b873 Gas Turbine Engin

7/31/2019 b873 Gas Turbine Engin

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Topic: Gas Turbine Engines.

Submitted By: Abhijit Velhankar.

Guide: Prof. V. N. Phadkule.

College: ALL INDIA SHRI SHIVAJI MEMORIAL

SOCIETYS COLLEGE OF ENGINEERING.

Year: 2003 2004.


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Seminar Approval Sheet:

The seminar report entitled Gas Turbine Engines by Mr.

Velhankar Abhijit A. is approved for the degree of B. E. Mechanical.

Prof. V. N. Phadkule Prof. V. N. Phadkule

(Head Of Mechanical Dept.) (Examinar) (Guide)


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ACKNOWLEDGEMENT

Though it may appear the following Eulogizing exposition of monotonous

beat of an usual acknowledgement. I assert, beyond the confines of the simple

sense of the word Gratitude. I size this opportunity to pass on my deep felt thanks

to those who have helped me

I express my deep sense of gratitude towards my able and acknowledge

guide Prof. V.N.PHADKULE whose guidance and constant inspiration led me

towards the completion of the seminar work.

I thank my colleagues for their cooperation in making this seminar a success.

MR.ABHIJIT A. VELHANKAR


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Abstract

The name GAS TURBINE means exactly what it says. A turbine type engine

that is operated by gas rather than one operated, for instance, by steam or water.

The gas, which operates the turbine, is the product of the combustion that take place

when a suitable fuel is mixed and burned with the air passing through the engine.

The seminar includes the working process of gas turbine engines, its types

and characteristics and its applications in military aircrafts.

Advantage of gas turbine engines over reciprocating engines forms the

concluding part.

A neutral view has been taken by including the disadvantages as well.


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Index:

Sr. No. Title Page No.

1Abstract.

01

2 Introduction. 02

3 History 03

4 Gas Turbine 06

5 Gas Turbine Process 07

6

Gas Turbine Engine

Centrifugal flow.

Axial flow.

Centrifugal-Axial flow.

11

7 Engine Theory 17

8Advantages & Disadvantages 23

9 Conclusion 25

10 References 26


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Introduction

There are many different kinds of turbines:

You have probably heard of a steam turbine. Most power plants use

coal, natural gas, oil or a nuclear reactor to create steam. The steam runs through a

huge and very carefully designed multi-stage turbine to spin an output shaft that

drives the plant's generator.

Hydroelectric dams use water turbines in the same way to generate

power. The turbines used in a hydroelectric plant look completely different from a

steam turbine because water is so much denser (and slower moving) than steam,

but it is the same principle.

Wind turbines, also known as windmills, use the wind as their motive

force. A wind turbine looks nothing like a steam turbine or a water turbine because

wind is slow moving and very light, but again, the principle is the same.

A gas turbine is an extension of the same concept. In a gas turbine, a pressurized gas

spins the turbine. In all modern gas turbine engines, the engine produces its own pressurized gas,

and it does this by burning something like propane, natural gas, kerosene or jet fuel. The heat that

comes from burning the fuel expands air, and the high-speed rush of this hot air spins the turbine.


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HISTORY

England

Sir Frank Whittle: Whittle is considered by many to be the father of the jet engine.

In 1930 Frank Whittle submitted his patent application for a jet aircraft engine.

The first Whittle engine was called the Power Jet W.1, after its manufacturer.

It flew in the British Gloster G.40 on May 15, 1941 with W 1 Whittle engine installed.

Germany


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VON OHAIN At the same time, von Ohain in Germany had been at work on

the development of a jet engine for aircraft. He built and ran his first demonstration

engine in 1937. His first flight engine was the HES 3B which used on HE178 and

flew on August 27,1939.

The Whittle and the von Ohain engines led to successful jet-powered fighter

aircraft by the end of World War II, the Messerschmitt Me262 that was used by

German Air Force.

It might be note that the early English production jet engine used centrifugalcompressor where as the production engine in Germany employed the more

advanced axial flow compressor.

America

America was a latecomer to the jet-propulsion field and with the help of British

Government; the General Electric Corporation was awarded the contract to built W.1

an American Version. The first jet engine airplane in America was made in October


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1942, in Bell XP-59A. The two General Electric I-A engines used in this airplane, the

I-A engine was rated at about 1300 lb of thrust. In late 1941, NAVY awarded the

contract to Westinghouse. Westinghouse engineers designed an engine with an

axial compressor and an annular combustion chamber. Shortly thereafter, several

other companies began to design and produce gas turbine engines.

Gas Turbine

As the principle of the gas turbine, a working

gas (air) is compressed by a compressor and

heated by combustion energy of the fuel at the first.

The working gas becomes the high temperature

and high pressure. The engine converts the energy

of working gas into the rotating energy of the

blades, making use of the interaction between the gas and the blades.


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As shown in the below figure, there are two types of the gas turbine. One is

the open cycle type (internal type), and another is the closed cycle type (external

type). Basic components of both types are the air compressor, a combustor and the

turbine.

The gas turbine can handle a larger gas flow than that of the reciprocating

internal combustion engines, because it utilizes a continued combustion. Then the

gas turbine is suitable as the high power engine. The gas turbine for airplanes

(called a jet engine) makes use of this advantage.

The Gas Turbine Process

Gas turbine engines are, theoretically, extremely simple. They have three parts:

Compressor- Compresses the incoming air to high pressure

Combustion area - Burns the fuel and produces high-pressure, high-

velocity gas

Turbine - Extracts the energy from the high-pressure, high-velocity gas

flowing from the combustion chamber

The following figure shows the general layout of an axial-flow gas turbine -- the sort of

engine you would find driving the rotor of a helicopter, for example:


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In this engine, air is sucked in from the right by the compressor. The

compressor is basically a cone-shaped cylinder with small fan blades attached in

rows (eight rows of blades are represented here). Assuming the light blue represents

air at normal air pressure, then as the air is forced through the compression stage its

pressure rises significantly. In some engines, the pressure of the air can rise by a

factor of 30. The high-pressure air produced by the compressor is shown in dark

blue.

This high-pressure air then enters the combustion area, where a ring of fuel

injectors injects a steady stream of fuel. The fuel is generally kerosene, jet fuel,propane or natural gas. If you think about how easy it is to blow a candle out, then

you can see the design problem in the combustion area -- entering this area is high-

pressure air moving at hundreds of miles per hour. You want to keep a flame burning

continuously in that environment. The piece that solves this problem is called a

"flame holder," or sometimes a "can." The can is a hollow, perforated piece of heavy

metal. Half of the can in cross-section is shown below:


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The injectors are at the right. Compressed air enters through the

perforations. Exhaust gases exit at the left. You can see in the previous figure that a

second set of cylinders wraps around the inside and the outside of this perforated

can, guiding the compressed intake air into the perforations.

At the left of the engine is the turbine section. In this figure there are two sets

of turbines. The first set directly drives the compressor. The turbines, the shaft, and

the compressor all turn as a single unit:

At the far left is a final turbine stage, shown here with a single set of vanes. It

drives the output shaft. This final turbine stage and the output shaft are a completely

stand-alone, freewheeling unit. They spin freely without any connection to the rest of

the engine. And that is the amazing part about a gas turbine engine -- there is

enough energy in the hot gases blowing through the blades of that final output

turbine to generate 1,500 horsepower and drive a 63-ton M-1 Tank! A gas turbine

engine really is that simple.


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In the case of the turbine used in a tank or a power plant, there really is

nothing to do with the exhaust gases but vent them through an exhaust pipe, as

shown. Sometimes the exhaust will run through some sort of heat exchanger either

to extract the heat for some other purpose or to preheat air before it enters the

combustion chamber.

The discussion here is obviously simplified a bit. For example, we have not

discussed the areas of bearings, oiling systems, internal support structures of the

engine, stator vanes and so on. All of these areas become major engineering

problems because of the tremendous temperatures, pressures and spin rates insidethe engine. But the basic principles described here govern all gas turbine engines

and help you to understand the basic layout and operation of the engine.


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Gas Turbine Engine

The gas turbine engine runs on a Brayton cycle using a continuous

combustion process. In this cycle, a compressor (usually radial flow for automotive

applications) raises the pressure and temperature of the inlet air. The air is then

moved into the burner, where fuel is injected, and combusted to raise the

temperature of the air. Power is produced when the heated, high-pressure mixture is

expanded and cooled through a turbine. When a turbine engine is directly coupled to

a generator, it is often called a turbo generator or turbo alternator.

The power output of a turbine is controlled through the amount of fuel

injected into the burner. Many turbines have adjustable vanes and/or gearing

to decrease fuel consumption during partial load conditions and to improve

acceleration.

Most of modern passenger and military aircraft are powered by gas turbine

engines, which are also called jet engines. There are several types of jet engines,

but all jet engines have some parts in common. Aircraft gas turbine engines can be

classified according to (1) the type of compressor used and (2) power usage

produces by the engine.

Compressor types are as follows:

1. Centrifugal flow

2. Axial flow

3. Centrifugal-Axial flow.


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Power usage produced is as follows:

1. Turbojet engines

2. Turbofan engines.

3. Turbo shaft engines.

Centrifugal Compressor Engines

Centrifugal flows engines are compress the air by accelerating air outward

perpendicular to the longitudinal axis of the machine. Centrifugal compressor

engines are divided into Single-Stage and Two-Stage compressor. The amount of

thrust is limited because the maximum compression ratio.

Principal Advantages of Centrifugal Compressor

1. Light Weight.

2. Simplicity.

3. Low cost.


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Axial Flow Compressor Engines

Axial flow compressor engines may incorporate one, two, or three spools (Spool is

defined as a group of compressor stages rotating at the same speed). Two-spool

engine, the two rotors operate independently of one another. The turbine assembly

for the low-pressure compressor is the rear turbine unit. This set of turbines is

connected to the forward, low-pressure compressor by a shaft that passes through

the hollow center of the high-pressure compressor and turbine drive shaft.

Advantages and Disadvantages

Advantages:

Most of the larger turbine engines use this type of compressor

because of its ability to handle large volumes of airflow and high-pressure

ratio.


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Disadvantages:

More susceptible to foreign object damage, Expensive to manufacture,

and It is very heavy in comparison to the centrifugal compressor with the

same compression ratio.

Axial-Centrifugal Compressor Engine

Centrifugal compressor engine were used in many early jet engines, the

efficiency level of single stage centrifugal compressor is relatively low. The

multi-stage compressors are somewhat better, but still do not match with

axial flow compressors. Some small modern turbo-prop and turbo-shaft

engines achieve good results by using a combination axial flow and

centrifugal compressor such as PT6 Pratt and Whitney of Canada which very

popular in the market today and T53 Lycoming engine.

Characteristics and Applications


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The turbojet engine:Turbojet engine derives its thrust by highly acceleratinga mass of air, all of which goes through the engine. Since a high " jet " velocity is

required to obtain an acceptable of thrust, the turbine of turbo jet is designed to

extract only enough power from the hot gas stream to drive the compressor and

accessories. All of the propulsive force (100% of thrust) produced by a jet engine

derived from exhaust gas.

The turboprop engine: Turboprop engine derives its propulsion by theconversion of the majority of gas stream energy into mechanical power to drive the

compressor, accessories, and the propeller load. The shaft on which the turbine is

mounted drives the propeller through the propeller reduction gear system.

Approximately 90% of thrust comes from propeller and about only 10% comes from

exhaust gas.

The turbofan engine: Turbofan engine has a duct-enclosed fan mounted atthe front of the engine and driven either mechanically at the same speed as the

compressor, or by an independent turbine located to the rear of the compressor drive

turbine. The fan air can exit separately from the primary engine air, or it can be

ducted back to mix with the primary's air at the rear. Approximately more than 75%

of thrust comes from fan and less than 25% comes from exhaust gas.

The turbo shaft engine: Turbo shaft engine derives its propulsion by the

conversion of the majority of gas stream energy into mechanical power to

drive the compressor, accessories, just like the turboprop engine but The

shaft on which the turbine is mounted drives something other than an aircraft

propeller such as the rotor of a helicopter through the reduction gearbox. The

engine is called turbo shaft.


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ENGINE THEORY

OPERATION

The jet engines are essentially a machine designed for the purpose of

producing high velocity gasses at the jet nozzle. The engine is started by rotating the

compressor with the starter, the outside air enter to the engine. The compressor

works on this incoming air and delivery it to the combustion or burner section with as

much as 12 times or more pressure the air had at the front. At the burner or

combustion section, the ignition is igniting the mixture of fuel and air in the

combustion chamber with one or more igniters which somewhat likes automobile

spark plugs. When the engine has started and its compressor is rotating at sufficient

speed, the starter and igniters are turn off. The engine will then run without further

assistance as long as fuel and air in the proper proportions continue to enter the

combustion chamber. Only 25% of the air is taking part in the actual combustion

process. The rest of the air is mixed with the products of combustion for coolingbefore the gases enter the turbine wheel. The turbine extracts a major portion of

energy in the gas stream and uses this energy to turn the compressor and

accessories. The engine's thrust comes from taking a large mass of air in at the front

and expelling it at a much higher speed than it had when it entered the compressor.

Thrust, then, is equal to mass flow rate times change in velocity.


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The more air that an engine can compress and use, the greater is the power or

thrust that it can produce. Roughly 75% of the power generated inside a jet engine is

used to drive the compressor. Only what is left over is available to produce the thrust

needed to propel the airplane.

JET ENGINE EQUATION

Since Fuel flow adds some mass to the air flowing through the engine, this

must be added to the basic of thrust equation. Some formulary does not consider the

fuel flow effect when computing thrust because the weight of air leakage is

approximately equal to the weight of fuel added. The following formulary is applied

when a nozzle of engine is " choked ; the pressure is such that the gases are

traveling through it at the speed of sound and cannot be further accelerated. Any

increase in internal engine pressure will pass out through the nozzle still in the form

of pressure. Even this pressure energy cannot turn into velocity energy but it is not

lost.


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Factors Affecting Thrust

The Jet engine is much more sensitive to operating variables. Those are:

1. Engine rpm.

2. Size of nozzle area.

3. Weight of fuel flow.

4. Amount of air bled from the compressor.

5. Turbine inlet temperature.


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6. Speed of aircraft (ram pressure rise).

7. Temperature of the air.

8. Pressure of air

9. Amount of humidity.

Note; item 8,9 are the density of air.

Engine Station Designations

Station designations are assigned to the various sections of gas turbine

engines to enable specific locations within the engine to be easily and accurately

identified. The station numbers coincide with position from front to rear of the engine

and are used as subscripts when designating different temperatures and pressures

at the front, rear, or inside of the engine. For engine configurations other than the

picture below should be made to manuals published by the engine manufacturer.

N = Speed (rpm or percent)

N1 = Low Compressor Speed

N2 = High Compressor Speed


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N3 = Free Turbine Speed

P = Pressure

T = Temperature

T = Total

EGT = Exhaust Gas Temperature

EPR = Engine Pressure Ratio (Engine Thrust in term of EPR). Pt7 / Pt2

Ex.: Pt 2 = Total Pressure at Station 2 (low pressure compressor inlet)

Pt 7 = Total Pressure at Station 7 (turbine discharge total pressure)


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Advantages

The turbine is light and simple: -

The only moving part of a simple turbine is the rotor. A turbine has no

reciprocating motion, and consequently runs smoother than a reciprocating engine.

A turbine will run on a variety of fuels: -

Any combustible fuel that can be injected into the airstream will burn in a

turbine. A turbine has this flexibility because the continuous combustion is not

heavily reliant on the combustion characteristics of the fuel.

A turbine produces low levels of emissions: -

Because of its multi-fuel capability; a fuel, which burns completely and

cleanly, can be used to reduce emissions.

Disadvantages

The turbine engine has a few drawbacks, which have prevented its

widespread use in automotive applications:

Turbine engines have high manufacturing costs: -

Because of the complicated design, manufacturing is expensive.


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A turbine engine changes speed slowly: -

A gas turbine is slow to respond (relative to a reciprocating engine) to

changes in throttle request.


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Conclusion:

Thus we have thoroughly gone through the gas turbine engine. The seminar

information shows the advantages, benefits, characteristics, and applications of gas

turbine engines.

It clearly states the superiority of gas turbine engines over reciprocating

engines. We have taken a neutral view of the topic.


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Reference Text:

Following are the sources from where the information for the seminar has

been collected:

1. www.howstuffworks.com

2. www.thai-engines.com

3. www.gasturbineengines.com

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b873 Gas Turbine Engin