ACA0208 lubricants and lubrication systems

lubricants primary function

reduce friction caused by metal-to-metal contact

solid lubricant

powdered form and does not dissipate heat rapidly

semisolid

greases, does not dissipate heat efficiently

liquids

dissipate heat and must be chemically stable for long periods of time

synthetic oils

acid and chemical based and non compatible with mineral or other manufacturers

Mixing of lubricants

Never mix synthetic and mineral; synthetics can be mixed but shouldn’t be mixed

Synthetic oil adv

Lower volatility

Less coking deposits

Improved chemical stability at high temps

Synthetic oil disadvantages

Very corrosive

Paint blisters/removals

Limited shelf life

current jet engine oil

MIL-L-23699

viscosity

property of fluid that resists the force tending to cause the fluid to flow

squeeze film

Ideally viscous thin film of lubricant preventing metal to metal contact

causes of Contamination of lubrication system

Metal particles

Coking

foreign objects

Oil contamination

most prevalent form of system contamination

small metal particles due to metal on metal

coking

carbon deposits formed by oil evaporation in parts where heat is concentrated

PON-6 or bowser

engine oil servicing unit

Function of lubrication system

To provide:

• Clean oil

• To necessary components

• At proper P and T (both are important)

To remove heat from engine

To contaminants at put in filters

What MUST oils be at for lubrication to be effective/prevent engine seizures/fires?

Proper pressure and temperature

wet sump system

reservoir is the accessory case or a sump mounted to the bottom of the gear case; oil reservoir is in the engine

Wet sump disadv

• Hard to cool oil

• Oil limited (res is smaller)

• Cannot adapt to unusual flight attitudes

disadv of wet sump

oil supply is limited, hard to cool the oil, system not adaptable to unusual flight altitudes for extended period of time

dry sump system

oil supply is carried in a tank located in the airframe or mounted on the engine; oil tank external to engine

three subsystems of a dry sump system

pressure subsystem

scavenge

breather pressurizing

pressure subsystem

supplies pressurized oil from the tank to the main engine and the accessory gear box/drive

scavenge subsystem

removes the oil from the main bearings and accessory drives, circulates through the oil coolers, and returns it to the tanks

breather pressurizing subsystem

uses compressor bleed air to pressurize the oil tank and engine bearing compartments; mins oil leakage + ensures proper spray patters

oil tank

Reservoir. SHAFT

Designed to supply constant oil at any attitude

Weighted swivel assembly

gravity ensures the weighted pick up end is constantly immersed in the oil supply

oil pump

supplies oil under pressure to engine parts; has one or both of pressure component and scavenge component

Scavenge oil pump

Greater capacity than pressure pump; prevents back pressure &/or accumulation of oil in sump cavities

Instruments in lubrication system

oil pressure gauge and oil temperature gauge

OPG - indicates pump discharge pressure

OTG - indicates temp of oil entering engine bearings

Oils systems have filters and thus

Bypass valve

oil pressure relief valve

In the pressure substrate; limits max pressure (relieves pressure) by bypassing oil back to the pump inlet (not reservoir) as needed

Scavenge subsystem

Removed oil from main engine bearing components and accessory drives, circulates the oil through coolers, then sends it back to tank

magnetic-chip detector

in the scavenged oil path

oil coolers

Scavenge system; reduces the temperature of the oil for re-circulation through the system

air-oil cooler

radiator type device

normally installed at the engine inlet

uses ambient/outside air

Regulates when outside air is allowed to pass

fuel-oil cooler/heat exchanger

cool hot oil taken from the bearings and preheat the fuel for combustion; bypasses already cold enough oil

oil temperature regulating valve

directs the flow of return oil into the fuel-oil heat exchanger, if necessary

Fuel temperature sensing switch

Located at the exit of the fuel-oil heat exchanger; activated air-oil cooler if fuel is too hot (which means oil is too hot)

2 functions of the breather pressurizing subsystem

• minimizes internal oil leakage by encasing the oil sumps with pressurized air

• ensure proper spray patterns of oil across the bearing by mixing pressurized air with the oil to form a fine oil mist

pressurization in the breather pressurizing subsystem is provided by the

compressor bleed air

Anaroid

Valve opens at seas level and closes as altitude rises — traps 29.92 pressure

Blow off valve

Opens if pressure is exceeds set limit