Principle of jet propulsion.

Compression

In an axial-flow compressor, a series of rotating blades pushes the air back and, in so doing, adds energy to that air. Each blade is basically a rotating wing, just like a propeller. There is one fundamental difference between the compressor and the propeller, though. With the compressor,

the blades are in a duct, and therefore, the added energy

results in an increase in the pressure of the air rather than an increase in the speed of the air. How pressure is produced, rather than speed, is

kind of interesting.

The axial-flow compressor is made of rows of blades, consisting of rotating blades followed by stationary blades.

A typical row of rotating blades has 30 to 40 blades and is called a rotor. Following each rotor is a stationary set of blades called a stator.

The rotor’s job is to increase the energy of the air and thus its pressure.

The stator increases the pressure of the air further by slowing it down from the speed at which it left the rotor. The pressure increase across a single stage of rotor-stator combination is fairly low, but multiple

stages can produce fairly high compressions with high efficiency. As the pressure increases from stage to stage, the volume of air decreases.

Thus the blades of the rotors and stators become smaller. 

It is not wise to try to increase the pressure too much across a single stage because this increases the chances of the blades stalling, just like a wing that is trying to produce too much lift. The stall causes the flow to reverse and is referred to as compressor stall. Rather than trying

to increase the pressure substantially across each stage, multiple stages are used to decrease the pressure gain across each stage. The result is that an entire compressor section of 10 to 12 stages may increase the pressure by a factor of 10 or more.

Combustion

One difference between the compression process in a jet engine and an internal combustion engine is that the compression of air is continuous in a jet engine. After the air is compressed, fuel is injected and burned in the burner, or combustor. The burner is merely a kind of firebox where the air-fuel mixture is burned.
In most engine designs, the burner is really several burners distributed around the central axis like a series of cans. After entering the inlet, the air splits, with part going along an outside volume and part going through the
combustion chamber. The air flowing down the outside of the combustion chamber is for cooling. The air going to the combustion chamber passes through a plate with holes, which is a flame stabilizer. The flame stabilizer enhances the mixing of the fuel with the air and prevents the flame from being extinguished by the rush of air.
For best combustion efficiency, the combustion temperature is kept as high as possible. Current temperatures at the end of the combustion chamber are on the order of 2800°F (1500°C). A typical melting point of steel is 2400°F (1300°C). This temperature is too hot for typical construction materials, so the burner must be cooled. Bleed air is brought in through holes in the wall of the burner to form a thin film covering the inside walls. 
The hot combustion gases do not burn through the combustion chamber walls because of the constantly replenished supply of
cool air. Most of the air taken in by a jet engine,
as much as 75 percent, is used for cooling, and therefore, typically only about 25 percent of the oxygen is consumed in the burner. This unused oxygen makes afterburners possible.
It is in the burner that the energy is given to the air through chemical combustion to produce propulsion. Before the energetic exhaust can be allowed to escape, however, there is some work for it to do.
Some of its energy must be extracted to power the compressor. This is done by the turbine following the burner.

Power Extraction

The turbine looks quite a bit like a single stage of a compressor, only here the first set of blades that follows the burner is fixed and does not rotate. These blades are called the turbine vanes. They are followed by a rotating set of turbine blades that drive a shaft connected to the compressor.
The purpose of the turbine vanes is to turn the exhaust into the turbine blades. This allows for greater energy transfer to the turbine blades.
A turbine is the reverse of a compressor. The air expands and cools through each turbine stage, and energy is removed from the air. There must be as many turbine sections as there are compressor sections, but not as many stages in each section. Thus a jet engine with two compressors, a low- and high-pressure section, will have two turbines, each powering one of the compressors with a separate shaft. The turbine-shaft-compressor combination is referred to as a spool. Most large jet engines are two-spool engines, meaning that they have a two-stage compressor driven by a two-stage turbine.
Although the exhaust loses some of its energy going through the
turbine, and thus becomes cooler, it is still very hot. The first vaneblade stage of the turbine sees temperatures similar to those in the burner, on the order of 2800°F (1500°C). Therefore, this turbine stage requires special cooling, including the film cooling from bleed air as is found in the burner. Notice that it is hollow, which is to allow internal cooling air, and that there are small holes on the surface. These holes allow a cool air pocket to form around the surface of the blade. This pocket is thin but allows the blades to survive the hot temperatures.
The pressure change across the turbine goes from high to low. In
the compressor, the pressure goes from low to high. Because of this, unlike the compressor, there is little problem with the turbine blades stalling. Therefore, the pressure change across a turbine stage can be much greater than the pressure change across an axial-flow compressor stage. Thus fewer stages are needed in the turbine than in the compressor. Even with the energy loss, the gas leaving the turbine still has a great deal of energy and can be used for propulsion.

Origin: Understanding Flight, 2nd Edition (David W. Anderson & Scott Eberhardt) 

Introduction.

     My name is Mattis and I'm a big fan of aviation and technology. It all started when I was a little kid, me and my famliy travelled pretty often to sunny resorts around Europe. That meant I flew a lot already in the low ages, something that has probably affected me. I loved the fact of family holidays, unlike the other kids, that I got to fly again. Still today, when I smell the scent of Jet A1(jet fuel), it brings me back to old times, a very nice feeling.
    When I reached approximately 15 years of age, I started getting more interested in the propulsion of the aircrafts, and especially jet engines. When I was younger the engine itself, hanging under the wing like a sort of magic box, seamed like science fiction to me, but when I actually decided to learn more about it, I found that it was an extraordinary piece of technology. Then I began to watch hundreds of Youtube videos all about this invention. I geuss it was then I, probably by accident, clicked on a video about a homemade jet engine and got a lot of inspiration. Most of it, of course, were just rubbish but so fascinating to a boy. And there, a spark was born, that were gonna provide me with a lot of fun and educating time. 
    This blog is going to be a summary of my time building a jet engine at home, using nothing but things accesable in any junkyard or supermarket. I will try, whenever I can, to upload new stuff. I'm currently studying to become an Aeronautical engineer and school has, of course, got to  be the first priority.
Here is a Youtube video of the test runs of the first jet engine prototype that I made.