Engines 8: Lubricants and Lubrications System Flashcards
What is the purpose of lubricants?
To reduce friction from metal to metal contact
What is the purpose of a lubrication system?
To provide an adequate supply of clean oil to bearings and gears at the proper temperature and pressure.
- Provide clean oil to components at proper temperature and pressure
- Remove heat from engine
- Remove contaminants
Why do gas turbine engines use synthetic oil?
It is better suited for higher temperatures
What are the advantages of synthetic oils?
- High stability at high temperatures
- Less coke deposits
What are the disadvantages of synthetic oils?
- Very corrosive
- A short shelf life of 3 years
Viscosity
The property of a fluid that resists the force tending to cause the fluid flow
Resistane to flow
What is the relationship between temperature and viscosity?
Inverse relationship; as temperature increases, viscosity decrease.
What are the different types of oil contamination?
- Metallic particles
- Corking (carbon deposits)
- Sand and dirt
What are the types of different lubrication systems?
Wet sump lubrication system
Dry sump lubrication system
What is the difference between a wet sump system and a dry sump system?
A wet sump system has its reservoir stored internally in the engine and a dry sump system has its reservoir stored externally from the engine
What are the disadvantages of a wet sump system?
- Oil supply is limited by sump capacity
- Harder to cool the oil
- Non adaptable to unusual attitudes
What are the advantages of a dry sump system?
- Temperature/viscosity can be better controlled
- Can carry a larger oil supply
What are the three subsystems of a dry sump system?
Pressure subsystem
Scavenge subsystem
Breather pressurizing subsystem
What is the purpose of the pressure subsystem?
Supplies oil under pressure to the engine main bearings and accessory drive gear
What is the purpose of the scavenge subsystem?
To return oil from the bearings and accessory section to the oil tank and to provide cooling for the oil
What is the purpose of the breather pressurizing system?
- Minimizes oil leaks
- Ensure proper spray patterns
This is done by ensuring that sea level pressure is maintained in the oil tank and engine bearing compartments
How does the pressure subsystem work?
An engine driven pump receives oil from the oil tank and sends it through an oil filter. After the oil filter, the oil travels to the pressure relief valve. After the relief valve, the oil travels through tubing to lubricate the engine bearings and accessory gear box by being sprayed out of nozzles in the engine
Oil Pressure Gauge
Displays oil pump discharge pressure
Indicates if a pump is working normally
Oil Temperature Gauge
Displays temperature of oil prior to entering the engine bearings
Indicates scavenge system performance
Oil Pressure Relief Valve
Limits the max pressure within the system
(Preset to relieve pressure by bypassing oil back to the inlet pump whenever pressure exceeds a safe limit)
What is the purpose of the oil coolers in the scavenge system?
To reduce the temperature of the oil so it can be recirculated throughout the system
What are the two types of oil coolers?
Air-oil coolers
Fuel-oil coolers
How does an air-oil cooler work?
Uses ambient air, passing through its fins, to cool the oil
How does an fuel-oil cooler/heat exchanger work?
Oil enters an inlet port, flows around the fuel lines, and goes out the outlet port
How does oil bypass the fuel-oil cooler/heat exchanger if cooling is not needed?
Through the oil temperature regulating valve
Oil Temperature Regulating Valve
Directs the flow of return oil into the fuel-oil cooler to allow cooling
Fuel Temperature Sensing Switch
A switch located at the fuel exit of the fuel-oil cooler. The switch sends a signal to the air-cooler to open the doors to allow air to pass through when the fuel temperature gets too hot.
