Frictional characteristics of IF-WS2 nanoparticles in simulated engine conditions

Burak Gullac*, Ozgen Akalin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

38 Citations (Scopus)


The efficacy of inorganic fullerene-like (IF) tungsten disulfide (WS2) nanoparticles as engine oil friction modifier additive was investigated using a high-stroke reciprocating piston ring-cylinder bore bench test system. Frictional characteristics of various IF-WS2 nanoparticle concentrations in mineral oil were experimentally analyzed in simulated engine conditions controlling oil temperature, speed, and normal load. Though the effect of IF-WS2 nanoparticles on piston ring and cylinder bore friction was minor in low concentrations, after a running period in a mixed lubrication regime with 10% additive, a considerable reduction in friction coefficient was observed when the IF-WS2 formulated oil was used. This reduction remains to some extent with reference mineral oil after solvent cleaning of themating components. The results show that a thin tribofilm gradually forms on the piston ring and the cylinder bore surfaces, reducing the friction coefficient in a mixed lubrication regime. However, in order to obtain the friction reduction there seems to be a threshold in the concentration of IF-WS2 in mineral oil and film development period. The effects of lubrication regime, contact load, speed, and surface roughness on tribofilm formation are also discussed. The presence of WS2 tribofilm formed on the piston ring and the cylinder bore surfaces was further verified using Raman spectroscopy.

Original languageEnglish
Pages (from-to)939-947
Number of pages9
JournalTribology Transactions
Issue number6
Publication statusPublished - 2010


Financial support for this study was provided by the Scientific and Technological Research Foundation of Turkey (TUBITAK Project: 104M274). IF-WS2 nanoparticles were supplied for this study by ApNano Materials, Inc., Israel. The authors thank Dr. Niles Fleischer and David Shalom of ApNano Materials Inc. and Dr. Mustafa Urgen of Istanbul Technical University for their advice and valuable suggestions.

FundersFunder number
Scientific and Technological Research Foundation of Turkey


    • Engine tribology
    • Nanotribology
    • Piston rings
    • Raman
    • Solid lubricant additives


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