TM 5-6115-434-12
(1)
Pneumatic and shaft power gas turbine engine (fig. 1-3). The gas turbine engine is a self-contained power
source and requires only a fuel supply and electrical starting power to maintain a constant output power and rpm
(revolutions per minute). Engine power is developed through compression of ambient air by a two-stage centrifugal
compressor; the compressed air, mixed with fuel and ignited, drives a radial inward-flow turbine wheel. The rotating
shaft power of the turbine wheel drives the compressor, the accessories, and the output drive shafts. A portion of the
compressed air developed by the compressor is available for external pneumatic power applications. An internal system
of pneumatic and electro-mechanical controls provide automatic and coordinated control of engine starts, acceleration,
and operation. A minimum of additional external controls are required to initiate the engine starting cycle, monitor engine
operation, and to stop engine operation. The gas turbine engine consists of a compressor and turbine section, accessory
drive section, fuel control system, bleed-air control system, engine electrical system, and engine lubrication system.
(a)
Compressor and turbine section. The compressor and turbine section is the power nucleus of the
engine. The two stage centrifugal compressor develops compressed air for fuel combustion and for external pneumatic
power. The single stage turbine incorporates a single combustion chamber which mixes compressed air with the fuel
spray from the fuel atomizer, ignites the full-air mixture and directs the products of combustion to the turbine wheel. The
turbine wheel converts the power developed in the combustion chamber to shaft power which drives the compressor
impellers and the accessory drive section.
(b)
Accessory drive section. The accessory drive section is a reduction gear system which reduces the
high rotational speeds developed by the turbine wheel to a usable rpm to drive the engine accessory and a dual pad gear
box for the 60 Hz and 400 Hz generators. In addition to mounting pads for the two generators, the accessory drive
section provides mounting pads and drive gear connection for the following engine accessories: Oil pump assembly; fuel
control unit; centrifugal switch assembly; cooling air fan; starter motor; and tachometer-generator.
(c)
Fuel system (fig. 1-4). The engine fuel system consists of components which function automatically
to regulate fuel flow to the combustion chamber and maintain near constant governed speed and safe operating
temperatures under varying conditions of starting, acceleration, and load application. Control components function by
sensing engine speed, turbine exhaust gas temperature and compressor air pressure and react by adjusting fuel flow to
maintain these reference indications within established limits. The fuel system consists of the following components
together with interconnecting lines and fittings: a one gallon fuel tank for fuel reserve during changeover from one
external fuel supply to another; a fuel boost pump to assure a constant inlet pressure to the fuel control unit; a fuel filter
assembly to filter fuel between the fuel boost pump and fuel control unit; a fuel control unit to regulate fuel flow to the
combustion chamber in response to engine rpm and load requirements; a fuel shutoff solenoid valve to provide
electrically actuated on and off control of fuel flow between fuel control unit and fuel atomizer assembly; a fuel atomizer
assembly to provide a controlled fuel spray pattern for proper fuel combustion; an acceleration and over temperature
control thermostat to prevent excessive exhaust gas temperatures during engine acceleration.
(d)
Bleed-air control system (fig. 1-4). The bleed-air control system automatically limits the amount of
compressed air available for external applications thus maintaining a safe engine operating temperature and preventing
an overload condition due to excessive demands for shaft power and pneumatic power. Automatic limiting of bleed-air is
accomplished by a pneumatic thermostat installed in the turbine exhaust that opens at a preset exhaust gas temperature
and bleeds control air from the load control valve thus causing the load control valve to modulate and reduce
1-4
