closed cycle has been called the "natural" cycle
for the GTE because it allows use of any fuel,
including nuclear, as an energy source. The typical
ship's steam plant is an example of a closed cycle
system.
BASIC GTE OPERATION THEORY
The following is a description of a practical
demonstration of how a GTE operates. Refer to
figure 1-7 as you read the description.
A balloon full of air (view A) does nothing
unless the trapped air is released. When the air
Figure 1-6.--The Brayton cycle.
is released, it escapes rearward, causing the
balloon to move forward (Newton's third law)
Expansion --The gases at constant pressure
(view B).
and increased volume enter the turbine and
expand through it. As the gases pass through the
If you could devise a way to keep the balloon
constantly full of air, it would continue to move
turbine rotor, the rotor turns kinetic energy into
mechanical energy. The expanding size of the
forward (view C) as long as the air is allowed to
passages causes further increase in volume and a
escape from it.
sharp decrease in pressure and temperature (line
If you place a fan or pinwheel in the
C-D).
escaping airstream, the pressure energy and
Exhaust--The gases are released through
velocity energy will cause the fan to rotate.
the stack with a large drop in volume and at
Then you can use the escaping air to do work
(view D).
constant pressure (line D-A).
Now, if you replace the balloon with a firmly
The cycle is continuous and repetitive in a
GTE. The functions occur simultaneously through-
mounted tube or container and keep it filled with
out the system.
air from a fan located in the air opening and
driven by an external source, you could use the
discharge air to turn a fan at the rear to do work
(view E).
OPEN, SEMICLOSED, AND
CLOSED CYCLES
If you add fuel and allow combustion to
Most internal-combustion engines operate on
occur (view F), the volume of air and the velocity
with which it passes over the exhaust fan are
an open engine cycle. This means the working
fluid is taken in, used, and discarded. The GTEs
greatly increased (Charles's law). The horsepower
the fan will produce is also increased. The
you will encounter in the Navy operate on the
open cycle. In the open cycle all the working fluid
continuous pressure created by the inlet fan, or
passes through the engine only once. The open
compressor, prevents the hot gases from going
cycle offers the advantages of simplicity and light
forward.
weight.
Now, if you attach a shaft to the compressor
Some GTEs operate on a semiclosed cycle.
and extend it back to a turbine wheel, you have
They use a regenerator, such as used on the John
a simple GTE (view G). It can supply power to
Sergeant. The regenerator simply transfers the
run its own compressor and still provide enough
heat from the turbine exhaust gas to the
power to do useful work. It could drive a
compressor discharge gas before that gas has
generator or propel a ship.
energy externally supplied (ahead of the
combustor).
By comparing view H with view G, you can
The third classification of cycles is the closed
see that a GTE is very similar to the balloon
cycle, in which energy is added externally. The
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