Jet Propulsion

Oil

What is oil used for?

• Lubrication.

There are two basic classifications of turbine engine lubrication systems. These are:

• Wet-sump• Dry-sump

Front Bearing

Chamber

Centre Bearing

Chamber

Rear Bearing

Chamber

Roller Bearing

Ball Bearing (Location Bearing)

Roller Bearing

Wet-Sump

• The wet-sump lubrication system was used in some early jet engines. But today only on the smaller engines such as auxiliary power units (APU) are designed with a wet-sump system.

• In a wet-sump system, pressurized oil is used to lubricate the bearings and gears.

• This oil is carried in the gear housing that serves as the oil reservoir.

• Oil that has lubricated the bearings and gears drains by gravity and is collected and directed back to the gear housing, where it is stored until it re circulates through the system.

Dry-Sump

• The oil, after serving its lubrication and cooling functions, is returned by scavenger pumps to a tank outside of the engine.

• There are two types of dry-sump lubrication systems:

• Hot-tank system• Cold-tank system

Hot-Tank System

• In a hot-tank lubrication system, the oil cooler is in the pressure systems and the scavenged oil is not cooled before it is returned to the tank.

• In the lubrication system the oil is carried in the oil tank and flows by gravity to the main pressure pump.

• From there, the pressurized oil flows through the filter and through the oil cooler, to the bearings.

• When the oil temperature is low, the temperature bypass valve is open and the oil flows directly to the bearings.

• When the temperature is high enough to require cooling, the valve restricts the flow of oil and forces it through the cooler.

• After leaving the oil cooler, the oil flows to jets which spray the oil into the bearings.

• The oil drains from the bearings and is collected by scavenger pumps and returned to the oil tank.

Cold-Tank System

• The cold-tank system is the same as the hot-tank system, except for the placement of the oil cooler and the temperature bypass and cooler bypass valves.

• The oil flows directly from the pressure pump through the main filter to the bearings.

• From the bearings, it drains down and is collected and returned to the oil tank by the scavenger pumps.

• If the oil is cool enough, it returns to the tank through the temperature bypass valve.

• If it is too hot, this valve closes, forcing the oil to flow through the cooler where it gives up the excess heat.