Characterization of Thermal Stability of Synthetic and Semi-Synthetic Engine Oils

Abstract

Engine oils undergo oxidative degradation and wears out during service. Hence it is important to characterize ageing of engine oils at different simulated conditions to evaluate the performance of existing oils and also design new formulations. This work focuses on characterizing the thermo-oxidative degradation of synthetic and semi-synthetic engine oils aged at 120, 149 and 200 °C. Apparent activation energy of decomposition of aged oils evaluated using the isoconversional Kissinger-Akahira-Sunose technique was used as a thermal stability marker. The temporal variation of stability at different ageing temperatures was corroborated with kinematic viscosity, oxidation, sulfation and nitration indices, total base number, antiwear additive content and molecular structure of the organic species present in the oils. At the lowest temperature employed, synthetic oil underwent higher rate of oxidation, while semi-synthetic oil was stable for longer time periods. At higher temperatures, the initial rate of change of average apparent activation energy of synthetic oil correlated well with a similar variation in oxidation number. A mixture of long chain linear, branched, and cyclic hydrocarbons were observed when semi-synthetic oil was degraded at higher temperatures.

Effects of Jatropha lubricant thermo-oxidation on the tribological behaviour of engine cylinder liners as measured by a reciprocating friction test

“…3c-d, the oxidative process generated changes in the viscosity of the three oils at both temperatures. It is well known that the oxidized products and polar components, namely, alcohols, esters, carbonyl compounds and benzene derivatives induce hydrogen bonding, dipole and van der Waals interactions among the constituents present in mineral and synthetic oils contribute to viscosity changes [37]. In a similar way, oxidation in vegetable oils leads to the formation of hydrogen bonds increasing intermolecular forces that increase viscosity [38].…”

Lubrication Performance of Engine Commercial Oils with Different Performance Levels: The Effect of Engine Synthetic Oil Aging on Piston Ring Tribology under Real Engine Conditions

“…The kinematic viscosity of the aged oil decreased, as it can be seen in Figure 9. This is expected [36] because high decomposition temperatures tend to break the hydrocarbons present in oil via the attack of oxygen via alkoxy and peroxy bond β-scission, which leads to a decrease in dynamic viscosity. However, viscosity in general may increase, mainly as a result of the formation of products with high molecular mass.…”

Research into the Effects of the Effective Microorganisms Addition on the Engine Oil Viscosity

“…After very long runs, the oil turns into a thick, black tar, unable to lubricate anything, and in extreme cases -even into a solid. The oxidation process is accelerated by high temperature, because it causes thermal decomposition of base oil hydrocarbons, viscosity modifiers and some refining additives [11,12]. The scheme of the deterioration of engine oil quality during operation is shown in Fig.…”