RECIPROCATING ENGINE

LUBRICANTS
PURPOSE

 To reduce friction between moving parts to prevent

wear of metal parts
 To remove a great deal of engine heat
 To create a seal between moving parts
 Cushion impact forces created by combustion
 Clean the internal components of the engine and
protect against corrosion
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LUBRICANTS
PURPOSE
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LUBRICANTS
PROPERTIES
 Theoretically, the perfect engine oil is thin enough to
circulate freely yet viscous enough to maintain
reasonable film strength
 In practice, the best oil for a given engine is a
compromise of those characteristics
 Several factors determine the proper grade of oil for
use in a particular engine :
- Engine operating loads
- Rotational speeds of bearings
- Operating temperatures
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LUBRICANTS
PROPERTIES
VISCOSITY : A measure of oil’s resistance to flow. Oil that
flows slowly is said to have a high viscosity. Conversely oil that
flows freely has a low viscosity.
 Oil viscosity is measured using an instrument known as
the Saybolt Universal Viscosimeter
 Measurement : A specific quantity of oil is heated to a
predetermined temperature. Then, the number of
seconds required for 60 cubic centimeters of heated oil to
flow through a calibrated orifice is recorded as a measure
of the oil’s viscosity. The recorded time is known as the
Saybolt Universal Seconds viscosity or SUS
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LUBRICANTS
PROPERTIES
VISCOSITY : Of all the factors that affect oil viscosity,
temperature has the greatest effect
 Oils used in reciprocating engines typically have a
relatively high viscosity for following reasons:
- Large operational clearances
- High operating temperatures
- High bearing pressures in reciprocating engines
require the cushion that higher viscosity oils
provide.
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LUBRICANTS
PROPERTIES
VISCOSITY INDEX
 In addition to having a viscosity rating, many oils are
assigned a viscosity index or VI number
 The viscosity index is a standard used to identify the
rate of change in viscosity for a given change in
temperature
 The index itself is based on a comparative analysis of
the temperature-induced viscosity changes of two
reference oils, arbitrarily chosen by the American
Society of Testing and Materials or ASTM.
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LUBRICANTS
PROPERTIES
SPECIFIC GRAVITY
 The specific gravity of oil is a comparison of its weight
to the weight of an equal volume of distilled water at a
specified temperature
 For example, water weighs approximately 8 pounds per
gallon. Therefore, oil with a specific gravity of 0.9
weighs 7.2 pounds per gallon (0.9 × 8 = 7.2)
 The American Petroleum Institute, or API, has
formulated a measurement for the specific gravity of
oils that is an expansion of the regular specific gravity
scale
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LUBRICANTS
PROPERTIES
COLOR
 Oil color is determined by the amount of light that
passes through an oil sample in a glass container when
placed in front of a light of known intensity

 The color test is conducted with a device known as an

ASTM union colorimeter
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LUBRICANTS
PROPERTIES
CLOUD POINT
 The cloud point is the temperature at which paraffin
wax and other solids normally held in a solution of oil
begin to solidify and separate into tiny crystals
 At this temperature, the oil begins to lose clarity and
appears cloudy or hazy

POUR POINT
 The pour point of oil represents the lowest
temperature at which it can flow or be poured
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LUBRICANTS
PROPERTIES
FLASH POINT AND FIRE POINT
 Flash point is the temperature at which oil begins to
emit ignitable vapours

 As temperature increases beyond the flash point, the

oil reaches its fire point when it emits sufficient vapour
to support a flame

 Typical lubricating oil has a fire point approximately

50 to 60 degrees Fahrenheit higher than the flash point
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LUBRICANTS
VARIOUS TESTS
CARBON RESIDUE TEST
 In the carbon residue test, a given amount of oil is
placed in a stainless steel receptacle and heated at a
controlled temperature until it evaporates

 The container is weighed before and after the test. The

difference in weight is then divided by the weight of the
original oil sample to obtain the percentage of carbon
by weight in the oil
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LUBRICANTS
VARIOUS TESTS
ASH TEST
 An ash test is an extension of a carbon residue test in that
it requires the carbon residue to be burned until only ash
remains
 The amount of remaining ash is then expressed as a
percentage by weight of the carbon residue
 New oil leaves almost no ash and is considered to be pure
 On the other hand, the ash left by used oil can be
analyzed for iron and lead content
 The amount of iron and lead in the remaining ash
provides clues to the amount of internal engine wear.
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LUBRICANTS
ENGINE OIL GRADING SYSTEM
• Most commercial aviation oils are assigned numerical
designations such as 80, 100, or 120 that approximate
the oil’s viscosity

• This practice has proven to be much more workable

than using actual Saybolt values to designate viscosity
because oil viscosity varies enough among commonly
used oils to produce several hundred grades when
using Saybolt values.
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LUBRICANTS
ENGINE OIL GRADING SYSTEM
• A system designed by the Society of Automotive
Engineers (SAE) further simplifies the oil grading
process.
• The SAE system scale divides all oils into seven groups,
ranging from SAE 10 to SAE 70
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LUBRICANTS
ENGINE OIL GRADING SYSTEM
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LUBRICANTS
TYPES OF OIL
• Castor oil - Pure vegetable oil derived from castor
beans. Poor chemical stability and tend to oxidize when
used in reciprocating engines
• Mineral-based oils - More chemically stable than
vegetable-based lubricants and are still widely used in
reciprocating engines
• Synthetic oils - are also used in reciprocating and
turbine aircraft engines. A blend of mineral and
synthetic oils is called a semi-synthetic
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LUBRICANTS
TYPES OF OIL
STRAIGHT MINERAL OIL
• MIL-L-6082E, a straight mineral oil with no additives,
was the principle type of oil used in aircraft engines

• Effective lubricant, but it has some limitations of

oxidization
ASHLESS-DISPERSANT OILS
• The most commonly used oil in reciprocating engines is
ashless-dispersant (AD) oil that conforms to
MIL-L-22851D
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LUBRICANTS
TYPES OF OIL
ASHLESS-DISPERSANT OILS
• This oil contains a dispersant that causes sludge-forming
materials to repel each other and remain in suspension
until trapped by the oil filter
• This characteristic helps oil passages and ring grooves
remain free of harmful deposits
• Ashless-dispersant oils contain an anti-wear, anti-foam
additive that does not leave metallic ash deposits in an
engine
• Ash deposits are undesirable because they can lead to
pre-ignition and spark plug fouling
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LUBRICANTS
TYPES OF OIL
MULTI-VISCOSITY OILS (SAE 15W50)
 Multi-viscosity oils were developed to help
address some of the drawbacks of single
viscosity oils
 For example, in a warm climate an SAE 10 oil will
get too hot and lose its ability to maintain an
adequate film on moving parts
 While in a cold climate, SAE 30 oil will not circulate
properly, especially when an engine is first started.
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LUBRICANTS
TYPES OF OIL
SYNTHETIC OILS
 The chemical composition of synthetic oils provides
multi-viscosity properties similar to automotive grades
SAE-5 to SAE-20
 They contain a blend of chemical additives and certain
diesters, which are synthesized extracts of mineral,
vegetable, and animal oils
 Synthetic oils have extremely low internal friction and
high resistance to thermal breakdown and oxidation.
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LUBRICANTS
TYPES OF OIL
EXTREME PRESSURE LUBRICANTS
 Extreme pressure (EP) lubricants, also known as hypoid
lubricants, are specially formulated to provide protection
under high loads
 A hypoid lubricant contains additives that bond to metal
surfaces to reduce friction under high pressures or high
rubbing velocities.
 A typical hypoid lubricant consists of a mineral-based oil
containing loosely held sulfur or chlorine molecules
 The spur-type gears in a propeller reduction case operate
under high tooth pressures and often require EP lubricants to
prevent gear failure