Jet Engine | How to work to give thrust of aircraft.

What is a jet engine?

A jet engine is a machine that converts energy-rich, liquid fuel into a powerful pushing force called thrust. The thrust from one or more engines pushes a plane forward, forcing air past its scientifically shaped wings to create an upward force called lift that powers it into the sky. That, in short, is how planes work—but how do jet engines work?

A jet engine uses the same scientific principle as a car engine: it burns fuel with air (in a chemical reaction called combustion) to release energy that powers a plane, vehicle, or other machine. But instead of using cylinders that go through four steps in turn, it uses a long metal tube that carries out the same four steps in a straight-line sequence—a kind of thrust-making production line! In the simplest type of jet engine, called a turbojet, air is drawn in at the front through an inlet (or intake), compressed by a fan, mixed with fuel and combusted, and then fired out as a hot, fast moving exhaust at the back.

A basic principle of physics called the law of conservation of energy tells us that if a jet engine needs to make more power each second, it has to burn more fuel each second. A jet engine is meticulously designed to hoover up huge amounts of air and burn it with vast amounts of fuel (roughly in the ratio 50 parts air to one part fuel), so the main reason why it makes more power is because it can burn more fuel.
Because intake, compression, combustion, and exhaust all happen simultaneously, a jet engine produces maximum power all the time (unlike a single cylinder in a piston engine).
Unlike a piston engine (which uses a single stroke of the piston to extract energy), a typical jet engine passes its exhaust through multiple turbine "stages" to extract as much energy as possible. That makes it much more efficient (it gets more power from the same mass of fuel).

Gas turbines

A more technical name for a jet engine is a gas turbine, and although it's not immediately obvious what that means, it's actually a much better description of how an engine like this really works. A jet engine works by burning fuel in air to release hot exhaust gas. But where a car engine uses the explosions of exhaust to push its pistons, a jet engine forces the gas past the blades of a windmill-like spinning wheel (a turbine), making it rotate. So, in a jet engine, exhaust gas powers a turbine—hence the name gas turbine.
Action and reaction

When we talk about jet engines, we to tend think of rocket-like tubes that fire exhaust gas backward. Another basic bit of physics, Newton's third law of motion, tells us that as a jet engine's exhaust gas shoots back, the plane itself must move forward. It's exactly like a skateboarder kicking back on the pavement to go forward; in a jet engine, it's the exhaust gas that provides the "kick". In everyday words, the action (the force of the exhaust gas shooting backward) is equal and opposite to the reaction (the force of the plane moving forward); the action moves the exhaust gas, while the reaction moves the plane.

But not all jet engines work this way: some produce hardly any rocket exhaust at all. Instead, most of their power is harnessed by the turbine—and the shaft attached to the turbine is used to power a propeller (in a propeller airplane), a rotor blade (in a helicopter), a giant fan (in a large passenger jet), or an electricity generator (in a gas-turbine power plant). We'll look at these different types of gas turbine "jet" engines in a bit more detail in a moment. First, let's look at how a simple jet engine makes its power.

All jet engines and gas turbines work in broadly the same way (pulling air through an inlet, compressing it, combusting it with fuel, and allowing the exhaust to expand through a turbine), so they all share five key components: an inlet, a compressor, a combustion chamber, and a turbine (arranged in exactly that sequence) with a driveshaft running through them.

But there the similarities end. Different types of engines have extra components (driven by the turbine), the inlets work in different ways, there may be more than one combustion chamber, there might be two or more compressors and multiple turbines. And the application (the job the engine has to do) is also very important. Aerospace engines are designed through meticulously engineered compromise: they need to produce maximum power from minimum fuel (with maximum efficiency, in other words) while being as small, light, and quiet as possible. Gas turbines used on the ground (for example, in power plants) don't necessarily need to compromise in quite the same way; they don't need to be either small or light, though they certainly still need maximum power and efficiency.

By NASA

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 gas 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 with many blades attached to a shaft. The blades spin at high speed and compress or squeeze 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. As the hot air is going to the nozzle, it passes through another group of blades called the turbine. The turbine is attached to the same shaft as the compressor. Spinning the turbine causes the compressor to spin.

Basic:-

Jet engines create forward thrust by taking in a large amount of air and discharging it as a high-speed jet of gas. The way they’re designed allows aircraft to fly faster and further compared to propeller-driven aircraft. Their development and refinement over the course of the last 65 years has made commercial air travel more practical and profitable, opening the world to business and recreational travelers.

“A typical jet engine is a gas turbine,” says Jeff Defoe, a postdoctoral associate in the MIT Gas Turbine Laboratory. “At its simplest, it’s composed of a compressor, which has blades like wings that spin very quickly. This draws in air and squishes it, making it a high-pressure gas. Then fuel is injected into the gas and ignited. This makes the gas both high-pressure and high-temperature.”

This high-pressure, high-temperature flaming flow of gas now goes through a turbine — essentially, another set of blades — that extracts energy from the gas, lowering the pressure and temperature. “The turbine draws the gas through the engine and out the back through a nozzle that markedly increases the velocity at the expense of pressure — the pressure decreases while the velocity increases,” says Defoe. “It’s the force of the expulsion of gas that provides the thrust to move the aircraft forward.”

Aside from the compression/fuel-ignition/turbine-power aspect of the jet engine, the shell around it also makes it more effective than an exposed propeller engine. “Without a shell around it, a propeller ‘sees’ air coming towards it at whatever speed the aircraft is traveling,” says Defoe. “This restricts how quickly the propeller can spin before the amount of resulting thrust tapers off, limiting the aircraft flight speed. Since the shell on the jet engine keeps the air entering the engine moving at nearly the same speed regardless of flight speed, the aircraft can fly faster.”

These days, jet engines are even more advanced than the basic turbine construction described above. Now they have huge fans in front, and instead of shooting the gas out of the back directly, it goes through a second turbine which powers the fan up front. While older jet engines took a smaller amount of air and accelerated it a lot, newer jet engines take in more air and accelerate it a little. The result is that the engine uses much less energy. “Until the 1970s, trans-pacific flights required refueling stops,” notes Defoe.

In the Gas Turbine Laboratory, Defoe and his colleagues are working to make jet engines quieter and even more efficient by exploring design changes such as taking the engines off the wings and putting them next to the fuselage, where the air molecules have been slowed down by friction. At their largest, jet engines can have fans with a diameter of over ten feet, but they can also be small enough to fit in the palm of your hand. It’s useful to note that massive gas turbines built with the same principles as jet airplane engines are also used for power generation in natural gas power plants.

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