Otto Fearguson Jr., age 14, of Columbus, Ohio, for his question:
HOW DOES A JET ENGINE PRODUCE POWER?
A jet engine builds up inside pressure that becomes power by two methods: burning a fuel that gives off hot gases and squeezing or compressing air that is mixed with fuel:
Some jet engines only burn fuel while others use a combination of burning fuel and compressing air. Gasoline, kerosene or some other chemical can be used as fuel.
After a jet engine has built up pressure, it exhausts burning gases from its tailpipe in a stream called the jet, or jet exhaust. This action drives the engine forward.
Thrust, or the forward driving force, is measured in pounds or in "newtons." The thrust stays about the same at all flying speeds, which makes a jet engine particularly useful in high speed aircraft.
A jet engine's power or ability to do work in a given period of time increases at higher flying speeds. It produces thrust by moving a relatively small volume of gases at high speed.
A turbojet is a jet engine that is used in many commercial and military airplanes. It uses either a centrifugal flow compressor or an axial flow compressor to build up thrust.
A centrifugal flow compressor squeezes the air by bringing it into the center of a rapidly spinning wheel which throws the air toward the rim. There it enters a nearly circular expanding passage where its speed decreases and its pressure increases.
An axial flow compressor has several disks with a large number of small wing like blades around their rims, as in an electric fan. These disks are attached to a shaft that spins at about 12,000 revolutions a minute. Between each pair of disks is a row of blades that do not rotate. The air flows parallel to the shaft. Each row of blades compresses the air a little more than did the preceding row. The air pressure is raised to 12 times that at the intake.
A turbojet engine requires about 1,200 gallons of fuel an hour.
After air is compressed in a jet, it rushes into a set of combustion chambers and is mixed with fuel and burned. This creates greatly expanded hot gases that rush toward the tailpipe.
Before the gases escape from the engine, they turn a turbine wheel, which spins the compressor. This uses energy from the exhaust gases. This turbine wheel must be made of materials able to stand temperatures as high as 1,600 degrees Fahrenheit.
To obtain a powerful thrust from a jet engine, a large mass of gas exhausted at high speed is needed. The mass of gas in the jet exhaust comes from the air and fuel taken into the engine. A turbojet of moderate size uses about 540,000 pounds of air an hour.