Lubrication And Cooling Systems Flashcards
Three main functions of an engine oil system.
- Lubrication: avoid metal to metal contact by creating a protective film, reducing the components wear.
- Cooling: Circulates throughout the engine absorbing heat.
- Cleaning: Picks up debris and removed through the oil filter.
What is the wet sump system?
In a wet sump system, the engine oil is stored in a sump at the bottom of the engine.
- Directly collects oil as it drains.
- Simpler and lighter than dry sump systems - found in smaller, less complex engines
What is a dry sump system?
The engine oil is stored in an external oil tank separate from the engine.
Once the oil is drained to the bottom of the engine, a scavenger pump collects the oil and returns it to the external tank, keep a relatively dry sump.
A pressure pump draws oil from the external oil tanks, send it through an oil filter and distributes it to the necessary engine components for lubrication, cooling and cleaning.
Usually found on high performance engines or in aerobatic aircraft.
Explain the engine-driven oil pump.
- Circulates oil
- Mechanically driven through gears or a belt
- Pressure relief valve = safety device that maintains a consistent oil pressure within the system
Explain oil lines, passages and galleries.
- Oil lines are hoses or pipes that transport oil from the pump to the various engine components and back to the sump or oil tank.
- Galleries = larger channels or reservoirs designed to distribute and collect oil as needed.
Explain oil sumps and scavenge pumps/
Oil sumps = containers at the bottom of the engine that collect and store oil after it has circulated.
Scavenge pumps = used in dry pump systems to remove oil from the engine sump and return it to the external oil tank. Help maintain consistent oil pressure and flow.
What is an oil cooler?
Heat exchanger designed to dissipate excess heat from the engine oil.
Uses airflow or coolant to remove excess hear, helping maintain the oil’s optimal operating temperature and viscosity.
Explain the oil tank and filter.
Oil tank = reservoir that stores oil in dry sump systems. Supplies oil to the pressure pump and receives oil returned by the scavenge pump.
Oil filter = removes contaminants from oil before it is distributed to the engine components.
Explain ashless dispersant oils?
Composition = refined mineral oils and contain ashless dispersant additives that help disperse contaminants.
Lubrication = provides superior lubrication and protection (due to dispersant additives)
Contaminant management = additives prevent contaminants from forming deposits on engine components.
Compatibility = compatible with most aero-engine materials and seals
Usage = commonly used in modern piston aircraft
Explain straight mineral oils.
Composition: refined base oils without any additives.
Lubrication: provides adequate lubrication
Contaminant management: do not actively prevent deposit formation or disperse contaminant within the oil.
Compatibility: compatible with most aero-engine materials and seals.
Usage: used during the break-in period of new or freshly overhauled piston aero engines, as their lack of additives allows for controlled wear and proper seating of engine components.
Explain detergent oils.
Composition: made form mineral oils without base stocks and contain detergent additives that help clean and neutralise acidic contaminants within the engine.
Lubrication: good lubrication and engine protection, although not as effective as AD oil in dispersing contaminants.
Contaminant management: detergent additives help clean engine components and neutralise acidic contaminants. May produce ash residues when burned, can contribute to deposit formation.
Compatibility: may not be compatible with all aero-engines materials and seals, especially in older engines.
Usage: less common in modern piston engines.
What oil offers superior lubrication?
AD oils
What is oil grade used for?
To specify the viscosity and performance characteristics of the oil.
E.g. SAE 40
What is the “commercial aviation number” in oil grading?
Double the SAE number.
What is the effect of lower temperature on oil?
- Oil becomes thicker
- More viscous
- Less efficient
What is the effect of higher temperature on oil?
- Oil becomes thinner
- Less viscous
- Improves flow and distribution
- Reduces oil’s ability to maintain a protective lubricating film between moving parts
What is the need for periodic oil changes?
- Maintaining health and longevity of the engine.
- Accumulates contaminants from the engine
- Looses effectiveness over time
What are the problems with the incorrect type of oil?
- Inadequate lubrication
- Damage to engine seals and gaskets
- Reduced performance
- Additive compatibility issues
Problems with incorrect oil quantity?
Low = inadequate lubrication, increased friction, wear, overheating, premature component failure, engine seizure, degrades more quickly due to increased workload.
High = can foam, reducing oil’s lubricating properties, increased wear, overheating, higher pressure in crankcase, oil leaks, blowing out seals and gasket. Can be forced into the combustion chamber, increased oil consumption, carbon build up, potential damage to spark plugs, catalytic converters, and other components.
Explain low oil pressure.
Could be due to:
- Oil leaks
- Inappropriate amount of oil filled
Oil pressure will reduce, if the engine runs out of oil, it will seize.
Explain high oil pressure
Most likely the result of a faulty oil pressure relieve valve.
can cause seals and junctions to fail, resulting in a loss of oil and possibly then engine failure.
Explain high oil temperature.
Resultant of prolonged high-power operation or while holding on the ground where the cooling airflow is minimum.
To reduce the temperature:
- Open cowl flats if fitted
- Reduced throttle settings
- Increase the airflow
Why does a piston engine need to be cooled?
To control and reduce the temperatures of the cylinder heads. If temperature increases too much, detonation can occur.
Improves the thermal efficiency, which reduces fuel consumption, increases engine life and increases effectiveness of the lubrication system.
Reasons to avoid rapid cooling and high engine temperature.
Rapid cooling - can cause “shock cooling”, leading to cracked cylinder heads, engine blocks and the engine agin at a faster rate. Can also cause spark plugs fouling.
High engine temperature - overheating can lead to detonation, reduced thermal efficiency, reduced engine life and effectiveness of the lubrication system.
Ways to cool an engine.
- Air - main method
- Water
- Through the exhaust - most heat is dissipated
- Oil cooler
- Cooling fins
- Ducts and baffles
- Cowl flaps
- Radiators
- Intercoolers
Cowl flaps
- Bottom of the engine cowling
- Cools engine by opening the flap to allow more air to flow through the engine compartment
- Most effective at high speeds
Radiator
- Cools engine by dispersing heat
- Engine’s coolant absorbs heat from the engine and then passes it through the radiator where it gets cooled down.
- Commonly used in diesel engine aircraft
Intercooler
- AKA “aftercoolers”
- Cools down the intake air after being compressed by a supercharger or turbocharger
- Can only be found in a supercharged or turbocharged engine
Cylinder head temperature (CHT)
- Fitted to show engine temperature at the cylinder head.
- Can be used when leaning the mixture.
What is good practice to avoid?
- Running the engine on the ground for long periods at high power settings.
- Running the engine on the ground for long periods at low power settings where little cooling airflow is.
- Prolonged climb at full/high power settings and low airspeed.
- Prolonged descent with the throttle closed
