Although the gas turbine engine differs radically in
construction from the conventional fourstroke, fiveevent cycle
reciprocating engine, both involve the same basic principle of
operation. In the piston (reciprocating) engine, the functions of
intake, compression, ignition, combustion, and exhaust all take place
in the same cylinder and, therefore, each must completely occupy the
chamber during its respective part of the combustion cycle. In the
gas turbine engine, a separate section is devoted to each function,
and all functions are performed at the same time without interruption.
1.6.
SUMMARY
The theory of gas turbine engine operation is based on the
laws or principles of physics. The principle of jet propulsion can
be illustrated by a toy balloon. When the balloon is inflated and
the stem is unsealed the balloon will move in a direction away from
the escaping jet of air. If the balloon is converted into a length
of pipe, and at the forward end an air compressor is installed to
supply air for combustion, and to expand the volume of air, fuel and
ignition are introduced and combustion takes place. Then, in the
path of the expanding gases a turbine rotor is installed. As the
gases pass through the turbine blades, the turbine rotor is rotated
at high speed. This turbine rotor is connected to the compressor
shaft, and we now have a means to rotate the compressor to replenish
the air supply. The remaining gases are discharged to the
atmosphere. The reaction of these gases is thrust, or movement of
the tube away from the escaping gases. This is a simple turbojet
engine. At present the Army has no requirement for this highspeed,
highaltitude powerplant. However, if we install another turbine
rotor after the rotor that drives the compressor, we have a
turboshaft engine that can be used to drive a transmission in a
helicopter or a propeller on a fixedwing aircraft.
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