The kinetics of changes in kinematic viscosity of engine oils under similar operating conditions

The lubricating oil, which is indispensable for the proper functioning of the engine, is subject to aging and it can be used as long as it fulfills its task properly by retaining specific physicochemical properties. The levels of specific physical and chemical properties of engine oil affect the quality and range of functions performed by the oil and, as such, they are a prerequisite for its suitability for a particular type of engine. Among the parameters and physicochemical quantity levels outlined in subject standards and literature, the preference is given to the kinematic viscosity and dynamic viscosity (some of the basic properties of fluids) [2, 4, 6, 10, 11]. Kinematic viscosity is always stipulated in the quality requirements relating to lubricating oils. It can increase or decrease during operation. An increase in viscosity is generally connected with progressive oxidation processes at elevated temperature, and a decrease with the shear of oil. The assessment of oil viscosity allows the user to estimate the time between oil changes. According to the current state of knowledge, the quality of engine oil can be determined through a series of tests, which include laboratory evaluation of the physicochemical properties, as well as through assessing its particular properties which, however, entails lengthy and costly operational research [1, 3, 8, 13, 15, 16, 18]. Knowledge and understanding of the characteristics of motor oils and developing effective methods of analysis enables the creation of systems of quality monitoring which may be conducted within the life cycle of the engine. A number of studies have been conducted to scientifically measure the quality of engine oils. Inayatullah et al. [5] used the technique of acoustic emission to analyze engine oil viscosity. Karpovich et al. [7] attempted to develop a universal instrument to measure and control the quality of motor oils. Their evaluation of the quality and condition of engine oil was centered around viscosity as a key performance indicator. Agoston et al. [1], on the other hand, have focused in their research on thermal aging of engine oils. They have shown that oil evaporation and oil burning have the most significant impact on the process of aging, thus leading to the loss of its key properties, which inevitably affects the overall performance of the engine oil. Wang [14] used the road tests in the assessment of engine oils. Special sensors have been installed in three vehicles and tested during the drive. The results of the study point out three stages of engine oil degradation: 1. Good condition 2. A rapid increase in acid number 3. A rapid increase in viscosity. Bassbasi et al. [3] proposed infrared spectroscopy to monitor and control as well as enable high-speed inspection of motor oils. Similarly, Wolak and Janocha [16] focused on the assessment of changes in physicochemical properties of engine oils, using the method of inArtur WolAk Grzegorz ZAjąc