CHAPTER 4

Components of a Jet Engine

be introduced to a complete jet engine from the

viewpoint of its major components, minus such

systems and units as the oil, fuel, electrical, and

afterburner systems. These systems are to be

covered in this course under the volume reserved

for jet engine accessories. If you should completely

break the jet engine down into its many small

components, you would find it very complex.

Therefore, we will try to treat this engine from

a practical viewpoint only so that you will under-

stand the general function of the major sections

of the engine and the relationship of these sections

to each other.

13.

General Engine Information

The J—57 engine was designed and manufac-

tured by the Pratt and Whitney Aircraft Company

which sublets some of the manufacturing to the

Ford Motor Company in order to get the required

number of engines manufactured. The engine is

used in many aircraft today, some of which are

the B—52, F—100, F—101. and the F—102. The

engine is an axial-flow, continuous-thrust engine.

It weighs about 4,100 pounds, less the accessories.

Without an afterburner, the engine is about 13

feet long and has a diameter of 40.5 inches. The

engine’s overall fuel-air ratio is 15 pounds of air

to 1 pound of fuel used. The engine uses a dual,

two-speed, tandem-mounted compressor, a “can-

anu1ar” combustion chamber, and a split three-

stage reaction turbine. Figure 22 shows a detailed

cutaway view of the engine with many of the

internal and external components identified. In

order that you may study the engine from an

external view and see the parts that have been

cut away in figure 22, see figure 23.

14.

The Primary Internal Components

This section, comprising as it does an overview

of the engine’s internal components, should give

you the working relationship and location of the

components, and thus prepare you for the more

detailed discussion of these components later in

the chapter. You will find it to your advantage

to study carefully figure 24 as you peruse this

section.

The N1 Compressor. The forward compressor

is the low-speed, low-pressure compressor called

the N1 compressor, which has nine stages of

compression. It is connected to the Nr. 2 and

the Nr. 3 turbine wheels by a shaft running inside

the first-stage turbine shaft and the second com-

pressor. The speed of the N1 compressor is not

governed directly and varies according to the load

applied to it by the density (pressure, temperature,

and humidity) of the incoming air in relationship

to the energy of the exhaust gases. This com-

pressor supplies air to the aft (high-pressure)

compressor, called the N2.

The N1 can overload the N2 compressor during

certain engine operating conditions. A bleed sys-

tem is incorporated to bleed off approximately 10

percent of the N1 compressor discharge air. This

reduction of airflow to the aft compressor prevents

compressor stall or surge and provides a better

acceleration rate.

The N9 Compressor. The aft compressor (N2)

is the high-speed, high-pressure compressor, which

has seven stages of compression, making a total

of sixteen compression stages in the engine. The

N2 is driven by the first-stage turbine wheel by

27

 

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