Jet Engines are commonly used on aircraft and work by the turbine or propeller blades at the front of the engine compressing the air inside the engine, where fuel is injected and combusted, creating thrust.

Jet Engines commonly use kerosene (distilled from oil, another form of petrol) as an airline fuel. (correct me if I'm wrong, I don't see how the boy from Home Alone managed to get Airline fuel to burn burglars)

Although Jet Engines don't have much accelleration, they can reach enormous speeds over time, allowing the creation of lift on the wings for the plane to take off.

Different types of jet engines use different types of aviation fuel. The typical turbine fuel is JP-5, which is akin to a thin kerosene. You can put out a cigarette in it, it won't blow up. The problem is if you get it to warm up and begin to evaporate, wherein the fast combustion takes over.

Another type of fuel is called Avgas, which is a very high octane gasoline (I've seen it run 131 r+m octane). Some idiots put it in their cars and lament the hulks of their ex-engine blocks after the explosion blows off the cylinder heads. A cheap way to do this is to add mothballs to gasoline, the dead vehicle result is the same.

Jet engines have fskloads of acceleration. The problem is trying to lift a hulking airframe off of the ground, like a 747. Creating enough inertia to get it going takes tons of thrust. V/STOL aircraft use jet engines, and they can take off vertically, as in the Harriers. Without the monster thrust, they'd just bob up and down on their tires.

A jet engine is a gas turbine engine. A gas turbine engine, like all good ideas is really pretty simple. Here's how you do it. Get yourself three things:
  • A compressor-any arrangement of blades that when spun will take inlet air and compresses it into a high pressure and temperature. The higher pressure creates higher yields from combustion.
  • A combustion chamber-this is where you squirt your fuel into and it will combust. Once you start a jet engine, fuel is injected and combusted constantly, so you'd better make it a good one, and you'd better make sure it can contain the combustion without blowing up the engine. Within the combustion chamber, there is a fuel source injecting fuel into the compressed air, and a constant flame front, so as fuel is injected into the air and ignited by the the fuel burning in front of it, and combustion occurs continuously until the engine is shut off.
  • A turbine-a set of blades that will spin as the ignited, expanding air from the combustion chamber moves through them. The turbine is connected to the compressor so that the engine compresses using the energy from combustion.
  • A final drive turbine-another set of turbines connected to a drive shaft. These can spin helicopter rotors, turbofans, propellers, etc.

Obviously jet engines aren't simple, or everyone would have one, but the concept is fairly simple. The trick is that jets are spun at very high rpms and high temperatures for long periods of time. This means that special bearings and drives must be made, epecially since the shaft connecting the compressor and the turbine runs through the center of the combustion chamber. The other reason that jet engines aren't common for most applications is that they are difficult to throttle. They make good power at a certain speed, but have trouble making power over a range, something a piston engine excels at. Another interesting thing is that a jet engine is an external combustion engine, unlike a piston engine.

A jet engine is any type of engine that works by burning a compressed air/ fuel mixture and shooting it out of the back for propulsion.

Turbojet

The turbojet works by sucking in air with many rows of axial turbines. These are alternating stator and rotor turbines. The rotors of course turn to suck in air. The stators break up the centrifugal air flow. They also slow down the air, inducing compression.

After passing though the compressor, the air pressure is several atmospheres and is moving at a high rate of speed. Some of the air is funneled into the combustion chamber, while other air is bypassed. Here, it is mixed with the fuel, usually JP-5 kerosene, and burned. This creates immense heat and pressure. This mixture is cooled down just past the combustion chamber by ducting additional cool bypassed air.

At this point, the exhaust travels though the turbines. These axial blades gently let the pressure out of the exhaust and give power via a shaft to the compressor in front.

Turbofan

This type of engine provides power to all airliners and many military aircraft. It is very fuel efficient and is quiet. A high bypass turbofan works exactly the same way as a turbojet except it has a huge low pressure fan in front. Most of this air bypasses the rest of the engine and provides most of the thrust. In a turbofan, the bypassed air provides most of the thrust, while in a turbojet, it is solely the exhaust. A turbofan is capable of flying to about Mach 1.5.

Ramjet

This is the simplest of all jet engines, so simple it can be built at home. Ramjets are capable of flying to Mach 6, far faster than other forms of jet engines. They have seen use in high supersonic cruise missiles. The Bomarc cruise missile used a ramjet engine. Once it reached Mach 5.5.

A ramjet has to be moving at transonic speeds before it will work well. At high speeds, air is shoved into the intake without the use of turbines. It is then passed through the combustion chamber, where it is mixed with kerosene, hydrogen, or methane, and burned. It then exits the engine.

Supersonic ramjets (ramjets that fly over Mach 1.5) work exactly the same way except that they have an additional diffuser in their front to slow down the air to subsonic speeds. Diffusers are usually conical, as seen in the SR-71. They slow down the air by compressing it.

Ramjets cannot start unless they are moving fairly fast already. Therefore, a ramjet aircraft must start with another power source, such as a turbojet or rocket.

A variation on the ramjet is the SCRAMjet. This is the Supersonic Combustion Ramjet. It works exactly the same way as a ramjet, except it burns fuel in a supersonic, as opposed to subsonic, flow. SCRAMjets are currently under development. They will be able to achieve speeds of Mach 25, which would allow them to fly to orbit with no rocket power.

Pulsejets

Pulsejets are noisy, loud, inneficient, but simple. They saw service in the V-1 Cruise Missile during World War II.

A pulsejet works exactly the same way as a ramjet except it pulses. At the intake, there are one-way reed valves. Fuel is injected in pulses, and exploded by a spark plug. The valves close when the fuel and air explodes, directing the thrust toward the rear. A pulsejet sounds exactly the same as a two-stroke gasoline engine, except many, many, many times louder.

Motorjets

This was in early form of jet. This type of jet was actually employed on an aircraft in 1910. It crashed. Later on, a motorjet was utilized in the Italian Caproni-Campini fighter in 1940.

A motorjet is very simple. It has not rotors in the back. It uses another engine for compression. The Caproni-Campini used a 700 horsepower gasoline engine to drive the compressors. The motorjet was doomed to failure because it was inneficient and underpowered.

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