Dear blog readers!

Last week was a special one at GKN in Trollhättan, we had what is called Training Days which is a week full of lectures and presentations from different disciplines within the company. The purpose of Training Days is to educate the personnel and to provide all employees with new information and possibilities so that one can develop in the daily work. Courses that were offered were everything between heart and lung rescue, employeeship and Additive Manufacturing (AM).

One course that all of us trainees attended to was the introduction course in Jet engine theory where the basics of how a jet engine works is stepped through. A great course for new employees but also very giving for employees who want to refurbish their knowledge. One thing, among many other things, that we went through is the intake of air and ways of compressing it. More specifically we went through the philosophies of radial compression (Centrifugal compressors) and axial compression.

Radial compression works by taking in air and compressing it by forcing it in a radial direction which usually ends up in the engine and aircraft being quite chubby looking. One typical aircraft ‘suffering’ from this look is the Swedish air force aircraft called Saab 29 Tunnan. The design of such a jet engine is quite simple but very robust with few rotating parts. Although being robust is a good thing, this very design allow for less parameters to be optimized or allow for changes in the design.

Another type of jet engine is an engine with an axial compressor instead. The air is being pushed axially along a rotating shaft from left to right seen in the picture above. This is often done by several compressor stages e.g. a Low Pressure Compressor (LPC) and a High Pressure Compressor (HPC), each compressor stage usually being a set of rotors. Here the design becomes a bit longer but less chubby and usually having a lot of different parameters that can be optimized or re-designed. An example of an aircraft having this kind of an engine is the Swedish air force aircraft called JAS 39 Gripen….and basically all other modern aircraft.

Common for the two different kind of engines is that there always has to be a combustion stage to add energy to the system. After the air has been compressed it is mixed with kerosene and ignited. The hot gas propagates further down in the engine, it sets the turbines in motion which are driving the different compressor stages and the fan which in turn allow for more air intake. Further, the gas is guided out from the engine, here though a nozzle which purpose is to further accelerate the gas so that a greater thrust can be achieved. After that it is all up to Newton’s Third Law to generate thrust in the direction of travel.

Thanks Newton!

The purpose of this blog post did not intend to give a short introduction in jet engine theory, but I guess that is what happens when one gets a bit to enthusiastic about technology, science and stuff. Perhaps you learned something or perhaps you found the lack of explanation annoying! Sorry about that!

One popular way of describing a jet engine can be done with the following figure.