Gas Turbine Aircraft Engine Design and Operation: The Way It Works
By Tim Patterson
Conventional gas turbine jet engines, like the turbofan, have been around for years. They power almost all commercial aircraft and are very reliable. Every time you board a commercial aircraft, this technology is providing safe and efficient power to get you to your destination.
A gas turbine engine varies greatly in design from the engine in your car. Air enters the front of the engine through the fan section, which runs on the N1 or low-pressure shaft. In high by-pass engines, which are the most efficient, 4 times the air that continues into the core of the engine, or more, is directed around the engine producing thrust. Then the air entering the core of the engine reaches the compressor section. Here, the air is compressed in stages as it continues rearward. Since air does not like to flow from areas of low pressure to high pressure, turbine engines rely on the cascade effect. The compressor, running on the N2 shaft or high-pressure shaft, contains stages of rotor blades. These rotor blades are small titanium airfoils radiating from the shaft. Just like an aircraft wing moving through the air, these blades are positioned to produce an area of low pressure on the top and high pressure underneath. Since these blades are angled forward, the low pressure area is facing forward in the engine and the high pressure faces rearward. In between each set of rotating rotor blades, there is a ring of stationary blades called the stator vanes. These are identical titanium airfoil shaped blades positioned opposite to the rotor blades. As the area of high pressure behind the rotor blades pass the area of low pressure in front of the stator blades, the air flows from the high pressure to low pressure. This is continued through the compressor section until the pressure is increased much higher than the outside pressure.
Once the air exits the compressor section of the turbine engine, it enters the combustion section. As a result of the increased pressure, the air is at higher temperature. Fuel is injected into this heated air and a spark is added to ignite the mixture. During combustion, the air rapidly heats and expands further. This increases the pressure in the combustion chamber forces the air rearward through the high-pressure compressor turbine. Here, energy from the expanding air is used to turn the turbine which transfers energy through the N2 shaft to power the compressor in the front of the engine. After passing through the compressor turbine the air continues to the power turbine. This is where most of the energy from the air transfers through the N1 shaft to the fan producing most of the engines thrust. The remaining air exits the rear of the engine and gives the engine about twenty percent of its total thrust.
The gas turbine engine basically uses the same intake, compression, power, and exhaust cycles as your automotive four stroke engine. Turbine engines only vary in operation from a four stroke engine. The simplicity of this engine has allowed it to remain the essential engine of commercial aviation.
About The Author
Tim Patterson is a commercial pilot and aviation enthusiast.
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