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Title: The Autoxidation of Branched Hydrocarbons in the Liquid Phase as Models for Understanding Lubricant Degradation
Author: Wilkinson, Julian James
Awarding Body: University of York
Current Institution: University of York
Date of Award: 2006
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The Autoxidation ofPristane (C19t40), Squalane (C30H62) and partially formulated lubricant basefluids in laboratory reactors and in research engines under controlled conditions have been used as simplified models of lubricants in passenger car engines in order to increase the understanding ofthe oxidation process ofthe lubricant within automotive engines, particularly within the ring pack area of the pIston. Pristane was oxidized in stainless steel reactors in the presence ofoxygen at a range of temperatures between 90 and 250°C, using either a continuous flow ofoxygen or a single charge of oxygen in a sealed reactor. A more detailed examination ofpristane oxidation at 170°C was also undertaken where the influence ofreaction time on the formation of oxidation products was carefully studied. The main products observed were predominantly tertiary alcohols and ketones with the same chain length aslfue starting material. Significant quantities of scission products were also formed, (with ketones and alkanes being the most abundant) consistent with the formation and decomposition oftertiary alkoxyl radicals. It was also found that products arising from tertiary alkoxy radicals became more favoured compared to products from secondary alkoxy radicals as the reaction progressed..'5-memb~red lact()nes were also ~bserved in significant quantities, as well:JlS lesser amounts ofcarboxylic acids. It was found that tertiary hydrogen atoms ofthe branched alkane substrate were 15.3, 12.6, and 9.0 fold more reactive than secondary hydrogen atoms at temperatures of90, 170, 230°C respectively. i ~'I t The experiments performed in the laboratory were oxidation tests performed in a res~arch engine capa~le ofpiston ring pack sampling and using a,Partia1ly formulated lubricant with detergent, or detergent and dispersant. These lubricants were then used to investigate the effect ofengine speed (1000-2000 rpm) and engine load (3375%) on the oxidation level of both sump and ring pack oil, it was found that both sump and ringpack oxidation levels increased as a function ofload. However engine speed was found to be inversely proportional oxidation level in the ringpack, and did not affect sump degradation. These results allow the calculation ofthe lubricant's flow rate through engine under different conditions to be examined. At 1500 rpm and 50 % load, the lubricant starting in the sump eventually flows through the piston and returns to the sump in 65.2:1: 7.8 hours. The viscosity of engine oils is a key consideration throughout their operating life, but the cause ofthe degradative viscosity increase during use is poorly understood. To examine this, the viscosity ofmodel mixtures were examined by basing the mixtures on the oxidation products observed during the oxidation ofpristane in the ],aboratory, in an I attempt to simulate the viscosity change observed during oxidation. It was found that polar oxidation products have little effect on viscosity at low concentrations, and viscosity increases are more likely to be caused by the formation ofhigh mass oxidation products, such as sludge precursors.
Supervisor: Not available Sponsor: Not available
Qualification Name: University of York, 2006 Qualification Level: Doctoral
EThOS ID:  DOI: Not available