nanoﬂuid additive for
engine lubrication oil
Yuh-Yih Wu and Mu-Jung Kao
Department of Vehicle Engineering, National Taipei University of Technology, Taipei, Taiwan
Purpose – Nanoparticles have been studied as additives to lubrication oils for reducing friction and wear. The purpose of this paper is to investigate
the effect of nanoﬂuid on engine oil and friction reduction in a real engine.
Design/methodology/approach – The nanoparticles were prepared using a high-temperature arc in a vacuum chamber to vaporize the Ti metal, and
then condensed into a dispersant to form the TiO
nanoﬂuid, which was used as lubricant additive. Experiments were performed in both real engine
running and test rig.
Findings – It was found that the engine oil with nanoﬂuid additive with an ethylene glycol dispersant of nanoparticles, had gelled after 10-h of engine
running. The problem of oil gelation (jelly-like) was solved by replacing the dispersant with parafﬁn oil. The engine oil with TiO
exhibited lower friction force as compared to the original oil. The experiment showed that a smaller particle size exhibits better friction reduction with
particle size ranging from 59 to 220 nm.
Research limitations/implications – The paper is restricted to ﬁndings based on the dispersed nanoparticles in ﬂuid as additive for engine
Practical implications – The test results are useful for the application of nanoﬂuid additive for engine oil.
Originality/value – Most previous researches in this ﬁeld were executed on tribotester, rather than the actual engine. This paper describes
experimental methods and equipment designed to investigate the application of TiO
nanoﬂuid as lubricant additive in internal combustion engine.
Keywords Engines, Engine oils, Friction, Testing, Tribology
Paper type Research paper
Nanoparticles, such as TiO
, CuO, PbS, ZnS, etc. can be
used as additives to lubricants for reducing friction and wear.
Studies report that engine oil with nanoparticle additive
delivers better friction reduction and anti-wear performance.
Wu et al. (2007) used nanoparticle additives of CuO, TiO
and nano-diamond to API-SF engine oil, and (Tarasov et al.,
2002) used copper nanopowder additive to SAE 30 motor oil.
A large number of papers have reported that the addition of
nanoparticles to lubricant is effective in improving tribological
properties (Chen et al. 1998; Xue et al., 1997; Liu and Chen,
2000; Chen and Liu, 2001, 2006; Zhou et al.1999, 2001;
Hu and Dong, 1998; Zhang et al., 2001; Qiu et al., 2001;
Ta o et al., 1996; Chinas-Castillo and Spikes, 2003; Rapoport
et al., 2001, 2003a, b, 2005; Li et al., 2006), as well. A low
concentration of nanoparticles ranging from 0.05 to 2.97
percent (Chen et al., 1998; Xue et al., 1997; Liu and Chen,
2000; Chen and Liu, 2001, 2006; Zhou et al., 2001; Hu and
Dong, 1998; Zhang et al., 2001; Qiu et al. 2001; Tao et al.,
1996) is sufﬁcient to improve tribological properties.
Nanoparticles range in size mostly from 2 to 120 nm (Chen
et al., 1998; Xue et al., 1997; Liu and Chen, 2000; Chen and
Liu, 2001, 2006; Zhou et al., 1999, 2001,; Hu and Dong,
1998; Zhang et al., 2001; Qiu et al., 2001; Tao et al., 1996;
Chinas-Castillo and Spikes, 2003; Rapoport et al., 1999) and
generally speaking, those of smaller size are likely to reduce
friction and increase anti-wear ability. The particle size should
not be too small, however; as Chinas-Castillo and Spikes
(2003) report, gold particles of 20 nm were more effective in
reducing friction and wear than those of 5 nm. Smaller
particles are able to form surface protective ﬁlm and rolling
effect (Zhou et al., 1999; Rapoport et al., 1999).
The mechanisms of friction-reduction and anti-wear of
nanoparticles in lubricant have been reported as producing a
colloidal effect, a rolling effect, and a protective ﬁlm. The
colloidal effect results from nanoparticles penetrating
elastohydrodynamic contacts (Chinas-Castillo and Spikes,
2003) or by providing hydrodynamic conditions of lubrication
(Wu et al., 2007; Tarasov et al., 2002; Chen et al., 1998; Xue
et al., 1997; Liu and Chen, 2000; Chen and Liu, 2001, 2006;
Zhou et al., 2001, 1999; Hu and Dong, 1998; Zhang et al.,
2001; Qiu et al., 2001; Tao et al., 1996; Chinas-Castillo and
Spikes, 2003; Rapoport et al., 1999, 2001). The rolling effect
of spherical particles provides a rolling friction mechanism
(Tao et al., 1996; Chinas-Castillo and Spikes, 2003; Rapoport
et al., 1999, 2001, 2003a,b). Protective ﬁlm comes from the
deposition of tribochemical reaction products produced by
nanoparticles during the friction process. This effect can
result in an anti-wear boundary ﬁlm (Chen et al., 1998;
Xue et al., 1997; Liu and Chen, 2000; Chen and Liu, 2001;
Zhou et al., 2001; Qiu et al., 2001; Chinas-Castillo and
Spikes, 2003; Rapoport et al., 2003, 2005; Li et al., 2006).
Nanoﬂuid, formed by adding a small amount of nanoparticles
into a ﬂuid dispersant, may provide higher thermal conductivity
and better lubrication in many applications (Lockwood et al.,
2005). Applied in internal combustion (IC) engines, nanoﬂuid
has two beneﬁts: improving tribological properties and
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Industrial Lubrication and Tribology
63/6 (2011) 440– 445
q Emerald Group Publishing Limited [ISSN 0036-8792]