29-03-2011, 12:17 PM
PRESENTED BY:
D.Chamundeswari
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Lubrication Systems
Classification of Lubricants
Animal
Vegetable
Mineral
Synthetic
Animal Lubricants
Lubricants with animal origin:
– Tallow
– Tallow oil
– Lard oil
– Neat’s foot oil
– Sperm oil
– Porpoise oil
These are highly stable at normal temperatures
Animal lubricants may not be used for internal combustion because they produce fatty acids
Vegetable Lubricants
Examples of vegetable lubricants are:
– Castor oil
– Olive oil
– Cottonseed oil
Animal and vegetable oils have a lower coefficient of friction than most mineral oils but they rapidly wear away steel
Mineral Lubricants
These lubricants are used to a large extent in the lubrication of aircraft internal combustion engines
There are three classifications of mineral lubricants:
– Solid
– Semisolid
– Fluid
Synthetic Lubricants
Because of the high operating temperatures of gas-turbine engines, it became necessary to develop lubricants which would retain their characteristics at temperatures that cause petroleum lubricants to evaporate and break down
Synthetic lubricants do not break down easily and do not produce coke or other deposits
Lubricating Oil Properties
Gravity
Flash Point
Viscosity
Cloud Point
Pour Point
Carbon-Residue Test
Ash Test
Precipitation Number
Corrosion and Neutralization Number
Oiliness
Extreme-Pressure (Hypoid) Lubricants
Chemical and Physical Stability
Gravity
The gravity of petroleum oil is a numerical value which serves as an index of the weight of a measured volume of this product
There are two scales generally used by petroleum engineers:
– Specific-gravity scale
– American Petroleum Institute gravity scale
Flash Point
The flash point of an oil is the temperature to which the oil must be heated in order to give off enough vapor to form a combustible mixture above the surface that will momentarily flash or burn when the vapor is brought into contact with a very small flame
Viscosity
Viscosity is technically defined as the fluid friction of an oil
To put it more simply, it is the resistance an oil offers to flowing
Heavy-bodied oil is high in viscosity and pours or flows slowly
Cloud Point
The cloud point is the temperature at which the separation of wax becomes visible in certain oils under prescribed testing conditions
When such oils are tested, the cloud point is slightly above the solidification point
Pour Point
The pour point of an oil is the temperature at which the oil will just flow without disturbance when chilled
Carbon-Residue Test
The purpose of the carbon-residue test is to study the carbon-forming properties of a lubricating oil
There are two methods:
– The Ramsbottom carbon-residue test
– The Conradson test
Ash Test
The ash test is an extension of the carbon-residue test
If an unused oil leaves almost no ash, it is regarded as pure
The ash content is a percentage (by weight) of the residue after all carbon and all carbonaceous matter have been evaporated and burned
Precipitation Number
The precipitation number recommended by the ASTM is the number of milliliters of precipitate formed when 10 mL of lubricating oil is mixed with 90 mL of petroleum naphtha under specific conditions and then centrifuged
Lubricant Requirements and Functions
Characteristics of Aircraft Lubricating Oil
Functions of Engine Oil
Straight Mineral Oil
Ash-less Dispersant Oil
Multi-viscosity Oil
Characteristics of Aircraft Lubricating Oil
It should have the proper body (viscosity)
High antifriction characteristics
Maximum fluidity at low temperatures
Minimum changes in viscosity with changes in temperature
High antiwear properties
Maximum cooling abilities
Maximum resistance to oxidation
Noncorrosive
Functions of Engine Oil
Lubrication, thus reducing friction
Cools various engine parts
Seals the combustion chamber
Cleans the engine
Aids in preventing corrosion
Serves as a cushion between impacting parts
Straight Mineral Oil
Straight mineral oil is one of many types of oil used in aircraft reciprocating engines
It is blended from selected high-viscosity-index base stocks
These oils do not contain additives, except for a small amount of pour-point depressant for improved fluidity at cold temperatures
Ashless Dispersant Oil
Most aircraft oils other than straight mineral oils contain a dispersant that suspends contamination such as carbon, lead compound and dirt
The dispersant helps prevent these contaminants from gathering into clumps and forming sludge or plugging oil passageways
Multiviscosity Oil
In certain circumstances, all single-grade oils have short comings
In cold-weather starts, single grade oil generally flows slowly to the upper reaches and vital parts of the engine
Multigrade oils have viscosity characteristics that allow for better flow characteristics at engine start
Characteristics of Lubrication Systems
Pressure Lubrication
Splash Lubrication and Combination Systems
Principal Components of a Lubrication System
Oil Capacity
In a pressure lubrication system, a mechanical pump supplies oil under pressure to the bearings
Oil flows into the inlet of the pump through the pump and into an oil manifold which distributes it to the crankshaft bearings
Splash Lubrication and Combination Systems
Although pressure lubrication is the principle method of lubrication on all aircraft engines, some engines use splash lubrication also
Splash lubrication is never used by itself
All lubrication systems are pressure systems or combination pressure/splash systems
Components of Lubrication Systems
Plumbing for Lubrication Systems
Temperature Regulator (Oil Cooler)
Oil Viscosity Valve
Oil Pressure Relief Valves
Oil Separator
Oil Pressure Guage
Oil Temperature Guage
Oil Pressure Pumps
Scavenge Pumps
Oil Dilution System
Plumbing for Lubrication Systems
Oil plumbing is essentially the same as is used in oil and hydraulic systems
When the lines will not be subject to bending, aluminum tubing is used
Synthetic hose is often used near the engine and other places on the aircraft that are subject to vibration or other movement
Temperature Regulator (Oil Cooler)
An oil temperature regulator is designed to maintain the temperature of the oil for an operating engine at the correct level
These regulators are often called oil coolers since cooling of engine oil is one of their main functions
Oil Viscosity Valve
The oil viscosity valve is generally considered a part of the oil temperature regulator unit and is employed in some oil systems
The viscosity valve consists essentially of an aluminum alloy housing and a thermostatic control element
The oil viscosity valve works with the oil cooler valve to maintain a desired temperature and keep the viscosity within required limits
Oil Pressure Relief Valves
The purpose of the oil pressure relief valve is to control and limit the lubricating pressure in the oil system
This is necessary to prevent damage caused by excessive system pressure and to ensure that engine parts are not deprived of fuel due to a system failure
Oil Separator
Air systems where oil of oil mist is present may require the use of an oil separator
These are often used on vacuum pump outlets
The oil separator contains baffle plates which cause the air to swirl and it deposits on the baffles
Oil Pressure Gauge
An oil pressure gauge is an essential component of any engine oil system
These gauges generally use a bourdon tube to measure the pressure
They are designed to measure a wide range of pressures
Oil Temperature Gauge
The temperature probe for the oil temperature gauge in the oil inlet line or passage between the pressure pump and the engine system
On some installations the temperature probe is located in the oil filter housing
These are normally electric or electronic
Oil Pressure Pumps
Oil pressure pumps may either be of the gear type or vane type
The gear type pump is used in the majority of reciprocating engines and uses close fitting gears that rotate and push the oil through the system