Friction and Wear Performance Evaluation of Bio-Lubricants and DLC Coatings on Cam/Tappet Interface of Internal Combustion Engines
: The environmental concerns associated with artificially formulated engine oils have forced a shift towards bio-based lubricants. The deposition of hard coatings on engine components and migrating to environmentally friendly green lubricants can help in this regard. Chemically modified forms of...
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| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI
2021
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| Subjects: | |
| Online Access: | http://irep.iium.edu.my/94137/1/94137_Friction%20and%20Wear%20Performance%20Evaluation.pdf http://irep.iium.edu.my/94137/ https://www.mdpi.com/1996-1944/14/23/7206 https://doi.org/10.3390/ma14237206 |
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| Summary: | : The environmental concerns associated with artificially formulated engine oils have forced
a shift towards bio-based lubricants. The deposition of hard coatings on engine components and
migrating to environmentally friendly green lubricants can help in this regard. Chemically modified
forms of vegetable oils, with better low-temperature characteristics and enhanced thermo-oxidative
stability, are suitable substitutes to conventional lubricant base oils. The research presented in this
manuscript was undertaken to experimentally investigate the wear and friction performance of a
possible future generation of an environmentally friendly bio-based lubricant as a potential replacement for conventional engine lubricants. In order to quantify the tribological benefits which can be
gained by the deposition of DLC coatings, (an (a-C:H) hydrogenated DLC coating and an (a-C:H:W)
tungsten-doped DLC coating) were applied on the cam/tappet interface of a direct acting valve
train assembly of an internal combustion engine. The tribological correlation between DLC-coated
engine components, lubricant base oils and lubricant additives have been thoroughly investigated in
this study using actual engine operating conditions. Two additive-free base oils (polyalphaolefines
(PAO) and chemically-modified palm oil (TMP)) and two multi-additive-containing lubricants were
used in this investigation. Real-time drive torque was measured to determine the friction force,
detailed post-test analysis was performed, which involved the use of a specialized jig to measure
camlobe wear. An optical profilometer was used to measure the wear on the tappet, high-resolution
scanning electron microscopy was employed to study the wear mechanism and energy-dispersive
X-ray spectroscopy was performed on the tested samples to qualitatively access the degradation of the
coating. When using additive-free TMP, a low friction coefficient was observed for the cam/tappet
interface. The presence of additives further improved the friction characteristics of TMP, resulting
in reduced average friction torque values. A tremendous enhancement in wear performance was
recorded with a-C:H-coated parts and the coating was able to withstand the test conditions with little
or no delamination. |
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