The internal cooling system cools internal components and ensures extended engine service.
A combination of several passages throughout the engine receives air from the main air-flow channel
and directs it to cool components located within heat-generating areas. The exits from the cooling
passages conduct the heated air to the main exhaust gas flow.
Some of the cooling air is extracted for bearing seal pressurization. This internal airflow is
guided to the appropriate bearing seal to protect against oil seepage while the engine is in operation.
The engine inlet is protected from ice forming on it by the anti-icing system. The walls and
struts of the inlet housing have internal passages through which hot, scavenged engine oil circulates.
The variable inlet guide vanes are supplied with hot air which is extracted from the centrifugal
compressor. The engine hot-air anti-icing system is shown in the schematic in figure 5.16.
This air first passes through a hot-air valve and is distributed by a tube which directs the air
into an annulus (circular structure) around the inlet-guide vane assembly. The anti-icing air is routed
through the stem of the vanes and is discharged at the base of the leading edge into the main airflow.
VARIABLE INLET GUIDE VANE SYSTEM
The inlet guide vane assembly, located in front of the first compressor rotor, consists of a
series of hollow blades positioned mechanically by a hydraulically operated synchronizing ring. The
guide vane control system schedules the positions of the variable inlet guide vanes in response to gas
producer speed and compressor inlet temperature. At low N1 speeds, a high angle of inlet air is required,
and the inlet guide vanes are in the closed position of approximately 45.5 of the engine centerline.
Guide vane positions are illustrated in figure 5.17.