Abere J O_MEng_2010

ABSTRACT
 This work investigated the tribological (lubrication) properties of four
vegetable oils - groundnut oil (GNO), red palm oil (RPO), palm kernel
oil (PKO) and refined cottonseed oil (RCSO). Their temperature-
dependent density and viscosity were investigated alongside other
properties namely: pH value, pour point, flash point, specific gravity
and specific heat capacity at constant pressure. Tests were conducted
up to 80 oC. All the four oils were sourced locally (South West Nigeria).
 The Ostwald Viscometer was employed for viscometry, the density
bottle for density determination; while other tests were conducted on
equipment available in some laboratories in Nigeria. The pH values
range between 3.37 for GNO at 27.8 oC and 5.01 for PKO at 27.9 oC.
Their pour points are from 0 oC for GNO to 21oC for PKO. Flash points
range between 318 oC for PKO and 325 oC for RCSO. The oils’ pH value,
pour point and flash point do not vary with temperature. Their Specific
heat capacities are between 2.0839 J/g oC for PKO to 3.7677 J/g oC for
RPO. Their densities (and specific gravities) decrease with increasing
temperature, ranging from 908.5 kg/m3 for PKO at 30 oC to 863.4
kg/m3 for RPO at 80 oC.
2

ABSTRACT
The density values within the test range (30 to 80 oC) were
fitted to a straight line model with 99% correlation.
Mathematical models were developed for density and
specific gravity respectively; thus density and specific
gravity values at any temperature of interest could be
evaluated. The kinematic and absolute viscosities of the
oils decrease with increasing temperature. For GNO,
kinematic viscosities range from 35.9552 centistokes (cS) at
30 oC to 7.8617 cS at 80 oC; for PKO, from 25.2219 to 5.2434
cS; RPO, from 33.3787 to 7.0183 cS and for RCSO, from
30.4482 to 7.0208 cS. The viscosity indices (VI) of the four
oils range from 183 for GNO to 206 for PKO.
Further investigations will consider the performance
characteristics of the oils in lubrication systems. The
potentials of our vegetable oils are thus presented for
appropriate industrial application.
3

1.1(a - g) General Background
1.2 Objectives of the Research
1.3 Purpose and Scope of Study
1.4(a, b) Significance of the Study
1.5(a - c) Properties of Lubricating Oils
4

1.1a General Background
 Tribology is the science and technology of interacting surfaces in relative
motion and of related subjects and practices [1]. The word ‘tribology’
originates from the Greek word “tribos” which means “rubbing”. The
science includes sub-areas such as friction, wear and lubrication [2].
 The subject (tribology) generally deals with the technology of lubrication,
control of friction and prevention of wear of surfaces having relative motion
under load [3]. The field of tribology includes analysis of friction, wear,
lubrication phenomena and the application of such principles to mechanical
design, product development, manufacturing processes and machine
operation [4].
 Friction is the resistance to bodies moving against each other and is always
present when bodies are in motion. Friction can either be dry or viscous and
in the former case we make a distinction between static and dynamic
friction; and in the latter case friction develops due to molecular forces
between adjacent fluid layers. Wear is a destructive process where surface
material is removed from one or both of the two bodies in relative motion.
Lubrication is a way of controlling both friction and wear [2].
5

1.1b General Background
 Lubrication is the introduction of a substance between the contact surfaces
of moving parts to reduce friction and to dissipate heat. A lubricant may be
oil, grease, graphite, or any substance - gas, liquid, semisolid, or solid - that
permits free action of mechanical devices and prevents damage by abrasion
and “seizing” of metal or other components through unequal expansion
caused by heat.
 In machining processes lubricants also function as coolants to forestall heat-
caused deformities [6]. Lubricants can be either solid or fluid type, and their
main purpose is to reduce the friction and protect the surfaces against wear
thus providing smooth running and a satisfactory operational life for
machine elements.
 Lubricants also transfer heat, carry away contaminants and debris, transmit
power, and prevent corrosion. Most lubricants are liquids (such as mineral
oils, synthetic esters, silicone fluids), but they may be solids for use in dry
bearings, greases for use in rolling-element bearings, or gases (such as air)
for use in gas bearings. Fluid film lubrication occurs when opposing
bearings surfaces are completely separated by a lubricant film [2].
6

1.1c General Background
 The function of tribological research is to bring about a reduction in the
adhesion, friction and wear of mechanical components to prevent their
failure and provide long, reliable component life through the judicious
selection of materials, operating parameters and lubricants [7].
 Mechanical systems such as bearings, gears and seals are examples of
components involving tribology. They are technically referred to as
‘tribosystems’. Wherever and however, two or more solid surfaces are in
contact with relative motion between the surfaces, tribology is involved.
 This requires the design and failure analysis of machine components -
bearings, gears, seals, etc. - and a study of the effects of pressure,
temperature, humidity, viscosity and other variables on its performance
under appropriate lubrication regime [9].
 The significant lubricating-fluid properties are: density, viscosity, specific
heat and thermal conductivity [10]. Base stock (oil) functions important to
tribology include viscosity and its variation with temperature, pressure and
shear rate, traction, visco-elasticity, bulk modulus and thermal properties.
7

1.1d General Background
 Recent developments has brought about the new field of “environmentally friendly
tribology”, “tribology for the environment” or simply “green tribology”. Thus, the
current focus in lubrication science and technology is on renewable, earth-friendly
and environmentally benign fluids for tribological applications.
 The way we use energy: fuels and lubricants; should not threaten our planet. Bio-
based fuels and lubricants are being researched to roll back the spectre of a warming
planet. Vegetable oils (VOs) are among the group of environmentally acceptable and
renewable lubricants for some interacting surfaces.
 VOs are used in various industrial applications such as lubricants, emulsifiers,
plasticizers, surfactants, plastics, solvents and resins. Research and development
approaches take advantage of the natural properties of these oils. They have superb
environmental credentials, such as being inherently biodegradable, having low eco-
toxicity and low toxicity towards humans, being derived from renewable resources
and contributing no volatile organic chemicals.
 These oils are extracted from the seeds of cotton, groundnut, oil palm, soybean, etc.
Some VOs used industrially include: palm, palm kernel, coconut, cotton, groundnut,
castor, tung, soybean, linseed from flax and rapeseed oils. Consequently, the
relatively low cost and the dependable supply of certain vegetable oils make them
important sources of industrial oils [11].
8

1.1e General Background
 Selecting the proper lubricant is important for sharp reduction of long-term
costs. The best-fit product selection can mean longer lubricant life, reduced
machine wear, reduced incipient power losses and improved safety.
 Suitable base stocks and additives reduce environmental impact. This is important
because there will be leaks, spills and eventual disposal of lubricant [14].
 Modern industry rests on a layer of lubricant which separates moving machine
elements from each other. The condition of oil used as a lubricant affects the
working condition of the machine significantly. The chemical and physical
properties of a lubricant have a direct effect on the lubrication situation [15].
 Interest in VO based lubricants (bio-lubricants) emerged, in recent time, due to
environmental concerns. Petroleum based lubricants (currently been used) represent
a large source of soil and water pollution. About half of these lubricants are being
spilled off in the environment, deliberately or accidentally. These reasons stimulate
the use of biodegradable, non-toxic lubricants.
 Biodegradable lubricants, mostly from vegetable oils, represent the
technical and environmental alternative for conventional lubrication. It has
been assessed that over 90% of all lubricants could be replaced by bio-
lubricants [11, 16 and 67].
9

1.1f General Background
 Petroleum-based lubricants are carcinogenic and constitute environmental
hazard when spilled or disposed. One of such is water system pollution.
 Bio-based lubricants offer significant health and environmental benefits
including resource renewability, biodegradability, as well as providing
satisfactory performance in a wide array of industrial applications.
 There is a growing worldwide trend of promoting VO as base oil for
automotive lubricants, metal working lubricants, quenching oils, hydraulic
oils, oilfield applications for avoidance of aquatic pollution, etc.
 Many tests and researches are being conducted to understand the potential
of renewable lubricants based on VO to replace the current mineral oil
based lubricants. VOs are recognized as rapidly biodegradable and are thus
promising candidates as base fluid in environmental-friendly lubricants and
tribosystems. Tribological (lubrication) properties of olive oil, coconut oil,
soya oil, canola oil and rapeseed oil have been investigated [16, 17, 18, 19,
20, 21 and 22].
10

1.1g General Background
 Groundnut oil, palm kernel oil, red palm oil and
refined cotton seed oil are available vegetable oils in
Nigeria; these four have been selected for
investigation.
 Adequate knowledge of the tribological (lubrication)
properties of these oils is needed for accurate analysis
and simulation in the design of lubricants and fluid
lubricated systems, where they may be adopted as
base oil to replace mineral oils.
 Tribological (lubrication) properties such as density,
viscosity, pour point, flash point, heat capacity, etc.
are the major input data for lubricant design.
11

1.2 Objectives of the Research
 The followings are the specific objectives of the research:
 1.To determine experimentally the density, viscosity, flash
point, pour point, specific gravity, heat capacity and pH
value of groundnut oil, palm kernel oil, red palm oil and
refined cotton seed oil.
 2. To investigate the influence of temperature on density
and viscosity of the selected oils. It is expected that the
density-temperature relationship will be modelled
empirically. The viscosity indices (which relate viscosity
with temperature) will also be determined for each oil.
12

1.3 Purpose and Scope of Study
 The purpose of this research is the investigation of some
tribological properties of selected vegetable oils with
respect to temperature variation.
 The selected oils are (1) groundnut oil, (2) palm kernel oil,
(3) red palm oil and (4) refined cotton seed oil.
 This research study shall determine some physical
properties – pH value, melting point, flashpoint and
flammability, and heat capacity.
 These tribological properties – density and viscosity of the
four oils will be investigated within the temperature range
of 30 to 80oC at 10oC intervals. Empirical equations
relating these properties with temperature would be
developed.
13

1.4aSignificance of the Study
 In view of current environmental realities and demands, both engine fuel and lubricant need to
compliment one another towards reducing emission of green house gases and toxic chemicals. Bio-
based or biodegradable fuels and lubricants are being developed from vegetable oils.
 Vegetable oil (VO) lubricants are being developed as alternatives to petroleum-based oil: they can
be circulated in internal combustion engines, or sprayed in one-time applications like those
necessary for lubricating train rails.
 Reasons for the current research and development activities on VO lubricants include: they do not
produce toxic fluids or volatile organic compounds, they are biodegradable, renewable and
recyclable and have a higher boiling point than petroleum-based oils.
 They can endure harsh and hot engines, offer less ash build-up and better engine performance over
mineral oil-based lubricants. VOs produce less green house gases (GHGs) compared to
conventional mineral oil-based lubricants. VOs have excellent lubricity, they have favorable
viscosity-temperature characteristics and high flash points. They are compatible with mineral oil
and additive molecules, exhibit relatively low lubricant consumption and longer oil drain intervals
and have good energy efficiency combined with public health. They are fire resistant, i.e. safer to
handle in relation to petroleum-based oils.
 VOs are food grade oils, applicable in the food processing industry. They offer performance equal
or better than petroleum-based oils at similar cost. Bio-based fluids are being developed from VOs
to eliminate the hazardous pollution caused by accidental oil spillage, which is especially
important in environmentally sensitive applications such as construction, hydropower, marine, oil
and gas, etc. [11, 16, 18, 21 and 58].
14

1.4b Significance of the Study
 Local sourcing of alternative lubricants (or base oils) is considered an effort in
the right direction. Apart from potential savings from reduced imports, it will
improve income and living standard of local producers. Locally available VOs
are applicable as lubricants for some interacting surfaces. But they are rather
tribologically unknown. The lubrication properties of local VOs are needed for
appropriate industrial application.
 It is important to take lubrication into account early in the product design
process. This will make it possible to optimize lubricant choice, manufacturing
method, surface hardening processes, etc., in order to obtain reduced wear and
friction [23]. Therefore, adequate lubrication design tools should be provided
for the engineer in order to enable predictions of friction and the risk of wear. A
lubricant’s application depends, among other factors, on desirable properties in
tandem with the design of a piece of machinery.
 The choice of locally available VO as base-oil for lubricant development would
be enhanced by the product of this work. Thus, future lubricants can be
developed from locally available VOs. This will make machinery operation
become more environmentally acceptable.
15

1.5a Properties of Lubricating Oils
 Viscosity : The viscosity of a fluid is defined qualitatively as its resistance to
flow. This resistance is primarily due to internal friction. For engineering
applications the oil viscosity is usually chosen to give optimum performance at
the required temperature.
 Kinematic viscosity (Pas or centistokes) is a measure of a liquid's flow under the
influence of gravity. It's handy to think of lubricant's kinematic viscosity as it's
"I.D. card”.
 Viscosity index (VI): A numbering scale that indicates the changes in oil
viscosity with changes in temperature. Viscosity index can be classified as
follows: low VI - below 35; medium VI - 35 to 80; high VI - 80 to 110; very
high VI - above 110.A high viscosity index indicates small oil viscosity changes
with temperature, i.e. Stable viscosity. A low viscosity index indicates high
viscosity changes with temperature.
 Pour point: The pour point is the lowest temperature at which oil will flow
under specified conditions. It does not vary with temperature. Its importance lies
in the ability of the oil to flow at low temperature. This property facilitates
storage and supports the starting of engines especially during cold climatic
condition.
16

1.5b Properties of Lubricating Oils
 Flash point: The flash point is the lowest temperature, to which a lubricant must be heated
before its vapour, when mixed with air, will ignite but not continue to burn. It remains constant
for oil irrespective of the operating temperature. This property reveals the extent of fire risk to
which the lubricant could be subjected [30]. A good lubricant should have a high flash point
hence lower fire risk.
 (pH) number : pH is the negative logarithm of the effective hydrogen-ion concentration or
hydrogen-ion activity in gram equivalents per litre of the lubricant [31]. It is a number on a
scale on which a value of 7 represents neutrality; lower numbers indicate increasing acidity
and higher numbers increasing alkalinity. On the pH scale, each unit of change represents a
tenfold change in acidity or alkalinity.
 Density and specific gravity: The density of a substance is the mass of a unit volume of it at a
standard temperature and pressure [33]. The specific gravity or relative density is the density
of a substance divided by that of water at the same temperature and pressure. Specific gravity
is dimensionless. Most lubricating oils have specific gravities in the range 0.85 to 0.95 [24].
The density of a fluid is required for flow rate calculations and for the conversion of kinematic
viscosity to dynamic viscosity. Density is used in lubrication to identify an oil or oil fraction.
The density of a lubricant in g/cm3 is very nearly numerically equal to its specific gravity.
Density is sensitive to temperature and pressure. The density – temperature relationship, i.e.
the thermal expansion, influences the pressure distribution as well as the energy dissipation
due to compression. The density – temperature relationship is especially important for the
performance of hydrodynamic parallel surface thrust bearings since it is the origin of the
density wedge.
17

1.5c Properties of Lubricating Oils
 Specific heat capacity: The specific heat capacity (J kg-1 C-1) of a substance is
the heat required to warm unit mass of it through 1 degree; it is the heat capacity
per unit mass of the substance [34]. Heat capacity is one of the basic thermo
physical and thermodynamic properties which characterize a liquid. They are
directly linked with temperature derivatives of basic thermodynamic functions
and are therefore indispensable for the calculation of differences in these
functions between different temperatures. It is an important property when the
oil acts as a coolant or heat transfer medium.
 Thermal conductivity: the thermal conductivity, k, is the quantity of heat, ∆Q,
transmitted during time ∆t through a thickness x, in a direction normal to a
surface, of area A, due to a temperature difference ∆T, under steady state
conditions and when the heat transfer is dependent only on the temperature
gradient. Thermal conductivity varies linearly with temperature and is affected
by polarity and hydrogen bonding of the molecules. The thermal conductivity of
most of the mineral and synthetic hydrocarbon based lubricants is in the range
between 0.14 W / m K at 0 oC and 0.11 W / m K at 400 oC.
18

2.0a Literature Review
2.0b Literature Review (Contd.)
2.0c Literature Review (Contd.)
19

2.0a LITERATURE REVIEW
 One of the interesting recent developments is a growing realization that bio-
resources present practical alternatives to fuels and lubricants derived from liquid
fossil fuels. The advantages of vegetable oils (VOs) as base fluids in lubricants are
perceived to be the following: non-toxicity, biodegradability, resource renewable,
affordable application cost, good lubricity and high viscosity index.
 In bio-based formulations, vegetable oils replace a mineral oil as the base, which is
typically 90% of a lubricant. Fatty acids make VOs naturally more slippery than
mineral oils, and their polar molecules make them stick to metal surfaces better.
 VOs are used in various industrial applications such as: lubricants, emulsifiers,
plasticizers, surfactants plastics, solvents and resins. Research and development
approaches take advantage of the natural properties of these oils.
 These oils are extracted from the seeds of cotton, groundnut, oil palm, etc.
Consequently, the relatively low cost and the dependable supply of certain VOs
make them important sources of industrial oils.
20

2.0b LITERATURE REVIEW (Contd.)
 Larsson et al. [23] investigated the properties of a number of lubricants namely:
naphthenic and paraffinic mineral oils, blends of the aforementioned oils,
polyalphaolefins and a polyglycol. Properties measured are: the viscosity,
elastohydrodynamic lubrication (EHL) friction coefficient, density, thermal
conductivity and heat capacity per unit volume. These were measured within
relatively broad pressure and temperature ranges.
 Hassan et al. [40], worked on the possibility of producing lubricating oil from
vegetable oil with palm olein (oil) as a case study. Some of the properties such as
viscosity, flash/fire point, pour point and specific gravity were analysed.
 Afeti et al. [45] investigated viscosity, density, thermal conductivity, specific heat
capacity, flash point, pour point, melting point and oxidation resistance of four oils
namely: coconut oil, palm kernel oil, groundnut oil and shea butter oil. Kinematic
viscosity and density readings were taken between 25 and 80oC. Thermal
conductivity and specific heat capacity were determined without reference to
temperature and pressure changes. It was found out that all the oils investigated have
a higher flash point compared to SAE40 engine oil.
 Abramovic and Klofutar [46] determined dynamic viscosities for the following VOs:
unrefined sunflower oil, refined sunflower oil, olive oil, refined corn oil unrefined
pumpkin oil, a mixture of refined VO and unrefined pumpkin oil; at temperatures
from 298.15 K (25oC) to 328.15 K (55oC).
21

2.0c LITERATURE REVIEW (Contd.)
 Fundamental properties of six ester base fluids, suitable for formation of
environmentally adapted lubricants were investigated by Pettersson [36]. All the
esters have high thermal conductivity and specific heat capacity in comparison with
the mineral oil studied.
 Fox and Stachowiak [44] investigated VOs as a potential source of environmentally
favourable lubricants, due to a combination of biodegradability, renewability and
excellent lubrication performance.
 Gitis [49] presented a multi-sensing technology, effective for tribology testing of
oils. Oils have to be characterised based on their properties as well as their
operational performance. Tribological properties such as density, viscosity, thermal
conductivity, and others are determined by adopting appropriate laboratory
equipment.
 Performance characteristics of oils often require tribometers and test engines.
Application-specific tribometers are usually developed for lubrication system testing
and simulation. For instance: aerospace tribological testing require spiral orbit
tribometer, automotive tribological testing would need engine test bed and the wear
testing machine is needed to investigate anti-wear additives in oils. Each level of
tribometry has its instrumentation challenge.
22

3.1 Materials
3.2 Experimental Procedures
23

3.1 Materials
 Four locally available vegetable oils were investigated,
namely:
 Groundnut Oil (GNO),
 Palm Kernel Oil (PKO),
 Red Palm Oil (RPO), and
 Refined Cottonseed Oil.
 Samples of groundnut oil and palm kernel oil were
collected from Ado – Ekiti. Refined cottonseed oil was
bought from Lagos, while red palm oil sample (first
grade) was collected from the Nigeria Institute for Oil
Palm Research (NIFOR), Benin City.
24

3.2 Experimental Procedures
 Properties determined are
pH value,
pour point,
flash point,
specific gravity, and
specific heat capacity.
• density and viscosity were investigated within temperature range of
30 to 80oC at 10oC interval.
• Apparatus for density and viscosity were improvised.
• Other properties were determined using available laboratories
including the Petroleum Analysis Laboratory (PAL), Petroleum
Training Institute (PTI), Warri. The experimental procedures adopted
for determination of investigated properties are presented in this
section.
25

3.2.1 pH Value.
 The test method used was that for pH determination for oil
and water samples. The apparatus consists of the Mettler
Toled (MX300) pHmeter and 50ml beakers. The pHmeter
was calibrated with buffers 4, 7 and 9. Oil samples were
poured into four beakers. The clean electrode of the
pHmeter was placed in the oil sample. When the reading
on the pHmeter got stable, the respective pH value was
recorded along with the temperature of oil sample.
26

3.2.2 Pour Point.
 The test method is the American Society for Testing and
Materials (ASTM) D97-85 standard test method for pour
point of petroleum oils. The apparatus consists of a test
jar, thermometer, cork, thermostatic bath maintained by
refrigeration and a refrigeration jacket. The test started by
heating of the oil sample. The oil sample was cooled and
examined at intervals of 3oC for flow characteristics. The
lowest temperature at which movement of the oil is
observed would be recorded as the pour point.
27

3.2.3 Flash Point.
 The test method was the ASTM D93 standard test method
for flash point. Apparatus consists of the Pensky-Martens
closed flash tester and a thermometer. The Pensky-
Martens closed flash tester is shown in Figure 3.1. Oil
sample would be heated at a slow constant rate with
continual stirring. A small flame would be directed into
the cup. The lowest temperature at which application of
the flame causes the vapor above the oil sample to ignite
would be recorded as the oil’s flash point.
28

Figure 3.1: Pensky-Martens Flash Point Tester.
29

3.2.4 Specific Gravity.
 The test method was the ASTM D1298 - 85 standard test
method for specific gravity or relative density.
 Apparatus consists of a hydrometer, 100ml measuring
cylinder and a thermometer. The oil sample would be
transferred into a cylinder. A hydrometer would be
lowered into the oil sample.
 After temperature equilibrium is reached, the hydrometer
scale would be read and the temperature of the sample
noted.
30

3.2.5 Density.
 Apparatus include electrically heated thermostatic (water)
bath, density bottle, digital mass balance, thermal
insulator interface between hot density bottle and digital
mass balance sensor and thermometer.
 The fixed volume density bottle was filled with oil sample
to its brim. The mass was determined at ambient
temperature (30oC). With the aid of the water bath, oil
sample in the bottle was heated to desired temperature,
and its mass recorded. Average values (mass) were noted
for oil within the temperature range of interest.
31

3.2.6 Viscosity.
 Apparatus for the experiment are Ostwald viscometer
(Figure 3.2), thermostatic (water) bath, stop watch,
thermometer, hand suction pump, electrical heater with
stirrer and holders.
32

Figure 3.2: Ostwald Viscometer.
33

3.2.6a Viscosity (contd.)
 A sample oil of fixed volume is charged to the lower receiving
vessel and the viscometer is placed in a thermostatic bath.
 After time is allowed for the sample oil to reach thermal
equilibrium (about 5 minutes), the sample is drawn up into the
efflux vessel by suction until the level is above the upper
etched index line.
 The fluid is then permitted to flow down through the capillary
by releasing the suction.
 When the fluid surface passes the upper etched index line, a
stopwatch is started. The stop watch is stopped when the
surface passes the lower etched index line of the efflux vessel.
 From this efflux time (t), the kinematic viscosity of the fluid is
calculated by multiplying it by the viscometer calibration
constant.
34

3.2.7 Specific Heat Capacity.
 The electrical method was employed for determination of
specific heat capacities of the four oils at atmospheric
pressure.
 Apparatus include well-lagged aluminium calorimeter,
thermometer, stirrer, heating coil, voltmeter, ammeter,
rheostat, 12V accumulator, switch, and stop-watch.
 The electrical circuit was connected as shown in
Figure 3.3.
35

Figure 3.3: Circuit Diagram for the Electrical Method.
36

Experimental results and empirical analyses are presented for:
1. pH Value.
2. Pour Point
3. Flash Point
4. Specific Gravity
5 Density
6. Viscosity
7. Viscosity Index
of the FOUR oils investigated.
37

Table 4.1: pH Value
Oil pH Value
Groundnut oil 3.37 at 27.8oC
Palm kernel oil 5.01 at 27.9oC
Red palm oil 4.36 at 28.5oC
Refined cottonseed oil 4.28 at 28.1oC
38

4.1 pH Value
 From the above results, the pH values of the oils show that they
are acidic; groundnut oil having the lowest (3.37), while palm
kernel oil has the highest (5.01). Since acids are formed in use by
contamination or oxidation in lubrication systems, the oil life of
vegetable oils reduce significantly in use as the acidic content
increases. To make these oils have a longer life, alkalinity could
be introduced for special properties and neutralization of fuel
combustion products that are acidic [55]. Acidic and alkalinity
(pH value) does not vary with temperature. It is influenced by
contamination or oxidation of the oil.
 Temperatures at which readings were taken were around the
ambient temperature during the experiment, which is 27oC. The
temperatures noted are for record purposes, oil pH remains
constant irrespective of operating temperature.
39

Table 4.2: Pour Point
Oil Pour Point
Groundnut oil 0oC
Palm kernel oil 21oC
Red palm oil 13oC
Refined cottonseed oil 5.5oC
40

4.2 Pour Point
 The standard range of pour point for lubricating oils is
between -45 oC and 30 oC [24, 29]. As observed from the
results, all the selected oils can be used as lubricants. The
high pour points of palm kernel oil (21oC) and red palm oil
(13 oC) is mainly due to the presence of high percentages of
wax in them compared to the other two oils. The lower
pour points of groundnut and refined cottonseed oils make
them suitable for low temperature (not cryogenic)
applications. The pour point of SAE 40 engine oil is -27 oC
[56]. SAE implies the Society of Automotive Engineers. The
oils have relatively higher pour points compared to SAE 40.
41

Table 4.3: Flash Point.
Oil Flash Point
Groundnut oil 320oC
Palm kernel oil 318oC
Red palm oil 322oC
Refined cottonseed oil 325oC
42

4.3 Flash Point
 The standard range of flash point for lubricating oils is
between 40 and 360 oC [28]. The flash point of SAE 40
engine oil is 260 oC [56]. From the results, flash points
of the four oils are, not only within acceptable range,
but well above that of SAE 40 engine oil. Flash point is
clearly related to safety. It is an indication of the
combustibility of the vapour of a lubricant. It is a
measure of the fire hazards. It is also useful in
determining whether oil has been contaminated [24,
29]. Thus the vegetable oils investigated present lesser
fire hazards compared to SAE 40.
43

Table 4.4: Specific Heat Capacity
Oil Specific Heat Capacity,
J/goC
Groundnut oil 2.6127
Palm kernel oil 2.0839
Red palm oil 3.7677
Refined cottonseed oil 2.3863
44

4.4 Specific Heat Capacity
 Afeti et al. [45] presented specific heat capacities of
groundnut and palm kernel oils as 2.03 and 1.61 J/g-K
respectively. The trend is similar to experimental
results, i.e. groundnut oil has higher heat capacity
compared to palm kernel oil. Heat capacity is one of
the basic thermo-physical and thermodynamic
properties which characterize a liquid. It is an
important property when the oil acts as a coolant or
heat transfer medium [36]. In lubrication applications,
these oils are promising candidates, as they could
transfer heat, among other functions, in fluid
lubricated machinery or tribosystem.
45

Table 4.5: Density, kg/m3
Temp-
erature, oC
Groundnut
oil
Palm
kernel oil
Red palm
oil
Refined
cottonseed
oil
Water
30 901.4 908.5 900.0 907.0 989.7
40 893.5 900.7 891.1 896.8 985.4
50 887.4 894.9 882.2 889.8 981.0
60 878.6 887.2 875.7 883.1 975.5
70 872.3 881.0 869.6 876.8 970.0
80 864.7 874.9 863.4 870.5 963.5
46

4.5 Density
 From the results in Table 4.5, densities of the oils
decrease as temperature increases. When compared
with the standard range of values for lubricating oils
(between 700.0 and 980.0 kg/m3), the densities of the
oils indicate their acceptability as lubricants. Table 4.5
as well shows that all the oils have densities lower than
that of water; this indicates a good demulsibility
property of the oils, i.e. being able to separate readily
from water when used as lubricants in circulatory
systems and in other lubricating systems. Figure 4.1
shows the variation of density with temperature for the
four oils.
47

860
865
870
875
880
885
890
895
900
905
910
915
0 20 40 60 80 100
Density,ρinkg/m3
Temperature in Degree Celcius (oC).
Figure 4.1: Density - Temperature Curves for the
Four Oils.
Groundnut Oil
Palm kernel Oil
Red Palm Oil
Refined Cottonseed Oil
48

Empirical Density – Temperature Relationship
1. Groundnut Oil:
ρGNO (T) = -0.73224 (T) + 923.1962 . . . . . (6)
2. Palm kernel oil:
ρPKO (T) = -0.67086 (T) + 928.0971 . . . (7)
3. Red palm oil:
ρRPO (T) = -0.72571(T) + 920.2476 . . . . (8)
4. Refined cottonseed oil:
ρRCSO (T) = -0.71200(T) + 926.4933 . . . . (9)
49

Table 4.7: Specific Gravity.
Oil Specific Gravity (S.G.)
Groundnut oil 0.8630 at 28.9oC
Palm kernel oil 0.8550 at 43.3oC
Red palm oil 0.8700 at 28.9oC
Refined cottonseed oil 0.8770 at 28.9oC
50

4.6a Specific Gravity
 The standard range of specific gravity for lubricating oils is
0.7000 to 0.9800 [28]. Hassan et al. [40] got the specific gravity
of crude palm oil as 0.8651; the temperature was not specified.
Dorfman [57] presented specific gravities (at 15.5oC) of
cottonseed oil, palm oil, palm kernel oil and groundnut (peanut)
oil as 0.9246 – 0.9280, 0.924 – 0.9279, 0.924 – 0.9258 and 0.917 –
0.9209 respectively; whereas at 25oC, the specific gravities of
cottonseed and groundnut oils are 0.915 – 0.921 and 0.912 – 0.920
respectively. Like density, it reduces with increasing
temperature. From the results (Table 4.7), all the oils have
specific gravities within acceptable range. Specific gravity of
mineral oil is commonly presented as API gravity in the
petroleum industry. API implies the American Petroleum
Institute. Specific gravity is often measured at 15.5oC. A number
of derivations are based on specific gravity of respective oil at
15.5oC. From the results, all the oils have specific gravities within
acceptable range.
51

4.6b Specific Gravity
 Specific gravity, like density, is affected by temperature change.
The hydrometer used earlier could not take readings at low
temperature (less than 25 oC), since the oils under study would
have solidified. As well it could be damaged at temperatures
higher than 50 oC. Therefore, the relationship between density
and specific gravity was explored to resolve this challenge. There
are cases, for instance, where specific gravity of oil at 15.5 or 15.6
oC is required. From the experimental measurements of density
of the oils and water at selected temperatures and atmospheric
pressure (Table 4.5); and based on the relationship between
density and specific gravity as shown below:
 Specific gravity = ρoil / ρwater …………….. (21)
 Specific gravities of the oils were calculated from results shown
in Table 4.5: “Densities of the four vegetable oils at varying
temperature”. This is shown in Table 4.8.
52

Table 4.8: Specific Gravities of the Four Oils at Varying Temperature
Temperature,
oC
Groundnut
oil
Palm kernel
oil
Red palm
oil
Refined
cottonseed oil
30 0.9108 0.9180 0.9094 0.9164
40 0.9067 0.9140 0.9043 0.9101
50 0.9046 0.9122 0.8993 0.9070
60 0.9007 0.9095 0.8977 0.9053
70 0.8993 0.9082 0.8965 0.9039
80 0.8975 0.9080 0.8961 0.9035
53

54
0.895
0.9
0.905
0.91
0.915
0.92
0 50 100
SpecificGravity
Temperature, Degrees Celsius.
Figure 4.1: Specific Gravity - Temperature
Curves for the Oils.

4.6.1 Empirical Specific Gravity – Temperature Relationship
(i) Groundnut oil (GNO):
sGNO (T) = -0.00026 (T) + 0.91782 . . . . . . . . . . (23)
 (ii) Palm kernel oil (PKO):
 sPKO (T) = -0.00020 (T) + 0.92267 . . . . . . . . . (24)
 (iii) Red palm oil (RPO):
 sRPO (T) = -0.00026(T) + 0.91493 . . . . . . . . . . (25)
 (iv) Refined cottonseed oil (RCSO):
 sRCSO (T) = -0.00024(T) + 0.92103 . . . . . . . . . (26)
 Using equations 23 to 26 to calculate the specific gravities for the four
oils at 15.5oC results in the following:
 Specific gravity of Groundnut Oil at 15.5oC is 0.92185,
 Specific gravity of Palm Kernel Oil at 15.5oC is 0.92577,
 Specific gravity of Red Palm Oil at 15.5oC is 0.91896,
 And Specific gravity of Refined Cottonseed Oil at 15.5oC is 0.92475.
55

Table 4.11: Kinematic Viscosities of the Oils (cst).
Temperature,
oC
Groundnut
oil
Palm kernel
oil
Red palm oil Refined
cottonseed oil
30 35.9552 25.5519 33.3787 30.4482
40 24.0244 16.2079 21.5281 21.0761
50 17.8914 12.1892 15.9077 14.4263
60 12.6054 8.7641 11.8318 11.1623
70 9.9248 6.6165 9.0020 8.7717
80 7.8617 5.2434 7.0183 7.0208
56

Table 4.12: Absolute Viscosities of the Oils.
Temperature,
oC
Groundnut
oil
Palm kernel
oil
Red palm oil Refined
cottonseed oil
30 32.4100 23.2136 30.0408 27.6165
40 21.4658 14.5985 19.1837 18.9010
50 15.8768 10.9081 14.0337 12.8365
60 11.0751 7.7755 10.3611 9.8574
70 8.6574 5.8291 7.8281 7.6910
80 6.7980 4.5875 6.0596 6.1116
57

4.7 Viscosity
 The relationship between absolute and kinematic viscosities is expressed
below:
 Absolute Viscosity = Kinematic Viscosity x Density
 Using the density values for oils at the respective temperature (Table 4.5)
and values of kinematic viscosity shown in Table 4.11, the absolute
viscosity was calculated. Table 4.12 shows the absolute viscosity values for
the oils.
 The standard kinematic viscosity for lubricating oils [28] is between 2 and
300 centistokes. Kinematic viscosity of SAE 40 engine oil at 40 oC is 119.8
and 13.0 at 100 oC [56]. Viscosity decreases with increasing temperature.
From the results, the four oils under study can be used as lubricants.
Performance characteristics of the oils in lubrication systems are needful for
effective industrial application. The temperature influence on a lubricant’s
viscosity (absolute and kinematic) is conventionally presented as its
viscosity index (VI).
58

4.8 Viscosity index
 Viscosity index indicates how much a lubricant's viscosity will change
according to changes in temperature between 40°C and 100°C, which
roughly define the normal temperature range of most operations. The
viscosity index is an entirely empirical parameter that compares the
kinematic viscosity of the oil of interest to the viscosities of two reference
oils that have a considerable difference in sensitivity of viscosity to
temperature. It is an arbitrary numbering scale that indicates the changes in
oil viscosity with changes in temperature. Viscosity index can be classified
as follows: low VI - below 35; medium VI - 35 to 80; high VI - 80 to 110;
very high VI - above 110.
 A high viscosity index indicates small oil viscosity changes with
temperature. A low viscosity index indicates high viscosity changes with
temperature. Therefore, a fluid that has a high viscosity index can be
expected to undergo very little change in viscosity with temperature
extremes and is considered to have a stable viscosity. A fluid with a low
viscosity index can be expected to undergo a significant change in viscosity
as the temperature fluctuates. The viscosity index can be calculated using
the mathematical expression given by Stachowiak and Batchelor [5].
59

Table 4.13: Viscosity Indices (VI) of the Oils.
S/N Oil U V* L** H** VI
1 Groundnut Oil 24.0244 16.465 349.005 171.7400 183.3304
2 Palm Kernel
Oil
16.2079 8.341 107.843 63.5133 206.7127
3 Red Palm Oil 21.5281 9.704 140.204 79.3176 194.9140
4 Refined
Cottonseed Oil
21.0761 11.718 193.822 104.334 193.0381
60

4.8a Viscosity Index
 The viscosity index is an inverse measure of the decline in oil
viscosity with temperature. High values indicate that the oil shows
less relative decline in viscosity with temperature.
 The viscosity index of most of the refined mineral oils available on
the market is about 100, whereas multi-grade and synthetic oils have
higher viscosity indices of about 150. [47]. The viscosity index of
SAE 40 engine oil is 102 [56].
 From Table 4.12, the vegetable oils studied possess relatively higher
viscosity indices. High viscosity index lubricants protect better in
operations with temperature variations. Failure to use oil with the
proper viscosity index when temperature extremes are expected may
result in poor lubrication and equipment failure [19].
 Thus these vegetable oils are highly potent environmentally friendly
lubricants and base fluids for bio-lubricant development.
61

5.1 (a,b & c) Conclusion
5.2 Areas of Further Work
62

5.1a Conclusion
 Earth’s environmental future rests in the use of renewable materials.
Vegetable oils are bio-resources, readily available on a renewable basis.
 The resulting data on locally available vegetable oils are useful for
lubrication analysis, toward appropriate application of vegetable oils as
base-oils or bio-lubricants.
 The pH values of the oils show that they are acidic; groundnut oil having
the lowest (3.37), while palm kernel oil has the highest (5.01). The high
pour points of palm kernel oil (21oC) and red palm oil (13oC) is mainly due
to the presence of high percentages of wax in them compared to the other
two oils.
 The lower pour points of groundnut oil (0oC) and refined cottonseed oil
(5.5oC) make them suitable for low temperature (not cryogenic)
applications. The pour point of SAE 40 engine oil is -27oC [56]. The oils
have relatively higher pour points compared to SAE 40. The flash point of
SAE 40 engine oil is 260oC [56].
63

5.1b Conclusion (contd.)
 The flash points of the four oils are, not only within acceptable range, but
well above that of SAE 40 engine oil. All the oils have specific gravities
within acceptable range (0.7000 to 0.9800).
 The empirical equations developed for specific gravity of the oils gave
results close to that of Dorfman [57]. Specific gravity of Groundnut Oil at
15.5oC is 0.92185, that of Palm Kernel Oil is 0.92577 and those of Red
Palm Oil and Refined Cottonseed Oil are 0.91896 and 0.92475
respectively.
 When compared with the standard range of values for lubricating oils
(between 700.0 and 980.0 kg/m3), the densities of the oils indicate their
acceptability as lubricants. The empirical equations developed can be
employed to evaluate the density of each oil at required temperature.
 The experimental results, i.e. groundnut oil having higher heat capacity
compared to palm kernel oil agree with the trend of similar results (as
shown in Afeti et al. [45]).
64

5.1c Conclusion (contd.)
 The viscosities of the oils are within the range 4 to 35
centistokes for temperature of 30 to 80 degrees Celsius.
 The viscosity index of SAE 40 oil is 102 [56]. The vegetable
oils studied possess relatively higher viscosity indices (in the
range 180 to 210) compared to mineral (engine) oils (between
100 and 150).
 With the current attention on environmentally acceptable,
biodegradable or renewable lubricants, local vegetable oils are
worth being considered.
65

GREEN TRIBOLOGY
 Green Tribology is defined as
the science and technology of the tribological aspects of ecological
balance and of environmental and biological impacts.
(Prof. P. Jost, Fifth World Tribology Conference, Kyoto, Japan, September 2009.)
 The specific field of green or environment-friendly tribology emphasizes
the aspects of interacting surfaces in relative motion, which are of
importance for energy or environmental sustainability or which have impact
upon today’s environment. This includes tribological technology that
mimics living nature (biomimetic surfaces) and thus is expected to be
environment-friendly, the control of friction and wear that is of importance
for energy conservation and conversion, environmental aspects of
lubrication and surface modification techniques, and tribological aspects of
green or renewable applications such as the wind-power turbines, tidal
turbines, or solar panels. It is clear that a number of tribological problems
could be put under the umbrella of ‘green tribology’ and is of mutual benefit
to one another. [iMechanica , 2010]
66

5.2 Areas of Further Work
 As a follow-up to this work, the effects of anti-wear additives in vegetable oils can
be studied using 3-ball and 4-ball wear testing machines. The oils could be evaluated
for functionality, depending on the desired application: hydraulic, automotive,
aerospace, hydro power generation, marine, mechanized agriculture, oil field and
food processing.
 Blends of the oils can be considered in other to take advantage of qualities possessed
by one relative to another. Bleaching of the oils can be investigated in relation to
their tribological properties and functional characteristics. The effect of ageing on
oil properties and performance could be investigated in other to determine their
optimal life span and eventual shelf life.
 The Application of vegetable oils as biodegradable and non-toxic lubricants in
Nigeria could be appraised; especially in the agricultural, food processing, marine
and offshore environment where aquatic pollution persists.
 With test engines, a comparative study can be conducted on wear, friction, viscosity,
lubricant degradation and exhaust emissions on vegetable oils and conventional
SAE grade engine oils.
67

Abere J O_MEng_2010

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