How do jet engines work?

Answer 1

The simple answer is: "Suck, Squeeze, Burn and Blow." Or, more accurately, air is taken into the inlet of a jet engine (suck) and then compressed (squeeze) by a series of rotors and stators. A fuel mixture is then injected into a chamber with the compressed air and ignited (burn). The subsequent combustion is directed aft and the resulting exhaust (blow) pushes the engine (and vehicle) forward. The exhaust gasses also turn a shaft connected to the inlet turbine which continues the compression process. It's really a lot more complicated than this, but this is the quick and dirty of how it works.

A modern jet engine is made up of several rows of spinning propeller blades called Rotors. As the airflow goes through each row, the air is accelerated and compressed. Behind the row is another set of blades that are not really turning---but attached to the out housing. These are called Stators. These help to re-direct the flow to be more efficient and prepare it to meet the next set of spinning blades. After going through several rows of Rotors, the air is compressed. This stage of the engine is called the Compressor.

The compressed gas enters a Combustion Chamber where fuel is added an a spark ignites the fuel/air mixture and this flame is self-sustaining. The hot gases want to expand and it passes through another set of Rotors and Stators that extract some energy out of the fast flowing air gases. This section of the engine is the Turbine stage because it acts like the turbines in a dam to pull energy out of flowing fluid. This engergy is used to turn the Turbine disc that is connected back to the Compressor stage, thus compressing the next amount of air entering the engine.

The gas escaping the engine has a great amount of energy and velocity and applies thrust to the engine and thus to the airplane.

Hi bypass commercial jets (Trent 900, GEnx) use outer guide vanes or OGV's to rotate and eject air before the compressor stage. The air rotates around the exhaust to reduce friction of exhaust gases increasing efficiency and reducing noise.

The steps in a jet engine are essentially the same as in a car engine: Intake, Compression, Combustion, Exhaust.

In modern jet engines, the air is pulled into the engine by a large disc of spinning blades called the fan. This is what you see if you look into the front [intake] of the engine. Behind the fan is the bypass duct [mentioned later] and the engine core.

The engine core contains more spinning components similar to the fan called 'compressors' that simply compress the air into a smaller area.

Behind the compressors is the combustion chamber, where the air is sprayed with jet fuel from a nozzle and ignited by a flame.

It then passes through one more spinning component called the turbine, which accelerates the air out the back of the engine. That turbine is connected to the compressors by a shaft running through the center of the engine and is what runs them.

The bypass duct [mentioned earlier] is simply a hollow area surrounding the engine core. Some of the air that gets taken in is routed by the fan through the bypass duct so that it totally bypasses the engine core, and mixes with the exhaust behind the engine. This makes the engine more efficient and muffles the sound of the exhaust, making the engine quieter. A better understanding of thrust

A common misconception about thrust is that the exhaust gasses expelled from the rear of the engine cause the engine and the attached aircraft to move forward. This is not true.

Although the expelled gasses do add a minimal amount of forward thrust, the majority of thrust created by the engine is from the aerodynamic forces generated by the aforementioned Rotors.We must first understand that Rotors are aerodynamic devices known as Airfoils because of their designed curvature. An Airfoil that passes through a body of air will cause a pressure differential that causes lift. The wings of an aircraft are examples of an airfoil, and as air passes around the wings, the curvature that engineers design into the wing will cause a higher pressure to act upon the underside of the wing, and a lower pressure to act upon the upper surface of the wing. As this pressure differential becomes greater, it eventually overcomes the combined forces of gravity and the mass of the aircraft, and the aircraft flies. This same principle can be used to explain why the Rotors are the primary source of forward thrust. As the rotors spin, they too will develop pressure differentials, but because they are mounted vertically like a propeller on a small plane, they will produce forward thrust, instead of creating upward lift as we are used to associating with horizontally mounted aircraft wings. NASA explanation of thrust See the the discussion page for more information.