The Assessment of Wear Metal Concentration in Engine Oils Originating From Agricultural Tractors in the Aspect of Their Operational Properties

One of the paths leading to the development of sustainable agriculture is to reduce the amount of energy lost during agricultural production. This can be accomplished through proper farm machinery management. The engine oil obtained at the end of the oil-change interval may be a valuable source of information on the processes and causes of wear of the tribological systems of the engine. This paper presents the results of studies on the wear metal concentration (Pb, Cr, Ni, Fe) in engine oils, taken from selected agricultural tractors, which were subject to replacement within the timeframe specified in the maintenance schedule. The statistical analysis of the test results has not revealed any statistically significant differences in the concentrations of the investigated elements in the used engine oils, depending on the mileage. Nevertheless, the calculated coefficients of correlation indicate a positive, weak correlation between the analysed elements and the engine oil consumption processes under operating conditions. INTRODUCTION One of the paths leading to the development of sustainable agriculture is to reduce the energy expenditure. Therefore, tractors and farm machines should be as much efficient as possible, both in terms of their power units and their power trains (Bietresato et al., 2015). Tractors and farm machines are characterized by a great variety of types and constructions, extended life span, and a high variability of working conditions compared to other vehicles. Such complex operating conditions are strongly influenced by the unique nature of agricultural production: tractors are used in variable weather conditions, they are operated with varying intensity during the year, they are associated with seasonal work and are driven mainly off-road. Non-operational factors, such as technical preparation of tractor operators as well as the quality of maintenance and repair facilities are also important (Tomczyk, 2009, 2012). All of these factors affect the specific (depending on the tractor type) wear processes including engine oil consumption. One of the basic tasks that must be undertaken to protect tractors from adverse operating conditions is to carry out, on a regular basis, the replacement of parts and consumables (Buchwald and Staszak, 2013; Rybacki and Buchwald, 2013). Lubricating oil, without which the engine would not be able to function properly, can operate in the engine as long as it performs its tasks properly (Wolak and Zając, 2017). Delays in servicing or replacing the consumables with improper substitutes can result in undesirable machine failures (Osuch et al., 2016). According to research (Jósko and Kołodziejski, 2008), one of the fundamental mistakes made by users of agricultural tractors is the failure to keep oil change periods. Another problem is the poor quality of technical services provided by local garages, including the use of improper oil. The engine oil obtained at the end of the oil-change interval