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Lubricants 2018, 6(3), 79; https://doi.org/10.3390/lubricants6030079

Impact of Fuel Contents on Tribological Performance of PAO Base Oil and ZDDP

1
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
2
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 73000, China
3
Energy and Transportation Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
*
Authors to whom correspondence should be addressed.
Received: 9 July 2018 / Revised: 9 August 2018 / Accepted: 27 August 2018 / Published: 7 September 2018
(This article belongs to the Special Issue Advanced Lubrication for Energy Efficiency)
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Abstract

Fuel and water contents are inevitable in automotive engine oils. This study intends to investigate the impact of the addition of gasoline (3–20%) and water (1%) on the lubricating performance of synthetic base oil (PAO), with or without an anti-wear additive (ZDDP), for a steel-cast iron contact. Fuel-added PAO showed an increase in the load carrying capacity. Oil electrical conductivity and total acid number (TAN) measurements showed slightly increased conductivity and marginally increased acidity at a higher fuel concentration. In contrast, an increased wear rate, proportional to the fuel concentration, was observed in a prolonged test with constant-loading. Results suggested that the fuel addition is a double-edged sword: reducing the scuffing risk by providing stronger surface adsorption and increasing the sliding wear rate by bringing down the oil viscosity. The PAO-water blend formed an emulsion and resulted in a significantly increased load-carrying capacity, again likely due to the higher polarity and possibly acidity. For the ZDDP-containing PAO, the addition of 1% water and 3% fuel generated 24% and 52% higher wear. The phosphate polymerization level was reduced on the worn surfaces by the introduction of water but the thickness of ZDDP tribofilm was not significantly affected. View Full-Text
Keywords: oil dilution; water; fuel; TAN; conductivity; scuffing; ZDDP oil dilution; water; fuel; TAN; conductivity; scuffing; ZDDP
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Zhou, Y.; Li, W.; Stump, B.C.; Connatser, R.M.; Lazarevic, S.; Qu, J. Impact of Fuel Contents on Tribological Performance of PAO Base Oil and ZDDP. Lubricants 2018, 6, 79.

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