Chapter 3 - Engine Systems Flashcards
What is the purpose of an engine oil system?
To lubricate and cool the main bearings and other load bearing parts of an engine.
What are the nine uses of oil in an aircraft?
Reduce friction
Reduce wear
Cleaning
Minimise corrosion
Cooling
Heating (oil to fuel heat exchange)
Hydraulic fluid
Chip detection
Engine status (oil Ts and Ps, torque)
What does fluid effectiveness as a lubricant depend on?
The viscosity of the fluid
What can friction between two surfaces cause?
Intense heat may be generated at points of contact, however small, and this can lead to localised welding. Subsequent damage is then caused when the two surfaces are torn apart.
Intense heat can also cause expansion and deformation of an entire surface/part, or even melting in extreme cases.
What are the two basic phases of lubrication?
Hydrodynamic (fluid film) lubrication
Boundary lubrication
What is Hydrodynamic (Film) lubrication?
Layer of oil between two surfaces is relatively thick
Keeps the two surfaces apart
Amount of friction generated is very small
What is Boundary lubrication?
Layer of oil between two surfaces is very THIN
Caused by high bearing loads, inadequate viscosity, oil starvation or loss of oil pressure
Thin oil film can rupture, which can increase wear, temperature and then lead to failure
Often occurs during starting conditions
Not a desirable phase
What is Mixed lubrication?
In practice, both Hydrodynamic (film) and Boundary lubrication phases occur at some time, giving mixed film lubrication.
Has qualities of both hydrodynamic and boundary lubrication regimes.
Generated lubricant film is not enough to separate the body completely, but hydrodynamic effects are present.
What is the Viscosity Index (VI) of a fluid?
An empirical measure of its change of viscosity with temperature.
Oil with a high VI preferable to one with a low VI.
What are the components of an engine oil system?
Oil tank
Oil pump
Filter assembly
Oil cooler
Monitoring instruments
Magnetic chip detectors
What oil pumps are present in an engine oil system?
Pressure Pump
Scavenger Pumps
Why is sump venting required?
Some air is returned to the sump by the scavenger pumps due to air leakage into the bearing housing. need to get rid of it.
What can be found in the oil filter assembly?
Filter
Bypass (in case filter blocks)
Blockage indicator
Non Return Valve (NRV) - Stops fuel flowing the wrong way back through the filters.
How does the bypass filter work in an oil filter assembly?
Opens when it detects a differential pressure across the filter.
Sends an indication to the cockpit.
What types of oil cooler may be found on aircraft?
Air-cooled = Fine for turboprop but impractical at high speeds due to drag
Fuel-cooled
LEARN + BE ABLE TO LABEL THE DIAGRAM IN THE COURSE MANUAL
Look at now
What is the purpose of magnetic chip detectors in an engine oil system?
Collect ferrous debris from the bearing chamber that can be analysed to monitor bearing performance and assess engine life.
What are the components of an Engine Fuel System?
Low Pressure (LP) cock
Fuel cooled oil cooler (FCOC)
Fuel filter
High Pressure (HP) fuel pump
Throttle valve
Fuel Control Unit
HP Shut-off valve
What is the LP fuel cock the boundary between?
The airframe fuel and the engine fuel
Final component in the airframe system
What is the primary function of the Fuel Cooled Oil Cooler (FCOC)?
Remove heat from the engine oil
What are the secondary functions of the Fuel Cooled Oil Cooler (FCOC)?
Heat the fuel
Removes ice crystals
Increases volatility (of fuel) for more efficient fuel ignition
Note - Turboprops use an air-cooled oil cooler instead as they fly at lower speeds so the drag penalty incurred is not too major
What is the purpose of the High Pressure (HP) fuel pump?
Driven by the engine
Provides a sufficient supply of fuel for engine operation
Raises the pressure of the fuel received from the aircraft fuel system to a level where efficient burner operation is possible
What is the purpose of a Fuel Control Unit (aka fuel control Valve)?
Modulates the pilot’s movement of the throttle to prevent the engine being overstressed/damaged fi handled poorly.
Controlled by the Engine Control Unit, which receives info from sensors within the engine.
What is the role of the HP shut-off valve?
Shuts off fuel to the engine burners
Note - Look in manual and learn diagram for engine fuel system + be able to label.
Look now
What device attracts ferrous debris in an engine oil system?
Magnetic chip detector
What provides oil pressure throughout the system?
Oil pumps
Would you put an oil cooling device in the low pressure or high pressure system?
In the LP system
Means the cooler does not need reinforcing (bigger + heavier) to withstand the pressure of the HP fuel
Note - Learn + be able to label and distinguish between the HP and LP systems and all their parts.
Look in manual now + learn
What is the purpose of oil pumps?
Create pressure and therefore flow to pump the oil through the oil system (LP or HP??)
