Mod-01 Lec-01 Introduction & Development of Jet Aircraft Propulsion
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Mod-01 Lec-01 Introduction & Development of Jet Aircraft Propulsion

September 2, 2019


Hello and welcome to this lecture series on
jet aircraft propulsion. This is a new course that is being offered
under the NP-TEL phase two initiatives; and this is primarily a course meant for the aerospace
engineering students. And there are two of us who are offering this
course my name is Pradeep and along with me my collogue Professor Bhaskar Roy both of
us from the aerospace engineering department IIT Bombay would be offering this course. So over the next few lectures, our aim, our
intension is to educate you with some of the basic aspects of jet aircraft propulsion. We would be primarily focusing on the aircraft
propulsion mode that is the air breathing mode of propulsion; we shall not be covering
rocket propulsion in this course. And so, this particular course that we are
offering is primarily intended for aerospace engineering students with some background
and prerequisites that we shall which I shall explain in a few minutes. And so before we go into some of those details,
let us take a very quick look at what does, what are the contents of this particular course. So, basically these courses consist of these
broad areas or topics. And we shall begin this course with a brief
introduction to this whole course on aircraft jet propulsion, which will be primarily covered
by Professor Bhaskar Roy. Following this, I shall be covering the thermodynamic
analysis of real cycles; I shall of course also give some quick review of an ideal cycle
of the jet engines followed by the real cycle and its thermodynamic analysis. Subsequently, we shall be discussing about
compressors and turbines, basically we will be discussing the various components in which
constitute an aircraft engines. And the two main components of the aircraft
engine are compressors and turbines. And we also have combustion systems which
we shall cover subsequently. And then we shall be taking up intakes and
propelling nozzles. And then Professor Roy will also be covering
aircraft engine install performance its sizing and matching in detail. And then towards the end of the course, we
will also be discussing in brief about ramjets, scramjets, and pulsejets. And more details of the syllabus and the contents
are to be put up on to the NP-TEL website. So, you are requested to take a look at the
details of the course and the various topics that will be covered in this course through
the NP-TEL website. So, the basic aim as I was mentioned in earlier
of this course is to give you an overview or and also, some in depth analysis of the
different components; that constitute an aircraft jet engine and what are different types jet
engines that are prevalent and what makes these jet engines different and what is the
need for these different types of jet engines; what are that components that are different
in each of these engines. So, these are some of the topics that we shall
be covering. And we as a mentioned we will also be taking
up the aircraft install performance and how it is matched or the various components of
the aircraft engine are matched, so that all these individual components operate as a single
unit, because though these components are designed separately ultimately all these components
have to fit into one single engine and operate as more or less a single unit; so, it is important
that there is a matching between these different components. Now, this course as a mentioned is made for
aerospace engineers and as and aerospace engineering students. And so, there are certain prerequisites that
are expected from you, regarding some basic courses that you need to have undergone to
be able to understand and appreciate various contents of this course. So, there are couple of courses that we feel
are prerequisites for this course, one is one of our own course that is in on introduction
to aerospace propulsion which we had offered under NP-TEL phase two and so that is one
of the courses that we strongly recommend that you undergo before taking up this course
or if you have undergone a course in engineering thermodynamics as well as a course in basic
fluid mechanics; as both these courses will be a helpful in your understanding of the
various topics which are to be discussed in this course. So, we strongly recommend that you have undergone
these courses before you start taking up this course. So, that you are able to appreciate and understand
the various aspects of a jet aircraft propulsion. And so during the next several lectures we
will be having about 42 lectures in total. And so during all these lectures we shall
be discussing various topics and what I shall do next is to take you through the contents
which shall be discussed in the subsequent lectures. So before that let me also mentioned about
the various text books that we recommend for this course. One of the text books that we recommend for
this course is by Michael and Thomas on aircraft power plants, which was published the seventh
edition of this book published by Tata McGraw hill in 2010. And the second text book which has been there
for quite some time and is popularly followed in many colleges is a by hill and Peterson,
which is mechanics and thermodynamics of propulsion; there is an earlier version of this available
that is published way back in 1992 by Addison Wesley. And the third book that we would recommend
is by Mattingly. So, this text book discusses primarily about
the cycle analysis in very much detail so mattingly’s text book discusses cycle analysis
in good detail and this is published by the AIAA education series and published in 2006. Another text book that you could also refer
to is by Ahmed Sayed on aircraft propulsion in gas turbine engines published by Taylor
and Francis, CRC press in 2008. And one of the classical text books on gas
turbine theory is by Saravanamuttoo, Rogers and Cohen; and this is gas turbine theory
2001 Pearson education series; and this book is primarily meant for land based gas turbine
engines but, they do have chapters for aircraft propulsion. There is also a text book which one of the
instructors of this course Professor Roy has written on aircraft propulsion published by
Elsevier India in 2008; so this also a text that I would strongly recommend that you can
take up for this particular course. So, these are some of the text books and reference
material that you should be referring through while undergoing this course; and in addition
if we come across some other interesting text books or reading material we shall also discus
those during the schedule of this course. And so we shall now look at what are the different
contents of the course in little more detail lecture by lecture starting from today’s
lecture. And so today’s lecture is basically an introductory
lecture, which both the instructors are going to handle. So part of this course, part of this particular
lecture will also be taken up by Professor Roy. It is primarily to do with introduction and
development of aircraft jet propulsion with little bit of historical perspective. The second lecture is to be taken by Professor
Roy on how the jet aircraft engines make thrust or how is thrust produced by the jet engines;
so, this is a very fundamental concept that you need to understand very well. And so, that will be discussed in detail during
the second lecture. The third lecture is on the basic performance
parameters of jet engines the second will be covered by Professor Roy. And subsequently, we shall look at the different
types of engines in detail starting with the turbo jet engine, the different forms of turbo
jet, the turbo jet with reheat, the multi spool engines, etcetera. And the lecture 5 will continue the discussion
on turbofans, turbo props and turbo shaft engines. In lecture 6 we shall take up the ideal and
real Brayton cycle joule Brayton cycle which I shall be taking on; and then we will also
discuss the differences between the ideal and real cycle and how is it that we can carry
out a cycle analysis of these cycles. And then we shall take up the jet engine cycles
for aircraft propulsion; the ideal joule bray ton cycle is basically a closed cycle; and
so, in aircraft engine as you know dose not really operate in a close cycle mode; and
there are certain differences between the ideal bray ton cycle as applied to jet aircraft
propulsion so we will discuss that in the seventh lecture. And then we will also be take up the different
components of the jet cycle thermodynamically and how do you analyze the performance of
these cycle components like the intake, the compressors, combustion chamber, turbine,
nozzle, etcetera that will be discussed in lecture-8. In lecture-9, we will have a tutorial session
we will take up cycle analysis and we will solve some problems from cycle analysis the
real cycle analysis of some of the engines; and that would give us some idea how we could
carry out the cycle analysis given some of the performance parameters. Lecture-10 will be detailed analysis of the
real cycles followed by a tutorial during lecture 11. And in lecture-12 onwards we will discuss
about the components in much more detail, we will start with the thermodynamics of compressors,
which Professor Roy will take up. In lecture-13, we will take up the thermodynamics
of turbines. Lecture-14 will be the axial compressors we
will discuss about two dimensional analytical models for axial compressors. Followed by in lecture-15 we will take up
the cascade analysis and how to estimate the loss and blade performance of cascades. Lecture-16, we shall devote to what is known
as the free vortex theory, and also about the single and multi stage characteristics
of an axial compressor. So, this will be followed by a tutorial on
axial compressors in lecture-17. Lecture-18 we shall devote for a centrifugal
compressor, what are the elements of centrifugal compressor. And then in lecture-19 we will take up centrifugal
analysis, its characteristics like surging, choking, etcetera in detail. In lecture-20, we will take up the next component
that is axial flow turbine and its 2 D analysis, cascade analysis. Lecture-21 is multi staging of axial turbines,
turbine cooling, etcetera, which again will be handled by Professor Roy. Lecture-22 is radial turbine aerodynamics
and thermodynamics, estimation of losses and efficiency followed by tutorial in lecture-23. In lecture-24 will start with the combustion
chambers, the mechanism of combustion and what are the parameters involved in combustion
chamber performance. In lecture-25, we will discuss about pressure
loss, combustion efficiency, combustion intensity. And then in lecture-26, we will discuss the
particle combustion system which is applied which is about it is in aircraft engines the
stability of combustion and fuel injection. In lecture-27 we will take up another component
of aircraft engine that is the intake and we will discuss the transport and military
aircraft intake separately. We will also discussing about different types
of aircraft intakes the subsonic intake, the transonic and the supersonic intake designs
that will be in lecture-28. Lecture-29, we will discuss about the nozzle,
the different types of nozzle, the fixed and variable geometry nozzles. And then in lecture-30, we will discuss about
the convergent divergent nozzle and their applications. Lecture-31 will be basically a tutorial session
on intakes and nozzles. And in lecture 32, we have engine off design
parameters and operation which will be discuss by Professor Roy. Lecture 33, we will discuss about engine component
matching and dimensional analysis. And in lecture 34, this will be continued
and we will discuss that in more detail of component matching and sizing. Lecture 35 will be installed performance of
engines. And there will be a tutorial session which
will be during lecture 36 on off design performance and matching. In lecture 37, we will discuss about use of
ramjets pulsejets in aircraft propulsion; and you might have already heard about ramjets
and pulsejets for we will discuss that in and little detail during that lecture. And take up some analysis thermodynamic analysis
of ramjets in lecture 38. And in lecture 39, we will discuss what flow
in diffusers, combustors and nozzles, as applied for a ramjet engine. Lecture 40 will be about design performance
of ramjet scramjet engines, and followed by a tutorial during lecture 41. And the last lecture that is lecture 42 we
shall be discussing about future of aircraft propulsion having discussed the conventional
propulsion as well as the propulsion concepts that are being used currently. We will then discuss about where is that the
aircraft propulsion is going in the future and what are different concepts that will
probably be used in future aircraft propulsion systems. So, these were the lecture wise schedule and
contents that we shall be discussing over this lecture series. And so in today’s lecture as we as I mentioned
we will discuss about fundamental aspects of jet aircraft propulsion, introduction to
jet aircraft propulsion and some amount of historical prospective of that. So, I guess if you have already undergone
the basic course of introduction to aerospace propulsion that we have already taken up in
NP-TEL; you would have already had some idea about what are the different types of aircraft
engines that are jet engines that are currently in use. So, let me give you some overview of what
are different types of jet engines that are existing; and also what are the different
basically the differences between different types of these jet engines. So, aircraft jet engines can be classified
into many of these groups which I am sure you would have already heard about. One of basic forms of the aircraft jet engines
is the turbojet. The turbojet engine can operate in two modes;
it could operate with an afterburner or without an afterburner. And afterburning is basically used to generate
additional thrust, when the aircraft has to cruse to super has to accelerate to supersonic
Mach numbers and also cruse at the same Mach number. So, it could operate either in the afterburning
mode or the non afterburning mode. The other form of the aircraft jet engine
is the turboprop. And turboprop is consists of a jet engine
one com one of the turbines of the jet engine drives a propeller and propeller generates
a substantial thrust in addition to the nozzle thrust itself. The turboprops are still used in transport
aviation, you might have seen some of the smaller jet engines which use turboprops;
and so turboprops can again be driven either by propeller it could be turboprops or the
turbo shaft; in fact they are also similar because turbo shaft is a engine used in helicopters;
And in helicopters as we know there is no jet thrust it is basically the thrust generated
by the main rotor blade. And in both these cases the propeller in the
case of turboprop or the rotor blade in the case of turbo shaft in driven by free turbine;
and it is in some cases mounted on the compressor shaft itself with a gear box. Now, the other popular type of aircraft engine
is the turbofan. We will discuss the classification of turbofan
in the next slide because, the many types of turbofans which are prevalent. And then some of the advanced concepts like
the unducted propfan and the ducted fan engines; and these both of these could either have
a single propeller system or a contra rotating prop fan system. So, some of these will again be discussed
in little more detail in later lectures or it has already been discussed in the earlier
course on introduction to aerospace propulsion. Now, turbofan as you knows is the engine that
is used in a most of the transport aircraft and the larger sized transport aircraft. The turbofan engines can as you can see constitute
of different types or different classes; it could either be broadly classified as forward
fan system and aft fan system or the other classification is the high bypass ratio system
and the low bypass ratio system. Now, let us take up the forward fan system
which is how most of the engines are in if the turbofan is a forward fan system; the
turbofan could either be operating in the mixed flow mode or in the unmixed flow mode;
the unmixed flow mode the bypass air does not makes with the core flow within the aircraft
within the engine itself; in the mixed engine flow mode, the bypass and the core flow mix
within the engine before the exit the nozzle; and therefore, they can operate in both the
modes that is non afterburning mode or with an afterburner mode. And the other type or classification of the
forward fan, turbo fan could be based on different spools. These engines could either be a single spool
system, two spool or three spool system; and they could be operating with either a geared
fan or an ungeared fan; that is with a gear box which will reduce the speed of the fan
or not. And depending upon bypass ratio the engines
could be classified as high bypass or a low bypass ratio engine. In a low bypass ratio engine, which is a similar
to that of a mixed flow engine; the engine could operate in non afterburning or an afterburning
mode; and with low bypass ratio the turbo fan approaches that of a turbojet engine because,
bypass ratios tend to be very low and they are sometimes use to military engines. Turbofans could also be operating let us say
with a prop fan operating in the where the propeller is or the prop fan is in the rear
of the engine. So, it is operating in the aft fan mode, that
is the fan is located not in the initial part of the engine but, the later part of the engine,
that is the aft fan mode of the engine. So, these are different types of engines and
their classification and what are how these different types of engines operate etcetera
will be discussed in more detail as we proceed. And so what we shall now do is to discuss
about the development of aircraft jet engines so Professor Roy will now take up the development
of aircraft jet engines in with some historical perspective in much more detail. My name is Bhaskar Roy; I am in aerospace
engineering department of IIT Bombay along with professor Pradeep; I will be participating
in the lecture series on jet aircraft propulsion talking about various aspects of jet propulsion. In today’s lecture Professor Pradeep has
already introduced to you, the various topics that we will be covering, the various aspects
of jet propulsion that we will be covering in the course of this entire lecture series
over approximately 42 lectures. He has also introduced to you the various
books, and the various prerequisites that are required for this propulsion course. In today’s lecture in the remainder of the
today’s lecture I will try to introduce to you the various aspects of development
of jet engine, with a certain touch of the historical perspective. Jet propulsion has been around for nearly
60 years now or little more than that. Over the period of this 60 or odd years, the
jet propulsion has improved and it has become one of the most glamorous field of engineering
and technology the world over. It makes the human being fly higher and faster
takes them all over the world in a very short space of time, meeting, both personal as well
as business requirements of various kinds of people. However, the development of this jet aircraft
propulsion has been going on long before the jet propulsion actually came into being and
started flying. Jet propulsion has a concept has been around
for quite some time, before they actually got materialized; and various aspects of jet
propulsion conceptually and technology have been in development for quite some time at
least for a period of 50 years before they actually flew. Today, we will try to take a look at how this
jet propulsion development took place, and where we are today, and the various aspects
of jet propulsion that make an aircraft engine such a fascinating technological marvel. We will see that jet propulsion as a concept
has been around for more than 100 years, if we start with how it all started. Sir Isaac Newton, he theorized for the first
time based on his own laws of motion; that if you have an acceleration of flow rear-ward
this could actually propel a machine forward at a sufficient speed to make a body move. Now, this is the theory that based on his
own laws of motion; that started the whole thinking that one could possibly have a jet
propulsion. And if you the working medium that he conceived
and people later on have a theorized and materialized, is the use of air. Now, this is an important aspect that you
use air, that is bend abundantly available atmosphere and you simply recycle the air
to create jet propulsion. This is an important aspect, in the sense
that if you have to continuously depend on other kind of material for creating propulsive
force, then you are dependence of the other kind of material could limit your propulsive
activity. Now that is exactly what is done in rocket
propulsion, that the material that is used for propulsion is completely generated by
human beings and stored inside the rocket body. But, in aircraft propulsion the material that
is fundamentally used for a propulsive purpose is the air itself. It is taking from the atmosphere and it is
giving back to the atmosphere; it comes into the engine and goes out of the engine back
into the atmosphere; and this is what Professor Pradeep mentioned as an open cycle that it
of it occurs in a cycle, it is taken inside the engine it goes through what we call thermo-dynamically
a cycle, and we will discuss that through the course of this lecture series in some
detail. And at the end of this operation of creation
of propulsive force, the air is ejected out of the cycle into the atmosphere back into
the atmosphere. Now this is an important concept and because
of the success of this concept, the jet aircraft propulsion has became such an all pervading
technological use in our life. Now, let us look at various aspects of how
the propulsive devices are developed. Surprisingly, in the 1920s immediately after
the world war one in US, under the high powered committee working under NACA, which was the
National Administrative Council for Aspects, various aspects of Aeronautical developments,
and they actually concluded that a jet engine was not a feasible proposition at that point
of time after going through various aspects of science and technology that is required
to make a jet engine work. And because of this high powered committee’s
recommendation, very little work was done in US on jet engine development. Now, we all of course know, that most of the
jet engine development have been going on for last 50 years a big chunk of it is actually
in US, but quite surprisingly prior to that prior to world war two, very little work was
going on in US because, this particular committee had decided that jet engine was not a feasible
proposition. However, Frank Whittle had later on Sir Frank
Whittle, he went ahead quietly and patented his concept of jet engine and we will have
a look at his jet engine in few minutes from now and he did that in England in 1930. And this patent is what is normally considered
the first patent of a jet engine or first patent granted to jet engine in the whole
world. Later on after the world war two, Sir Frank
Whittle actually migrated to US; and he spent most of his developments, developing years
in US, developing various forms of jet engine, starting of course from his own concept of
jet engine. Doctor Hans Von Ohain working independently
in Germany, along the same time as Frank Whittle also went ahead, and patented in Germany,
his concept of jet engine in 1936. Now, these two are independent development
they had no connection with each other and those days remember, the communication channels
were not very easily established. So, they did their work independently, developed
the concept independently and went ahead and patented them independently, in their own
countries. And this engine developed by Doctor Hans Von
Ohain actually flew with the Heinkel aircraft in 1939; and this was indeed the first jet
engine to fly. So, the jet engine developed in Germany by
Doctor Von Ohain was indeed the first jet engine to fly before Sir Frank Whittle’s
engine. Now after the world war two we know that the
world was in term all, and after the world two Doctor Von Ohain also migrated to US,
and he also developed many of his later developments in USA. So, both the further figures of the jet engine
development the mode in jet engine development later on did most of their work in US; and
that also explains why after the world war two many of the jet engine were indeed developed
in US. Of course, we have seen lot of development
also going in England and Germany and many other countries in Europe. Let us take a quick look at the fundamental
concept of how a jet propulsion device indeed creates a propulsive force. Now, as I mention the typical aircraft actually
uses air, now what we see in this simple hand sketch is that air comes into the to propulsive
device from the front; and this air comes in with a certain velocity let us say Va;
and this is the scenario you would have when the aircraft is indeed flying; so, when the
aircraft is flying it is coming in with a certain velocity which is matching with the
flight speed of the aircraft; so, the flight speed of the aircraft makes a certain amount
of air come inside the jet propulsion device; and then the propulsive device does its propulsive
work on this air; and then lets it out through the rear with another velocity which is V
e. And the Newton’s laws quite clearly tell
us that if you are to get a positive amount of force created out of this device, it is
necessary that V e should be substantially higher than V a; and then the amount of mass
that is activated; so, the product of the mass that is activated; and the acceleration
or the change of velocity that takes place over this propulsive device indeed creates
the propulsive force. Now this is the simple concept based on which
the propulsive devices have been created; so, all jet aircraft engines that we will
be talking about over the period of this lecture series will indeed be operative based on this
fundamental concept. Now, let us see how the whole concept have
indeed developed. You see the key to a practical jet engine
was the gas turbine from which it indeed derives its name. The basic jet engine is technically also referred
to as a gas turbine engine; and the key to this is actually the operation of a turbine
or gas turbine, which is used to extract energy from the engine itself; and you will need
this gas turbine to drive a compressor. So you have a coupling of a turbine and a
compressor, which is an absolute necessity for working of this kind of an engine. And you need a combination of turbine and
compressor, which then creates a loop energy loop inside the engine and this energy loop,
is the key to the development of practical jet engine. Now, gas turbine is an old concept; it is
been around for a very long time. The development actually practical development
started in 1930s; compressor development started actually a little later, but the patent for
a stationary turbine was granted to John Barber in England way back in 1791; that is a little
more than 200 years back. So turbine as a concept or gas turbine as
a concept has been around for little more than actually 200 years. Now, turbines have been around turbines have
been around as a wind turbines; they have been around as water turbines literally for
hundreds of years; people have been using the concept of using either water or air to
rotate a turbine like rotor to develop energy, to develop shaft power and to develop work;
and this is how the wind turbines have been developed; they have been around for centuries
now; the water turbines have been around for also centuries. So the concept of using flowing fluid whether
its water or air to run a turbine in a rotating mode and to create shaft power and to get
work out of it as a concept has been around for literally centuries. Gas turbine as a concept has been around for
now little more than 200 years. The first gas turbine was successfully run
technologically proven was built in 1903 according to the documents that are available by a Norwegian
engineer Egidius Elling; now this is little more than 100 years back. The point is making a gas turbine work you
need gas, you need turbine material, that can with stand the gas temperature and pressure,
and hence there are certain technological requirements for making a gas turbine work. So, in design and practical engineering and
certain aspects of material requirement of metallurgy quite often prevented actual manufacturing
of these engines on large scale. So, large scale use of gas turbine came off
a little later even though it was proven way back in 1903; mark the date 1903 is also the
year in which Wright brothers flew their first aircraft. Now this is the engine, which was created
by Sir Frank Whittle, and this particular engine you are looking at is indeed the engine
that flew. So the first patent he created was way back
in 1930, this it jet engine flew about 7 or 8 years after that, a little after Doctor
Von Ohain’s engine flew in Heinkel aircraft, now this engine is conceptually and in detail
somewhat different form Doctor Von Ohain’s engine. Now this consists of for example, a centrifugal
compressor a number of these cylinders that you see around that look like gas cylinders,
they are indeed the combustion chambers and on the side you can see a centrifugal compressor,
we will have a look at what a centrifugal compressor is later on in this course in some
detail. And on this one what you can see here is the
back of the engine the jet nozzle; the nozzle through which, the jet comes out a hot jet
which is been gone through which is gone through a process of compression in the centrifugal
compressor or process of combustion in these combustion chambers, which are wrapped around
the engine they supply the hot gas, which is been compressed; so, it goes into a turbine,
which one is not able to see here very clearly, and then it comes out through this jet for
creation of jet thrust so, this is what Sir Frank Whittle’s jet engine was that flew
for the first time around 1938. If on the other hand if you look at the Heinkel
engine that was created by Doctor Von Ohain that looks little a more like various kinds
of jet engines that we see today. Now this is the engine this is of course,
a picture taken in a museum, and you can see the various modern components of the jet engine,
you can see the compressors over here, and then you have the combustion chamber, and
then you have the turbine, and it looks more like a modern jet engine and the jet nozzle
through which the jet hot jet finally, comes out. Now, this is Von Ohain’s concept of jet
engine and this is the kind of engine that indeed flew as Heinkel engine. Heinkel was a business man who supported the
work of Doctor Von Ohain who was indeed a proper academician and a researcher, and this
engine was as we now the first jet engine that flew. Now this is the kind concept that you would
see you see what happens is if you look at Sir Von Ohain’s engine it is a sleek long
engine that takes in air from the front and lets out air from the rear creating jet propulsion
force. If for example, if you put such a engine inside
the body of the aircraft this is the scenario, you would probably have with you the engine
is good in proper buried inside the body of an aircraft; and air has to be ingested into
this engine; so, you would need rather long air intake system; we will be talking about
the intake system later on in this course. And this intake system delivers the air into
it takes from the atmosphere delivers it inside the engine; the engine does it is various
kinds of technological work on the air, and then the hot air or gas is finally, let out
through a long tail pipe creating a propelling jet. Now this is how the jet thrust would indeed
be created, if you have an engine that is buried inside an aircraft and this is how
the whole business indeed started that you have one engine buried inside aircraft; in
those days, in the early days, the aircraft were indeed small and one engine was considered
quite often sufficient to make the aircraft fly. The typical components of the jet engine are
for example, shown here and we will be looking at them more and more as we go along in this
lecture series you have you would indeed have a rotary compressor, which we shall see is
quite different from the piston compressor which you would normally do in other courses
and we have done a little bit of that in the introduction jet propulsion course, this rotary
compressor then actually moves in a rotary shaft which is indeed to run by the turbine. So what just now I was saying is that you
need a turbine to run the compressor so if turbine compressor is a kind of a combination,
which is buried inside this jet engine device, and this is essential or key to the development
of the jet engines, in the sense the turbine compressor combination creates the high pressure
air or working medium, which is then ingested with a fuel and raise to high temperature,
so that one finally creates high temperature and pressure gas, which is used to create
the propelling jet. So, quick key to the development of jet engine
was indeed development of turbine and immediately there after development of rotary compressor
and we shall see various kinds of compressors as we go along in this lecture series. Here, we look at a very simple schematic of
a modern gas turbine based jet engine. Typically, you would have the air coming in
from the front ingested into this jet engine through this opening that is available, and
these are to be properly geometrically designed, and the air has it comes in goes through a
rotary compressor has we just saw, the rotary compressor or the process of compression may
be done in stages. The typically compression process we would
be studying in this course, effectively refers to what is also known as aerodynamic compressor,
as oppose to positive displacement compressor, which we you do in piston engines. Now this kind of compression, which is a rotary
compressor uses rotary compressor uses various laws of aerodynamics to create the compression
of air. This compressed air is then delivered into
this combustion chamber in which fuel is indeed burned very small amount of fuel is burnt
and that is sufficient to raise the temperature of the air to very high temperatures; so,
what we have is air infused with a small amount of fuel and one may call it then gas; fundamentally
it is air; and then this hot highly compressed and high temperature gas is then released
on to the turbine, which is indeed also a rotary turbine and this rotary turbine extracts
work out of it as is required of a turbine all kinds of turbine, and this turbine then
through the shaft runs the compressor. So, this what I was saying that you need a
mechanical coupling of the turbine compressor, and this turbine compressor coupling creates
the high pressure gas inside of which is the stomach of the engine and that is where the
fuel is burnt, and the combination of turbine compressor combustion chamber often referred
to as a co engine creates the high pressure high temperature gas, and this is then let
out through the nozzle which creates the jet propulsion thrust. So, this the development that is taken place
so, all the aircraft engine that we will be talking about over the course of this lecture
series will have some form of rotary compressor, it will have some form of combustion chamber
and some form of rotary turbine and we will be also talking about various aspects of the
intakes shapes and their geometries and various kinds of nozzles that create the that help
create the final thrust and their geometries. These are the various things that we will
be talking about over the course of this lecture series. We will take a look at a very modern aircraft
jet engine. You see if you just go back very quickly to
the earlier one discriminate schematic actually shows the line drawing or just a cutout lets
us say 2D cut out of the rotary compressor combustion chamber turbine. It looks at this movement reasonably a simple
device. The moment you look at a three-dimensional
picture of a modern aircraft jet engine, and this particular picture is indeed a picture
of a actual modern jet engine. You can actually see inside of this literally
hundreds probably thousands of parts. This is the mechanical engineering that goes
into creation of a modern jet engine; the front parts or the parts that we referred
to as the rotary compressor, and then you have the combustion chamber here, and then
you have the rotary turbines over here; all these and then you have the shaft system along
shaft system which as you can in this engine and most of the engine that we will see later
on are actually hallow shafts. And of course, they need to be hallow these
parts need to be devised very carefully, because they are going on an aircraft. In an aircraft one of the most important parameters
that we will see a later on in this course is the thrust to weight ratio; so, weight
of these engine is a crucial point in the development and design of these kind of jet
engine. Every part will have to be literally weighed
in and should qualify to be on an aircraft engine so, these hundreds of parts that go
to it are very carefully designed and weighed in and their utility have to be completely
justified to be inside an aircraft engine. Hence, you can see here that an aircraft engine
indeed consists of literally hundreds and thousands of parts, which actually finally
make an aircraft engine that is worthy of putting on an aircraft and flying on an aircraft
various kinds of aircraft; whether it is large aircraft or small aircraft; some of the basic
requirements of aircraft are very similar; We shall have a look at various kinds of engines
that go into various kinds of aircraft, and over the course of this lecture series we
will have a look at all these parts that you are looking at, and how these parts have been
put in place to make up a whole aircraft jet propulsion system.

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