The document provides an overview of jet propulsion concepts, including the functions of various engine components like compressors and turbines. It explains the principles of airflow, combustion types, and the role of elements such as afterburners and reverse thrust for improved performance. Key topics include the differences between centrifugal and axial flow compressors, as well as the behavior of air pressure and temperature through the engine process.

1. Jet Propulsion

2. Recap Quiz
• What does the compressor do?
• What is the difference between Rotor Blades and
Stator Blades?
• How is the Turbine driven?
• Name the 3 types of Combustion Chambers?
• Briefly explain what happens to the temperature
and pressure as the air goes through the engine?
• Name 2 different types of jet engines?
• What is a Compressor Surge and how is it solved?

3. • What does the compressor do?
The function of the compressor in a jet engine is to
increase the pressure of airflow through the
engine.
• What is the difference between Rotor Blades
and Stator Blades?
Rotor blades push the air back to the Stator blades.
These then compress the air increasing its
pressure.
• How is the Compressor driven?
By the Turbine

4. • Name the 3 types of Combustion Chambers?
Can, Cannular and Annular.
• Briefly explain what happens to the temperature and
pressure as the air goes through the engine
Pressure: As the air goes through the compressors, it
increases. Once it is ignited, the pressure drops and
continues to drop as the air goes out the exhaust.
Temperature: As the air goes through the compressors
the temperature increases slowly. Once it is ignited in
the combustion chamber, there is a rapid increase. IT
then slowly decreases as it leaves the exhaust.

5. • Name 2 different types of jet engines?
Turbojet, Turboshaft, Turboprop, Turbofan,
• What is a Compressor Surge and how is it solved?
A compressor surge (stall) is a situation of abnormal
airflow resulting from a stall of the airfoil within
the compressor of a jet engine. The compressors
are unable to cope with the amount of air entering
the engine.
This is solved by having a bleed valve.
A double shaft.

6. Intakes
• An engine’s air inlet duct is normally
considered an airframe part, and not a part of
the engine. However, the duct, itself, is so
important to engine performance.

7. The inlet duct has two engine functions:
• It must be able to recover as much of the total
pressure of the free air-stream as possible and
deliver this pressure to the front of the engine
with minimum loss.
• The duct must deliver air to the compressor
inlet under all flight conditions with as little
turbulence and pressure variation as possible.

8. • Most inlet ducts on subsonic airplanes are of the divergent
type. Air flowing into a divergent duct expands slightly and
converts some of its velocity energy into pressure.
• Rectangular inlets are designed to absorb the shockwaves
produced.

9. Compressors
Centrifugal flow
• Centrifugal compressors were used on many
of the earliest gas turbine engines because of
their ruggedness, light weight and high
pressure ratio for each stage of compression.
• A typical centrifugal compressor consists of
three components: the impeller, the diffuser,
and the manifold.

10. Eye of the
impeller
Impeller
Diffuser
Manifold

11. • Air enters the eye of the fast-rotating impeller and is
accelerated to a high velocity as it is slung to the outer
edge by centrifugal force. The high-velocity air then
flows into the diffuser, which fits closely around the
outside edge of the impeller.
• There it flows through divergent ducts where some of
the velocity energy is changed into pressure energy.
• The air, which has slowed down and has had its
pressure increased, flows into the manifold through a
series of turning vanes.
• From the manifold, the air flows into the combustion
section of the engine.

12. Axial flow compressor
• Axial-flow are compressors in which the air passes
axially or straight through the compressor.
• They are heavier than a centrifugal compressor, but
they are capable of a much higher overall compression
ratio, and they have a smaller cross-sectional area,
which makes them easier to streamline.
• Axial-flow compressors have therefore become the
standard for large gas turbine engines and are also used
on many small engines.

13. • Axial-flow compressors are made up of a
number of stages of rotor blades that are
driven by the turbine, and that rotate
between stages of fixed stator vanes.
• Both the rotor blades and stator vanes have
airfoil shapes and are mounted so that they
form a series of divergent ducts through which
the air flows.

15. Combustion
Air distribution
• Approximately 82% of the air from the
compressor passes around the outside of the
inner flame tube.
• This air is then passes into the flame tube via a
number of large and small ‘dilution’ holes into
the inside of the flame tube where it is heated
by the combustion flame

16. • Approximately 18% of the air passes immediately
into the flame tube where it is split into another
two main flows: -
• A. Approximately half of the air passes around
and through the end baffle plate and swirls into
the flame tube. It can be seen that this air flow
produces a forward flow right at the point where
the fuel is sprayed in.
• B. Approximately half the airflow passes through
swirl vanes situated around the fuel jet. This swirl
air hits the forward flow to produce what is
known as a ‘Re-Circulating Vortex’.

18. Afterburners
• An afterburner is an additional component on
some jet engines. Its purpose is to provide an
increase in thrust.
• Afterburning is achieved by injecting
additional fuel into the jet pipe downstream of
the turbine. It is burnt using the remaining
oxygen.
• This heats and expands the exhaust gases further,
and can increase the thrust of a jet engine by 50%
or more.

19. Reverse Thrust
• Modern aircraft are normally so heavy to land at
such a high speed that the aircraft brakes cannot
be depended upon for complete speed control.
• Thrust reversal is the temporary diversion of
an aircraft engine's exhaust so that the exhaust
produced is directed forward, rather than
rearwards.
• This acts against the forward travel of the aircraft,
providing deceleration

20. CLAM SHELL
DOORS
FORWARD THRUSTREVERSE THRUST

21. TARGET
DOORS
FORWARD THRUSTREVERSE THRUST