Influence of biodiesel on the performances of farm tractors: Experimental testing in stationary and non-stationary conditions M. Simikic a , M. Tomic a, * , L. Savin a , R. Micic b , I. Ivanisevic c , M. Ivanisevic a a University of Novi Sad, Faculty of Agriculture, 21000 Novi Sad, Trg Dositeja Obradovi ca 8, Serbia b University of Novi Sad, Mihajlo Pupin Technical Faculty, Ðure Ðakovi ca bb., Zrenjanin Serbia c Zobnatica ad, Suboticki Put bb, 24300 Backa Topola Serbia article info Article history: Received 27 June 2017 Received in revised form 23 December 2017 Accepted 19 January 2018 Keywords: Biodiesel Tractor Stationary test Non-stationary test abstract This paper demonstrates the results of testing the performance of tractors using fossil diesel, biodiesel, and blends of biodiesel and fossil diesel. The results of tests conducted in stationary and non-stationary conditions indicate that, in contrast to fossil diesel, the use of biodiesel and blends of biodiesel and fossil diesel reduce the power of engine and drawbar power, and increase specific fuel consumption. Thermal efficiency slightly improves with biodiesel blends. The differences become notable with bigger share of biodiesel in the blend. However, the changes are less notable regarding the differences in heating value, which is the result of complete combustion. Use of different fuels, compared to use of fossil diesel only, reduces the CO emission and temperature of exhaust fumes, and increases the CO 2 emission and NOx. At maximum load, the difference between the parameters measured in stationary and non-stationary conditions is minimal. On the other hand, at lower loads, the load variable formed in non-stationary conditions of testing becomes noticeable which results in greater differences. However, decrease in engine power and increase in fuel consumption using biodiesel significantly deteriorated the exploita- tion characteristics of plowing tractors (production efficiency was reduced by 12.87% and fuel con- sumption per unit of cultivated area was increased by up to 21.63%). © 2018 Elsevier Ltd. All rights reserved. 1. Introduction Variable and unpredictable price of oil, its limited availability, as well as its negative impact on the environment, health and safety, indicate the importance and necessity of developing alternative domestic fuels that are available, renewable, and environmentally friendly. Over the last decade, biodiesel has become the best- known renewable liquid fuel because it satisfies these criteria. Also, an advantage of biodiesel is that its use does not require any particular adjustments of engine or fuel injection system [1], as well as the fact that it is a non-toxic and biodegradable fuel [2]. Biodiesel represents methyl esters of fatty acids of vegetable oils or animal fats. In commercial production, it is obtained through the process of transesterification in alcohol (most commonly methanol) using suitable catalysts [3]. Transesterification of vege- table oils can be catalyzed by bases, acids and enzymes. Homoge- nous base catalysts (NaOH or KOH) or heterogeneous catalysts are typically used [4]. The reaction time, yield, and quality of the product depend on the type and quality of raw material, as well as the process parameters (molar ratio of oil and methanol, the catalyst amount, reaction temperature, reaction time, blending speed and alike [5]). Nevertheless, homogenous catalysts cause a series of problems relating to relatively expensive and complex procedures of neutralization, washing and separation. On the other hand, heterogeneous catalysts partially solve the problem of diffi- cult separation of the end product [6]. Still, the problem of meth- anol insolubility in oil remains (this requires intensive mixing), as well as the negative effect of water and unsaturated fatty acids in oil, and a relatively long reaction time. In order to find the solution to these problems, contemporary research has been focused on the development of technologies and equipment for performing transesterification in supercritical conditions. This involves high temperatures and pressures necessary for the reaction (over 240  C and 8.09 MPa) [7]. Biodiesel has also attracted a lot of attention over the last decade * Corresponding author. E-mail addresses: simikic@polj.uns.ac.rs (M. Simikic), milanto@polj.uns.ac.rs (M. Tomic), savlaz@polj.uns.ac.rs (L. Savin), rmicic@beotel.rs (R. Micic), igor. ivanisevic@zobnatica.rs (I. Ivanisevic), mladen.ivanisevic@polj.uns.ac.rs (M. Ivanisevic). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene https://doi.org/10.1016/j.renene.2018.01.069 0960-1481/© 2018 Elsevier Ltd. All rights reserved. Renewable Energy 121 (2018) 677e687