Experiment No: 03
Name of Experiment: Study the Exhaust System of Gas Turbine Engine
Objectives:

To understand the function and design of the exhaust system in gas turbine engines.

To study how exhaust gases are directed and expelled to produce thrust.

To examine the effect of exhaust system design on engine performance.

To analyze the materials and construction used in exhaust systems to handle high
temperatures and stresses.
Exhaust System of Gas Turbine Engines
The exhaust system of a gas turbine engine plays a vital role in both the ejection of waste gases
and the generation of thrust, essential for the propulsion of aircraft. The system is designed to
handle the hot, pressurized exhaust gases from the engine’s combustion process and direct
them out of the engine to generate the required thrust for flight.
Basic Function of Exhaust System:
1. Ejection of Waste: The exhaust system expels the byproducts of the combustion process,
such as hot gases and various emissions, from the engine.
2. Thrust Generation: By directing the exhaust gases backward, the exhaust system creates
forward thrust, which propels the aircraft forward. This is especially significant in
turbojet engines, where most of the thrust comes from the high-velocity exhaust gases.
Types of Engine Exhaust Systems:

Turbojet Engine Exhaust: In a turbojet engine, the exhaust gases create most of the
thrust by accelerating through the exhaust nozzle. The high velocity of the gas exiting
the nozzle results in the forward thrust required for flight.

Turboprop Engine Exhaust: In turboprop engines, the exhaust gases contribute only a
small amount of thrust. The majority of the engine’s power is used to drive the propeller,
and thus, the exhaust gases are not the primary source of thrust.
Exhaust System Design and Performance:
The exhaust system design significantly influences the performance of a gas turbine engine. Key
factors in this design include:

Jet Pipe and Nozzle Area: The size and shape of the jet pipe and the propelling nozzle
affect the turbine entry temperature, mass airflow, and the velocity and pressure of the
exhaust gases.

Exhaust Nozzle Design: The nozzle directs the exhaust gases into the atmosphere, and
the design can impact thrust and efficiency. Some nozzles are specially designed to
optimize thrust or to reduce the noise produced by the high-velocity exhaust gases.
Temperature Considerations in Exhaust Systems:

Exhaust Gas Temperature: The temperature of the gases entering the exhaust system
can range from 550 to 850°C, depending on the type of engine. With afterburning, the
temperature can rise to over 1,500°C or higher. This requires the use of materials that
can withstand extreme heat and prevent damage to the engine and surrounding aircraft
structures.

Material Requirements: Materials used in the exhaust system, particularly for
components like the nozzle and turbine blades, must be resistant to high temperatures
and mechanical stress. Special alloys are often used for turbine blades to ensure they
can tolerate these extreme conditions without cracking or melting.
Turbine Stage and Exhaust Nozzle:

Turbine Stage: The turbine stage rotates at a high speed and converts the thermal
energy of the combustion gases into mechanical energy to drive the compressor and
other components. The turbine blades are subjected to extremely high temperatures,
and special cooling methods are used, such as internal cooling passages to maintain
acceptable material temperatures.

Exhaust Nozzle: After passing through the turbine, the exhaust gases expand and
accelerate through the nozzle. The nozzle’s function is to convert the thermal and
pressure energy of the gases into kinetic energy, creating a high-velocity jet that
provides thrust. The nozzle design plays a crucial role in achieving the desired jet velocity
and thrust.
Noise Suppression in Exhaust Systems:

Noise Issues: High-speed exhaust gases exiting from the turbojet engine can create
significant noise, which is a challenge for both the aircraft and the surrounding
environments.

Noise Suppression Devices: To reduce this noise, many turbojet engines use noise
suppression devices, such as corrugated or lobe-type suppressors. These devices alter
the turbulent mixing of the exhaust gases, changing the frequency content to favor
higher frequencies. Higher frequencies are more easily absorbed by the atmosphere,
resulting in a quieter engine.

Jet Noise Suppression Principle: The principle behind jet noise suppression is to
encourage the mixing of the exhaust gases in a way that reduces the low-frequency
noise that is typically associated with jet engines. This is achieved by modifying the
exhaust flow using specialized nozzle designs or additional components that modify
airflow characteristics.
Discussion
The exhaust system in gas turbine engines is crucial for expelling combustion byproducts and
generating thrust, with its design varying by engine type—primary for turbojets and secondary
for turboprops. The jet pipe and nozzle shape impact gas velocity, pressure, and thrust, while
high exhaust temperatures (550°C to over 1,500°C with afterburning) require heat-resistant
alloys and cooling methods like internal passages. Noise from high-speed exhaust in turbojets is
mitigated by suppressors that shift noise to higher, less disruptive frequencies. Material
durability under extreme conditions balances performance with cost, reflecting the complexity
of exhaust system engineering.
Conclusion
The exhaust system’s role in thrust and waste ejection is vital, tailored to engine type, and
optimized by nozzle design. It handles extreme temperatures with advanced materials and
cooling, while noise suppression addresses environmental concerns. This study highlights the
exhaust system’s integration of design, function, and innovation, with potential for future
improvements in efficiency, noise reduction, and material resilience.
Questions & Answers:
1. How does an Exhaust System work in a Gas Turbine Engine?
Answer:
The exhaust system of a gas turbine engine works by directing and expelling the hot gases
generated during the combustion process. Here’s how it functions:

Combustion: The engine burns fuel mixed with compressed air, creating hightemperature, high-pressure gases.

Turbine Stage: These gases pass through the turbine stage, where the turbine blades
extract energy from the hot gases to drive the compressor and other components. The
turbine is made from heat-resistant materials like special steel alloys.

Exhaust Nozzle: After the turbine, the gases expand through the exhaust nozzle. This
nozzle accelerates the gases to a high velocity, generating thrust through the reaction
force (Newton’s Third Law of Motion).

Noise Suppression: To reduce the noise created by the high-speed exhaust gases, the
exhaust system often includes noise suppression devices that alter the flow and
frequency of the jet exhaust.

Thrust Generation: The rapid expulsion of exhaust gases through the nozzle results in
forward thrust that propels the aircraft. The design and size of the nozzle are critical in
controlling the speed and direction of the exhaust flow to achieve the desired thrust.
Aviation and Aerospace University Bangladesh
(AAUB)
LAB REPORT
Experiment No : 03
Name of Experiment: Study the Exhaust System of Gas Turbine Engine
Date of Performance:
Date of Experiment Submission: 10/ 04/ 25
Submitted by: Sheikh Muaaz
Student ID: 22014003
Department: Aerospace Engineering
Batch: AE-03
Course Name: Aerospace Propulsion
Course Code: ASE 4645
Course Instructor: Flt Lt Nazmul Hasan Anik Chawdhury
Lab Instructor: Rijon Sarker
Submitted to: Flt Lt Nazmul Hasan Anik Chawdhury