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FUNDAMENTALS OF GAS TURBINE ENGINE..
PRINCIPLES AND SHORT NOTES..
-NISARG MISTRY

INTRODUCTION –
The gas turbine engine is an Internal combustion engine that uses air as the working fluid .
The engine extracts chemical energy from fuel and converts it to mechanical energy using the
gaseous energy of the working fluid (air) to drive the Turbine . In case of turboprop engine the
turbine also drives the propeller (will be discussed further) which ,in turn ,propel the aircraft.

THE GAS TURBINE CYCLE -
The basic principle of the airplane turbine engine is identical to any and all engine that extract
energy from chemical fuel. The basic 4 steps for any internal combustion engine are :
The basic 4 steps can be assumed as – SUCK , Squeeze , BANG , BLOW
1. Intake of air
2. Compression of the air.
3. Combustion , where fuel is injected and burned to convert the stored energy.
4. Expansion and Exhaust , where the converted energy is put to use ..
In the case of a Piston engine , such as the engine in a car or reciprocating aircraft engine ,
the intake , compression , combustion , and exhaust steps occur in the same place i.e cylinder
head at different times as the piston goes up and down.

In case of a turbine engine , however these same 4 steps occur at the same time but in
different places , As a result of this fundamental difference , the turbine has engine sections
called –
1. The Inlet section
2. The compressor section.
3. The combustion section (aka the Combustor).
4. The Turbine & Exhaust section.
The turbine section of the gas turbine engine has the task of producing usable output shaft
power to drive the compressor . In addition , it must also provide power to drive the engine
accessories. It does this by expanding the high temperature , pressure and velocity gas and
converting the gaseous energy to mechanical energy in the form of shaft power (aka shaft horse
power).
A large mass of air must be supplied to the turbine in order to produce the necessary power .
This mass of air is supplied by the compressor , which draws the air into the engine and
squeezes it to provide high-pressure air to the turbine . The compressor does this by converting
mechanical energy from the turbine to gaseous energy in the form of pressure and temperature.

If the compressor and the turbine were 100% efficient , the compressor would supply all the air
needed by the turbine . At the same time , the turbine would supply the necessary power to
drive the compressor . In this case , a perpetual motion (a state in which movement or action is or
appears to be continuous and unceasing.) machine would exist . However , frictional losses and
mechanical system inefficiencies do not allow a perpetual motion machine to operate . Additional
energy must be added to the air to accommodate for these losses . Power output is also desired
from the engine (beyond simply driving the compressor); thus, even more energy must be added
to the air to produce this excess power. Energy addition to the system is accomplished in the
combustor . Chemical energy from fuel as it is burned is converted to gaseous energy in the
form of high temperatures and high velocity as the air passes through the combustor. The
gaseous energy is converted back to mechanical energy in the turbine , providing power to drive
the compressor and the output shaft.
WHY COMBUSTION IS NECESSARY (THE ACTUAL FACT)..

Important constructional parts or sections of GTE –
1) – Air Inlet Duct
2) - Compressor.
3) - Diffuser.
4) - Combustor.
5) - Turbine.
6) - Exhaust.
• Inlet is also a part of Airframe not engine . Since it is the constructional part of the engine we
Study it in Engine construction.

Types of Gas Turbine Engines -
GTE
Thrust Producing Engines
Torque Producing Engines
1) – Turbojet Engine.
2) - Turbofan Engine. 1) - Turboprop Engine.
2) - TurboShaft
Engine.

Turbojet Engine –
1) – Turbojet Derives its thrust by accelerating a small mass of air which goes through the engine.
2) - All of the propulsive force is derived from the imbalance of forces within the engine itself.
Characteristics of Turbojet -
• Low thrust at low forward speed.
• Relatively High thrust specific Fuel Consumption (TSFC) at low altitudes & airspeed.
• Long takeoff Roll.
• Small frontal area resulting in low drag and reduces Ground clearance problems.
• Light Specific Weight.
• Ability to take Advantage of Ram pressure.

Turboprop Engines -
Propulsion in turboprop engine is greatly accomplished by propeller . Only a small amount of Approx – 10%
Of jet thrust is Avail.
Characteristics of A Turboprop Engine -
• High propulsive efficiency at low airspeed , which results in shorter takeoff rolls but falls rapidly as
airspeed increases .
• The propeller can accelerate large qty. of air at zero forward velocity of airplane.
• More complicated design and heavier weight than turbojet.
• Lower TSFC.
• Large Frontal area of propeller and engine that requires Longer landing gears for low wing aircraft .
• Possibilities of Efficient Reverse Thrust.

Turboshaft Engine -
 A GTE that delivers power through a shaft to operate something other than a propeller , this type
Of Engine is k/a Turboshaft Engine.
 This Engine’s construction is like Turboprop Engine.
 The engine uses almost all exhaust energy to drive the O/P shaft.
 This type of GTE is mostly used in Helicopters.
 Turboshaft Engine is used in APU (Auxiliary PWR Unit).
 This type of GTE is used for Vertical Takeoffs and Landings.

Characteristics of Turboshaft Engine -
 Lowest TSFC.
 Accelerates Large mass of air through large velocity change.
 Used for vertical TOs and Landings.
 More complicated design & Heavy weight.
 Used for short Distance Flights.

Turbofan Engine -
 A turbofan engine may be considered as a cross b/w Turbojet & Turboprop.
 A Turbofan Engine Accelerates a Large volume of air then a Turbojet.
 The fan is driven by set of core engine turbine designed to drive the Fan only.
 This GTE can be a HIGH-BYPASS or LOW-BYPASS . Now a days its Ultra High Bypass – PW1127.
 The ratio of the amount of air that Bypass (passes Around) the core of engine to the amount of
air that passes through the core is called BYPASS RATIO.
 The fan air can account for around 80% of total engine Thrust.
 Mostly used engine.
 The advantage of using High Bypass engine are greater efficiencies and Reduced Engine noise.

Characteristics of Turbofan Engine -
 It increases thrust at low forward speed which results in short takeoffs.
 TSFC is B/W Turbojet & Turboprop , resulting in increased operating economy & Aircraft Range over turbojet.
 Noise level Reduction of 10 to 20% over turbojet which results in reduced fatigue cracks in nearby parts.
 The Turbofan is superior to the turbojet in Hot day performance.
 Thrust Reversers are most efficient .
 Better cooling of Engine due to bypass air.
 Ground Clearance are less than turboprop but not as good as Turbojet.

Thrust Specific Fuel Consumption (TSFC) -
Thrust specific Fuel Consumption is a measure of the number of pounds of fuel burned per hour for each
Pound of thrust produced.
Principle of GAS TURBINE ENGINE -
The basics operation of GTE is relatively simple . Air is brought into the front of the engine and compressed
Fuel is mixed with this air and burned , the heated exhaust gases rush out the back of the engine . The parts
Of GTE works together to change fuel energy to energy of motion , to cause the greatest thrust for the fuel
Used.
HOT SECTION – Combustion and Turbine section.
COLD SECTION – Air compressor and diffuser section.
Rest to be continued in next presentation…..

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FUNDAS OF GAS TURBINE ENGINE

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FUNDAS OF GAS TURBINE ENGINE