1) – Cools
2) – Lubricates – reduces friction between moving parts.
3) – Flushing – Small particles of metal wear etc. comes out because of metal movement cause wear & by Flushing they are removed, it also decreases friction caused by them.
4) – Sealing – Seals the gap between Cylinder & Pistons.
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PISTON has following ring sets
1. Compression ring
2. Oil lubrication ring
Bottom oil ring prevents oil from leaking out.
Middle oil ring is Scraper ring & it scraps oil as it moves.
As engine becomes old, gap between Cylinder & Piston increases and therefore Oil Consumption increase, causing Oil burning and giving indication by Blue Smoke coming out of the Exhaust.
Ring Land is the Gap between Piston Rings.
Wet Sump System – There is no separate Oil tank the Engine Sump itself work as a Oil Tank.
It has only one pump which is both Pressure/Delivery pump & a Scavenge pump.
It has a by pass cooler & a by pass line to it.
Oil press & Temperature are being measured as oil is being delivered to the Engine.
Dry Sump – has a separate oil tank.
It has two pumps
1) Scavenge Pump – to prevent over flowing of Oil to the Engine.
The capacity of Scavenge Pump is more the Delivery/Pressure Pump.
2) Delivery/Pressure Pump– to deliver Oil to the Engine. It has two filters
(a) Coarse – removes big Impurities
(b) Micronesh – removes small Impurities
It has a Oil pressure Relief & a Pressure Relief valve should the Oil Pressure exceed a pre-determined value, it will open & put excess oil back to the tank.
Oil tank has 2 functions
1) It stores Additional oil for Long flights
2) It provides Oil to CSU.
(a) Coarse – removes big Impurities
(b) Micronesh – removes small Impurities
It has a Oil pressure Relief & a Pressure Relief valve should the Oil Pressure exceed a pre-determined value, it will open & put excess oil back to the tank.
Oil tank has 2 functions
1) It stores Additional oil for Long flights
2) It provides Oil to CSU.
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There is airspace in the oil tank, above the oil & tank is vented into the atmosphere.
The airspace is provided for 3 reasons –
1) To allow for expansion of oil (Oil when hot expands)
2) To remove air mixed with oil (To prevent frothing of oil).
3) To allow for Displacement of oil from Variable Pitch Propellers.
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Frothing of oil – Oil mixed with air.
Crankcase has Breather lines, should the breather lines be clogged, press in the crankcase will increase & Oil Consumption will increase.
Breather lines Equalize Pressure in Crankcase with Atmosphere Pressure.
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SPLASH SYSTEM
t is a Wet Sump System in which as Crankshaft rotates it Splashes Oil on different moving parts of the Engine causing cooling.
Viscosity of Oil governs rate of flow of Oil on different parts. Therefore Oil of correct grade must be used.
If Temperature increases Viscosity decreases & vice versa (Viscosity depends on the Temperature).
That is why Engine must be operated with in certain limit of Oil Temperature.
Oil Pressure is a Vital Parameter in a Piston engine Aircraft because it governs/shows amount of Oil going into the Engine.
Oil temperature & Pressure are interrelated. If Temperature increases pressure decrease & vice versa.
Abnormally high oil temperature indicates that oil carried in the tank is less & therefore pressure is low.
If oil pressure decreases, it may lead to engine failure if temperature is high.
If only oil pressure is low & oil temperature is normal, the reason, may be
1) Leak in the oil pressure gauge line
2) Blockage/Fault in the oil pressure gauge line
OIL HOT POT – In big A/c oil tanks have HOT POT, in which the hot oil coming from the engine is mixed with cold oil stored in the oil tank, & is re-circulated.
Oil Dilution – allowing fuel to go into oil, It is normally done in winters after the last flight of the day, since in the night when the air temperature decreases it causes oil to cool down and increases its viscosity which causes resistance to flow and does not engine parts sufficiently. Oil Dilution is done to facilitate engine start next morning and reduce resistance caused by the high viscosity of the oil to engine parts.
Fuel is of low viscosity than oil, when mixed with oil it decreases viscosity of oil as well giving easier engine start the following next day.
As engine, runs temperature increases & fuel will evaporate leaving no harmful additives.
Oil Pressure tube works on the principle of BOURDON TUBE.
It is a pressure sensitive tube, it is a current tube.
It is a current tube, & once pressure increases it becomes straight giving the pressure indication.
Oil temperature gauges work on-
(a) Bourdon tube principle
(b) Electrical
(a) Bourdon Tube is kept along with oil & it is sealed & is kept in the tank, as oil temperature increases in the case, temperature of the tube also increases & therefore pressure also increases & Bourdon Tube straightens.
(b) Electrical – Whetstone Bridge is used – temperature increases resistance decreases and this changes current flow
H2O vapor
Oil Contamination can be due to-
- O2
- H2O vapor
(a) H2O vapor – gets dissolved in oil
(b) O2 – oil running at high temperature reacts with O2 & gets oxidized, when oil is oxidized its color becomes darker & it’s viscosity decreases, for this reason oil must be changed at periodic intervals