Jet engine seminar report

Jet engines Seminar Report 2017-
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1. INTRODUCTION
A jet engine is a reaction engine discharging a fast-moving jet that generates thrust by jet
propulsion. This broad definition includes air breathing jet engines (turbojets, turbofans,
ramjets) In general, jet engines are combustion engines. In common parlance, the term jet
engine loosely refers to an internal combustion air breathing jet engine. These typically feature a
rotating air compressor powered by a turbine, with the leftover power providing thrust via a
propelling nozzle , this process is known as the Brayton thermodynamic cycle. Jet aircraft use
such engines for long-distance travel. Early jet aircraft used turbojet engines which were
relatively inefficient for subsonic flight. Modern subsonic jet aircraft usually use more complex
high-bypass turbofan engines. These engines offer high speed and greater fuel efficiency than
piston and propeller aero engines over long distances.
Dept.Of Mechanical Engineering 1 St. Mary’s Polytechnic College Palakkad

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2. THE HISTORY OF JET ENGINE
• Sir Isaac Newton in the 18th century was the first to theorize that a rearward-channeled
explosion could propel a machine forward at a great rate of speed. This theory was based on
his third law of motion. As the hot air blasts backwards through the nozzle the plane moves
forward.
• Henri Giffard built an airship which was powered by the first aircraft engine, a three-
horse power steam engine. It was very heavy, too heavy to fly.
• In 1874, Felix de Temple, built a monoplane that flew just a short hop down a hill with
the help of a coal fired steam engine.
• Otto Daimler, in the late 1800's invented the first gasoline engine.
• In 1894, American Hiram Maxim tried to power his triple biplane with two coal fired
steam engines. It only flew for a few seconds.
• The early steam engines were powered by heated coal and were generally much too
heavy for flight.
• American Samuel Langley made a model airplanes that were powered by steam engines. In
1896, he was successful in flying an unmanned airplane with a steam-powered engine,
called the Aerodrome. It flew about 1 mile before it ran out of steam. He then tried to build
a full sized plane, the Aerodrome A, with a gas powered engine. In 1903, it crashed
immediately after being launched from a house boat.

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• In 1903, the Wright Brothers flew, The Flyer, with a 12 horse power gas powered
engine.
• From 1903, the year of the Wright Brothers first flight, to the late 1930s the gas powered
reciprocating internal-combustion engine with a propeller was the sole means used to propel
aircraft.
• It was Frank Whittle, a British pilot, who designed the first turbo jet engine in 1930. The
first Whittle engine successfully flew in April, 1937. This engine featured a multistage
compressor, and a combustion chamber, a single stage turbine and a nozzle.

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3. ABOUT INVENTORS
Dr. Hans von Ohain and Sir Frank Whittle are both recognized as being the co-inventors of the
jet engine. Each worked separately and knew nothing of the other's work. Hans von Ohain is
considered the designer of the first operational turbojet engine. Frank Whittle was the first to
register a patent for the turbojet engine in 1930. Hans von Ohain was granted a patent for his
turbojet engine in 1936. However, Hans von Ohain's jet was the first to fly in 1939. Frank
Whittle's jet first flew in in 1941.
Sir Frank Whittle was an English aviation engineer and pilot, the son of a mechanic, Frank
Whittle joined the Royal Air Force or RAF as an apprentice. He joined an RAF fighter
squadron in 1928 and became a test pilot in 1931. The young RAF officer was only 22 when he
first thought to use a gas turbine engine to power an airplane. While often regarded as the father
of modern jet propulsion systems, the young Frank Whittle tried without success to obtain
official support for study and development of his ideas. He had to persist his research on his
own initiative and received his first patent on turbojet propulsion in January 1930.
With private financial support, he began construction of his first engine in 1935. This engine,
which had a single-stage centrifugal compressor coupled to a single-stage turbine, was
successfully bench tested in April 1937; it was only a laboratory test rig, never intended for use
in an aircraft, but it did demonstrate the feasibility of the turbojet concept. The modern turbojet
engine used in many British and American aircraft is based on the prototype that Frank Whittle
invented.
The firm of Power Jets Ltd., with which Whittle was associated, received a contract for a
Whittle engine, known as the W1, on July 7, 1939. This engine was intended to power a small
experimental aircraft. In February 1940, the Gloster Aircraft Company was chosen to develop
the aircraft to be powered by the W1 engine - the Pioneer. The historic first flight of the Pioneer
took place on May 15, 1941, with Flight Lieutenant P. E. G. Sayer as pilot.

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born: June 1, 1907, Coventry, Warwickshire, England
died: Aug. 8, 1996, Columbia, Md., U.S.
Doctor Hans Von Ohain was a German airplane designer who invented an operational jet
engine. Hans Von Ohain obtained his doctorate in Physics at the University of Göttingen in
Germany and then became the junior assistant to Hugo Von Pohl, director of the Physical
Institute at the University. German aircraft builder, Ernst Heinkel asked the university for
assistance in new airplane propulsion designs and Pohl recommended his star pupil. Hans Von
Ohain, was investigating a new type of aircraft engine that did not require a propeller. Only
twenty-two years old when he first conceived the idea of a continuous cycle combustion engine
in 1933, Hans Von Ohain patented a jet propulsion engine design similar in concept to that of
Sir Frank Whittle but different in internal arrangement in 1934.
Hans Von Ohain joined Ernst Heinkel in 1936 and continued with the development of his
concepts of jet propulsion. A successful bench test of one of his engines was accomplished in
September 1937. A small aircraft was designed and constructed by Ernst Heinkel to serve as a
test bed for the new type of propulsion system - the Heinkel He178. The Heinkel He178 flew
for the first time on August 27, 1939. The pilot on this historic first flight of a jet-powered
airplane was Flight Captain Erich Warsitz.
Hans Von Ohain developed a second improved jet engine, the He S.8A, which was first flown
on April 2, 1941.
born: Dec. 14, 1911 , Dessau, Germany
died: March 13, 1998, Melbourne, Fla., U.S.

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4. TYPES OF JET ENGINE
4.1 Turbojet
The turbojet is the oldest kind of general-purpose air breathing jet engine. Two engineers, Frank
Whittle in the United Kingdom and Hans von Ohain in Germany, developed the concept
independently into practical engines during the late 1930s.
The turbojet engine consists of four sections: compressor, combustion chamber, turbine section,
and exhaust. The compressor section passes inlet air at a high rate of speed to the combustion
chamber. The combustion chamber contains the fuel inlet and igniter for combustion. The
expanding air drives a turbine, which is connected by a shaft to the compressor, sustaining
engine operation. The accelerated exhaust gases from the engine provide thrust. This is a basic
application of compressing air, igniting the fuel-air mixture, producing power to self-sustain the
engine operation, and exhaust for propulsion.
Figure 4.1 turbojet

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4.2 Turboprop
A turboprop engine is a turbine engine that drives a propeller through a reduction gear. The
exhaust gases drive a power turbine connected by a shaft that drives the reduction gear
assembly. Reduction gearing is necessary in turboprop engines because optimum propeller
performance is achieved at much slower speeds than the engine’s operating rpm. Turboprop
engines are a compromise between turbojet engines and reciprocating power plants. Turboprop
engines are most efficient at speeds between 250 and 400 mph and altitudes between 18,000 and
30,000 feet. They also perform well at the slow airspeeds required for takeoff and landing, and
are fuel efficient.
Figure 4.2 turboprop
A turboprop engine is a type of turbine engine which drives an aircraft
propeller using a reduction gear.The gas turbine is designed specifically for
this application, with almost all of its output being used to drive the
propeller. The engine's exhaust gases contain little energy compared to a
jet engine and play only a minor role in the propulsion of the aircraft.

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The propeller is coupled to the turbine through a reduction gear that
converts the high RPM, low torque output to low RPM, high torque. The
propeller itself is normally a constant speed (variable pitch) type similar to
that used with larger reciprocating aircraft engines.

4.3 Turbofan
The turbofan is a type of air breathing jet engine that is widely used for aircraft propulsion. The
turbofan is basically the combination of two engines, the turbo portion which is a conventional
gas turbine engine, and the fan, a propeller-like ducted fan. The engine produces thrust through
a combination of these two portions working in concert; engines that use more jet thrust relative
to fan thrust are known as low bypass turbofans, while those that have considerably more fan
thrust than jet are known as high bypass. Most commercial aviation jet engines in use today are
of the high-bypass type, and most modern military engines are low-bypass,
Figure 4.3 turbofan

Turbofans were developed to combine some of the best features of the turbojet and the
turboprop. Turbofan engines are designed to create additional thrust by diverting a secondary air
flow around the combustion chamber. The turbofan bypass air generates increased thrust, cools
the engine, and aids in exhaust noise suppression. This provides turbojet-type cruise speed and
lower fuel consumption.
The inlet air that passes through a turbofan engine is usually divided into two separate streams
of air. One stream passes through the engine core, while a second stream bypasses the engine
core. It is this bypass stream of air that is responsible for the term “bypass engine.” A turbofan’s
bypass ratio refers to the ratio of the mass airflow that passes through the fan divided by the
mass airflow that passes through the engine core.

4.4 Turboshaft
The fourth common type of jet engine is the turboshaft. It delivers power to a shaft that drives
something other than a propeller. The biggest difference between a turbojet and turboshaft
engine is that on a turboshaft engine, most of the energy produced by the expanding gases is
used to drive a turbine rather than produce thrust. Many helicopters use a turboshaft gas turbine
engine. In addition, turboshaft engines are widely used as auxiliary power units on large aircraft.
Figure 4.4 turboshaft
A turboshaft engine is made up of two major parts assemblies: the gas generator and the power
section. The gas generator consists of thecompressor, combustion chambers with ignitors and
fuel nozzles, and one or more stages of turbine. The power section consists of additional stages
of turbines, a gear reduction system, and the shaft output. The gas generator creates the hot
expanding gases to drive the power section. Depending on the design, the engine accessories
may be driven either by the gas generator or by the power section.
In most designs the gas generator and power section are mechanically separate so that they may
each rotate at different speeds appropriate for the conditions. This is referred to as a free power

turbine. A free power turbine can be an extremely useful design feature for vehicles, as it
allows the design to forego the weight and cost of complex multi-ratio transmissions and
clutches.

4.5 Ramjet
A ramjet, sometimes referred to as a flying stovepipe or an athodyd (an abbreviation
of aero thermodynamic duct), is a form of airbreathing jet engine that uses the engine's forward
motion to compress incoming air without an axial compressor. Because ramjets cannot produce
thrust at zero airspeed, they cannot move an aircraft from a standstill. A ramjet-powered vehicle,
therefore, requires an assisted take-off like a rocket assist to accelerate it to a speed where it
begins to produce thrust. Ramjets work most efficiently at supersonic speeds around Mach 3
(2,300 mph; 3,700 km/h). This type of engine can operate up to speeds of Mach 6 (4,600 mph;
7,400 km/h).
Figure 4.5 ramjet
Ramjets can be particularly useful in applications requiring a small and simple mechanism for
high-speed use, such asmissiles. Weapon designers are looking to use ramjet technology
in artillery shells to give added range; a 120 mm mortar shell, if assisted by a ramjet, is thought
to be able to attain a range of 35 km (22 mi). They have also been used successfully, though not
efficiently, as tip jets on the end of helicopter rotors.

5. PARTS OF A JET ENGINE
Figure 5.1 parts of a jet engine
Fan - The fan is the first component in a turbofan. The large spinning fan
sucks in large quantities of air. Most blades of the fan are made of
titanium. It then speeds this air up and splits it into two parts. One part
continues through the "core" or center of the jet engine, where it is acted
upon by the other jet engine components.
The second part "bypasses" the core of the jet engine. It
goes through a duct that surrounds the core to the back of the jet engine
where it produces much of the force that propels the airplane forward.
This cooler air helps to quiet the jet engine as well as adding thrust to the
jet engine.
Compressor - The compressor is the first component in the jet engine
core. The compressor is made up of fans with many blades and attached to
a shaft. The compressor squeezes the air that enters it into progressively
smaller areas, resulting in an increase in the air pressure. This results in an

increase in the energy potential of the air. The squashed air is forced into
the combustion chamber.
Combustor - In the combustor the air is mixed with fuel and then
ignited. There are as many as 20 nozzles to spray fuel into the airstream.
The mixture of air and fuel catches fire. This provides a high temperature,
high-energy airflow. The fuel burns with the oxygen in the compressed air,
producing hot expanding gases. The inside of the combustor is often made
of ceramic materials to provide a heat-resistant chamber. The heat can
reach 2700°.
Turbine - The high-energy airflow coming out of the combustor goes
into the turbine, causing the turbine blades to rotate. The turbines are
linked by a shaft to turn the blades in the compressor and to spin the
intake fan at the front. This rotation takes some energy from the high-
energy flow that is used to drive the fan and the compressor. The gases
produced in the combustion chamber move through the turbine and spin
its blades. The turbines of the jet spin around thousands of times. They
are fixed on shafts which have several sets of ball-bearing in between
them.
Nozzle - The nozzle is the exhaust duct of the jet engine. This is the jet
engine part which actually produces the thrust for the plane. The energy
depleted airflow that passed the turbine, in addition to the colder air that
bypassed the engine core, produces a force when exiting the nozzle that
acts to propel the engine, and therefore the airplane, forward. The
combination of the hot air and cold air are expelled and produce an
exhaust, which causes a forward thrust. The nozzle may be preceded by a
mixer, which combines the high temperature air coming from the jet

engine core with the lower temperature air that was bypassed in the fan.
The mixer helps to make the jet engine quieter.

6. HOW A JET ENGINE WORKS
Figure 6.1 jet engine working
1. For a jet going slower than the speed of sound, the engine is moving through the air at
about 1000 km/h (600 mph). We can think of the engine as being stationary and the cold
air moving toward it at this speed.
2. A fan at the front sucks the cold air into the engine and forces it through the inlet. This
slows the air down by about 60 percent and its speed is now about 400 km/h (240 mph).
3. A second fan called a compressor squeezes the air (increases its pressure) by about eight
times, and this dramatically increases its temperature.
4. Kerosene (liquid fuel) is squirted into the engine from a fuel tank in the plane's wing.
5. In the combustion chamber, just behind the compressor, the kerosene mixes with the
compressed air and burns fiercely, giving off hot exhaust gases and producing a huge
increase in temperature. The burning mixture reaches a temperature of around 900°C
(1650°F).
6. The exhaust gases rush past a set of turbine blades, spinning them like a windmill. Since
the turbine gains energy, the gases must lose the same amount of energy—and they do

so by cooling down slightly and losing pressure.
7. The turbine blades are connected to a long axle (represented by the middle gray line) that
runs the length of the engine. The compressor and the fan are also connected to this axle.
So, as the turbine blades spin, they also turn the compressor and the fan.
8. The hot exhaust gases exit the engine through a tapering exhaust nozzle. Just as water
squeezed through a narrow pipe accelerates dramatically into a fast jet (think of what
happens in a water pistol), the tapering design of the exhaust nozzle helps to accelerate
the gases to a speed of over 2100 km/h (1300 mph). So the hot air leaving the engine at
the back is traveling over twice the speed of the cold air entering it at the front—and
that's what powers the plane. Military jets often have an after burnerthat squirts fuel into
the exhaust jet to produce extra thrust. The backward-moving exhaust gases power the
jet forward. Because the plane is much bigger and heavier than the exhaust gases it
produces, the exhaust gases have to zoom backward much faster than the plane's own
speed.

7. HOW THE AIR FLOWS THROUGH A JET ENGINE
Jet engines move the airplane forward with a great force that is produced by a tremendous
thrust and causes the plane to fly very fast. All jet engines, which are also called gas turbines,
work on the same principle. The engine sucks air in at the front with a fan. A compressor
raises the pressure of the air. The compressor is made up of fans with many blades and
attached to a shaft. The blades compress the air. The compressed air is then sprayed with fuel
and an electric spark lights the mixture. The burning gases expand and blast out through the
nozzle, at the back of the engine. As the jets of gas shoot backward, the engine and the aircraft
are thrust forward.
The air goes through the core of the engine as well as around the core. This causes some of the
air to be very hot and some to be cooler. The cooler air then mixes with the hot air at the engine
exit area.
A jet engine operates on the application of Sir Isaac Newton's third law of physics: for every
action there is an equal and opposite reaction. This is called thrust. This law is demonstrated in
simple terms by releasing an inflated balloon and watching the escaping air propel the balloon
in the opposite direction. In the basic turbojet engine, air enters the front intake and is
compressed, then forced into combustion chambers where fuel is sprayed into it and the mixture
is ignited. Gases which form expand rapidly and are exhausted through the rear of the
combustion chambers. These gases exert equal force in all directions, providing forward thrust
as they escape to the rear. As the gases leave the engine, they pass through a fan-like set of
blades (turbine) which rotates the turbine shaft. This shaft, in turn, rotates the compressor,
thereby bringing in a fresh supply of air through the intake. Engine thrust may be increased by
the addition of an afterburner section in which extra fuel is sprayed into the exhausting gases
which burn to give the added thrust. At approximately 400 mph, one pound of thrust equals one
horsepower, but at higher speeds this ratio increases and a pound of thrust is greater than one

horsepower. At speeds of less than 400 mph, this ratio decreases.
In a turboprop engine, the exhaust gases are also used to rotate a propeller attached to the
turbine shaft for increased fuel economy at lower altitudes. A turbofan engine incorporates a
fan to produce additional thrust, supplementing that created by the basic turbojet engine, for
greater efficiency at high altitudes. The advantages of jet engines over piston engines include
lighter weight with greater power, simpler construction and maintenance with fewer moving
parts, and efficient operation with cheaper fuel.

8. WHAT IS THRUST?
Thrust is the forward force that pushes the engine and, therefore, the airplane forward. Sir Isaac
Newton discovered that for "every action there is an equal and opposite reaction." An engine
uses this principle. The engine takes in a large volume of air. The air is heated and compressed
and slowed down. The air is forced through many spinning blades. By mixing this air with jet
fuel, the temperature of the air can be as high as three thousand degrees. The power of the air is
used to turn the turbine. Finally, when the air leaves, it pushes backward out of the engine. This
causes the plane to move forward.
.

9. USES OF JET ENGINE
• Jet engines are usually used as aircraft engines for jet aircraft. They are also used for
cruise missiles and unmanned aerial vehicles.
• In the form of rocket engines they are used for fireworks, model rocketry, spaceflight,
and military missiles.
• Jet engines have also been used to propel high speed cars, particularly drag racers, with
the all-time record held by a rocket car. A turbofan powered car Thrust SSC currently
holds the land speed record.
• Jet engine designs are frequently modified for non-aircraft applications, as industrial
gas turbines. These are used in electrical power generation, for powering water, natural
gas, or oil pumps, and providing propulsion for ships and locomotives. Industrial gas
turbines can create up to 50,000 shaft horsepower. Many of these engines are derived
from older military turbojets such as the Pratt & Whitney J57 and J75 models. There is
also a derivative of the P&W JT8D low-bypass turbofan that creates up to 35,000 HP.

10. JET ENGINES AND CAR ENGINES
One way to understand modern jet engines is to compare them with the piston engines used in
early airplanes, which are very similar to the ones still used in cars. A piston engine (also
called a reciprocating engine, because the pistons move back and forth or "reciprocate") makes
its power in strong steel "cooking pots" called cylinders. Fuel is squirted into the cylinders
with air from the atmosphere. The piston in each cylinder compresses the mixture, raising its
temperature so it either ignites spontaneously (in a diesel engine) or with help from a sparking
plug (in a gas engine). The burning fuel and air explodes and expands, pushing the piston back
out and driving the crankshaft that powers the car's wheels (or the plane's propeller), before the
whole four-step cycle (intake, compression, combustion, exhaust) repeats itself. The trouble
with this is that the piston is driven only during one of the four steps—so it's making power
only a fraction of the time. The amount of power a piston engine makes is directly related to
how big the cylinder is and how far the piston moves; unless you use hefty cylinders and
pistons (or many of them), you're limited to producing relatively modest amounts of power. If
your piston engine is powering a plane, that limits how fast it can fly, how much lift it can
make, how big it can be, and how much it can carry.
A jet engine uses the same scientific principle as a car engine: it burns fuel with air (in a
chemical reaction called combustion) to release energy that powers a plane, vehicle, or other
machine. But instead of using cylinders that go through four steps in turn, it uses a long metal
tube that carries out the same four steps in a straight-line sequence—a kind of thrust-making
production line! In the simplest type of jet engine, called a turbojet, air is drawn in at the front
through an inlet (or intake), compressed by a fan, mixed with fuel and combusted, and then
fired out as a hot, fast moving exhaust at the back.

Three things make a jet engine more powerful than a car's piston engine:
1. A basic principle of physics called the law of conservation of energy tells us that if a
jet engine needs to make more power each second, it has to burn more fuel each
second. A jet engine is meticulously designed to hoover up huge amounts of air and
burn it with vast amounts of fuel (roughly in the ratio 50 parts air to one part fuel), so
the main reason why it makes more power is because it can burn more fuel.
2. Because intake, compression, combustion, and exhaust all happen simultaneously, a jet
engine produces maximum power all the time (unlike a single cylinder in a piston
engine).
3. Unlike a piston engine (which uses a single stroke of the piston to extract energy), a
typical jet engine passes its exhaust through multiple turbine "stages" to extract as
much energy as possible. That makes it much more efficient (it gets more power from
the same mass of fuel).

11. CONCLUSION
The Jet engine's invention changed the future. With jet engines, planes can carry more cargo,
fly faster, and go farther than any propeller plane. Today, the fastest passanger jet flies from
london to new york in 7-8 hours. Planes have made it easier to see new places, and experience
new cultures. Billions of people have flown in airplanes and the number keeps getting bigger,
so it's safe to say that it's changed these peoples lives, and has changed the world. War's are
also fought with jets. In the Iraq war we've used jets to fight terrorism, and also in Afganistan.
Plus, old battleships have been converted to aircraft carriers because fighter jets are simply
better. Jet's have changed the way people lived. They've made traveling faster, and more
efficient, and have made a big change in militaries all over the world. The jet engine changed
history.

12.REFERENCES
https://en.wikipedia.org/wiki/Jet_engine
http://www.explainthatstuff.com/jetengine.html
https://theinventionofthejetengine.weebly.com/conclusion.html

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