WIXLIB

ACTA UNIVERSITATIS AGRICULTURAE ET SILVICULTURAE MENDELIANAE BRUNENSISVolume 63126Number 4, EMPERATURE DEPENDENCEVISCOSITY AND DENSITYOF DIFFERENT BIODIESEL BLENDSVojtěch Kumbár1, Antonín Skřivánek11Department of Technology and Automobile Transport, Mendel University in Brno, Zemědělská 1, 613 00 Brno,Czech RepublicAbstractKUMBÁR VOJTĚCH, SKŘIVÁNEK ANTONÍN. 2015. Temperature Dependence Viscosity andDensity of Different Biodiesel Blends. Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis,63(4): 1147–1151.The main goal of this paper is to assess the effect of rapeseed oil methyl ester (RME) concentrationin diesel fuel on its viscosity and density behaviour. The density and dynamic viscosity were observedat various mixing ratios of RME and diesel fuel. All measurements were performed at constanttemperature of 40 C. Increasing ratio of RME in diesel fuel was reflected in increased density valueand dynamic viscosity of the blend. In case of pure RME, pure diesel fuel, and a blend of both (B30),temperature dependence of dynamic viscosity and density was examined. Temperature range inthe experiment was 10 C to 80 C. Considerable temperature dependence of dynamic viscosityand density was found and demonstrated for all three samples. This finding is in accordance withtheoretical assumptions and reference data. Mathematical models were developed and tested.Temperature dependence of dynamic viscosity was modeled using a polynomial 3rd polynomialdegree. Correlation coefficients R 0.796, 0.948, and 0.974 between measured and calculatedvalues were found. Temperature dependence of density was modeled using a 2nd polynomial degree.Correlation coefficients R 0.994, 0.979, and 0.976 between measured and calculated values wereacquired. The proposed models can be used for flow behaviour prediction of RME, diesel fuel, andtheir blends.Keywords: biodiesel, density, viscosity, modelingINTRODUCTIONIn the Czech Republic, biofuels are being testedas additives to conventional fuels such as petrol anddiesel. The new commitment of the European Unionis to increase the share of biofuels in conventionalfuels up to 10% by 2020. Now (according withČSN EN 590) the current state it is about 7%.The term biofuel means liquid or gaseous fuel thatis produced from biomass. Biofuels may include thefollowing products: biodiesel, bioethanol, biogas,biomethanol, bioDME (dimethyl ether), bio-ETBE(ethyl tert-butyl ether), bio-MTBE (methyl tertbutyl ether), synthetic biofuels, hydrogen and purevegetable oil (Vlk, 2006). Currently biodiesel (madefrom oil crops, e.g. rapeseed and sunflower) andbioethanol (made from crops containing sugar andstarch, e.g. beet or cereals) rank among most widelyused biofuels. These two liquid fuels can replacediesel fuel and petrol on a massive scale. They canbe used in engines of modern cars. The enginesmay include unmodified (for low biofuel content)or modified (for high biofuel content). In addition,these fuels shall be distributed through the existinginfrastructure (Vlk, 2004).Production of biodiesel is a well establishedprocedure and the technology will probably staybasically the same. The term biodiesel refers to fattyacid methyl esters (FAME). They are products of aprocess called esterification, where the reactantsare vegetable oil or animal fat and methanol in thepresence of a catalyst. A by-product of this processis glycerine which can be used in cosmetics andpharmaceutical industry. Currently 80% of annualworld production of biodiesel uses rapeseed oil. The1147

1148Vojtěch Kumbár, Antonín Skřiváneksame ratio applies to the Czech Republic, as well. Inthis case, we refer to the biofuel as rapeseed methylester (Králová, 2007).From theoretical point of view, pure RME canbe used in diesel engines directly without anychemical modifications. However, the drawbacksof this approach are its worse properties comparedto diesel including viscosity, density, stability, andcetane number. As a result, it is more commonlyused in a blend with conventional diesel fuel.This article addresses issues connected with theviscosity/density of RME, diesel fuel, and blends.MATERIALS AND METHODSRME, diesel fuel, and 8 of their mutual blendswith different mixing ratios have been chosen forthe experiment. Samples with volume of 1000 mlwere used. Detailed description is given in Tab. Ibelow.I: Blends of RME and diesel used in the experimentDiesel %Viscosity measurements were performed usingthe Anton Paar DV-3P rotational viscometer. Thisdevice measures torque force required to overcomeresistance of rotating cylinder or disk immersed inthe measured material sample. The rotating cylinderor spindle is connected via spring to motor sharotating at defined speed. Rotation of the sha ismeasured electronically and provides accurateinformation about the position of the sha , hencethe spindle (see Fig. 1). The dynamic viscosityvalue in [mPa·s] is then acquired using internalcalculation algorithm. For constant viscosity liquids,the resistance against motion increases with the sizeof spindle. Measurement range for determination ofmaterial rheological properties can be adjusted byselecting the appropriate combination of spindleand rotation speed. To obtain relevant results, it isnecessary to know essential rheological propertiesof given sample. Obviously, it is necessary tocorrectly classify the material prior any testing takesplace (Kumbár and Sabaliauskas, 2013).Standard spindle labeled LCT was used in theexperiment. The spindle is most appropriate for1: Schematic of device geometryliquids featuring very low viscosity. On the rotationalviscometer the number of spindle revolutions wasset to 100 per minute and the sampling frequencywas set to 1 Hz.The temperature dependence of viscosity wasmeasured using the following procedure: 200 ml ofthe measured sample cooled to 10 C was placedinto a beaker. This beaker with the sample wasthen placed into working vessel of the rotationalviscometer. Then, the measuring spindle (LCT)and a calibrated temperature sensor Pt 100 wereimmersed as well. A er that the actual dynamicviscosity measurement began. The sample wasfurther heated up to 80 C. Presented procedureis in accordance with the references (Kumbár andPolcar, 2012; Kumbár and Dostál, 2014).Using a simple conversion, we can calculate thekinematic viscosity from the dynamic viscositymeasured. The kinematic viscosity is the ratio ofdynamic viscosity and density of measured sample: [mm2·s 1; mPa·s, g·cm 3], (1)where .kinematic viscosity, .dynamic viscosity, and .density.Density measurements were performed usingMohr scales. Sample temperature was 40 C. Thisvalue represents a comparative temperature fordistilled liquids according to the ISO 8217 standard.A mathematical model was created using theStatistica 10 so ware. Accuracy (suitability) offitted functions was determined by the correlationcoefficient R; the degree of significance (p 0.05).RESULTS AND DISCUSSIONExamination of RME concentration in dieselfuel revealed that with increasing concentration,the density of blend increase dependence is almost

1149Temperature Dependence Viscosity and Density of Different Biodiesel Blendslinear. This result was expected in accordancewith the references (Alptekin and Canakci, 2008;Ramírez-Verduzco et al., 2011). Then, a mathematicalmodel was constructed. In the model, the followinglinear regression formula was used (Kumbár andVotava, 2014):y a1 · x a0.(2)A er substitution, the formula reads as follows: 0.0005 · c 0.7855 [g·cm 3],The influence of the RME concentration indiesel fuel with respect to dynamic viscosity wasmonitored. Once again it was proven that withincreasing RME concentration, the dynamicviscosity dependence is nearly linear, as statedin (Borges et al., 2011) and (Joshi and Pegg, 2007).The general formula has been used (2). A ersubstitution, the relationship is as follows: 0.005 ·c 1.3659 [mPa·s],(3)where .density andc .volume concentration.Very high correlation coefficient R 0.999 wasacquired. For pure diesel fuel, the density was0.785 g·cm 3 and for pure RME (B100), it was0.835 g·cm 3. Density values of blend samples arelisted in Tab. II below.(4)where .dynamic viscosity andc .volume concentration.The correlation coefficient value in this group wasas high as R 0.996. For pure diesel fuel, the dynamicviscosity was 1.352 mPa·s. For pure RME (B100), thevalue was 1.881 mPa·s. Dynamic viscosity values ofblend samples are listed in Tab. II below.II: Density and viscosity values of various blends of diesel fuel and RMENo.Diesel FuelRMETemperatureDensityDynamic ViscositymPa·sml%ml% 1.8812: Effect of RME concentration in diesel fuel on its flow behaviour 3

1150Vojtěch Kumbár, Antonín SkřivánekValues of density and dynamic viscosity providedsource data for charts shown in Fig. 2. Individualvalues of the equation coefficients are included inthe corresponding figures.For three samples (pure diesel fuel, pure RMEB100 and B30 blend) temperature dependence ofdynamic viscosity and density was monitored. Asexpected and in accordance with the references(Maggi, 2006; Knothe and Steidley, 2007; Yuanet al., 2009), higher temperature was connectedto decrease of dynamic viscosity and density ofsamples, see Fig. 3 and Fig. 4. For the individualcharts, mathematical models were constructedusing 3rd polynomial degree (5) for the temperaturedependence of dynamic viscosity and using2nd polynomial degree (6) for the temperaturedependence of the density. The general relationshipswere as follows:y a3 · x3 a2 · x2 a1 · x a0andy a2 · x2 a1 · x a0.3: Dependence of temperature and dynamic viscosity4: Dependence of temperature and density(5)(6)