How a Jet Engine
This is a picture of 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
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 image above shows how the air
flows through the engine. 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
A jet engine operates on the application
of Sir Isaac Newton's third law of physics:
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.
Different engine types.
courtesy of the US Air Force Museum and NASA
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