longer conforms to that of typical gasoline (thesame applies to PRFs where there is already one less degree of free-dom). Table 1 lists the properties of all gasoline surrogates used inthis study.

3. Results and discussion

3.1. Neat ethanol

The RON of neat ethanol is measured here as being in the rangeof 108.0–108.5, due to measurement drift as detailed in the Exper-imental Methods (note that both values are themselves the aver-age of five standard test ratings). This RON variability, however,is well within the rating tolerance of ±1.4 ON in the ‘Fit-for-UseProcedure’ that applies to any fuel having a RON between 105.2and 110.6 [19]. The measured MON of ethanol is 90.7.

Table 2 shows the RON and MON data of ethanol from the liter-ature and this study. While several other octane number data forethanol are readily found in the literature, it is believed that themeasurements obtained by Hunwartzen [12] and Anderson et al.[15] are the most reliable, since they comply with the ASTM andDIN standards concerning the proper configuration of the CFR en-gine to handle the high fuel flow rate of ethanol.

In comparison, both the RON and MON values of ethanol ob-tained in this study are in good agreement with those reported pre-viously [12,15]. Considering that the standard specifies a ratingtolerance of ±1.4 ON, the variability in the different reportedRON values of ethanol is within the limits of the test method[19]. Nonetheless, the MON measured in this study is similar tothe average value reported by Anderson et al. [15] (90.7 vs. 90.5),but is 1.0 ON greater than that from Hunwartzen [12].

3.2. Ethanol/gasoline blends

3.2.1. Research Octane Number (RON)Fig. 1a shows the RON values of different ethanol/gasoline

blends on a volume basis. The RON clearly shows a non-linear rela-tionship with the volumetric concentration of ethanol. The RONvalues reported by the API [16] in 2010 for ethanol/gasoline blends

Table 1Properties of this study’s gasoline and its surrogates.

Fuel RONa MONa Composition (% volume)

Toluene Isooctane n-Heptane H/C ratio

Gasoline 91.5 82.1 See Table 4 1.85 b

PRF91 91.0 91.0 0 91.0 9.0 2.25TRF91-15 91.0 88.4 15.0 72.6 12.4 2.04TRF91-30 91.3 86.1 29.8 53.2 17.0 1.85TRF91-45 91.1 83.5 45.0 34.7 20.3 1.67

a As measured in the present study using the standard RON and MON tests.b This H/C value is in accordance with AS2877 [40].

Table 2Reported RON and MON for neat ethanol.

RON MON Year Reference

108.6 ± 0.4 a 89.7 ± 0.3a 1982 [12]108.6–108.8 89.5–91.4 2012 [15]108.0–108.5 90.7 2012 This study

a Average ± 95% confidence interval.

90

92

94

96

98

100

102

104

106

108

110

Ethanol content, % (v/v)

RO

N

This studyAPI (2010)Anderson et al. (2012)

90

92

94

96

98

100

102

104

106

108

110

0 10 20 30 40 50 60 70 80 90 100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Ethanol content, mole fraction

RO

N

This studyAPI (2010)Anderson et al. (2012)Linear estimation

Fig. 1. Measured RONs of ethanol/gasoline blends versus ethanol content. Recentliterature data [15,16] are included for reference.


up to approximately 30% (v/v) ethanol are very similar to thosemeasured in this study. However, the RONs of ethanol/gasolineblends (base gasoline with an average RON = 92.2 and

MON = 84.7) reported by Anderson et al. [15] are more synergistic.These differing degrees of synergism are an inevitable consequenceof the different gasoline compositions.

It has been suggested that the ON of ethanol/gasoline blendscan be better interpreted on a mole basis, as chemical reactionrates scale in proportion with the molar composition of the air–fuelmixture [22]. The volumetric and molar concentrations of theseblends will differ significantly, since the molecular weight of etha-nol is significantly lower than that of gasoline. Fig. 1b shows theRON values of ethanol/gasoline blends plotted against the molefraction of ethanol. In contrast to Fig. 1a, the RON values now showan almost linear relationship with the molar concentration of eth-anol. In light of this, Anderson et al. [22] suggested the use of a mo-lar weighted ON to estimate the ON of ethanol/gasoline blends. Forthe present study, this can be written as

RONest ¼ ð1� xeÞRONg þ ðxeÞRONe; ð3Þ

where xe is the mole fraction of ethanol in the blend, RONest, RONg

and RONe are the estimated blend’s RON and the measured RONof gasoline and ethanol respectively. As shown in Fig. 1b, there isgood agreement between this study’s estimated RONs and the mea-sured values, with an average difference of approximately 0.4 ON.The maximum deviation is 0.7 ON, and that corresponds to theblend with 20% (v/v) ethanol. Of all the parameters used in calculat-ing the mole fraction of each ethanol/gasoline blend, the largestuncertainty lies in the molecular weight of gasoline, which is as-sumed to be 100 g/mol (see Section 2.6). A sensitivity analysis ofthe molecular weight of gasoline within a reasonable range of 90to 110 g/mol however showed that the mole fraction of the blendswas only weakly dependent on these variations in the molecularweight of gasoline.

3.2.2. Motor Octane Number (MON)The MON values of ethanol/gasoline blends exhibit trends that

are very similar to those observed in the RONs of these blends.Fig. 2a shows the non-linear relationship between the MON andthe volumetric concentration of ethanol. On the other hand, an al-most linear relationship can be observed in the MONs of ethanol/gasoline blends when plotted against the molar concentration ofethanol (Fig. 2b). This study’s measured MON values closely matchthe linear estimated MONs, with a maximum deviation of only 0.4ON. The MON values of ethanol/gasoline blends reported by the API[16] agree well with those from this study when plotted againstboth the volumetric and the molar concentration of ethanol. Forease of comparison, data from Anderson et al. [15] for a differentbase gasoline (average RON = 88.2 and MON = 81.7) were plottedin Fig. 2 instead of those discussed in the previous section. Evenwith a similar MON in the base gasoline, the ethanol blending ofAnderson et al. [15] results in MONs that are significantly morenon-linear with ethanol content.

80

82

84

86

88

90

92


MO

N

This studyAPI (2010)Anderson et al. (2012)

80

82

84

86

88

90

92

0 10 20 30 40 50 60 70 80 90 100


MO

N

This studyAPI (2010)Anderson et al. (2012)Linear estimation

Fig. 2. Measured MONs of ethanol/gasoline blends and the calculated blendingMONs of ethanol versus ethanol content. Recent literature data [15,16] are includedfor reference.

Table 3Reported RON and MON for neat toluene.

RON MON Year Reference

120 103.5 1958 [43]120 109 1988 [25]120 a 107 2012 This study

a The RON of neat toluene was obtained from [43].


3.3. Blending behaviour of ethanol with n-heptane, isooctane andtoluene

The previous section has shown that different gasoline blend-stocks when blended with ethanol exhibit varying degrees ofnon-linearity in octane numbers with respect to ethanol content.A parametric study of the potential interactions among major gas-oline components is thus necessary in an attempt to understandthe associated blending characteristics.

To simplify this analysis, three components representative ofgasoline, namely toluene, isooctane and n-heptane, were blendedwith ethanol. Isooctane and n-heptane are branched and linear al-kanes, which act as surrogates for the major paraffinic fraction ofgasoline. Toluene is a commonly used surrogate for the aromaticfraction of gasoline. Aromatics are important in this context since,like ethanol, they are used to increase the octane number of gaso-line, despite having a relatively high cost to produce (and signifi-cant value as commodity chemicals) as well as generallyaccepted negative environmental effects [42].

Among these four components, a total of six first-order interac-tion pairs are present, namely ethanol/isooctane, ethanol/n-hep-tane, ethanol/toluene, isooctane/n-heptane, isooctane/toluene,and n-heptane/toluene blends. Of these six interaction pairs, thatof isooctane/n-heptane is linear by volume, as defined by the oc-

tane scale [19,20]. Similarly, blending toluene with either isooc-tane or n-heptane was previously found to yield anapproximately linear change in ON with respect to toluene content[28] (see Appendix A for more details). A study was thus conductedon blends of ethanol/isooctane, ethanol/n-heptane and ethanol/tol-uene, as detailed below.

Due to the difficulty in measuring the high RON of neat toluene,which approaches the upper limit of the test method (valid work-ing range = 40–120 ON [19,20]), its RON value of 120 was obtainedfrom a report published by the American Society for Testing Mate-rials (ASTM) [43]. As shown in Table 3, a similar RON value of neattoluene was reported by Heywood [25], suggesting that the RONmeasurement from the ASTM report [43] is repeatable. DifferentMON values of toluene, however, were reported in the literature.Data from the ASTM [43] reported a MON of 103.5 for neat toluene,while according to Heywood [25] it is 109. Since there is a signifi-cant spread in the MON data, a MON measurement was performedon neat toluene. Its MON was found to be 107, which is bracketedby the values reported previously in the literature.

3.3.1. Research Octane Number (RON)Fig. 3a and b show the RON values of isooctane, n-heptane and

toluene with respect to the volumetric and molar concentration ofethanol respectively. Blends of ethanol and isooctane are of partic-ular interest. While a survey of the limited literature on ethanol/PRF blends has revealed no detailed information on the blendingcharacteristics of these fuels, the RON values of blends with 20–80% (v/v) ethanol concentration exceed that of neat ethanol (theRON peaks at 110.2 with 40% ethanol). Such a significant relativeRON improvement, particularly at a low ethanol concentration, isnot observed in other PRF blends, suggesting the presence of somesignificant synergism between ethanol and isooctane.

Likewise, the addition of ethanol to n-heptane results in a sig-nificant non-linear increase in ON. This is likely due to the effec-tiveness of ethanol in suppressing the low-temperaturechemistry of n-heptane [30].

While blending isooctane and n-heptane with ethanol results insynergism, ethanol/toluene blends clearly exhibit an antagonisticblending effect. The antagonistic effect is so significant that beyond40% (v/v) ethanol, the difference between the RON of a blend andthat of neat ethanol is negligible. Of all blends, toluene-E80 hasthe lowest RON of 107.9, which is effectively the same as that ofneat ethanol.

3.3.2. Motor Octane Number (MON)Fig. 4 shows the MON values of blends of ethanol/n-heptane,

ethanol/isooctane and ethanol/toluene. As expected, n-heptaneblends synergistically with ethanol in the MONs both on a volumeand a mole basis. For ethanol/isooctane blends, some synergism(on a volume basis) is found at low ethanol content of up to 20%(v/v), beyond which almost linear blending is observed. This is incontrast to the more significant synergism of these blends whenevaluated on a mole basis. On the other hand, antagonistic blend-ing in the MON can be observed in ethanol/toluene blends. On avolume basis, the antagonistic effect of the blends is more pro-nounced, amounting to a significant reduction in the MON even

65

70

75

80

85

90

95

100

105

110

115

120


RO

N

Toluene

Isooctane

n -Heptane

65

70

75

80

85

90

95

100

105

110

115

120

0 10 20 30 40 50 60 70 80 90 100


RO

N

Toluene

Isooctane

n -Heptane

Fig. 3. Measured RONs of blends of ethanol/isooctane, ethanol/n-heptane andethanol/toluene versus ethanol content. The RON of neat toluene was obtained from[43].

60

65

70

75

80

85

90

95

100

105

110


MO

N

Toluene

Isooctane

n -Heptane

60

65

70

75

80

85

90

95

100

105

110

0 10 20 30 40 50 60 70 80 90 100


MO

N

Toluene

Isooctane

n -Heptane

Fig. 4. Measured MONs of blends of ethanol/isooctane, ethanol/n-heptane andethanol/toluene versus ethanol content.


with a small amount of ethanol present in the blend. Nonetheless,analysis based on molar fractions is argued to be of greater signif-icance, since reaction rates scale with the molar composition, aspreviously discussed.

Overall, these results demonstrate that ethanol blends synergis-tically with isooctane and n-heptane to increase the RONs andMONs, and antagonistically decreases the octane numbers whenblended with toluene. At 20% (v/v) or greater ethanol content,blends of ethanol/isooctane and ethanol/toluene have RONs thatdiffer by less than 3 ON, and are within 3 ON of the RON of neatethanol. This is despite a full 20-point difference in the RONs ofneat isooctane and toluene.

3.4. Ethanol/PRF91 blends

3.4.1. Research Octane Number (RON)Having established the ON relationships in different binary

blends, it is interesting to determine if such relationships remainimportant in the blends of gasoline surrogates and ethanol. Hence,the octane numbers of gasoline surrogates blended with ethanolwere measured, starting with the simple binary mixture PRF91(91% isooctane and 9% n-heptane (v/v)).

Fig. 5 shows the RONs of different ethanol/PRF91 blends plottedagainst the volumetric concentration of ethanol. Although simi-

larly non-linear in RONs with respect to ethanol content, thenon-linearity is significantly more pronounced compared to thatobserved in ethanol/gasoline blends. A blend with 40% (v/v) etha-nol would yield a similar RON to that of neat ethanol. Of interestis that the RON values of these blends at 60% and 80% (v/v) ethanolconcentration would exceed that of neat ethanol, which possessesa greater charge cooling effect than either of the blends. This sug-gests significant synergism between ethanol and PRF91, as hasbeen observed in the binary blends of ethanol/isooctane and etha-nol/n-heptane.

Fig. 5b illustrates the RON values of ethanol/PRF91 blends withrespect to the molar concentration of ethanol. In contrast to the al-most linear relationship observed in ethanol/gasoline blends, sig-nificant non-linearity is observed for ethanol/PRF91 blends. Againthis suggests that, although having very similar RONs, the autoig-nition chemistry of gasoline can be significantly different from thatof PRF91 when blended with ethanol. The use of binary mixtures ofn-heptane and isooctane to capture the autoignition behaviour of agasoline blendstock, therefore, is deemed insufficient. This obser-vation agrees with what has been reported in a recent study [28].

Further tests were conducted on other PRFs to confirm theirsynergistic blending with ethanol. Fig. 6 shows the measuredRON values of ethanol/PRF blends versus ethanol content. As ex-pected, all ethanol/PRF blends are significantly synergistic. A small

90

92

94

96

98

100

102

104

106

108

110


RO

N

Gasoline (this study)PRF91

90

92

94

96

98

100

102

104

106

108

110

0 10 20 30 40 50 60 70 80 90 100


RO

N


Fig. 5. Measured RONs of ethanol/PRF91 blends versus ethanol content.

40

50

60

70

80

90

100

110


RO

N

PRF100

PRF90

PRF80

PRF60PRF0

PRF20

PRF40

40

50

60

70

80

90

100

110

0 10 20 30 40 50 60 70 80 90 100


RO

N

PRF100 PRF90

PRF80

PRF60PRF0PRF20

PRF40

Fig. 6. Measured RONs for different ethanol/PRF blends versus ethanol content.


amount of ethanol added to any PRF blend increases the RON of theblends significantly.

3.4.2. Motor Octane Number (MON)Fig. 7 shows the MON values of different ethanol/PRF91 blends

with respect to the volumetric and the molar concentration of eth-anol. It is again clear that the non-linearity in the MONs of theseblends is significantly more pronounced compared to that of etha-nol/gasoline blends, and significant synergism due to ethanolblending is present. Of note is that the RON and MON of gasolinein this study differ by approximately 9 ON, while PRF91 has thesame RON and MON values by definition.

3.5. Ethanol/TRF91 blends

3.5.1. Research Octane Number (RON)Prior results in this study have shown that aromatic content

may have a significant role in the autoignition of blends of ethanoland gasoline or gasoline surrogates. Fig. 8 shows the measuredRON values of different ethanol/TRF blends with respect to the vol-umetric concentration of ethanol. The RONs of these blends do notscale linearly with ethanol content. The extent of non-linearity,however, differs for each TRF surrogate. TRF91-15 exhibits thegreatest blending synergism in RONs with ethanol, followed byTRF91-30 and lastly TRF91-45 with the highest toluene content.

This is consistent with earlier results, where ethanol/PRF91 blendspossess the greatest non-linearity in RONs. These results suggestthat increasing the toluene content and hence lowering the isooc-tane content in a surrogate, while maintaining a constant RON, re-duces the octane enhancing effect of ethanol.

In comparison with gasoline, the TRF surrogates exhibit a moresignificant non-linear relationship in RONs when blended withethanol. For example, adding 40% (v/v) ethanol to TRF91-30 wouldyield a RON of 106, which is a significant increase of approximately4 ON over that of gasoline-E40. Increasing the toluene content ordecreasing the PRF content helps narrow this gap, where theRON of TRF91-45-E40 differs from that of gasoline-E40 by only2.5 ON.

Fig. 8b shows the RON values of different ethanol/TRF blends ona mole basis. Similar to Fig. 8a, significant non-linearity is found forethanol/TRF blends, and ethanol/TRF91-45 blends exhibit the leastsynergism when blended with ethanol.

3.5.2. Motor Octane Number (MON)Fig. 9 illustrates the MON values of different ethanol/TRF blends

with respect to the volumetric and the molar concentration of eth-anol. While every surrogate in this study has a RON similar to thatof gasoline, the MONs of these surrogates differ considerably fromone to another. Of all surrogates, PRF91 has the highest MON (91ON), followed by TRF91-15 (88.4 ON), TRF91–30 (86.1 ON), and

80

82

84

86

88

90

92

94

96


MO

N


80

82

84

86

88

90

92

94

96

0 10 20 30 40 50 60 70 80 90 100


MO

N


Fig. 7. Measured MONs of ethanol/PRF91 blends versus ethanol content.

90

92

94

96

98

100

102

104

106

108

110


RO

N

Gasoline (this study)Gasoline (Anderson et al.)PRF91TRF91-15TRF91-30TRF91-45

90

92

94

96

98

100

102

104

106

108

110

0 10 20 30 40 50 60 70 80 90 100


RO

N


Fig. 8. Measured RONs for different ethanol/TRF blends versus ethanol content.Recent literature data from Anderson et al. [15] are included for reference.


lastly TRF91-45 (83.5 ON). This decrease in MONs is consistentwith increasing toluene content in the surrogates. The results againclearly show a non-linear relationship between MONs and the eth-anol content. Blending ethanol with these surrogates results insynergism, with the greatest gain in ON usually observed with20–40% (v/v) of ethanol in a given blend.

3.5.3. Octane sensitivityFig. 10 shows the blends’ octane sensitivity, which can be de-

fined by the following,

octane sensitivity ¼ RON �MON: ð4Þ

Of all base fuels, gasoline is the most sensitive fuel with an octanesensitivity of approximately 9 ON. On the other hand, PRF91, by def-inition, has no octane sensitivity. It is clear that the octane sensitiv-ity increases with the toluene concentration in a blend.

Adding a small amount of ethanol to gasoline and its surrogatesalso raises the octane sensitivity significantly. Beyond 40% (v/v)ethanol, however, the octane sensitivity of a blend becomes almostindependent of gasoline/surrogate content. This suggests that,even at a low concentration, ethanol has a significant impact onthe chemistry of a blend.

3.6. Implications for the RONs and MONs of ethanol/gasoline blends

Earlier results showed clearly that the octane numbers of theproduction gasoline of Anderson et al. [15] blended with ethanolwere significantly different to those of the present study. These dif-ferences of course arise from these studies’ differing gasoline com-positions. Gasoline is a complex mixture of hydrocarbons, whichare commonly grouped into five major classes, i.e. linear paraffins,branched paraffins, naphthenes, olefins and aromatics. Interactionsbetween these different classes of hydrocarbons have been studiedin the past [11]. For example, it is well established that hydrocar-bons of the same class interact linearly with one another with re-gards to the ON, while significant non-linearity is readily found inblends of paraffins and olefins [11,44,45]. However, the blendingbehaviour of ethanol with gasoline remains less clear, especiallyat high concentrations.

In this present study, blends of both ethanol/isooctane and eth-anol/n-heptane were shown to exhibit significant synergism intheir RONs. In contrast, blends of toluene/ethanol were antagonis-tic in their RONs. Consistent with these trends, a progressive in-crease in the toluene content in TRFs of a constant RON resultedin increasingly linear TRF/ethanol blending. These results showthat the antagonism of ethanol’s blending with toluene acts againstits synergism with isooctane and n-heptane.


MO

N

Ethanol content, mole fraction

MO

N

80

82

84

86

88

90

92

94

96


80

82

84

86

88

90

92

94

96

0 10 20 30 40 50 60 70 80 90 100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1


Fig. 9. Measured MONs for different ethanol/TRF blends versus ethanol content.Recent literature data from Anderson et al. [15] are included for reference.

0

2

4

6

8

10

12

14

16

18

0 10 20 30 40 50 60 70 80 90 100Ethanol content, % (v/v)

Sens

itivi

ty (R

ON

- M

ON

)

Gasoline (this study)PRF91TRF91-30TRF91-15TRF91-45

Fig. 10. Octane sensitivity of gasoline and its surrogates blended with ethanol.

Table 4Composition of this study’s gasoline as determined by ASTM D6730, and of gasoline(‘B92E0’) studied by Anderson et al. [15].

Component This study (% volume) Anderson et al. [15] (% volume)

Total Paraffins 48.9 64.3iso-Paraffins 35.3 48.3n-Paraffins 13.7 15.9Aromatics 31.7 26.0Naphthenes 11.4 3.9Olefins 8.0 5.8Ethanol <0.01 <0.1MTBE <0.01 N/A


Further, the greater synergism in the RONs of ethanol/gasolineblends reported in Anderson et al. [15] compared to that observedin this study (Fig. 1a) coincides with their higher paraffin content(64.3% vs. 48.9%) and lower aromatic content (26.0% vs. 31.7%) intheir base gasolines (Table 4). Similarly, another study reported[46] that between two base gasolines (one with 38.5% aromatics

and 46.8% paraffins; the other with 26.9% aromatics and 59.8% par-affins), the addition of ethanol increases the ON of the latter moreeffectively. Likewise, da Silva et al. [47] measured the ON of twogasoline blendstocks blended with 25% (v/v) ethanol, and foundthat the blending RON of ethanol is significantly higher for theblendstock with lower aromatic content (9% vs. 33%). If the individ-ual surrogate components (n-heptane, isooctane and toluene)grossly represent the blending behaviours of the respective paraf-fin and aromatic classes of hydrocarbons in gasoline, such resultsfor the blending of production gasolines with ethanol are consis-tent with those observed for the blending of PRFs/TRFs (and theirpure components) with ethanol, i.e. the antagonism of ethanol’sblending with aromatics may act against its synergism withparaffins.

If correct, this has implications for fuel design. Exploitation ofthis synergism of ethanol and paraffins may enable a given octanenumber to be achieved with lower aromatic and lower ethanolcontent, i.e. it makes more effective use of the ethanol. Whilstthe design of optimal gasoline/ethanol blends depends on manyfactors, both technical and non-technical, the observations re-ported in this study may nonetheless have environmental and/oreconomic benefits. In particular, if ethanol production for fueluse is likely to remain small relative to gasoline, it may make great-er economic and/or environmental sense to blend this ethanolmore uniformly through all production gasolines, and exploit theobservations in this study, rather than burn this ethanol at higherconcentrations such as E85 or hydrous ethanol. Of course, quanti-fication of these potential benefits can only be determined throughfurther study, and is outside the scope of this present work.

4. Conclusions

This paper reported the RONs and MONs of ethanol blendedwith production gasoline, four gasoline surrogates, n-heptane, iso-octane and toluene. The ethanol concentration was varied fromzero to 100%, resulting in a clear picture of the variations of theRONs and MONs in all cases. Of initial interest was the almost lin-ear variation of the RON and MON with ethanol content of blendswith an Australian production gasoline. This was in contrast withother recent studies which demonstrated varying synergism be-tween US production gasolines and ethanol [15,16]. Such differ-ences arose from differing gasoline compositions among thevarious studies, each with notably different aromatic content butsimilar RON and MON.

This, in turn, prompted a systematic study of the variation inthe RONs and MONs of ethanol blended with four gasolinesurrogates, as well as with n-heptane, isooctane and toluene. Bothn-heptane, isooctane and their PRFs blended synergistically withethanol, whilst toluene blended antagonistically. Of particular notewas that the RON of some blends of isooctane and ethanol ex-ceeded that of neat ethanol. Consistent with these trends, a pro-gressive increase in the toluene content in TRFs of a constant

40

50

60

70

80

90

100

110

0 10 20 30 40 50 60 70 80 90 100Toluene content, % (v/v)

MO

N

PRF40PRF60PRF80PRF100

Fig. A.2. Predicted MONs of different PRFs blended with toluene using the modelfrom Morgan et al. [28]. The dashed line indicates the 45% cap of aromatic contentin Australian gasoline.


RON resulted in increasingly linear ethanol/TRF blending. Together,these results show that the antagonism of ethanol’s blending withtoluene acts against its synergism with isooctane and n-heptane,and more broadly suggest that the antagonism of ethanol’s blend-ing with aromatics may act against its synergism with paraffins.

If correct, this explains the different trends in the octane num-bers of ethanol/gasoline blends in the literature and in this study,and also has implications for fuel design. In particular, exploitationof this synergism of ethanol and paraffins may enable a given oc-tane number to be achieved with lower aromatic and lower ethanolcontent, i.e. it makes more effective use of the ethanol. Whilst thedesign of optimal gasoline/ethanol blends depends on many fac-tors, both technical and non-technical, the observations reportedin this study may nonetheless have environmental and/or eco-nomic benefits. Quantification of these potential benefits can onlybe determined through further study building on the present work.

Acknowledgements

This research was supported by the Advanced Centre for Auto-motive Research and Testing (www.acart.com.au) and the Austra-lian Research Council.

Appendix A

A.1. Blending behaviours of toluene/isooctane/n-heptane blends

As mentioned in Section (2.7), the RON model for TRF blends byMorgan et al. [28] was sufficiently accurate, yielding a maximumerror of ±1 ON for the aforementioned gasoline surrogates. There-fore, this model was used to investigate the blending behaviours ofthese blends.

Figs. A.1 and A.2 show the predicted RON and MON values offour different PRFs with respect to the volumetric concentrationof toluene. On first sight the octane numbers of these blends exhi-bit some degree of non-linearity with the presence of a significantchange in gradient at a toluene concentration of approximately90% (v/v). This is believed to be a result of shortcomings in fittingthe model at high toluene concentrations, and a further optimisedmodel is likely to yield octane numbers that are more linear withtoluene content.

In this study, the toluene content of all gasoline surrogates iscapped at 45% (v/v), in accordance with the Australian standard[41]. In light of this, the RON or MON of any TRF blend containing

40

50

60

70

80

90

100

110

120

0 10 20 30 40 50 60 70 80 90 100Toluene content, % (v/v)

RO

N

PRF40PRF60PRF80PRF100

Fig. A.1. Predicted RONs of different PRFs blended with toluene using the modelfrom Morgan et al. [28]. The dashed line indicates the 45% cap of aromatic contentin Australian gasoline.

up to 45% (v/v) toluene is approximately linear even with the cur-rent model, as can be seen in Figs. A.1 and A.2. This observation isin agreement with a recent study, which proposed the use of a lin-ear molar-weighted model to predict the octane numbers of anyTRF blend [37].

Appendix B

B.1. The Modified RON

As detailed in a previous study by the authors [17], the ‘modi-fied RON’ test, in which the temperature of the air–fuel mixtureentering the engine is fixed at 36 �C (a representative temperatureof the PRF-only mixtures from the standard RON test), would en-sure a fully vaporised and unsaturated air–fuel mixture enteringthe engine (Fig. B.1). Hence, the relative contribution of the fuelchemistry and the charge cooling could be determined by compar-ing the standard and modified RON test results [17].

Fig. B.2a and c show how the intake air temperature (IAT) mea-sured upstream of the carburettor varies with ethanol content forthese modified RON tests. In comparison with the IAT of52 ± 2 �C in a standard RON test, the required IAT in the case ofneat ethanol in the modified test is now approximately 170 �C,

Fig. B.1. Schematic of the intake system (cross-section) of the CFR engine in theRON configuration [17].

98

100

102

104

106

108

110

112


RO

N

40

60

80

100

120

140

160

180

IAT

(°C

)

Standard RON

Modified RON

IAT for Modified RON

Standard IAT

65

70

75

80

85

90

95

100

105

110


RO

N

40

60

80

100

120

140

160

180

IAT

(°C

)

Standard RON

Modified RON


Standard IAT

102

104

106

108

110

112

114

10 20 30 40 50 60 70 80 90 100

40 50 60 70 80 90 100

10 20 30 40 50 60 70 80 90 100Ethanol content, % (v/v)

RO

N

40

60

80

100

120

140

160

180

IAT

(°C

)

Standard RON

Modified RON


Standard IAT

Fig. B.2. Measured RON values, and the associated IATs for (a) ethanol/isooctane,(b) ethanol/n-heptane [17] and (c) ethanol/toluene blends under standard andmodified conditions.

Table C.1Measured RONs and MONs of toluene blended with ethanol, and the associatedvolume fractions of ethanol.

Fuel RON MON vethanol

Toluene 120a 107 0Toluene-E10 112.8 101 0.1Toluene-E20 110.9 97 0.2Toluene-E40 108.6 93.3 0.4Toluene-E60 108.1 91.9 0.6Toluene-E80 107.9 91.1 0.8Ethanol 108.0 b 90.7 1

a The RON of toluene was obtained from [43].b The RON of ethanol measured for this specific batch of measurements. See the

Experimental Methods for more details.

Table C.2Measured RONs and MONs of gasoline and its surrogates blended with ethanol, andthe associated volume fractions of ethanol.


Gasoline 91.5 82.1 0Gasoline-E10 95.2 84.2 0.1Gasoline-E20 98.3 85.5 0.2Gasoline-E40 102.1 87.7 0.4Gasoline-E60 104.6 89 0.6Gasoline-E80 106.4 90.2 0.8PRF91 91.a 91.a 0PRF91-E10 98.7 94.3 0.1PRF91-E20 103.8 95.3 0.2PRF91-E40 108.0 94.5 0.4PRF91-E60 108.4 93.4 0.6PRF91-E80 108.4 92.2 0.8TRF91-30 91.3 86.1 0TRF91-30-E10 97 89.4 0.1TRF91-30-E20 101.4 91.1 0.2TRF91-30-E40 106 92.1 0.4TRF91-30-E60 107.1 92 0.6TRF91-30-E80 107.5 91.4 0.8TRF91-15 91 88.4 0TRF91-15-E10 97.8 91.7 0.1TRF91-15-E20 102.6 93.2 0.2TRF91-15-E40 107.1 93.6 0.4TRF91-15-E60 107.7 92.6 0.6TRF91-15-E80 107.8 91.7 0.8TRF91-45 91.1 83.5 0TRF91-45-E10 96 87.2 0.1TRF91-45-E20 100.2 89.1 0.2TRF91-45-E40 104.6 90.9 0.4TRF91-45-E60 106.3 91.2 0.6TRF91-45-E80 107.1 91.1 0.8Ethanol 108.0 b 90.7 1

a The RON and MON of a PRF are by definition [19,20].b The RON of ethanol measured for this specific batch of measurements. See the



which is testimony to the strong charge cooling that ethanolprovides.

Comparison of the standard and the modified RON measure-ments for the different blends are of interest. For example,Fig. B.2a shows significant differences between the standard andmodified test results for the ethanol/isooctane blends in somecases. The ‘modified RON’ of neat ethanol is now 103.5, suggestingthat the charge cooling of ethanol alone contributes to a large 5point increase in ON. The ethanol/isooctane blends (10–80% v/vethanol), shown earlier in Fig. 3 as having a similar RON to ethanol,

now show a higher RON than that of ethanol in all cases. This dem-onstrates the importance of the autoignition chemistry of theseblends. It is clear that relatively small quantities of ethanol havea profound effect on the autoignition chemistry of isooctane. Fur-ther work will be required to identify the source of this interestingphenomenon.

Similarly, Fig. B.2b presents the modified RON values for etha-nol/n-heptane blends, which have been reported previously [17].The results suggest that the autoignition chemistry dominatesthe charge cooling effects for these blends initially, while thecharge cooling of ethanol starts to have a greater effect on RONsas ethanol is further increased.

Fig. B.2c compares the standard and the modified RON values ofdifferent ethanol/toluene blends. As expected, similar antagonistic

Table C.3Measured RONs and MONs of different PRFs blended with ethanol, and the associatedvolume fractions of ethanol.


PRF0 0a 0a 0PRF0-E30 54.3 – 0.3PRF0-E40 69.7 64.5 0.4PRF0-E50 83.8 – 0.5PRF0-E60 94.7 83.8 0.6PRF0-E70 101.6 – 0.7PRF0-E80 104.7 88.9 0.8PRF0-E90 106.5 – 0.9PRF10 10a 0PRF10-E20 45.9 – 0.2PRF10-E30 61.1 – 0.3PRF10-E40 75.6 – 0.4PRF10-E50 87.6 – 0.5PRF10-E60 96.6 – 0.6PRF20 20a 20a 0PRF20-E20 53.3 – 0.2PRF20-E30 67.4 – 0.3PRF20-E40 80.7 – 0.4PRF20-E50 91.5 – 0.5PRF20-E60 99.1 – 0.6PRF20-E80 105.8 – 0.8PRF30 30 a 30 a 0PRF30-E10 46.5 – 0.1PRF30-E20 60.8 – 0.2PRF30-E30 74.2 – 0.3PRF30-E40 85.5 – 0.4PRF30-E50 94.7 – 0.5PRF40 40a 40 a 0PRF40-E10 55 – 0.1RF40-E20 68.5 – 0.2PRF40-E30 80.6 – 0.3PRF40-E40 90.4 – 0.4PRF40-E50 97.9 – 0.5PRF40-E60 102.7 – 0.6PRF40-E80 106.6 – 0.8PRF50 50 a 50 a 0PRF50-E10 63.8 – 0.1PRF50-E20 75.8 – 0.2PRF50-E30 86.4 – 0.3PRF50-E40 94.5 – 0.4PRF60 60 a 60 a 0PRF60-E10 72.6 – 0.1PRF60-E20 83.5 – 0.2PRF60-E30 92 – 0.3PRF60-E40 98.9 – 0.4PRF60-E60 105.5 – 0.6PRF60-E80 107.6 – 0.8PRF70 70 a 70 a 0PRF70-E10 80.9 – 0.1PRF70-E20 90.3 – 0.2PRF70-E30 97.4 – 0.3PRF80 80 a 80 a 0PRF80-E10 89.5 – 0.1PRF80-E20 97 – 0.2PRF80-E40 105.7 – 0.4PRF80-E60 107.7 – 0.6PRF80-E80 108.3 – 0.8PRF90 90 a 90 a 0PRF90-E5 94.1 – 0.05PRF90-E10 97.6 – 0.1PRF90-E20 103.6 – 0.2PRF100 100 a 100 a 0PRF100-E10 106.8 99.9 0.1PRF100-E20 109.4 99.1 0.2PRF100-E40 110.2 95.9 0.4PRF100-E60 109.6 94.2 0.6PRF100-E80 109 92.6 0.8Ethanol 108.5b 90.7 1

a The RON and MON of a PRF are by definition [19,20].b The RON of ethanol measured for this specific batch of measurements. See the


Table D.1Measured RON values, and the associated IATs for blends of ethanol/n-heptane [17],ethanol/isooctane and ethanol/toluene blends under standard and modifiedconditions.

Fuel StandardRON

ModifiedRON

Standard IAT(�C)

ModifiedIATa

PRF0-E40 69.7 67.6 51.7 100PRF0-E50 83.8 81.6 51.7 112PRF0-E60 94.7 93.8 51.7 124PRF0-E80 104.7 102.4 51.7 144PRF100-

E10106.8 106.8 51.7 58

PRF100-E20

109.4 108.9 51.7 64

PRF100-E40

110.2 108.2 51.7 89

PRF100-E60

109.6 107.1 51.7 114

PRF100-E80

109 105.1 51.7 140

Toluene-E10

112.8 111.9 51.7 73

Toluene-E20

110.9 109.3 51.7 79

Toluene-E40

108.6 105.6 51.7 100

Toluene-E60

108.1 104.3 51.7 120

Toluene-E80

107.9 103.8 51.7 142

Ethanol 108.0b 103.5 51.7 168

a The modified IATs were adjusted such that the mixture temperature becameapproximately 36 �C. See Ref. [17] for more details.

b The RON of ethanol measured for this specific batch of measurements. See theExperimental Methods for more details.


blending is found in the modified RONs of these blends, althoughthe modified RONs are found to decrease at a slightly greater rate

with increasing ethanol content, relative to the standard RONmeasurements.

Appendix C

C.1. Standard RON and MON data

Tables C.1 C.2 C.3.

Appendix D

D.1. Modified RON data

Table D.1.

References

[1] Marinov NM. A detailed chemical kinetic model for high temperature ethanoloxidation. Int J Chem Kinet 1999;31(3):183–220.

[2] Farrell AE, Plevin RJ, Turner BT, Jones AD, O’Hare M, Kammen DM. Ethanol cancontribute to energy and environmental goals. Science 2006;311(5760):506–8.doi:http://dx.doi.org/10.1126/science.1121416.

[3] Hill J, Nelson E, Tilman D, Polasky S, Tiffany D. Environmental, economic, andenergetic costs and benefits of biodiesel and ethanol biofuels. Proc Natl AcadSci 2006;103(30):11206–10. doi:http://dx.doi.org/10.1073/pnas.0604600103.

[4] Macedo IC, Seabra JE, Silva JE. Green house gases emissions in the productionand use of ethanol from sugarcane in Brazil: the 2005/2006 averages and aprediction for 2020. Biomass Bioenergy 2008;32(7):582–95. doi:http://dx.doi.org/10.1016/j.biombioe.2007.12.006.

[5] Bringezu S, Schütz H, O’Brien M, Kauppi L, Howarth RW, McNeely J. Towardssustainable production and use of resources: assessing biofuels. Tech. rep.,International Panel For Sustainable Resource Management, United NationsEnvironment Programme; 2009. <http://www.unep.org/pdf/biofuels/Assessing_Biofuels_Full_Report.pdf>.

[6] Anderson JE, Hardigan PJ, Ginder JM, Wallington TJ, Baker RE. Implications ofthe energy independence and security act of 2007 for the US light-duty vehiclefleet. SAE Technical Paper 2009-01-2770; 2009.

http://refhub.elsevier.com/S0016-2361(13)00704-7/h0005


http://dx.doi.org/10.1126/science.1121416

http://dx.doi.org/10.1073/pnas.0604600103

http://dx.doi.org/10.1016/j.biombioe.2007.12.006

http://dx.doi.org/10.1016/j.biombioe.2007.12.006


[7] Hsieh WD, Chen RH, Wu TL, Lin TH. Engine performance and pollutantemission of an SI engine using ethanol–gasoline blended fuels. Atmos Environ2002;36(3):403–10. doi:http://dx.doi.org/10.1016/S1352-2310(01)00508-8.

[8] Kapus PE, Fuerhapter A, Fuchs H, Fraidl GK. Ethanol direct injection onturbocharged SI engines-potential and challenges. SAE Technical Paper 2007-01-1408; 2007.

[9] Kar K, Cheng W, Ishii K. Effects of ethanol content on gasohol pfi engine wide-open-throttle operation. SAE Int J Fuels Lubric 2009;2(1):895–901.

[10] Wallner T, Miers SA, McConnell S. A comparison of ethanol and butanol asoxygenates using a direct-injection, spark-ignition engine. J Eng Gas TurbPower 2009;131:032802.

[11] Ghosh P, Hickey KJ, Jaffe SB. Development of a detailed gasoline composition-based octane model. Indus Eng Chem Res 2006;45(1):337–45.

[12] Hunwartzen I. Modifications of CFR test engine unit to determine octanenumbers of pure alcohols and gasoline-alcohol blends. SAE Technical Paper820002; 1982.

[13] SAE. Alternative motor fuels. SAE J1297; 2007.[14] Andrae JCG. Development of a detailed kinetic model for gasoline surrogate

fuels. Fuel 2008;87(10–11):2013–22.[15] Anderson JE, Leone TG, Shelby MH, Wallington TJ, Bizub JJ, Foster M, et al.

Octane numbers of ethanol–gasoline blends: measurements and novelestimation method from molar composition. SAE Technical Paper 2012-01-1274; 2012. doi:http://dx.doi.org/10.4271/2012-01-1274.

[16] Determination of the potential property ranges of mid-level ethanol blends:final report. Tech. rep. American Petroleum Institute (API); 2010. <http://www.api.org//media/Files/Policy/Alternatives/E10- Blending-Study-Final-Report.pdf>.

[17] Foong TM, Morganti KJ, Brear MJ, da Silva G, Yang Y, Dryer FL. The effect ofcharge cooling on the RON of ethanol/gasoline blends. SAE Int J Fuels Lubr2013;6:34–43.

[18] Kar K, Last T, Haywood C, Raine R. Measurement of vapor pressures andenthalpies of vaporization of gasoline and ethanol blends and their effects onmixture preparation in an si engine. SAE Int J Fuels Lubr 2009;1(1):132–44.

[19] ASTM International, Standard test method for research octane number ofspark-ignition engine fuel. ASTM D2699-11; 2011.

[20] ASTM International, Standard test method for motor octane number of spark-ignition engine fuel. ASTM D2700-11; 2011.

[21] Yates A, Bell A, Swarts A. Insights relating to the autoignition characteristics ofalcohol fuels. Fuel 2010;89(1):83–93.

[22] Anderson JE, Kramer U, Mueller SA, Wallington TJ. Octane numbers of ethanol–and methanol–gasoline blends estimated from molar concentrations. EnergyFuels 2010;24(12):6576–85.

[23] Deutsches Institut für Normung. Determination of knock characteristics(octane number) of alcohols and alcohol/fuel mixtures using the CFR engine.DIN 51756-7; 1986.

[24] Rose RA, Stott GM, editor. A guide to operational and maintenance problemson ASTM-CFR engines. Alberta Research Council, Alberta; 1978.

[25] Heywood JB. Internal combustion engine fundamentals. New York: McGraw-Hill; 1988.

[26] Curran HJ, Gaffuri P, Pitz WJ, Westbrook CK. A comprehensive modeling studyof n-heptane oxidation. Combust Flame 1998;114(1–2):149–77.

[27] Curran HJ, Gaffuri P, Pitz WJ, Westbrook CK. A comprehensive modeling studyof iso-octane oxidation. Combust Flame 2002;129(3):253–80.

[28] Morgan N, Smallbone A, Bhave A, Kraft M, Cracknell R, Kalghatgi G. Mappingsurrogate gasoline compositions into RON/MON space. Combust Flame2010;157(6):1122–31. doi:http://dx.doi.org/10.1016/j.combustflame.2010.02.003.

[29] Mehl M, Chen JY, Pitz WJ, Sarathy SM, Westbrook CK. An approach forformulating surrogates for gasoline with application toward a reducedsurrogate mechanism for CFD engine modeling. Energy Fuels2011;25(11):5215–23.

[30] Haas FM, Chaos M, Dryer FL. Low and intermediate temperature oxidation ofethanol and ethanol-PRF blends: an experimental and modeling study.Combust Flame 2009;156(12):2346–50. doi:http://dx.doi.org/10.1016/j.combustflame.2009.08.012.

[31] Cancino LR, Fikri M, Oliveira AAM, Schulz C. Autoignition of gasoline surrogatemixtures at intermediate temperatures and high pressures: experimental andnumerical approaches. Proc Combust Inst 2009;32(1):501–8.

[32] Huang C, Golovitchev V, Lipatnikov A. Chemical model of gasoline-ethanolblends for internal combustion engine applications. SAE Technical Paper 2010-01-0543; 2010.

[33] Dagaut P, Togbe C. Experimental and modeling study of the kinetics ofoxidation of ethanol- gasoline surrogate mixtures (e85 surrogate) in a jet-stirred reactor. Energy Fuels 2008;22(5):3499–505.

[34] Frassoldati A, Cuoci A, Faravelli T, Ranzi E. Kinetic modeling of the oxidation ofethanol and gasoline surrogate mixtures. Combust Sci Technol2010;182(4):653–67.

[35] Naik CV, Puduppakkam K, Wang C, Kottalam J, Liang L, Hodgson D, et al.Applying detailed kinetics to realistic engine simulation: the surrogate blendoptimizer and mechanism reduction strategies. SAE Int J Engines2010;3:241–59. doi:http://dx.doi.org/10.4271/2010-01-0541.

[36] Chaos M, Zhao Z, Kazakov A, Gokulakrishnan P, Angioletti M, Dryer FL. APRF+toluene surrogate model for simulating gasoline kinetics. In: Proceedingsof the 5th US combustion meeting, San Diego, CA, March 25–28; 2007.

[37] Pera C, Knop V. Methodology to define gasoline surrogates dedicated to auto-ignition in engines. Fuel 2012;96(0):59–69. doi:http://dx.doi.org/10.1016/j.fuel.2012.01.008.

[38] Kalghatgi GT. Fuel anti-knock quality-part I: Engine studies. SAE TechnicalPaper 2001-01-3584; 2001.

[39] Kalghatgi GT. Fuel anti-knock quality – Part II: Vehicle studies – how relevantis motor octane number (MON) in modern engines? SAE Technical Paper 2001-01-3585; 2001.

[40] Standards Australia. Methods of test for fuel consumption of motor vehiclesdesigned to comply with Australian Design Rules 27 and 40, AS2877-1986;1986.

[41] Australian Government, Fuel Standard (Petrol) Determination 2001; 2001.[42] Jain AK, Babu VSS, Saxena M, Aigal AK, Singal SK, Koganti RB, et al. Effect of

gasoline composition (olefins, aromatics and benzene) on automotive exhaustemissions – a literature review. SAE Technical Paper 2004-28-0081(0); 2004.doi:http://dx.doi.org/10.4271/2004-28-0081.

[43] Knocking characteristics of pure hydrocarbon. Tech. rep. Special TechnicalPublication No. 225, American Society for Testing and Materials; 1958.

[44] Leppard WR. The autoignition chemistries of primary reference fuels, othermixtures and blending octane numbers. SAE Technical Paper 922325; 1992.

[45] Morganti KJ, Foong TM, Brear MJ, da Silva G, Yang Y, Dryer FL. The research andmotor octane numbers of liquefied petroleum gas (LPG). Fuel2013;108:797–811. doi:http://dx.doi.org/10.1016/j.fuel.2013.01.072.

[46] de Menezes EW, Cataluna R, Samios D, da Silva R. Addition of an azeotropicETBE/ethanol mixture in eurosuper-type gasolines. Fuel 2006;85:2567–77.doi:http://dx.doi.org/10.1016/j.fuel.2006.04.014.

[47] da Silva R, Cataluna R, de Menezes EW, Samios D, Piatnicki CMS. Effect ofadditives on the antiknock properties and Reid vapor pressure of gasoline. Fuel2005;84:951–9. doi:http://dx.doi.org/10.1016/j.fuel.2005.01.008.

http://dx.doi.org/10.1016/S1352-2310(01)00508-8










http://dx.doi.org/10.4271/2012-01-1274


















http://dx.doi.org/10.1016/j.combustflame.2010.02.003

















http://dx.doi.org/10.4271/2010-01-0541



http://dx.doi.org/10.4271/2004-28-0081




the octane numbers of ethanol blended with gasoline and its surrogates

Documents