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Tomic M.,University of Novi Sad | Savin L.,University of Novi Sad | Micic R.,Scientific Technological Center | Simikic M.,University of Novi Sad | Furman T.,University of Novi Sad
Energy | Year: 2014

Harsh requirements regarding the exhaust gases emission have conditioned the development of new systems in the engine, as well as the development of ecological fuels. Sulfur extraction considerably impairs the lubrication properties of diesel fuel. This has consequences in the rapid wear of the elements that constitute the fuel injection system. Additives for the improvement of lubrication properties are added with the aim of eliminating the adverse effect of fuel. The problem related to the use of those additives lies in the fact that they contain heavy aromatic solvents such as methyl naphthalene, methyl naphthalene and biphenyl which are harmful to health. Therefore, the aim of this research is to determine whether there is a possibility to use biodiesel for the improvement of lubrication properties of fossil diesel with low sulfur content instead of standard additives.In this research biodiesel obtained from sunflower oil was blended with fossil diesel which did not have additionally added additives for the improvement of lubrication properties. The obtained results were compared with the other researches on the use of fossil diesel with added standard additives. The blends of fossil diesel and biodiesel content of 1-7%vv-1 were used here. The experimental research used different test fuels for the testing of chemical and lubrication properties of fuel, tractor engine performance and exhaust gas emissions.By adding biodiesel, fossil diesel properties remained within the limits set by the standard EN 590 while lubrication properties were significantly improved. On the other hand, power of tractor engine did not change significantly. Although biodiesel had lower heating value with respect to fossil diesel, blending 5, 6 and 7%vv-1 of biodiesel caused slight increase in the engine power. Tests of exhaust gas emissions indicated that the addition of biodiesel reduced the content of CO2 and CO. The problems related to the use of biodiesel as an additive can be reduced by oxidation fuel stability, increased specific fuel consumption, reduced thermal efficiency and increased NOx emission. © 2013 Elsevier Ltd. Source

Micic R.D.,Scientific Technological Center | Bosnjak Kiralj M.S.,University of Novi Sad | Panic S.N.,University of Novi Sad | Tomic M.D.,University of Novi Sad | And 2 more authors.
Fuel | Year: 2015

Catalytic activity of calcium oxide as a heterogeneous catalyst was investigated for transesterification of sunflower oil to methyl esters. The primary objective of this study was to investigate the catalyst activity (biodiesel yield) as a function of its active phase and textural properties imposed by different activation temperatures: 500, 700, 800, 900, 1000 and 1100 °C. Therefore the catalyst activity, basicity, textural and bulk properties were correlated. X-ray diffraction analysis (XRD) showed Ca(OH)2 next to CaO phase in all samples activated up to 900 °C. Their fraction changed, however, with activation temperature increase, leading to pure CaO in samples activated above 900 °C. The same samples, however, performed with the lowest activity in the series, in which the catalyst sample calcined at 800 °C showed the maximal activity. Simultaneous thermal analysis (TG-DTA) indicated two-step dehydroxylation of CaO, suggesting different fractions but also positions of hydroxyl groups upon calcination at different temperatures. Both Fourier transformed infrared spectroscopy (FTIR) and temperature programmed desorption (TPD) of CO2 preadsorbed on CaO surface indicated the sample activated at 700 °C with the highest basicity. It is unique in the series containing basic sites of both strong and medium strength. High basicity of that sample, however, happened not to be enough for the highest activity, possibly due to poor textural properties, as revealed by results of low temperature nitrogen adsorption (LTNA). Maximal specific surface area, total pore volume and dominant fraction of a high-diameter mesopores were found in the case of the sample activated at 800 °C. Thus, a complex function of active sites of medium strength, possibly induced by a specific hydroxyl groups coverage, as well as mesoporosity directing an unrestricted mass transfer, resulted in the maximal activity of the CaO sample activated at 800 °C. © 2015 Elsevier Ltd. All rights reserved. Source

Nazarenko A.I.,Scientific Technological Center | Usovik I.V.,Moscow State University
Acta Astronautica | Year: 2013

The new approach to gravitation effect determination in calculating the flux of sporadic micrometeoroids in the near-Earth space is proposed. The technique is based on integration of the equations of motion of sporadic micrometeoroids with accounting for bending their trajectories when particles are approaching the Earth. The technique and results of calculation of the gravitational focusing factor kg for various conditions are presented. The feature of the proposed technique for calculating coefficient kg consists in the fact that this coefficient does not explicitly depend on the values of particles velocity at the last point. The results of investigation of coefficient kg have shown that, for the given initial velocity of micrometeoroids, the values of this coefficient depend on deflection of its direction from the direction to the Earth center. It is shown that for low-altitude orbits the flux density can increase up to 60%. The distribution of probabilities of various directions of particles flying to spacecraft structural elements is found to be non-uniform. © 2012 Published by Elsevier Ltd. Source

Tomic M.,University of Novi Sad | Micic R.,Scientific Technological Center | Kiss F.,University of Novi Sad | Dedovic N.,University of Novi Sad | Simikic M.,University of Novi Sad
Energy Conversion and Management | Year: 2015

This study aims to investigate the influence of various reaction parameters (temperatures, working pressures and reaction time) on biodiesel yields and environmental and economic performance of rapeseed oil transesterification in supercritical methanol. Experiments were carried out in a laboratory-scale batch reactor. Results were statistically analysed and multiple regression models which describe and predict biodiesel yields with high certainty at different reaction conditions were provided. The highest biodiesel yield (93 wt%) was achieved at 350 °C and 12 MPa after 15 min of reaction. The lowest direct costs and life cycle environmental impacts (in terms of GHG emissions and fossil energy demand) are achieved at the highest yield due to the lowest oil consumption per unit of biodiesel produced. The results of sensitivity analysis showed that even at significantly lower oil feedstock prices this observation stands firm. © 2015 Elsevier Ltd. All rights reserved. Source

Micic R.D.,Scientific Technological Center | Tomic M.D.,University of Novi Sad | Kiss F.E.,University of Novi Sad | Nikolic-Djoric E.B.,University of Novi Sad | Simikic M.,University of Novi Sad
Energy Conversion and Management | Year: 2014

Experiments with transesterification of rapeseed oil in supercritical alcohols (methanol, ethanol and 1-propanol) were carried out in a batch reactor at various reaction temperatures (250-350 °C), working pressure (8-12 MPa), reaction time, and constant 42:1 alcohol to oil molar ratio. Influence of different alcohols and reaction conditions on biodiesel yield was investigated using linear multiple regression models. Temperature had the highest impact on yields, followed by reaction time and pressure. With increased molecular weight of alcohols, relative importance of temperature for explanation of yields decreased and relative importance of time and pressure increased. Economic assessment has revealed that transesterification in supercritical methanol has the lowest direct material and energy costs. Yield has crucial impact on process economics. Direct costs decrease with increase in biodiesel yields. Even at very low prices of oil feedstock the lowest cost is achieved at the highest yield. © 2014 Elsevier Ltd. All rights reserved. Source

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