Gas Turbine Engines & Components
A gas turbine, also known as a combustion turbine, is a type of continuous and internal combustion engine. The basic operation of a gas turbine engine is as such: atmospheric air flows through the compressor where it is brought to higher pressure. Here, energy is added by spraying fuel into the air and igniting it to create a high-temperature flow. This pressurized gas enters the turbine, producing a shaft work output used to drive the compressor. The unused energy comes out in the form of exhaust gases. Each part of the gas turbine has an important role in its operation, but the most critical components of it are the compressor, combustion chamber, and the turbine. This blog will explain each part as well as its role within the engine as a whole.
The compressor, as its name suggests, provides the compression aspect of the gas turbine thermodynamic cycle. There are two primary types of gas turbine compressors: axial and centrifugal. Both types serve the same basic purpose: to take in air and pressurize it. In an axial compressor, the air is compressed while it continues in the original direction of flow parallel to the axis of the compressor rotor. The compressor is located at the very front of the engine, where its purpose is to take in ambient air, increase the speed and pressure, and discharge the air through the diffuser into the combustion chamber. In a centrifugal configuration, the centrifugal compressor draws in air at the center or the eye of the impeller, subsequently accelerating it around and outward.
After flowing through the compressor, air is slowed down and split into two streams as it enters the next stage of the engine, the combustion chamber. The smaller of the two streams is fed into the chamber where it is mixed with atomized fuel and burned to cause a combustion. The larger stream is then fed into the chamber to cool the temperature to a level that is suitable for the turbine inlet. Combustion can be carried out through a series of elements spaced around the engine, or in a single annular passage in conjunction with fuel-injection. One of the most prominent problems faced by the combustion chamber is the difficulty of achieving uniform exit-temperature.
The next component is the turbine itself. Operation of the turbine is based on the reaction principle with hot gases expanding through one or two-spooled turbines. In a turbine driving an external load, the expansion takes place in a high-pressure turbine that drives the compressor while the rest of the expansion process takes place in a separate “free” turbine connected to the engine. Extreme temperatures at the turbine inlet and high compressor blade stresses require the use of metallic alloys for the turbine blades. Blades must also be cooled by colder air drawn in from the compressor and fed through internal passages.
Aviation is by far the most prevalent used for gas turbine engines, where they serve as the means of power for jet propulsion. However, in addition to this, gas turbines are used to power trains, ships, electrical generators, pumps, gas compressors, tanks, and more.
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