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

1
Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai 600036, India
2
National Center for Combustion Research and Development, Indian Institute of Technology Madras, Chennai 600036, India
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Author to whom correspondence should be addressed.
Academic Editor: Boris Zhmud
Lubricants 2015, 3(1), 54-79; https://doi.org/10.3390/lubricants3010054
Received: 18 October 2014 / Revised: 26 January 2015 / Accepted: 6 February 2015 / Published: 17 March 2015
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. View Full-Text
Keywords: Synthetic oil; semi-synthetic oil; degradation; oxidation; thermogravimetry; apparent activation energy; thermal stability Synthetic oil; semi-synthetic oil; degradation; oxidation; thermogravimetry; apparent activation energy; thermal stability
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Tripathi, A.K.; Vinu, R. Characterization of Thermal Stability of Synthetic and Semi-Synthetic Engine Oils. Lubricants 2015, 3, 54-79.

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