Lubrication System in Gas Turbine Engines

In gas turbine engines, the lubrication system directs oil to the sump and gear box to cool rotating components, reduce friction, prevent corrosion, and collect worn metal particles via filtration. The system then draws up the accumulated oil for reuse.

The lubrication system in gas turbine engines consists of three subsystems: pressure system, scavenge (return) system, and vent system.

1) Pressure System

The main components of the pressure system are the oil tank, pressure pump, pressure regulating valve, oil filter, filter bypass valve, final chance filters, and oil jets.

The oil stored in the tank is delivered through the pressure pump and filter to the bearings supporting the engine shaft and to the gear box.

The pressure system is divided into two types: full-flow and pressure-regulated. In pressure-regulated systems, oil is supplied to the engine at a constant pressure and flow rate. In full-flow systems, the oil flow rate and pressure vary with the engine’s RPM.

In some gas turbine engines, a fuel-oil heat exchanger is installed in the pressure line, allowing oil to be stored in the tank at elevated temperatures. This lubrication system configuration is known as a hot tank.

2) Scavenge (Return) System

The main components of the scavenge system are the scavenge pump, magnetic chip detectors, filters, and the fuel-oil heat exchanger.

The oil-air mixture from the engine bearings and gear box is drawn by scavenge pumps. Metal particles suspended in the oil are captured by magnetic chip detectors and filters. The oil-air mixture passing through the scavenge pumps enters the fuel-oil heat exchanger, where heat is transferred from the oil to the fuel. The cooled oil-air mixture is then directed to a deaerator located within the tank, which separates the air from the oil.

In some engines, the oil is stored cold in the tank. This configuration, where the heat exchanger is part of the scavenge system, is known as a cold tank.

3) Vent System

The vent system equalizes pressure in the sump and releases air entering the sump to the atmosphere.

In gas turbine engines, the enclosed space surrounding the bearings is referred to as the sump. Sealing elements are used between moving and stationary components within the sump. To prevent oil from leaking past these seals, the sump is pressurized with external air. This pressurized air enters the sump through the seals, maintaining internal pressure and retaining the oil inside.

In some engine bearing assemblies, no vent system is present, and air entering the sump is routed directly to the tank via the scavenge pumps.

The oil-air mixture sent to the tank by the scavenge pumps pressurizes the tank. The accumulated air in the tank is expelled through the tank vent line.

Both the sump and tank vent lines contain oil vapor along with air. Directly releasing the air-oil vapor mixture to the atmosphere would result in oil loss. Therefore, before discharge to the atmosphere, the air-oil vapor mixture passes through centrifugal air-oil separators called deoilers. The deoilers recover oil vapor from the vent air and return it to the system, while releasing the cleaned air to the atmosphere.