The labyrinth/honeycomb seal combines a
The gear train of the accessory drive is driven
by the engine rotor through an accessory drive
rotating seal having a serrated surface with a
stationary seal having a honeycomb surface. The
shaft coupling. The reduction gearing within the
case provides suitable drive speeds for each engine
serrations cut into the honeycomb to maintain
accessory or component. Because the operating
close tolerances over a large temperature range.
The fishmouth seals are sheet metal, circular,
rpm of the rotor is so high, the accessory
reduction gear ratios are relatively high. The
stationary, interlocking seals used to prevent
accessory drives are supported by ball bearings
excessive leakage of hot combustion gas from the
assembled in the mounting bores of the accessory
primary airflow.
case.
Accessories provided in the accessory drive
FUEL OIL SYSTEM
section include the fuel control, with its
governing device; the HP fuel oil pump or pumps;
The fuel oil system has a number of functions.
the oil sump; the oil pressure and scavenging
Primarily, it provides filtered, pressurized, and
pump or pumps; the auxiliary fuel pump; and a
accurately metered fuel for combustion. While
starter. Additional accessories, which may be
doing this, it controls the power output of the GG,
which in turn determines the amount of power
included in the accessory drive section or which
may be provided elsewhere, include a starting fuel
delivered by the engine from the PT. Additionally,
pump, a hydraulic oil pump, a generator, an air-
the fuel system may provide pressurized fuel as
oil separator, and a tachometer. Most of these
a hydraulic medium to actuate the fuel controls.
In some engines it controls the angle of the
accessories are essential for the operation and
control of any GTE. The particular combination
variable compressor stator vanes.
and arrangement and location of engine-driven
All fuel systems are not alike, but they all
accessories depend on the use for which the GTE
have certain elements in common. For example,
is designed.
they must have a fuel pump, a fuel control, a
The three common locations for the accessory
pressurizing valve or its equivalent, a fuel
drive section are on the side of the air inlet
manifold, and fuel nozzles or vaporizers. The
housing, under the compressor front frame, or
fuel pump capacity is great enough to perform
under the compressor rear frame. One manu-
any required hydraulic functions in addition to
facturer of a generator engine used by the
providing combustion fuel. Excess fuel is bypassed
U.S. Navy had the reduction gear attached to the
in the fuel control and returned to the LP side
forward end of the compressor and the accessories
of the pump. Pressure in excess of the capability
mounted to the reduction gear.
of this bypass is dumped by a relief valve in the
pump assembly. The fuel pump and fuel control
LUBRICATION SYSTEM
are usually assembled together and mounted on
the gearbox.
The GTE lubrication system is designed to
ACCESSORY DRIVE SYSTEM
the desired pressures and temperatures. In some
installations, the lubrication system also furnishes
A popular misconception exists that the GTE
oil to various hydraulic systems. Heat absorbed
has only one moving part because the turbine and
by the lube oil is transferred to the cooling
the compressor are on the same rotating shaft.
medium in a lube oil cooler.
This is not true. A GTE requires a starting device
The lubrication system shown in figure 1-35
(which is usually a moving part), some kind of
is the dry-sump type, with a common oil supply
control mechanism, and power takeoffs to drive
from an externally mounted oil tank. The system
other components, such as the lube oil and fuel
includes the oil tank, the lube oil pressure pump,
pumps. The accessory drive section of the GTE
takes care of these various accessory functions.
the scavenging pumps, the oil cooler, oil filters,
the pressure-regulating valve, and filter and cooler
The primary function of the accessory drive
bypass valves.
section is to provide space for the mounting of
All bearings and gears in the engine and
the accessories required for the operation and
accessory drives are lubricated and cooled by the
control of the engine. The accessory drive section
lubrication system. The lube oil supplied to each
also serves as an oil reservoir and/or sump and
bearing in a GTE is specifically controlled by a
houses the accessory drive gears and reduction
calibrated orifice which provides the proper flow
gears.
1-28
