MECHANICAL
ENGINEERING
SEMINAR
PRESENTATION
ON
“ JET ENGINE”
Presented By:
Sagar Kumar Pattnaik
8th Semester, Regd No- 0601222357
Department of Mechanical
Engineering
JET ENGINE
Jet Engine is an engine that discharges a fast moving jet of
fluid to generate thrust in accordance with Newton’s Third
Law of Motion . This broad definition of jet engines
includes turbojets, turbofans, rocket, ramjets , pulsejets and
pump-jets, but in common usage, the term generally refers
to a gas turbine Brayton cycle engine, an engine with a
rotary compressor powered by a turbine.
HISTORY
Timeline of Jet Power* Jet engines can be dated back to the first
century AD, when
Hero of Alexandria invented the aeolipile. It
was simply
considered a curiosity.
* Jet propulsion -Invention of the rocket by the
Chinese in the
11th century.
* In Ottoman Turkey in 1633 Lagari Hasan Çelebi
a cone shape rocket was invented.
* For Army Dr.Hans Von Ohain and Sir Frank
Whittle are both recognized as being the coinventors of the Jet Engine.
Ohain's jet was the first to fly in
1939.
Frank Whittle's jet first flew in
1941.
Sir Frank Whittle(left) and Dr.Hans
Von Ohain
TYPES OF JET ENGINE
*Water jet
*Motorjet
*Turbojet
*Turbofan
*Rocket
*Ramjet
*Turboprop, Turboshaft(similar)
*Propfan/Unducted Fan
*Pulsejet
*Pulse detonation engine
*Air-augmented rocket
*Scramjet
*Turborocket
WORKING OF JET ENGINE
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.
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.
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.
Compressor and Combustor
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.
Combuster- 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.
Turbine and Nozzle
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.
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.
DIFFERENT TYPES OF JET ENGINE
*Turbojet EngineThe Basic idea of the Turbojet Engine is simple. Air taken
in from an opening in the front of the engine is compressed
to 3 to 12 times its original pressure in compressor. Fuel is
added to the air and burned in a combustion chamber to
raise the temperature of the fluid mixture to about 1,100°F
to 1,300° F. The resulting hot air is passed through a
turbine, which drives the compressor. If the turbine and
compressor are efficient, the pressure at the turbine
discharge will be nearly twice the atmospheric pressure,
and this excess pressure is sent to the nozzle to produce a
high-velocity stream of gas which produces a thrust.
Substantial increases in thrust can be obtained by
employing an afterburner. It is a second combustion
chamber positioned after the turbine and before the nozzle.
*Turboprop Jet Engine -
A Turboprop Engine is a Jet Engine attached to a
propellor. The turbine at the back is turned by the hot
gases, and this turns a shaft that drives the propellor. Some
small airliners and transport aircraft are powered by
turboprops.
Like the turbojet, the turboprop engine consists of a
compressor, combustion chamber, and turbine, the air and
gas pressure is used to run the turbine, which then creates
power to drive the compressor. Compared with a turbojet
engine, the turboprop has better propulsion efficiency at
flight speeds below about 500 miles per hour.
*Turbofan Jet Engine-
A Turbofan Engine has a large fan at the front, which sucks
in air. Most of the air flows around the outside of the engine,
making it quieter and giving more thrust at low speeds. Most
of today's airliners are powered by turbofans. In a turbojet
all the air entering the intake passes through the gas
generator, which is composed of the compressor, combustion
chamber, and turbine. In a turbofan engine only a portion of
the incoming air goes into the combustion chamber. The
remainder passes through a fan, or low-pressure compressor,
and is ejected directly as a "cold" jet or mixed with the gasgenerator exhaust to produce a "hot” jet.
*Turboshaft Engines-
-
This is another form of gas-turbine engine that operates much
like a Turboprop System. It does not drive a propellor. Instead,
it provides power for a helicopter rotor. The turboshaft engine
is designed so that the speed of the helicopter rotor is
independent of the rotating speed of the gas generator. This
permits the rotor speed to be kept constant even when the
speed of the generator is varied to modulate the amount of
power produced.
*Ramjets-
The most simple jet engine has no moving parts. The
speed of the jet "rams" or forces air into the engine. It is
essentially a turbojet in which rotating machinery has
been omitted. Its application is restricted by the fact that
its compression ratio depends wholly on forward speed.
The ramjet develops no static thrust and very little thrust
in general below the speed of sound. As a consequence, a
ramjet vehicle requires some form of assisted takeoff,
such as another aircraft. It has been used primarily in
guided-missile systems. Space vehicles use this type of
jet.
CONCLUSION
Jet engines can be dated back to the first century AD.
The patent for a stationary turbine was granted to
John Barber in England in 1791. The broad definition
of jet engines includes turbojets, turbofans, rockets,
ramjets, pulse jets and pump-jets, but in common
usage, the term generally refers to a gas turbine
Brayton cycle engine, Most jet engines are internal
combustion engines By the 1960s all large civilian
aircraft were also jet powered, The ascension of the
jet engine to almost universal use in aircraft took
well under twenty years.
The turboprop has a wide rotating fan that takes and
accelerates the large mass of air but only till the
limited speed of any propeller driven airplane.
When the plane speed exceeds this limit, propellers
no longer provide any thrust.The turbojets and other
similar engines accelerate much smaller mass of the
air and burned fuel, but they emit it at the much
higher speeds possible with a de Laval nozzle. This is
why they are suitable for supersonic and higher
speeds.
The propulsive efficiency is highest when the engine
emits an exhaust jet at a speed that is the same as the
airplane velocity.Rocket engines are best suited for high
speeds and altitudes. Rocket engines are more efficient
than even scramjets.
A turbojet engine is a type of internal combustion engine
often used to propel aircraft. If the jet velocity exceeds
the aircraft flight velocity, there is a net forward thrust
upon the airframe.
The efficiency of a jet engine is strongly dependent upon
the overall pressure ratio and the turbine inlet
temperature of the cycle. Turbojet engines take a
relatively small mass of air and accelerate it by a large
amount, whereas a propeller takes a large mass of air and
accelerates it by a small amount. The high-speed exhaust
of a turbojet engine makes it efficient at high speeds
(especially supersonic speeds) and high altitudes. Very
small aircraft generally use conventional piston engines to
drive a propeller Most modern jet engines are actually
turbofans, where the low pressure compressor acts as a
fan. Turbofans are used for airliners because they give an
exhaust speed that is better matched to subsonic
airliner's flight speed, In the 1960s there was little
difference between civil and military jet engines.Today's
military turbofans, however, have a relatively high specific
thrust, to maximize the thrust for a given frontal area, jet
noise being of less concern in military uses relative to civil
uses.
THANK
YOU
VERY MUCH