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1. TSINGHUA SCIENCE AND TECHNOLOGY
ISSN 1007-0214 09/24 pp286-289
Volume 9, Number 3, June 2004
Effects of Nano-Particles on the Tribological and
Thermal Properties of Piston Ring-Cylinder Liner*
LIU Xiaojun ( ) LIU Kun ( )**
JIAO Minghua ( )
WANG Wei ( ) DING Shuguang ( )
School of Mechanical and Automobile Engineering, Hefei University of Technology, Hefei 230009, China
Abstract: The effects of ultra-dispersed diamond (UDD) on the friction force, wear, and temperature of tri-
bological pairs have been investigated. The experimental tests were carried out on a modified piston ring-
cylinder liner bench tester with different particle mass fractions of 0, 0.02%, and 0.10%. The results show
that compared with a pure fluid, the mixture of the fluid and UDD not only reduces the friction and wear, but
also reduces the bulk temperature of the specimen. The mechanism by which the UDD lubricant improves
the tribological properties has some relationship with surface topography, because it can increase the bearing
capability of surfaces.
Key words: ultra-dispersed diamond; wear; surface topography; piston ring; cylinder liner
Introduction
The lubrication effects of solid particles dispersed in
oil depend on the combination of a large number of
factors. In addition to geometry and operating condi-
tions, the size and the concentration of solid particles
also play a significant role. In fact, modelling of such
phenomena is indeed complex, yet very important and
well worth to further research.
This mode of lubrication was first proposed by
Rylander[1]
, and has recently gained much attention in
the archives of tribology[2,3]
. Yousif and Nacy[4]
inves-
tigated the effect of solid particles on the tribological
behavior from the viewpoint of viscosity. Yue and
Zhou[5]
summarized the application of nano-particles
in tribology. Dai and Khonsari’s[6]
work focused on the
theoretical prediction of the lubrication of bearings
with fluids containing microstructures, and they also
studied the contact behavior based on the assumption
that the bounding surfaces were smooth. Elwell[7]
demonstrated a lapping effect on bearing surfaces
when bearings were subjected to very small size con-
taminants, similar results also appeared in Zhang’s
work[8]
. Based on experiments, Hargreaves and Shar-
ma[9]
investigated the influence of solid particles on wear.
Yet to the author’s knowledge and within the open
literature, very little research has been pursued on the
thermal performance in the presence of solid particles,
particularly for nano-particles. The achievements so far
are inadequate to describe the thermal and tribological
performance of tribological pairs in the presence of
solid particles.
This paper focuses on the experimental investigation
of the effects of the ultra-dispersed diamond (UDD) on
the thermal and tribological properties based on a
bench-test-simulated piston ring-cylinder liner. The ef-
fects will be characterized relative to the wear, friction,
temperature variation, etc. The relationship between
temperature and mixed lubrication will also be
investigated.
Received: 2003-12-15; selected from Proceedings of the
Symposium on Frontiers and Challenges of Mechanical
Science and Technology
Supported by the National Natural Science Foundation of
China (No. 50275046)
To whom correspondence should be addressed.
E-mail: liukun@mail.hf.ah.cn; Tel: 86-551-2901340-8350

2. LIU Xiaojun ( ) et al Effects of Nano-Particles on the Tribological and 287
1 Experimental Test
Figure 1 shows the experimental device. The recipro-
cating motion of the piston ring specimen was
achieved by a real crankshaft-connecting rod system of
an engine. The crank radius was 57 mm and the length
of connecting rod was 175 mm. A motor drove the
crankshaft. In the experiments, the cylinder remained
static. Both the piston ring and the cylinder specimens
were cut from real piston rings and cylinders. The ring
material was chromium-plated cast iron and the cylin-
der material was cast iron. The width of the nominal
contact area was 10 mm, and the height of the ring was
2.5 mm. The lower cylinder specimen was mounted on
a group of rollers, with a sensor was connected to
measure the friction between the piston ring and the
cylinder liner at one end of the cylinder specimen. The
side clearance of the lower cylinder specimen ensured
the alignment and established uniform contact between
the piston ring and the cylinder liner. The working
temperature of the piston assembly was set by a heater
system between the oil shield and the guard shield.
Two thermometers measured the bulk temperature of
the cylinder specimen and the environmental
temperature.
The specimen ran in for 4 h with pure oil (15W/30)
under a load of 6.0 MPa at 1000 r/min crank speed. A
stepwise loading procedure was used after running in.
Each loading step lasted for 20 min until the load
reached the required value.
Fig. 1 Experimental system schematic
1, Connecting rod; 2, Piston; 3, Thermometer; 4, Shield; 5, Heater; 6, Piston ring specimen;
7, Cylinder specimen; 8, Sensor; 9, Piston ring specimen; 10, Roller; 11, Crank shaft
2 Results and Discussion
The influence of the liquid-solid lubricant on the wear
was investigated with an 8.75-MPa load at 1500 r/min
engine speed. Table 1 shows the change of the wear
and bulk temperature of the cylinder liner after 12 h
running. The presence of the UDD reduces the wear
and also affects thermal properties of the tribological
pair. The effect of the UDD on the temperature and its
relation with the lubrication is shown in Fig. 2 which
shows the change of bulk temperature with load. For
pure oil and the 0.02% UDD (mass fraction, CUDD),
there is a sudden rise in temperature when the load is
higher than 9 MPa, which means mixed lubrication,
and asperity contact occurred. From Fig. 2, we can see
that the 0.10% UDD postponed the appearance of as-
perity contact, but the mechanisms need to be investi-
gated in more detail.
Table 1 Effect of UDD concentration (CUDD) on wear
and bulk temperature
CUDD / % Temperature ( ) Wear (mg)
0.00 187 21.5
0.02 157 5.8
0.10 151 8.4
It is not easy to describe the friction variation of a
reciprocating tribological pair because of the existence
of dead centers and inertia. A filter was added to elimi-
nate the inertia effect. Figure 3 shows the change of fric-
tion force within one stroke. Both ends correspond to

3. 288 Tsinghua Science and Technology, June 2004, 9(3): 286 289
the dead centers where the velocity is zero, BDC
means bottom dead center and TDC means top dead
center. At the dead center, the relatively high friction
force means asperity contact and mixed lubrication,
but the presence of the UDD could reduce the peak
value in the curve, the details will be shown in a sepa-
rate paper.
Fig. 3 Measured friction force variation
at 250 r/min, 8 MPa
The change of the functional property of the surface
topography should play an important role in the tribologi-
cal process. It is known that at different surface height,
the surface topography has different functional proper-
ties. To characterize functional properties of surface to-
pography, the surface bearing area curve may be clas-
sified into three zones according to the DIN 4776 stan-
dard[10]
. The peak zone is the part above the 5% sur-
face bearing ratio. The valley zone is the part below
80% of the surface bearing ratio which depicts the void
volume or fluid retention property. The core zone is
then the part between 5% and 80% surface bearing
area ratio. Three parameters are defined as the surface
bearing index Sbi, the core fluid retention index Sci, and
the valley fluid retention index Svi. A larger surface
bearing index indicates a flat top of the surface and a
larger valley fluid retention index indicates good fluid
retention in the valley zone. The changes of surface
functional properties were investigated at different
UDD concentrations. Table 2 lists the three-functional
parameters and root-mean-square (RMS) values of the
surface topography before and after wear at different
UDD concentrations. The surface roughness was
measured with a Taylorsurf-6. Compared with pure oil,
the presence of the UDD could significantly increase
the bearing capability of the surface, which is perhaps
one reason for the decrease of the wear of the tri-
bological pair.
Fig. 2 Change of bulk temperature with load
at 1000 r/min crank speed
Table 2 Change of surface functional properties at
different UDD concentrations
CUDD=0 CUDD=0.02% CUDD=0.10%Surface
functional
properties
Before
wear
After
wear
Before
wear
After
wear
Before
wear
After
wear
RMS ( m) 0.38 0.21 0.46 0.24 0.49 0.36
Sbi 0.83 0.85 0.50 1.27 0.73 1.26
Sci (×10-4
) 2.16 4.23 2.65 1.10 2.43 0.82
Svi(×10-4
) 0.36 0.56 0.28 0.35 0.46 0.26
3 Conclusions
The results obtained from these tests are preliminary in
nature, but they clearly show the influence of the UDD
on the tribological property of the tribological pair.
The presence of the UDD reduced friction and wear in
the mixed zone. An important finding in this experi-
ment is that the UDD also reduced the bulk tempera-
ture. The mechanism by which the UDD lubricant im-
proved the tribological properties has some relation-
ship with surface topography, because it can increase
the bearing capability of surfaces.
References
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National Academic Standings Announced,
Tsinghua Ranks First in Nine Areas
The Assessment Center for Degree and Research Education of Higher Education and Scientific Research Institu-
tions has announced its latest evaluation results on academic standings in China.
The assessment took place in 2003 and examined a total of 42 fields. Tsinghua received ratings for 15 subjects, 9
of which ranked highest in the country. They are: mechanical engineering, optical engineering, instrument science
and technology, power engineering and thermal engineering, electrical engineering, architecture, hydraulic engi-
neering, nuclear science and technology, and business administration.
Mechanical engineering, electronic science and technology, as well as information and communications engi-
neering were ranked first in the country in the Center’s first assessment, which took place in 2002.
The Center plans to update the list of academic standings every three years. A third assessment is scheduled to
get underway this year.
(From http://news.cic.tsinghua.edu.cn/eng_news.php?id=466)