Knowing the Jet Engine?What is it exactly?
TURBO FAN
All turbofan engines work on the same principle. A large fan at the front
of the engine draws air in. A portion of the air enters the compressor, but a
greater portion passes on the outside of the engine—this is called bypass air.
The air that enters the compressor then passes through several stages of
rotating fan blades that compress the air more, and then it passes into the
combustor. In the combustor, fuel is injected into the airstream, and the fuel-air
mixture is ignited. The hot gasses produced expand rapidly to the rear, and the
engine reacts by moving forward. Fan
casings, therefore, need to be strong enough to contain errant blades and
damage-tolerant to withstand the punishment of a loose blade-turned-projectile.
NASA has spearheaded research into improving jet engine fan casings,
ultimately discovering a cost-effective approach to manufacturing
damage-tolerant fan cases that also boast significant weight reduction. In an
aircraft, weight reduction translates directly into fuel burn savings,
increased payload, and greater aircraft range.
Triaxial carbon braid used as an alternative to aluminum or other solid metal in
the manufacture of braided fan containment cases for jet engines. The braided
fan case has a toughness superior to aluminum and enables significant
reductions in weight and fuel consumption. The use of braided reinforcements
also allows for a low-cost, repeatable manufacturing process.
Jet engine
The jet engine is the power plant of today's jet aircraft, producing not
only the thrust that propels the aircraft but also the power that fuels many of
the aircraft's other systems.
Jet engines operate according to Newton's third law of motion, which states
that every force acting on a body produces an equal and opposite force. The jet
engine works by drawing in some of the air through which the aircraft is
moving, compressing it, combining it with fuel and heating it, and finally
ejecting the ensuing gas with such force that the plane is propelled forward.
The power produced by such engines is expressed in terms of pounds of thrust, a
term that refers to the number of pounds the engine can move.
Design
A jet engine is contained within a cowling, an external casing that opens
outward, somewhat like a rounded automobile hood, to permit inspection and
repair of the interior components. Attached to each engine (a typical 747 uses
four) is a pylon, a metal arm that joins the engine to the wing of the plane.
Through pumps and feed tubes in the pylons, fuel is relayed from wing tanks to
the engine, and the electrical and hydraulic power generated by the engine is
then routed back to the aircraft through wires and pipes also contained in the
pylons.
At the very front of the engine, a fan helps to increase the flow of air
into the engine's first compartment, the compressor. As the fan drives air into
it, the compressor—a metal cylinder that gradually widens from front to
rear—subjects the incoming air to increasing pressure. To accelerate the
progress of the air through the engine, the compressor is fitted with blades
that rotate like simple household fans. In the incredibly brief time it takes
air
The parts of a jet engine—they can number 25,000—are made in various ways. The
fan blade is made by shaping molten titanium in a hot press. When removed, each
blade skin is welded to a mate, and the hollow cavity in the center is filled
with a titanium honeycomb. The turbine disc is made by powder metallurgy, while
the compressor blades and the combustion chamber are both made by casting.
to reach the inner end of a typical compressor, it has been squeezed into a
space 20 times smaller than the intake aperture.
Expanding as it leaves the high-pressure compressor, the air enters the
combustor, an interior engine cylinder in which the air will be mixed with fuel
and burned. The combustion chamber is actually a ring, shaped something like a
car's air filter. The air that passes through this ring as it exits the
compressor is ignited, while another, larger stream of air merely passes
through the center of the ring without being bumed. A third stream of air being
released from the compressor is passed outside the combustion chamber to cool
it.
As the air from the compressor mixes with fuel and ignites in the combustor
to produce an incredibly hot volume of gas, some of that gas leaves the engine
through the exhaust system, while another, smaller portion is routed into the
engine's turbine. The turbine is a set of fans that extend from the same shaft
which, further forward in the jet engine, rotates the compressor blades. Its
job is to extract enough energy from the hot gases leaving the combustor to
power the compressor shaft. In some models, the turbine is also used to
generate power for other components of the plane. Because the turbine is
subjected to intense heat, each blade has labyrinthine airways cut into it.
Cool air from the compressor is routed through these passages, enabling the
turbine to function in gas streams whose temperature is higher than the melting
point of the alloy from which it is made.
The bulk of the gas that leaves the combustor, however, does so through the
exhaust system, which must be shaped very carefully to insure proper engine
performance. Planes flying beneath the speed of sound are equipped with exhaust
systems that taper toward their ends; those capable of supersonic travel
require exhaust systems that flare at the end but that can also be narrowed to
permit the slower speeds desirable for landing. The exhaust system consists of
an outer duct, which transmits the cooling air that has been passed along the
outside of the combustor, and a narrower inner duct, which carries the burning
gases that have been pumped through the combustor. Between these two ducts is a
thrust reverser, the mechanism that can close off the outer duct to prevent the
unheated air from leaving the engine through the exhaust system. Pilots engage
reverse thrust when they wish to slow the aircraft.
MATERIAL
* The LP compressor blades, or fan blades, are those blades that you can see at the front
of the engine. the blades are made from titanium.
* High-Pressure Compressor are either made from titanium or in some cases from a nickel alloy.
* Combustion Chamber The fuel injector stems are usually made from a nickel alloy called
Inconel 625 because of its high strength and its ability to withstand high
temperatures.
* Turbine Blades they are made from a material called single-crystal
nickel. This is formed by a very special process in which the metal grains in
the blade are lined up parallel to the blade by a process called directional
solidifying.
* Cowling made up from molded aluminum sheeting.
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