Turbine Engines

The history of turbine engines date back to nearly a century ago when Frank Whittle was the first to register a patent in 1930; six years later Hans von Ohain registered his independent work (Bellis, 2012). Frank Whittle, as an English aviation engineer and pilot, gained private financial support to start designing and manufacturing his first turbojet in January 1930 (Bellis, 2012). His first engine was a single-stage centrifugal compressor attached to a single-stage turbine was tested in 1937 (Bellis, 2012). The jet engine has become very complex engine based on simple concepts; in simplest terms, the jet engine produces thrust for flight by compressing, combustion, and accelerating air out the exhaust faster than when it came in the inlet. Throughout my career, I have maintained, troubleshot, and repaired several different types of turbine engines, all of which are similar because of this theory of operation. When looking at a jet engine, everyone usually sees the fan blades, but before this component, there is the inlet, or intake, which is the structure in front of the fan. For aircraft that cannot fly supersonically, the inlet is a basic housing that directs air straight into the fan; for much faster aircraft, the inlet is longer and contains a slight curve as it leads to the fan. This is because when the aircraft is flying at supersonic speeds, the air entering the jet engine must be slowed to subsonic speeds (“the jet engine,” n.d.). It is very important for the inlet or intake to allow the engine to operate at maximum efficiency throughout the entire flight and at all power settings (“the jet engine,” n.d.). Some problems with intakes are, among other things, engine stall when traveling at low speeds and high angle of attacks, crosswinds across the inlet can cause disruption to the smooth flow of incoming air, and ice accumulation along the intake can disrupt airflow and can be sucked into the fan, causing severe damage to the engine.
The intake leads to the engine compressor. There are two types of compressors; the centrifugal compressor and the axial flow compressor. The centrifugal compressor is still used on some small jet engines, while axial flow compressors have become more convenience for larger aircraft and those that require greater performance; this is because the axial flow compressor can couple several stages of stator vanes and rotor blades to produce higher pressures than the centrifugal compressor (“the jet engine”, n.d.). The centrifugal compressor brings air in and forces it outward from the center of the compressor, because of the centrifugal force applied to the air. This would make it harder to couple several centrifugal compressors together without adding excessing weight because the air would have to be brought back into the center of the engine for the next stage of centrifugal compression. Another important component of the axial compressor section is the variable stator vanes. Between each row of spinning blades, there is a row of stator vanes that straighten and direct air onto the next row of spinning blades. Several rows of these stator vanes are able to swing, similar to a door on hinges, to open and close the passage of air that leads to the next stage of blades. This is to prevent excessive air entering the next stage of compression and potentially causing a stall or surge and to optimize the fuel and air mixture in the next component of the engine.
As the air is compressed, the temperature rises; this is important for the combustion of the air and fuel mixture in the combustion chamber. As the air enters the combustion chamber, fuel nozzles spray a fine mist to mix with the hot air. In the combustion chamber, there are usually two igniters, which can be activated together or independently, that provide a high energy electrical spark for an ignition source for the air and fuel mixture.
There are three types of combustion chambers; can, can-annular, and the annular chambers. The can, or multiple chamber, type of combustion chamber is used on centrifugal compressor engines (“the jet engine,” n.d.). This type of combustion chamber looks similar to cans being placed around the engine axially. Each can serves as its own combustion chamber, with the exception of being connected to allow combustion to spread throughout each can during startup (“the jet engine,” n.d.). The annular type is a singular tube that wraps around the center of the engine with an inner and outer casing that contains the combustion within. This is more advantageous than the can type because is lighter weight and for the same power output, it is 25 percent less in length (“the jet engine,” n.d.). The can-annular design combines the best of the can type and annular type by keeping the ease of overhaul and testing of the can type and the light weight of the annular type (the jet engine,” n.d.).
When combustion occurs, the heated air is extremely hot, therefore the air that is not used for combustion is mixed with the heated air and accelerated towards the exhaust of the engine. As it leaves the combustion chamber, the extremely turbulent air is straightened by a row of stator vanes. This is important because the air is directed onto a row of turbine blades that spin the turbine which drives the compressor to keep the engine self-sustained.
After a couple stages of turbine stators and blades, the air enters the exhaust section of the jet engine. When the air enters the exhaust, it is again straightened by several struts. There are a wide variety of exhaust nozzles that augment the exhaust air to aid in the specific performance the jet engine requires. Some engines use any bypass air to mix with the exhaust air to heat it so it can again mix with fuel and be reignited for added thrust. The exhaust nozzle can vector to give the aircraft more maneuverability. But most of the exhaust nozzles seem to take a convergent form. This is because the convergent nozzle increases pressure thus increasing the velocity of the exiting air.
Some jet engines can produce thrust upwards of 40,000 pounds. It simply depends on what the engine will be used for; a small corporate jet to the supersonic fighter jet to the work horse C-17 Globemaster III cargo jet.

References
Bellis, M. (2012). Jet engines - hans von ohain and sir frank whittle . Retrieved from http://inventors.about.com/library/inventors/bljetengine.htm
The jet engine components . (n.d.). Retrieved from http://www.pilotfriend.com/training/flight_training/tech/jet_engine_components.htm