Fuel 90 (2011) 1968–1979

Contents lists available at ScienceDirect

Fuel

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

Experimental investigation on injection characteristics of bioethanol–diesel fueland bioethanol–biodiesel blends

Eloisa Torres-Jimenez a, M. Pilar Dorado b, Breda Kegl c,⇑a Dep. Mechanics and Mining Engineering, University of Jaen, C/Alfonso X el Sabio, 23700 Linares (Jaen), Spainb Dep. of Chemical Physics and Applied Thermodynamics, EPS, Ed Leonardo da Vinci, Campus de Rabanales, Universidad de Cordoba, 14071 Cordoba, Spainc Faculty of Mechanical Engineering, University of Maribor, Smetanova 17, SI-2000 Maribor, Slovenia

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

Article history:Received 25 September 2010Received in revised form 19 November 2010Accepted 30 November 2010Available online 14 December 2010

Keywords:BiodieselBioethanolInjection systemInjection timing

0016-2361/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.fuel.2010.11.042

⇑ Corresponding author.E-mail address: breda.kegl@uni-mb.si (B. Kegl).

This paper analyses the fuel injection characteristics of bioethanol–diesel fuel and bioethanol–biodieselblends considered as fuel for diesel engines. Attention is focused on the injection characteristics whichsignificantly influence the engine characteristics and subsequently the exhaust emissions. In this contextthe following injection characteristics have been investigated experimentally: fuelling, injection timing,injection delay, injection duration, mean injection rate, and injection pressure. The tested fuels were neatmineral diesel fuel, neat biodiesel made from rapeseed oil, bioethanol/diesel fuel and bioethanol/biodie-sel blends up to 15% (v/v) bioethanol with an increment of 5%. The fuels blends were experimentallyinvestigated in a fuel injection M system at rated condition (FL, 1100 rpm), peak torque (FL, 850 rpm),and maximum pump speed (1100 rpm) for different partial loads (PL 75% and PL 50%), at ambient tem-perature.

It has been proven that for all operating regimens tested, the addition of bioethanol to biodiesel reducesfuelling, injection timing, injection duration, mean injection rate and maximum injection pressure andincreases injection delay compared to pure biodiesel. Meanwhile, increasing bioethanol in diesel fuelshows no significant variations or a slightly increase in fuelling, injection timing, injection duration,and mean injection rate and a decrease in injection delay and maximum injection pressure, comparedto pure diesel fuel.

The influence of bioethanol in biodiesel is much more significant that in diesel fuel; it has a beneficialeffect on biodiesel injection characteristics because bioethanol addition brings them nearer to the dieselfuel one and it is expected to decrease biodiesel NOx emissions.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction gen presence in biodiesel and ethanol represents a potential in

Nowadays, the necessity of finding alternative fuels toreplace progressively those produced from petroleum is generallyaccepted. The most common biofuels today are bioethanol andbiodiesel. Ethanol can be produced from biomass by fermentationof sugar, by converting the starch content of biomass feedstocksinto alcohol (bioethanol) or by hydration of ethylene which isobtained from petroleum and other sources. Biodiesel is producedby the transesterification of vegetable oil or animal fat feedstock,and it is the mostly used biofuel which can substitute diesel fueltotally or partially in a diesel engine. Ethanol usually replacesgasoline in petrol engines and biodiesel makes the same for dieselengines, but diesel fuel blended with low concentrations ofethanol can also run a diesel engine.

An important advantage of biofuels is related to their oxygencontent, which it is not present in fossil fuels like diesel. The oxy-

ll rights reserved.

reducing particulate emissions [1,2]. Furthermore, oxygen contentreduces carbon monoxide (CO) and unburned hydrocarbon (HC)emissions [3] because this element favors a complete combustionand an increase in thermal efficiency.

Nowadays, many investigations are focused on the influence ofbiodiesel and their blends with mineral diesel on engine perfor-mance and exhaust emissions, showing a slight decrease in enginepower and an increase in NOx emissions [4,5]. To moderate the NOx

emissions, several strategies have been proposed, depending onthe fuel and injection system type [6–10]. Several studies haveshown that biodiesel burns in a diesel engine with much less totalhydrocarbons (THC), carbon monoxide (CO) and particulate matter(PM) in the exhaust, although there was an increase in nitrogenoxides (NOx) [5,11–13]. It has been demonstrated that byintroducing ethanol fuel by port injection, NOx and smoke opacitysimultaneously decrease about 35–85% compared to those of theneat biodiesel–fueled engines [14].

In case of ethanol–diesel blends, PM in exhaust also decreasedsubstantially and a slight decrease was observed in NOx. The effect

Table 1Bioethanol (C2H5OH) properties (ISO 9001).

Property Unit Specification Result

Minimum assay (purity) % (v/v) >99.8 99.8Boiling point �C Min 78.3/max 78.8 78.8Density 20� kg/m3 Min 790/max 793 791Water content % <0.2 <0.2

E. Torres-Jimenez et al. / Fuel 90 (2011) 1968–1979 1969

on CO and THC are less clear although both were still well belowthe regulated emissions limit [15–17]. When using biodiesel–die-sel fuel blends and biodiesel–ethanol–diesel fuel blends, it wasfound that CO and HC were significantly reduced at high engineload, whereas NOx increased, compared to the use of diesel fuel[6,18]. New regulations require diesel engines to lower sulfuremissions considerably, making ethanol–diesel fuel blends andethanol–biodiesel blends much more attractive as a practical fuelto use because ethanol and biodiesel have virtually no sulfurcontent. Finally, it has been demonstrated that ethanol additionto biodiesel reduces its main harmful emissions and improvesbrake thermal efficiency compared to those of pure biodiesel, butemissions were still higher and brake thermal efficiency lowerthan those of diesel fuel [19].

Fuel injection characteristics depend on both, the type of injec-tion system and fuel properties [20–24]. A significant influence ofbiodiesel combustion temperature on injection characteristicshas already been demonstrated [25]. It is known that higher den-sity, sound velocity and bulk modulus of fuel cause advanced injec-tion timing in mechanically controlled in-line injection systems,thus increasing combustion temperature. This may be one of thereasons for increased NOx emission [8,26,27]. Fuel properties donot influence the injection timing in electronically controlled com-mon rail injection systems [28]. In spite of this, investigations showthat the usage of biodiesel in common rail systems may also in-crease NOx [29]. Anyhow, the mechanically controlled in-line injec-tion system is still widely used in heavy-duty engines. This justifiesthe efforts to reduce harmful emissions by using various fuels insuch a system.

One of the main problems of blending two different fuels is thattheir chemical composition can lead to their separation. If a blendof various fuels separates after some time period it means that theconcentration of each fuel injected into the cylinder may vary overthe time. Because the engine management is optimized for a spe-cific fuel, the engine characteristics will vary with respect to time.

In a previous research, the authors demonstrated that bioetha-nol–biodiesel blends remain stable from �18 �C up to 30 �C [30].Furthermore, cold weather properties, such as cloud point andpour point, are improved by adding bioethanol to biodiesel. Theother properties are also improved or their variation is not signif-icant with respect to diesel fuel. An exception is the flash point be-cause all samples showed bioethanol flash point which is very low[31].

In case of ethanol–diesel fuel blends, the nonpolar hydrocar-bons present in diesel fuel has no affinity with the polar ethanol,leading to phase separation [32]. Previous researches have pre-sented various kinds of additives to avoid phase separation be-tween diesel fuel and ethanol [18,33–35]. In the present study,no stability additives have been used.

In the effort to achieve the reduction of engine emissions andfuel consumption, while keeping other engine performances atan acceptable level, the injection system plays an important role.It is also possible to predict to some extent the engine characteris-tics on the basis of injection characteristics. Some important injec-tion characteristics are injection pressure, injection duration,injection timing and fuelling. In general, mean injection pressurehas to be as high as possible while keeping the maximal injectionpressure at a low level and the injection timing influences theharmful NOx emissions [7,20].

In this paper, the most important injection characteristics ofbioethanol–diesel fuel and bioethanol–biodiesel blends are ana-lyzed and compared to those of pure diesel fuel. Fuel injectioncharacteristics properties like fuelling, injection timing, injectiondelay, injection duration, mean injection rate and pressure aretested at rated condition, which means full load (FL) and pumpspeed (1100 rpm), peak torque condition (FL, 850 rpm), and at

two partial loads (PL 75% and PL 50%) at pump speed of1100 rpm at ambient temperature. Only samples up to 15% of bio-ethanol in diesel and in biodiesel were tested since we assume thathigher bioethanol concentrations would show ignition problemswhen used to run a diesel engine; furthermore, the heating valuewould significantly differ from that of a diesel fuel causing impor-tant reduction in engine power.

2. Tested fuels and their properties

Injection characteristics of eight samples were determined. Thetested samples were neat mineral diesel fuel (D100), 5% bioetha-nol/diesel fuel blend (v/v) (E5D95), 10% bioethanol/diesel fuelblend (v/v) (E10D90), 15% bioethanol/diesel fuel blend (v/v)(E15D85), neat biodiesel (B100), 5% bioethanol/biodiesel blend(v/v) (E5B95), 10% bioethanol/biodiesel blend (v/v) (E10B90), and15% bioethanol/biodiesel blend (v/v) (E15B85).

The fuel properties have a noticeable influence on the responseof the injection system. For this reason, in a previous study, wedetermined experimentally the most important physical andchemical properties of pure diesel fuel, bioethanol–diesel fuelblends, pure biodiesel, and bioethanol–biodiesel blends and theirinfluence on engine characteristics was also presented [36,31].These properties are summarized in Tables 2 and 3.

Bioethanol (from Carlo Erba Company, Milano – Italy) was pro-duced from the fermentation of sugars and its main properties areshown in Table 1. The diesel fuel (from Petrol d.d. Ljubljana –Slovenia) was used without flow improver additives. Biodiesel(from Biogoriva d.o.o. – Slovenia) was produced from rapeseedoil. According to Table 3, the purity of the tested biodiesel isguaranteed as the ester content is higher than the minimum valueprescribed by the biodiesel standard EN 14214.

The tested pure fuels are conforming to their respective stan-dards for properties limitation; diesel fuel is conforming to Euro-pean standard EN 590, pure biodiesel is conforming to EN 14214,and bioethanol satisfies ISO 9001 specifications.

The measurement of sound velocity in fuel is based on theprinciple of pressure wave propagation on a specified length ofthe high pressure (HP) tube, instrumented by two piezoelectricbased pressure transducers, located at both ends of the tube. Asmall plunger-type pump was used to induce a pressure wavewhich was registered by both transducers and simultaneouslyacquired by a measuring system (NI 9234 placed in NI 9163). Noamplifiers were used. Fig. 1 shows characteristic pressure wavetraces of both sensors.

The sound velocity was measured at different pressures up to700 bar for all tested neat fuels, bioethanol–diesel blends andbioethanol–biodiesel blends. Fig. 2 shows the dependence of fuelsound velocity on pressure. It can be observed that sound velocitydecreases by decreasing pressure and/or by adding bioethanol. Thelower bioethanol sound velocity, compared to other fuels tested, iscaused by the lower bioethanol density, and consequently by thelower bulk modulus. According to this affirmation, biodiesel fuelshows the highest sound velocity and bioethanol the lowest oneamong the tested fuels.

Table 2Physical and chemical properties of diesel fuel and bioethanol–diesel fuel blends.

Property Unit Limits (D100) Tested fuels

EN 590 min/max D100 E05D95 E10D90 E15D85

Density at 15 �C kg/m3 820/845 837.3 834.3 831.7 829.4Cloud point �C �3 �3 19 21Pour point �C – �9 �9 �12 �36CFPP �C �8 �8 �7 �8Flash point �C >55 66.0 25.0 25.0 25.0Lubricity WS 1.4 lm max. 460 448.0 399.0 406.0 395.0Cetane index – min. 46 51.8 – – –Sulfur content, WD-XRF mg/kg max.10.0 31.0 – – –Neat calorific value MJ/kg – 42.91 – – –Total contamination mg/kg max. 24 2 – – –Carbon residue %(m/m) max. 0.30 <0.01 – – –FPT – – 1.02 1.01 1.01 1.01Pressure/volume -kPa/ml 20/300 17/300 13/300 12/300Elemental analysis (%w/w) 86.13 C 84.55 C 82.94 C 81.31 C

13.87 H 13.84 H 13.80 H 13.76 H0 O 1.61 O 3.26 O 4.93 O

Kinematic viscosity (40 �C) mm2/s 2.4.5 2.78 2.53 2.31 2.19Water content mg/kg max. 200 50 100 130 140Corrosion Cu, 3 h at 50 �C Rating Class 1 1a 1a 1a 1aFT-Infrared analysis – – No undesirable components found

Table 3Physical and chemical properties of biodiesel and bioethanol–biodiesel blends.

Property Unit Limits (B100) Tested fuels

EN 14214 min/max B100 E05B95 E10B90 E15B85

Density 15 �C kg/m3 860/900 882.6 878.0 873.5 869.0CFPP �C �10 �10 �9 �12Cloud point �C – �3 �4 �5 �5Pour point �C – �6 �6 �9 �9Flash point �C min 120 138.5 25.0 25.0 25.0Lubricity WS 1.4 lm – 175 167 161 174FPT – – 6.08 4.40 2.90 2.36Pressure/volume kPa/ml 105/50 105/70 105/110 105/140Element composition (CHN) – 76.68%C 76.88%C 77.03%C 76.44%C

11.07% H 11.36%H 11.31%H 10.93%HKinematic viscosity (40 �C) mm2/s 3.5/5 4.477 4.041 3.575 3.244Water content mg/kg max. 500 150 230 250 230Corrosion Cu, 3 h at 50 �C Rating Class 1 1a 1a 1a 1aIR spectrum – No undesirable component foundNeat calorific value MJ/kg – 42.36 – – –Ester content % (m/m) min. 96.5 97.3 – – –Iodine number g iodine/100 g max. 120 112 – – –Acidity number mg KOH / g max. 0.5 0.27 – – –Linolenic acid methyl ester % (m/m) max. 12.0 6.8 – – –Methanol content % (m/m) max. 0.20 <0.01 – – –Phosphorus content mg/kg max. 10.0 <5 – – –Monoglycerides content % (m/m) max. 0.8 0.59 – – –Diglycerides content % (m/m) max. 0.20 0.14 – – –Triglycerides content % (m/m) max. 0.20 <0.05 – – –Free glycerol % (m/m) max. 0.02 0.006 – – –Total glycerol % (m/m) max. 0.25 0.176 – – –Total contamination mg/kg max. 24 14 – – –Sulfur content, WD-XRF mg/kg max. 10 5.8 – – –

Fig. 1. Principle of sound velocity measurement.

1970 E. Torres-Jimenez et al. / Fuel 90 (2011) 1968–1979

3. Fuel injection system and test procedure

The eight samples were tested in a mechanically controlled fuelinjection M system, which consist of a plunger-in-barrel assembly,

a high pressure (HP) tube, and an injector. The scheme of theexperimentally investigated system, which includes the transduc-ers for pressure, needle lift and injection timing determination, isshown in Fig. 3. The main specifications of this system are givenin Table 4.

The injection M system was mounted on Fiedman-Maier type12H100_h test bed for a conventional fuel injection pump. The testbench and fuel injection system were instrumented in order tomeasure basic parameters characteristics of system operation. Adiaphragm-type pressure transducer (AVL 31DP 1200E) was ap-plied at the high pressure pipe inflow just behind the injectionpipe. Its special-purpose four-element strain gage (full-bridge con-figuration) was connected to the National Instrument module

Fig. 2. Sound velocity of fuels under various conditions.

Fig. 3. Schematic diagram of an in-line fuel injection M system.

Table 4Test injection system main specifications.

Injection model Direct injection system with walldistribution (M system)

Fuel injection pump type Bosh PES 6A 95D 410 LS 2542Pump plunger (diameter � lift) 9.5 mm � 8 mmFuel tube (length � diameter) 1024 mm � 1.8 mmInjection nozzle (number � nozzle

hole diameter)1 � 0.68 mm

Maximal needle lift 0.3 mmStart of delivery (pump injection

timing)30 �C ABTC

E. Torres-Jimenez et al. / Fuel 90 (2011) 1968–1979 1971

bridge amplifier (SCXI-1520). A piezoelectric-type pressure trans-ducer (Kistler 6227) with charge amplifier Kistler was applied forthe measurement of pressure traces within the high pressure tubejust ahead of the injector. Its very high frequency response enabledthe accurate dynamic measurement of pressure variation. A spe-cially designed variable-inductance sensor was applied for needlelift pickup. An iron core was placed within two inductance coilsand attached to the injector needle. The coils formed two legs ofWheatstone bridge which was excited by an alternating currentof 6 V at 50,000 Hz. With the core in the null position, the induc-tance of the two coils is equal and the bridge is balanced. A coremotion causes a proportional change in inductance of each coil,

and the bridge is unbalanced. The output voltage is thus propor-tional to the core motion. The bridge amplifier (HBM KWS 3085)was applied for bridge excitation and output voltage pickup. Thehigh frequency of the excitation current enabled a satisfactory fre-quency response necessary for dynamic displacement measure-ment. The top dead center (TDC) position was measured by anoptic sensor. A disk with a single cutout was attached to the pumpshaft, and a light source with photo detector was applied to pro-vide a TDC position signal. The injected fuel quantity was mea-sured by collecting the injected fuel over 500 cycles into a testglass.

A computer-aided measuring system was used to acquire elec-tric signals from the applied sensors. The system incorporates apersonal computer (Pentium III 600 MHz, 256 MB RAM) and a mul-tifunction card (AT MIO 16 E2). Electric signals were conditionedby an SCXI data conditioning system. Differential analogue inputsignals were led to the module (SCXI-1520) which was used as abridge amplifier at the same time. This made a simultaneous mea-surement of all high speed variables possible. The multifunctioncard, data acquisition system, and application software are allproducts of National Instruments.

LabVIEW software was used to build the computer applicationsfor data acquisition, data analysis, and control algorithms. Theseapplications were used to control the operation of the multifunc-tion card (data acquisition, DC voltage output) and for data loggingand postprocessing.

The following parameters (variables) were measured:

� Pressure pI (pressure transducer AVL 31DP 1200E).� Pressure pII (piezoelectric transducer KISTLER 6227).� Needle lift hn (variable-inductance sensor).� Fuelling.

It should be noted that throughout this paper it is assumed thatthe pump load is not determined by the fuelling but by the rack po-sition. This means that at a single operating regime the use of var-ious fuels will cause the fuelling to be slightly different.

An operating regime is defined by load (rack position) andpump speed. For each regime, the pressure at the first monitoringpoint of the fuel injection system pI and the pressure at the secondmonitoring point pII as well as the needle lift hn histories have beenmeasured during the experiments.

As an example, Fig. 4 shows the injection characteristics forE15D85 at peak torque condition, and also for E15B85 at PL 50%and at pump speed of 1100 rpm. From those graphics, the peak

Fig. 4. Pressures pI and pII and needle lift hn histories.

1972 E. Torres-Jimenez et al. / Fuel 90 (2011) 1968–1979

pressures pI and pII can be determined. Here, it has to be pointedout that the pressure history pII is not the actual injection pressurehistory. This is because pII is measured at the end of the HP tubebefore the injector and not in front of the nozzle hole. The differ-ence is, therefore, due to the pressure wave propagation in theinjector and due the delay, caused by the distance between theinjector inflow and outflow (nozzle hole). For this reason, the startof injection (of needle lifting) does not coincides with the 175 barof pressure pII (175 bar is the needle opening pressure). Likewise,the moment of needle closing does not coincide with the needleclosing pressure of pII. Despite this, pressure pII offers a goodapproximation to the injection pressure in the sense that the fuelinfluence on the injection pressure is well reflected in fuel influ-ence on pII. Furthermore, the injection duration and injection tim-ing as well as injection delay at the known angle of the start of fueldelivery (injection pump timing) can be determined also.

4. Fuel influence

The experiments were performed for neat diesel D100, neat bio-diesel B100, and their blends with bioethanol up to 15% at differentoperating regimes, at ambient temperature (20 �C) and a constantpump injection timing of 30� of crankshaft angle before top deadcenter (CA BTC).

Experimental results at rated condition (FL, 1100 rpm) are pre-sented in Figs. 5 and 6 for D100, E15D85, B100, and E15B85 fuels.According to Fig. 5, the addition of bioethanol decreases the max-imal injection pressure pII. It is also evident that maximal pressure

FL 1100 rpm

Fig. 5. Fuel influence on press

pII decreases more, when bioethanol is added to biodiesel than todiesel fuel. Furthermore, the history of pressure pII of E15B85 blendis very close to those of neat D100. From Fig. 6, where the needlelift history is shown, it can be observed that biodiesel injectiontiming is advanced with respect to that of diesel fuel and biodieselinjection duration is longer. The addition of bioethanol retards theinjection timing in diesel and biodiesel fuel. It has to be pointed outthat this influence is more significant in biodiesel. Furthermore, theneedle lift history of E15B85 is practically the same as that of D100.This means that the injection timing, injection duration, and injec-tion delay of E15B85 is very close to those of D100.

The influence of bioethanol in the biodiesel and diesel fuels atpeak torque condition is similar to that obtained at rated condition.From Figs. 7 and 8, the injection characteristics comparison con-firms that E15B85 blend gives very close injection system behaviorto D100.

To get a better understanding of the influence of bioethanolcontent in the diesel and biodiesel fuels on injection characteris-tics, the most important injection characteristics of E05D95,E10D90, E15D85, B100, E05B95, E10B90, E15B85 are comparedto those of neat D100. Throughout this paper, the term relative willbe used to emphasize that the actual value of the parameter isdivided by the corresponding parameter for D100.

4.1. Fuelling

The comparison of relative fuelling at various operating regimesis presented in Fig. 9. At constant pump injection timing and a

ure pII at rated condition.

FL 1100 rpm

Fig. 6. Fuel influence on needle lift hn at rated condition.

FL 850 rpm

Fig. 7. Fuel influence on pressure pII at peak torque condition.

FL 850 rpm

Fig. 8. Fuel influence on needle lift hn at peak torque condition.

E. Torres-Jimenez et al. / Fuel 90 (2011) 1968–1979 1973

constant rack position, the fuelling of B100, bioethanol–diesel fueland bioethanol–biodiesel blends is higher or equal than those ofD100. B100 always shows the highest fuelling at all tested operat-ing regimes. One can observe no significant changes or a slightlyincrease in fuelling with increased bioethanol content in dieselfuel, meanwhile fuelling decreases for higher concentration of bio-ethanol in biodiesel. In all cases tested, the bioethanol additioninfluence on fuelling is more evident in biodiesel than in dieselfuel. At all tested operating regimes, the fuelling obtained withE15B85 closes to those of D100 fuel.

Fuelling variation is caused by various densities and viscositiesof the samples. The higher fuelling of B100 is a consequence of itshigher bulk modulus and its higher kinematic viscosity. Injectiontiming and injection duration are directly related to fuelling. Nextsections will show how those physical properties modify theseinjection characteristics.

4.2. Injection timing

Injection timing or start of injection is a very important param-eter that significantly influences all engines characteristics [37,38]due to the fact that this factor influences the mixing quality of theair–fuel mixture and, consequently, the combustion process andharmful emissions. The deviations in density and consequently inbulk modulus, which affects the speed of sound, modify theinjection timing. According to this it is expected that higherconcentrations of bioethanol will cause retarded injection timing.Nevertheless, viscosity also affects injection timing. Lower viscos-ity means lower friction while the fuel travels through the highpressure (HP) tube and through the nozzle, leading to an easierpropagation and consequently to an advanced injection timing.

According to Fig. 10 we can say that the lower density of bioeth-anol, compared to that of biodiesel [31], is the predominant

Fig. 9. Relative fuelling using different fuels at different operation regimes.

1974 E. Torres-Jimenez et al. / Fuel 90 (2011) 1968–1979

property that affects the injection timing because the bioethanoladdition to biodiesel leads to retard injection timing.

In case of bioethanol–diesel fuel blends, the low tested bioeth-anol concentration leads to no significant variations or a slightlyincrease in injection timing, which can be caused by the lowerviscosity of bioethanol compared to that of diesel fuel [36]. Never-theless this tendency is not so clear. As an example, we can com-pare the needle lift history, Fig. 6, and injection timing, Fig. 10, atrated condition (FL, 1100 rpm). From Fig. 10 one can observe thatE15D85 leads to advance injection timing, and this is confirmedin Fig. 6 also. On the other hand, from Fig. 6, one can observe thatafter the earlier start of needle opening by E15D85 with respect toD100, in the central part of the needle opening, E15D85 leads to re-tard needle lift curve. It is clearly evident that the maximal needlelift is reached earlier by D100 then by E15D85, Fig. 6. The bioeth-anol addition to diesel fuel means that the tendency of the needlelift curve changes after injection timing (Fig. 10). The injection tim-ing behavior could be the result of the interaction of viscosity anddensity.

Due to the fact that injection timing is advanced for biodieselwith respect to diesel fuel [39–41], adding bioethanol to biodieselhave the advantage of bringing it nearer to the diesel fuel. At ratedcondition, a low concentration of bioethanol causes biodiesel toreach diesel fuel injection timing, meanwhile at other tested oper-ating regimes, higher contents of bioethanol in the biodiesel areneeded.

According to a previous study [41], with the advanced injectiontiming of biodiesel the pressure in the cylinder increases and theNOx emissions increase also. So, from the results obtained, wecan expect that the addition of bioethanol to biodiesel offers a pos-sibility to reduce NOx emissions, because the injection timing is re-tarded. Nevertheless and for the same reason, it could be expectedthat NOx emissions will be higher in case of bioethanol–diesel fuelblends, moreover this increment would be also supported by the

enhanced combustion efficiency, provided by the bioethanol oxy-gen content.

4.3. Injection delay

When using bioethanol–biodiesel fuel blends, the already men-tioned retarded injection timing with respect to the pure biodiesel,means that the injection delay (time interval between the start ofdelivery and the start of injection) becomes gradually higher (seeFig. 11).

Due to the higher density, viscosity and bulk modulus of biodie-sel compared to those of diesel fuel, the injection delay changes,but the addition of bioethanol decreases that difference, bringinginjection delay close to that of diesel fuel. A previous study, basedon testing a high pressure injection system (common rail system),revealed a shorter injection delay for increasing ethanol in biodie-sel when using a blend containing 20% anhydrous ethanol and 80%biodiesel by volume [42]. These results are in contrast to thoseobtained in this study (where a mechanically controlled in-linepump has been tested), so it can be observed that the type ofinjection system, together with injection pressure, influence theinjection delay significantly.

In general, the diagrams of Fig. 11 show that by adding bioeth-anol injection delay of biodiesel increases meanwhile the delay de-creases or has no significant influence for diesel fuel. These resultsare in concordance with the tendency derived from injectiontiming, Fig. 10.

4.4. Injection duration

At tested partial loads, the injection duration of all tested fuelsis higher than that of D100 (Fig. 12). At all operating regimes, thetendency shows that an increment of bioethanol concentration inbiodiesel leads to decreased injection duration; meanwhile the

Fig. 10. Relative injection timing using different fuels at different operation regimes.

Fig. 11. Relative injection delay using different fuels at different operation regimes.

E. Torres-Jimenez et al. / Fuel 90 (2011) 1968–1979 1975

duration increases or it does not change substantially when bioeth-anol is added to diesel fuel. The advanced injection timing, caused

by the addition of bioethanol to diesel fuel, leads to longerinjection duration. Meanwhile, the retarded injection timing of

Fig. 12. Relative injection duration using different fuels at different operation regimes.

1976 E. Torres-Jimenez et al. / Fuel 90 (2011) 1968–1979

bioethanol–biodiesel blends leads to decrease injection duration.The results show that the injection duration of pure biodiesel is al-ways higher than that of diesel fuel. This result is in accordancewith that obtained by Radu et al. [39] who burnt waste oil biodie-sel in a diesel engine.

At tested full load operating regimes, the content of 10% bioeth-anol or less in the biodiesel gives the injection duration very closeto that obtained with D100. It seems that at partial loads highercontent of bioethanol in biodiesel is needed to obtain the fuelinjection duration of D100.

4.5. Mean injection rate

Mean injection rates at various regimes are shown in Fig. 13. Inmost cases, for bioethanol–diesel fuel blends the variation of meaninjection rate is equal or less than 1% compared to that of D100, soit can be said that bioethanol addition to diesel fuel does not mod-ify substantially this injection characteristic. In case of diesel fuelblends, the higher fuelling obtained by bioethanol addition leadsto slightly increase mean injection rate. The decreasing fuelling,caused by bioethanol addition in biodiesel, shows the opposite ten-dency. For bioethanol–diesel fuel blends, the higher fuelling iscompensated by the longer injection duration resulting in almostthe same mean injection rate in most of the cases studied, mean-while for biodiesel blends the lower fuelling has more influenceon mean injection rate than the shorter injection duration causedby bioethanol addition.

In all cases tested the influence of bioethanol addition on meaninjection rate is more evident in biodiesel than in diesel fuel. Withhigher content of bioethanol in biodiesel, the mean injection ratedecreases. However, even by using E15B85 blend the mean injec-tion rate is higher than that of D100.

Experimental results of pII at different operating regimens arepresented in Fig. 14. In general, these diagrams show that the

maximum pressure pII decreases with increasing bioethanol con-tent in biodiesel, meanwhile the variation of this injection char-acteristic is not significant or slightly lower when bioethanol isadded to diesel fuel. At peak torque condition, the influence ofbioethanol content in biodiesel is even more evident. The differ-ence between the injection pressures of different fuels arisesdue to different fuel density, viscosity, bulk modulus, and soundvelocity. The maximum pressure pII for bioethanol–biodieselblends is always somewhat higher than that for diesel fuel.Lower maximum injection pressure is expected to have a bene-ficial effect on NOx emissions.

In all cases tested, the influence of bioethanol addition on max-imum pressure pII is more evident for biodiesel than for diesel fuel,and the blend E15B85 gives the best results because they are theclosest to those of diesel fuel.

5. Conclusions

In the present study, fuel injection characteristics of bioetha-nol–diesel fuel and bioethanol–biodiesel blends have been experi-mentally studied with the aim of finding the variations in thoseparameters compared to their respective pure fuel values (dieselfuel or biodiesel), and to determine their possible commercialusage which would lead to cleaner emissions and lower depen-dence on petroleum products.

The main conclusions, related to the influence of various con-centrations up to 15% bioethanol in diesel fuel and in biodieselon the main characteristics of an in-line injection system, are sum-marized as follows:

1. For all injection characteristics studied, the influence of bioeth-anol in biodiesel is much more significant that in diesel fuel,and it has a beneficial effect from the point of view of biodieselinjection characteristics because bioethanol addition brings

Fig. 13. Relative mean injection rate using different fuels at different operation regimes.

Fig. 14. Relative maximum injection pressure pII using different fuels at different operation regimes.

E. Torres-Jimenez et al. / Fuel 90 (2011) 1968–1979 1977

1978 E. Torres-Jimenez et al. / Fuel 90 (2011) 1968–1979

them nearer to these of diesel fuel. It seems that the E15B85blend gives the best results because in most operating regimesits injection characteristics are the closest to those of diesel fuelor they are even better.

2. B100 shows the highest fuelling at all operating conditionstested. Biodiesel fuelling decreases by bioethanol addition. Bio-ethanol addition does not modify substantially diesel fuel fuel-ling or increases it just slightly. Fuelling variation is aconsequence of various densities and viscosities of tested fuels.The higher bulk modulus and kinematic viscosity of biodieselleads to increase fuelling.

3. Injection timing and consequently injection delay are signifi-cantly influenced by the type of injection system (in-line orcommon rail injection system). When using a low pressureinjection system (no common rail), injection timing of biodie-sel is retarded by bioethanol addition and injection delayincreases due to lower density of bioethanol. The variationin injection timing caused by bioethanol addition is expectedto decrease biodiesel NOx emissions. Injection timing isadvanced slightly when increasing bioethanol content in die-sel fuel and injection delay decreases due to bioethanol lowerviscosity.

4. An increment of bioethanol concentration in biodiesel leads to adecrement in injection duration, meanwhile the duration doesnot change or slightly increases when bioethanol is added todiesel fuel.

5. In general, mean injection rate varies almost negligible whenbioethanol is added to diesel fuel because higher fuelling iscompensated by longer injection duration. For biodiesel blends,the lower fuelling has more influence than the shorter injectionduration caused by bioethanol addition which leads to adecrease in mean injection rate.

6. In most cases studied, bioethanol addition in biodieseldecreases maximum injection pressure more than bioethanoladdition in diesel fuel. In case of bioethanol–biodiesel blendsit is expected that bioethanol offers a possibility to reduceNOx emissions with respect to neat biodiesel.

7. Based on the injection characteristics tested, blends up to 15%bioethanol in diesel fuel and 15% bioethanol in biodiesel canbe recommended as fuel for diesel engines, provided that fur-ther engine performance tests support this conclusion.

Acknowledgment

This research was supported by the European Community’sSixth Framework Programme in the scope of the Civitas II MobilisProject. Authors are also grateful for the Provision of a ResearchMobility Grant to E. Torres-Jimenez from the ‘‘Junta de Andalucía’’,Spain IAC09-II-5387.

References

[1] Miyamoto N, Ogawa H, Nurun NA, Obata K, Arima T. Smokeless, low NOx, highthermal efficiency, and low noise diesel combustion with oxygenated agents asmain fuel. SAE paper 980506; 1998.

[2] Bertoli C, Del Giacomo N, Beatrice C. Diesel combustion improvements by theuse of oxygenated synthetic fuels. SAE paper 972972; 1997.

[3] Nabi N, Shahadat MZ, Rahman S, Beg RA. Behavior of diesel combustion andexhaust emission with neat diesel fuel and diesel–biodiesel blends. SAE paper2004-01-3034 2004.

[4] Dorado MP, Ballesteros E, Arnal J, Gomez J, Gimenez FJL. Testing waste olive oilmethyl ester as a fuel in a diesel engine. Energy Fuel 2003;17(6):1560–5.

[5] Dorado MP, Ballesteros E, Arnal J, Gomez J, Lopez F. Exhaust emissions from adiesel engine fueled with transesterified waste olive oil. Fuel 2003;82(11):1311–5.

[6] Nabi MN, Akhter MS, Zaglul Shahadat MM. Improvement of engine emissionswith conventional diesel fuel and diesel–biodiesel blends. Bioresour Technol2006;97(3):372–8.

[7] Kegl B. Numerical analysis of injection characteristics using biodiesel fuel. Fuel2006;85(17–18):2377–87.

[8] Kegl B. Experimental investigation of optimal timing of the diesel engineinjection pump using biodiesel fuel. Energy Fuel 2006;20(4):1460–70.

[9] Szybist JP, Boehman AL, Taylor JD, McCormick RL. Evaluation of formulationstrategies to eliminate the biodiesel NOx effect. Fuel Process Technol2005;86(10):1109–26.

[10] Zhang Y, Boehman AL. Impact of biodiesel on NOx emissions in a common raildirect injection diesel engine. Energy Fuel 2007;21(4):2003–12.

[11] Kegl B. Effects of biodiesel on emissions of a bus diesel engine. BioresourTechnol 2008;99(4):863–73.

[12] Rakopoulos CD, Antonopoulos KA, Rakopoulos DC, Hountalas DT, GiakoumisEG. Comparative performance and emissions study of a direct injection dieselengine using blends of diesel fuel with vegetable oils or bio-diesels of variousorigins. Energy Convers Manage 2006;47(18–19):3272–87.

[13] Dorado MP, Ballesteros E, Arnal JM, Gomez J, Gimenez FJL. Testing wasteolive oil methyl ester as a fuel in a diesel engine. Energy Fuel 2003;17(6):1560–5.

[14] Lu X, Ma J, Ji L, Huang Z. Simultaneous reduction of NOx emission and smokeopacity of biodiesel-fueled engines by port injection of ethanol. Fuel2008;87(7):1289–96.

[15] Hansen AC, Zhang Q, Lyne PWL. Ethanol–diesel fuel blends—a review.Bioresour Technol 2005;96:277–85.

[16] Lapuerta M, Armas O, Herreros JM. Emissions from a diesel–bioethanol blendin an automotive diesel engine. Fuel 2008;87(1):25–31.

[17] Kass MD, Thomas JF, Storey JM, Domingo N, Wade J, Kenreck G. Emissions froma 5.9-l diesel engine fueled with ethanol diesel blends. SAE paper 2001-01-2018; 2001.

[18] Kwanchareon P, Luengnaruemitchai A, Jai-In S. Solubility of a diesel–biodiesel–ethanol blend, its fuel properties, and its emission characteristicsfrom diesel engine. Fuel 2007;86(7–8):1053–61.

[19] Banapurmath NR, Tewari PG. Performance, combustion, and emissionscharacteristics of a single-cylinder compression ignition engine operated onethanol–biodiesel blended fuels. Proc Inst Mech Eng Part A: J Power Energy2010. doi:10.1243/09576509JPE850:1-1.

[20] Yamane K, Ueta A, Shimamoto Y. Influence of physical and chemical properties ofbiodiesel fuels on injection, combustion and exhaust emission characteristics in adirect injection compression ignition engine. Int J Engine Res 2001;2(4):249–61.

[21] Bannikov MG, Tyrlovoy SI, Vasilev IP, Chattha JA. Investigation of thecharacteristics of the fuel injection pump of a diesel engine fuelled withviscous vegetable oil–diesel oil blends. Proc Inst Mech Eng Part D-J AutomobEng 2006;220(6):787–92.

[22] Canakci M. Combustion characteristics of a turbocharged DI compressionignition engine fueled with petroleum diesel fuels and biodiesel. BioresourTechnol 2007;98(6):1167–75.

[23] Zhang GD, Liu H, Xia XX, Yang QL. Study on the injection process of adirect-injection diesel engine fuelled with dimethyl ether. Proc Inst Mech EngPart D-J Automob Eng 2004;218(11):1341–7.

[24] Wallace FJ, Hawley JG. Analysis of the effect of variations in fuel line pressure inhigh-speed direct injection diesel engines, with high-pressure common rail fuelinjection systems on heat release, cylinder pressure, performance, and NOxemissions. Proc Inst Mech Eng Part D-J Automob Eng 2005;219(3): 413–22.

[25] Çetinkaya M, Ulusoy Y, Tekìn Y, Karaosmanoglu F. Engine and winter road testperformances of used cooking oil originated biodiesel. Energy Convers Manage2005;46(7–8):1279–91.

[26] Kegl B, Kegl M, Pehan S. Optimization of a fuel injection system for diesel andbiodiesel usage. Energy Fuel 2008;22(2):1046–54.

[27] Mittelbach M, Tritthart P, Junek H. Diesel fuel derived from vegetable oils,2: emission tests using rape oil methyl ester. Energy Agric 1985;4:207–15.

[28] Boehman AL, Morris D, Szybist J, Esen E. The impact of the bulk modulus ofdiesel fuels on fuel injection timing. Energy Fuel 2004;18(6):1877–82.

[29] McCormick RL, Graboski MS, Alleman TL, Herring AM, Tyson KS. Impactof biodiesel source material and chemical structure on emissions ofcriteria pollutants from a heavy-duty engine. Environ Sci Technol 2001;35(9):1742–7.

[30] Torres-Jimenez E, J Svoljšak-Jerman M, Gregorc A, Dorado MP, Kegl B.Comparative study of various renewable fuels blends to run a diesel powerplant. In: International conference on renewable energies and power quality(ICREPQ’10); 2010. p. 1–5.

[31] Torres-Jimenez E, Svoljšak-Jerman M, Gregorc A, Lisec I, Dorado MP, Kegl B.Physical and chemical properties of ethanol�biodiesel blends for dieselengines. Energy Fuel 2010;24(3):2002–9.

[32] Reyes Y, Aranda DAG, Santander LAM, Cavado A, Belchior CRP. Actionprinciples of cosolvent additives in ethanol�diesel blends: stability studies.Energy Fuel 2009;23(5):2731–5.

[33] Cheenkachorn K, Fungtammasan B. Biodiesel as an additive for diesohol. Int JGreen Energy 2009;6(1):57–72.

[34] Cheenkachorn K, Narasingha MH, Pupakornnopparut J. Biodiesel as an additivefor diesohol. In: The joint international conference on sustainable energy andenvironment, Thailand; 2004. p. 171–5.

[35] Fernando S, Hanna M. Development of a novel biofuel blend usingethanol�biodiesel�diesel microemulsions: EB-diesel. Energy Fuel 2004;18(6):1695–703.

[36] Torres-Jimenez E, Svoljšak-Jerman M, Gregorc A, Lisec I, Dorado MP, Kegl B.Physical and chemical properties of ethanol diesel fuel blends. Fuel 2010;90(2):795–802.

E. Torres-Jimenez et al. / Fuel 90 (2011) 1968–1979 1979

[37] Bauer H. Diesel-engine management. Stuttgart, Germany: Robert Bosch;1999.

[38] Stone R. Introduction to internal combustion engines. Hampshire, UK:Palgrave MacMillan; 1995.

[39] Radu R, Petru C, Edward R, Gheorghe M. Fueling an DI agricultural diesel enginewith waste oil biodiesel: effects over injection, combustion and enginecharacteristics. Energy Convers Manage 2009;50(9): 2158–66.

[40] Ozsezen AN, Canakci M, Sayin C. Effects of biodiesel from used frying palm oilon the performance, injection, and combustion characteristics of an indirectinjection diesel engine. Energy Fuel 2008;22(2):1297–305.

[41] Kegl B, Hribernik A. Experimental analysis of injection characteristics usingbiodiesel fuel. Energy Fuel 2006;20(5):2239–48.

[42] Park SH, Suh HK, Lee CS. Nozzle flow and atomization characteristics ofethanol blended biodiesel fuel. Renew Energy 2010;35(1):144–50.