This paper is focused on the impacts of the biodegradable hydraulic and transmission fluid (Universal Tractor Transmission Oil) on operation of tractor hydraulic and transmission systems. The fluid was used in the hydraulic and transmission systems of a Zetor Proxima 6321 tractor. Fluid samples were taken from the Zetor Proxima 6321 tractor at intervals of 250 engine hours. These samples were subjected to an infrared spectroscopy analysis in order to measure the total acid number and perform the ferrography analysis. This paper proves minimal impacts of the biodegradable hydraulic fluid on operation of the Zetor Proxima 6321 tractor. The biodegradable fluid meets the requirements for the operation of agricultural tractors in terms of low impacts on the wear of hydraulic components.

The purpose of this study was to investigate and to process the current literary knowledge of the physico-chemical properties of vegetable oil raw used for biodiesel production in terms of its qualitative stability. An object of investigation was oxidative stability of biodiesel. In the study, we focused on the qualitative physico-chemical properties of vegetable oils used for biodiesel production, oxidative degradation and its mechanisms, oxidation of lipids, mechanisms of autooxidation, effectivennes of different synthetic antioxidants in relation to oxidative stability of biodiesel and methods of oxidative stability determination. Knowledge of the physical and chemical properties of vegetable oil as raw material and the factors affecting these properties is critical for the production of quality biodiesel and its sustainability. According to the source of oilseed, variations in the chemical composition of the vegetable oil are expressed by variations in the molar ratio among different fatty acids in the structure. The relative ratio of fatty acids present in the raw material is kept relatively constant after the transesterification reaction. The quality of biodiesel physico-chemical properties is influenced by the chain length and the level of unsaturation of the produced fatty acid alkyl esters. A biodiesel is thermodynamically stable. Its instability primarily occurs from contact of oxygen present in the ambient air that is referred to as oxidative instability. For biodiesel is oxidation stability a general term. It is necessary to distinguish ‘storage stability' and ‘thermal stability', in relation to oxidative degradation, which may occur during extended periods of storage, transportation and end use. Fuel instability problems can be of two related types, short-term oxidative instability and long-term storage instability. Storage instability is defined in terms of solid formation, which can plug nozzles, filters, and degrade engine performance. Biodiesels are more susceptible to degradation compared to fossil diesel because of the presence of unsaturated fatty acid chain in it. The mechanisms of oxidative degradation are autoxidation in presence of atmospheric oxygen; thermal or thermal-oxidative degradation from excess heat; hydrolysis in presence of moisture or water during storage and in fuel lines; and microbial contamination from contact with dust particles or water droplets containing fungi or bacteria into the fuel. The oxidation of lipids is a complex process in which unsaturated fatty acids are reacted with molecular oxygen by means of free radicals. The radicals react with lipids, and cause oxidative destruction of unsaturated, polyunsaturated fatty acids, therefore, known as lipid peroxidation. The factors such as heat, oxygen, light, and some metal ions, especially iron and copper, also play a significant role in creating oxidation. Oxidative products formed in biodiesel affect fuel storage life, contribute to deposit formation in tanks, and they may cause clogging of fuel filters and injection systems. The volatile organic acids formed as secondary by products of the oxidative degradation, may stimulate corrosion in the fuel system. Poor stability can lead to increasing acid numbers, increasing fuel viscosity, and the formation of gums and sediments. In general, antioxidants can prevent oxidation. Biodiesel, because it contains large numbers of molecules with double bonds, is much less oxidatively stable than petroleum-based diesel fuel. Oxidation stability is the important parameter to determine the storage of biodiesel for longer period of time. Biodiesel samples were evaluated according to methods on the base of kept in contact with pure oxygen at elevated temperatures and pressures. The results show that the performance antioxidants variation is observed for biodiesel. The most commonly used primary synthetic antioxidants

Müllerová D., Landis M., Schiess I., Jablonický J., Prístavka M., 2011. Operating parameters and emission evaluation of tractors running on diesel oil and biofuel. Res. Agr. Eng., 57 (Special Issue): S35-S42.This work is aimed at the evaluation of the operating parameters and emission of two tractors: Hürlimann H-488 DT and Hürlimann XB Max 100. The measurements were done on a test bench in the laboratory of the Agroscope Reckenholz-Tänikon Research Station ART, Ettenhausen, Switzerland during February 2010. The goal of this paper was to evaluate the operating parameters of the two models of tractors by using classical diesel oil and biofuel, as well as to evaluate the emission (greenhouse gases, dangerous exhaust gases and carcinogens), to make statistical analysis of the results and the conclusion about the samples used and the impact on engine parameters, environment and human health. From the results achieved, it is possible to state the following facts. In each way, the emissions of rape seed methylester (RME) and diesel are equivalent. The values of CO and HC and also particles are lower for RME. But NO x values are lower for diesel oil. It is liquid that the newer engine of Hürlimann XB Max 100 decreases emission of CO, HC and NO x significantly.

Tkáč Z., Majdan R., Drabant Š., Jablonický J., Abrahám R., Cvíčela P., 2010. The accelerated laboratory test of biodegradable fluid type "ertto". Res. Agr. Eng., 56: 18-25.The accelerated laboratory tests can evaluate the properties of new biodegradable fluids under relatively short time. These test results are the ground for the continuity of the tests under operation conditions in machine. The paper presents the test of new biodegradable hydraulic fluid type "Environmentally responsible tractor transmission oil" by designed special test device. The test evaluation was realized by technical state of concrete hydrostatic pump UD 25 which is used in tractors Zetor Forterra. This pump was loaded by cyclic pressure loading during the test with tested fluid. The evaluated parameter was flow efficiency of hydrostatic pump which reached the value 7.3% after the test. The reached value hints a high quality of the tested fluid (the limit value per standard is the flow efficiency decrease -20%).

Majdan R., Tkáč Z., Kosiba J., Abrahám R., Jablonický J., Hujo Ľ., Mojžiš M., Ševčík P., Rášo M., 2013. Evaluation of tractor biodegradable hydraulic fluids on the basis of hydraulic pump wear. Res. Agr. Eng., 59: 75-82.Two types of biodegradable hydraulic fluids (HEES and HEPR) with the mineral oil-based hydraulic fluid (HV) were compared. The tests were performed using a test bench. During the tests with a tractor hydraulic pump, the fluids were loaded by a cyclic pressure load. The tests of fluids were evaluated on the basis of wear of the pump. Evaluation parameters were the flow characteristics of the pump and the cleanliness level of tested fluids. The temperature of the fluid under which the test was performed was measured in real operating conditions of the Zetor Forterra 11441 tractor. It is possible to state upon the test results that the mineral oil-based fluid was classified in the first place, the biodegradable fluid of the HEPR type in the second place, and the biodegradable fluid of the HEES type received the last position.