of Turbojet Engine
The 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. The afterburner increases the temperature of the
gas ahead of the nozzle. The result of this increase in temperature is
an increase of about 40 percent in thrust at takeoff and a much larger
percentage at high speeds once the plane is in the air.
The turbojet engine is a reaction
engine. In a reaction engine, expanding gases push hard against the front
of the engine. The turbojet sucks in air and compresses or squeezes it.
The gases flow through the turbine and make it spin. These gases bounce
back and shoot our of the rear of the exhaust, pushing the plane forward.
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. Modern turboprop engines are equipped with propellers that have a
smaller diameter but a larger number of blades for efficient operation
at much higher flight speeds. To accommodate the higher flight speeds,
the blades are scimitar-shaped with swept-back leading edges at the blade
tips. Engines featuring such propellers are called propfans.
Hungarian, Gyorgy Jendrassik who worked for the Ganz
wagon works in Budapest designed the very first working turboprop engine in
1938. Called the Cs-1,
Jendrassik's engine was first tested in August of 1940; the Cs-1 was abandoned
in 1941 without going into production due to the War. Max Mueller designed the
engine that went into production in 1942.
of Turbofan 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 gas-generator exhaust to produce
a "hot" jet. The objective of this sort of bypass system is to increase
thrust without increasing fuel consumption. It achieves this by increasing
the total air-mass flow and reducing the velocity within the same total
of Turboshaft Engine
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.
of Ramjet Engine
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.
courtesy of NASA
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