Measurement of the temperature dependent viscosity of biodiesel fuels

Micro heat exchangers may be used for winterisation of biodiesel at temperatures below 273 K. For a proper design of our micro heat exchangers the viscosity of biodiesel must be known around a temperature of 273 K. Therefore, different samples of biodiesel were examined in the range of 258-303 K and empirical equations for the temperature dependent viscosities computed. Above temperatures of 273 K an exponential equation based on the usual Arrhenius form describes all measurements well. Below 273 K the viscosity sharply rises within 2 K and then further increases. The reason is the precipitation of crystalline saturated methyl esters.     

Prediction of the density and viscosity in biodiesel blends at various temperatures

Biodiesel defined as mono-alkyl esters of vegetable oils and animal fats, has had a considerable development and great acceptance as an alternative fuel for diesel engines. Density and viscosity are two important physical properties to affect the utilization of biodiesel as fuel. In this work, mixtures of biodiesel and ultra low sulfur diesel (ULSD) were used to study the variation of density (ρ) and kinematic viscosity (η) as a function of percent volume (V) and temperature (T), experimental measurements were carried out for six biodiesel blends at nine temperatures in the range of 293.15-373.15 K. Both, density and viscosity increases because of the increase in the concentration of biodiesel in the blend, and both of them decrease as temperature increases. One empirical correlation was proposed to estimate the density: ρ = α·V + β·T + δ; and three empirical correlations were developed to predict the kinematic viscosity: η = exp[ln(γ) + ?·V + ω/T + λ·V/T²], η = exp[ln(γ) + ω/T + λ·V/T²] and η = exp[ln(γ) + ω/T + λ·V/T]. The corresponding parameters were optimized by the Levenberg-Marquardt method. The estimated values of density and viscosity are in good agreement with the experimental data because absolute average prediction errors of 0.02% and 2.10% were obtained in the Biodiesel(1) + ULSD(2) system studied in this work.     

Predicting the surface tension of biodiesel fuels from their fatty acid composition

The emergence of biodiesel fuels as diesel fuel substitutes has led to several studies on their properties. Surface tension, which plays a role in atomization, has lacked attention compared to other properties. This paper presents a method to predict the surface tension of biodiesel fuels based on the fatty acid composition. Several binary, ternary, and quaternary mixtures of fatty acid ethyl ester gas chromatographic (GC) standards were prepared, and we found that a mass-average equation predicted the surface tension of these mixtures within ±3.5% of their measured values. Six complex mixtures of fatty acid methyl ester GC standards that simulated typical oils used as biodiesel fuels were also prepared. For these complex mixtures the predicted surface tensions of the mixtures, calculated from a mass-average equation, were 2–6% higher than the measured values. A mass-average equation was developed in which we used a weighted surface tension for the individual components, and we found that this method predicted the surface tension of the simulated oils within ±4.5% of their measured values. Five natural vegetable oils were used to produce biodiesel fuels by the transesterification process. The predicted surface tensions of these fuels were all within ±3.5% of their measured values. The surface tensions of 15 biodiesel types were then predicted, based on their fatty acid composition as published in the literature. These results show that the differences in surface tension between biodiesel types are not the main cause of the reported differences in engine tests.     

An empirical approach in predicting biodiesel viscosity at various temperatures

A thermodynamic model is proposed for the determination of kinematic viscosities of saturated fatty acid methyl esters (FAMEs) of various chain lengths at different temperatures. The linearity of the natural logarithm of viscosity-carbon number, plot is limited to a narrow carbon number range. The predicted viscosities of FAMEs of C_12:0-C_18:0, which are commonly found in vegetable oils and used as biodiesels, agree well with the experimental values. The highest difference is 0.354 cSt (5.60%), for methyl stearate at 40 °C. When the proposed method for viscosity calculation of saturated FAMEs are used in combination with the methods for viscosities of biodiesel the mixtures, the predicted viscosities agree well with the values reported in the literatures and the measured values. The differences between the predicted viscosities and those reported in the literatures (at 40 °C) are 1.08 to 8.56% (for eight different vegetable oil methyl esters). The differences between the predicted viscosities and the measured values for coconut methyl esters, at 25, 40 and 50 °C are 9.20, 5.53 and 5.57%, respectively. The differences are slightly higher than those of palm oil methyl esters (4.48, 2.06 and 2.48%, respectively).The proposed method can also be applied to predict the viscosities of free fatty acids and it is speculated it may be applied to other homologous series as well.     

Estimation of the content of fatty acid methyl esters (FAME) in biodiesel samples from dynamic viscosity measurements

In order for biodiesel to be commercialized as pure biofuel or blending stock for diesel fuels, it must meet a set of requirements defined in standard specifications for a safe and satisfactory engine operation, one of these specifications is the content of fatty acid methyl esters (FAME). Besides, this parameter indicates the performance of the transesterification reaction for biofuel production from vegetable oils. There are several methods to determinate FAME content in biodiesel samples (chromatography, nuclear magnetic resonance spectroscopy and FTIR spectroscopy); however, they take long times and high cost for FAME content determination. From a practical point of view, in industrial biodiesel production is usually necessary to estimate the FAME value quickly. This paper presents correlations experimentally obtained from different oil feedstocks in order to estimate the biodiesel FAME content from the biodiesel dynamic viscosity, a fast determination parameter.     

Temperature-dependent kinematic viscosity of selected biodiesel fuels and blends with diesel fuel

The kinematic viscosities of four biodiesel fuels—two natural soybean oil methyl esters, one genetically modified soybean oil methyl ester, and one yellow grease methyl ester—and their 75, 50, and 25% blends with No. 2 diesel fuel were measured in the temperature range from 20 to 100°C in steps of 20°C. The measurements indicated that all these fuels had viscosity-temperature relationships similar to No. 2 diesel fuel, which followed the Vogel equation as expected. A weighted semilog blending equation was developed in which the mass-based kinematic viscosity of the individual components was used to compute the mixture viscosity. A weight factor of 1.08 was applied to biodiesel fuel to account for its effect on the mixture viscosity. The average absolute deviation achieved with this method was 2.1%, which was better than the uncorrected mass average blending equation that had an average absolute deviation of 4.5%. The relationship between the viscosity and the specific gravity of biodiesel fuels was studied. A method that could estimate the viscosity from the specific gravity of biodiesel fuel was developed. The average absolute deviation for all the samples using this method was 2.7%. The accuracy of this method was comparable to the weighted mass-based semilog blending equation.     

Predicting the viscosity of biodiesel fuels based on the mixture topological index method

To predict the viscosity of any given biodiesel fuel (FAME mixture), a novel topological index based on the distance matrix and adjacent matrix of the molecular structure is proposed. The new topological index can reflect the information of the molecular structure for fatty acid methyl ester (FAME), such as the size of molecular, unsaturated bond and branch degree. Combined with the modified Grunberg–Nissan or Hind equation, the topological index values of the FAME mixture were calculated. Then, relates the topological index values of the FAME mixtures with the viscosities of them, two linear regression equations were obtained. Using these regression equations, the viscosity of biodiesel fuels were predicted. The results show the modified Grunberg–Nissan equation with a higher precision of prediction than the Hind equation regression equation.     

Transient free convection flow over an isothemal vertical cylinder with temperature dependent viscosity

A numerical analysis is performed to study the influence of temperature-dependent viscosity and Prandtl number on unsteady laminar free convection flow over a vertical cylinder. The governing boundary layer equations are converted into a non-dimensional form and a Crank-Nicolson type of implicit finite-difference method is used to solve the governing non-linear set of equations. Numerical results are obtained and presented for different viscosityvariation parameters and Prandtl numbers. Transient effects of velocity and temperature are analyzed. The heat transfer characteristics against the viscosity-variation parameter are analyzed with the help of average skin-friction and Nusselt number and are shown graphically.     

Viscosity measurement of biodiesel at high pressure with a falling sinker viscometer

In this work, we report the measurement of the viscosity of biodiesels derived from waste cooking oil and vegetable oil under high pressure. Using a falling sinker-type viscometer, dynamic viscosity measurements were made at pressures up to 140 MPa which are typically to be found in common-rail automotive diesel engines. Reproducible and reliable viscosity data were obtained from sinker fall times and calibration data. The biodiesel viscosities were compared to that of petrochemical diesel fuels also under high pressure. Both fuel types were found to increase exponentially with pressure with the biodiesels being slightly the more viscous. Above 140 MPa, a marked increase in sinker fall time was observed. This was due to a pressure-freezing effect which is known to also occur with longer chain molecules found in petrochemical diesel, oils, fatty acids and biodiesel.     

An empirical approach for predicting kinematic viscosities of biodiesel blends

Kinematic viscosity (η) is an important property of diesel fuels, including biodiesels, which are marketed mostly as the blends in many countries around the world. In this study, the free energy of viscous flow (ΔG_vis) for a non-associated liquid mixture is assumed to be the summed of ΔG_vis of individual components. Hence, the Eyring’s equation, η = Ae(−ΔG_vis/RT), is transformed to ln η_blend = a + bn₁ + c/T + dn₁/T (where, a, b, c and d, T and n₁ are thermodynamically related constants, absolute temperature and mole fraction of biodiesel, respectively). The transformed equation is used to predict kinematic viscosity of biodiesel blends (η_blend) of different degree of blending at any temperatures from pour point to 100 °C. The predicted kinematic viscosities are in good agreement with those reported in literatures at all temperatures. The highest deviation is ±5.4% and the average absolute deviation (AAD) is less than 2.86%. The transformed equation can also be used to predict kinematic viscosities of pure fatty acid methyl esters in diesel fuel. Methyl ricinoleate is an exception. The AAD is 4.50% and the deviation is as high as 12.80%. The high deviation suggests that molecular interactions between methyl ricinoleate and diesel fuel is high and cannot be ignored.     

Flame temperature analysis of biodiesel blends and components

Meeting sustainable energy demand with minimum environmental impact is a major area of concern in the energy sector. Alternative fuels such as biodiesel, ethanol etc. have been quite promising for fulfilling both these aspects. While biodiesel reduces emissions of CO, life cycle CO₂, SO_x, volatile organic compounds (VOC) and particulate matter (PM) significantly, the propensity for the production of NO_x is an important problem that requires extensive research. NO_x emission from a direct-injection diesel engine is mainly due to formation of thermal NO that is described by Zeldovich mechanism. Thus, studying temperature profile during biodiesel combustion can provide useful insights to the formation and destruction of NO_x. The main objective of this work is to investigate the effect of component methyl esters of biodiesel on open air flame temperature distribution and the effect of blending biodiesel with diesel and oxygenates (ethanol and methyl acetate) on open air flames. This objective was achieved by obtaining thermocouple measurements and thermal infrared imaging of local flame temperatures of wick-generated open air flames. A relationship between blend proportions and relative flame temperatures were obtained. In general, it was found that blending oxygenates such as ethanol and methyl acetate into petroleum diesel tended to increase the flame temperature in comparison with straight diesel fuel. The analyses of relative flame temperatures of different components of biodiesel were performed to evaluate the effect of unsaturation level and the hydrocarbon chain length on the flame temperature. It was found that the saturated methyl esters resulted in greater flame temperatures in comparison to unsaturated methyl esters. It was also revealed that shorter chained fatty acid methyl esters lead to higher flame temperatures as compared to its longer chained counterparts.     

Some aspects of biodiesel oxidative stability

Biodiesel, an “alternative” diesel fuel derived from vegetable oils, animals fats or used frying oils, largely consists of the mono-alkyl esters of the fatty acids comprising these feedstocks. One of the major technical issue facing biodiesel is its susceptibility to oxidation upon exposure to oxygen in ambient air. This susceptibility is due to its content of unsaturated fatty acid chains, especially those with bis-allylic methylene moieties. Oxidation of fatty acid chains is a complex process that proceeds by a variety of mechanisms. Besides the presence of air, various other factors influence the oxidation process of biodiesel including presence of light, elevated temperature, extraneous materials such as metals which may be even present in the container material, peroxides, and antioxidants, as well as the size of the surface area between biodiesel and air. Approaches to improving biodiesel oxidative stability include the deliberate addition of antioxidants or modification of the fatty ester profile. This article discusses some factors influencing biodiesel oxidative stability and their interaction. Resulting approaches to improving this property of biodiesel are related to these factors and the corresponding mechanisms.     

The kinematic viscosity of biodiesel and its blends with diesel fuel

As the use of biodiesel becomes more wide-spread, engine manufacturers have expressed concern about biodiesel’s higher viscosity. In particular, they are concerned that biodiesel may exhibit different viscosity-temperature characteristics that could result in higher fuel injection pressures at low engine operating temperatures. This study presents data for the kinematic viscosity of biodiesel and its blends with No. 1 and No. 2 diesel fuels at 75, 50, and 20% biodiesel, from close to their melting point to 100°C. The results indicate that while their viscosity is higher, biodiesel and its blends demonstrate temperature-dependent behavior similar to that of No. 1 and No. 2 diesel fuels. Equations of the same general form are shown to correlate viscosity data for both biodiesel and diesel fuel, and for their blends. A blending equation is presented that allows the kinematic viscosity to be calculated as a function of the biodiesel fraction.     

An ideal feedstock, kusum (Schleichera triguga) for preparation of biodiesel: Optimization of parameters

Kusum (Schleichera triguga), a non-edible oil bearing plant has been used as an ideal feedstock for biodiesel development in the present study. Various physical and chemical parameters of the raw oil and the fatty acid methyl esters derived have been tested to confirm its suitability as a biodiesel fuel. The fatty acid component of the oil was tested by gas chromatography. The acid value of the oil was determined by titration and was found to 21.30 mg KOH/g which required two step transesterification. Acid value was brought down by esterification using sulfuric acid (H₂SO₄) as a catalyst. Thereafter, alkaline transesterification was carried out using potassium hydroxide (KOH) as catalyst for conversion of kusum oil to its methyl esters. Various parameters such as molar ratio, amount of catalyst and reaction time were optimized and a high yield (95%) of biodiesel was achieved. The high conversion of the feedstock into esters was confirmed by analysis of the product on gas chromatograph-mass spectrometer (GC-MS). Viscosity and acid value of the product biodiesel were determined and found to be within the limits of ASTM D 6751 specifications. Elemental analysis of biodiesel showed presence of carbon, hydrogen, oxygen and absence of nitrogen and sulfur after purification. Molar ratio of methanol to oil was optimized and found to be 10:1 for acid esterification, and 8:1 for alkaline transesterification. The amounts of H₂SO₄ and KOH, 1% (v/v) and 0.7% (w/w), respectively, were found to be optimum for the reactions. The time duration of 1 h for acid esterification followed by another 1 h for alkaline transesterification at 50 ± 0.5 °C was optimum for synthesis of biodiesel.     

Biomass to fuels: A water-free process for biodiesel production with phosphazene catalysts

Non-ionic triamino(imino)phosphoranes (phosphazenes) give excellent results as base catalysts for the water-free alcoholysis of vegetable fatty esters. Two phosphazene catalysts, with different intrinsic basicities, P₁-t-Bu and P₄-t-Bu, together with reaction parameters, such as temperature, alcohol/oil molar ratio, or catalyst concentration, have been studied. It was found that activity can be directly correlated to the basicity of the catalyst. Very high biodiesel yields (93–95% mol) were achieved under mild reaction conditions with methanol and ethanol. The catalyst can be recovered and recycled.     

Graphical method to select vegetable oils as potential feedstock for biodiesel production

Chemical compositions of 80 vegetable oils were collected from literature and the properties of the obtainable biodiesel (methyl esters) have been predicted by empirical relationships. The purpose has been to check the viability of predicting if a biodiesel could meet the EN 14214 standards knowing only the fatty acid profile (FAP) of the parent oil. Two parameters were used in this investigation: (i) average number of carbon atoms in the fatty acid chains, (ii) average number of double bonds (C?C) per molecule. Two new empirical relationships have been proposed to predict the viscosity and the cetane number of biodiesel from the two parameters. The range of values of the two parameters leading to biodiesel meeting the EN 14214 standard for viscosity, cetane number, iodine value, and cold filter plugging point have been graphically obtained by overlapping the corresponding level surfaces. Practical applications: This work provides biodiesel producers with indications of the quality of biodiesel without the need for analytical testing of the product (indeed, of the product itself). Only the fatty acid profile of the starting vegetable oil is required. The quality of biodiesel can be estimated by using a chart developed in this work, allowing to estimate, e.g. if the biodiesel meets the European standards. The work can be useful to rapidly screen oil seed crops in studies of genetic engineering that require high throughput.     

The effect of temperature and pressure on the physicochemical properties of petroleum diesel oil and biodiesel fuel

Three commercial fuels were studied: biodiesel (based mainly of the fatty acids methyl esters of rapeseed oil), diesel oil Ekodiesel Ultra (standard petroleum diesel oil with sulphur content less than 10 mg/kg), and ON BIO 10 (blend of 20 vol.% of biodiesel with 80 vol.% of standard petroleum diesel oil with sulphur content less than 10 mg/kg). The speeds of sound were measured within the temperatures from 293 to 318 K and at pressures from 0.1 to 101 MPa. The densities and heat capacities were measured under atmospheric pressure in the temperature range from 273 to 363 K and 283 to 359 K, respectively. Using the experimental results, the physicochemical properties such as: density, isentropic bulk modulus, heat capacity, and isobaric thermal expansion were calculated in the same temperature and pressure range as the speed of sound was measured. The results obtained show that although the bulk modulus of ON BIO 10 is higher than that of diesel oil Ekodiesel Ultra over the whole pressure range, the difference is rather small and can be compensated by temperature. Isobaric thermal expansivity of biodiesel decreases with pressure slightly less than that of the diesel oil Ekodiesel Ultra. It is approximately independent of temperature and composition of the fuel at pressures 40 ± 5 MPa.     

A critical look at the microalgae biodiesel

The quantitative production of microalgae oil is often overestimated. The cost of the salts invested in the production of 1 kg algal diesel approximates the actual price of 1 kg mineral diesel. Total sum of electrical energy expenses for production of biodiesel from microalgae is several‐fold higher than the energy income from combustion of the same quantity. The biological value of cultivated microalgae as food is much higher than as fuel. An opinion is shared that money ought to be invested in microalgal biomass production as a food additive, forage, and pharmaceuticals. The aim is to prevent making too hasty steps and investments in microalgal biodiesel.     

Production of biodiesel fuel from tall oil fatty acids via high temperature methanol reaction

Tall oil fatty acids are a byproduct of the paper industry and consist predominantly of free-fatty acids (FFAs). Although this feedstock is ideal for biodiesel production, there has been relatively little study of its conversion to biodiesel. Thus, the purpose of this study was to investigate the high temperature reaction of methanol with tall oil at subcritical and supercritical pressures to produce fatty acid methyl esters. This study investigates the effects of mixing, pressure, temperature, and methanol to oil molecular ratio in order to determine the potential use of tall oil as a biodiesel feedstock. In this work, tall oil fatty acids were successfully reacted with supercritical and subcritical methanol in a continuous tubular reactor, resulting in a reaction that is primarily temperature dependent. Conversions at subcritical pressures of 4.2 MPa and 6.6 MPa were 81% and 75%, respectively. Pressure seemed to have little correlation to conversion in both regimes, and conversions were comparable between the two. Additionally, it was found that tall oil fatty acids react well with methanol to give comparable conversions at the relatively low molecular flow ratio of 5:1 methanol to tall oil. Both of these observations suggest that hydrolyzed triglycerides or free fatty acid feedstocks would make the primary high temperature biodiesel reaction and the subsequent separation and purification operations less expensive than was previously believed.     

Reducing the crystallization temperature of biodiesel by winterizing methyl soyate

Methyl soyate, made from typical soybean varieties, has a crystallization onset temperature (T _co) of 3.7°C and, as a biodiesel fuel, is prone to crystallization of its high-melting saturated methyl esters at cold operating temperatures. Removal of saturated esters by winterization was assessed as a means of reducing theT _co of methyl soyate. Winterizing neat methyl esters of typical soybean oil produced aT _co of −7.1°C, but this was not an efficient way of removing saturated methyl esters because of the low yield (26%) of the separated liquid fraction. However, aT _co of −6.5°C with 86% yield was obtained by winterizing the neat methyl esters of a low-palmitate soybean oil; aT _co of −5.8°C with 77% yield was obtained by winterizing methyl esters of normal soybean oil diluted with hexane.