7 Parts of Gas Turbine Engines and their Functions Explained
Parts of gas turbine engines include; air inlet, compressor, combustor, turbine, fuel nozzle, exhaust, and auxiliary systems.
This article discusses the parts of gas turbine engines, as follows;
1). Air Inlet (as one of the Parts of Gas Turbine Engines)
Air inlet in a gas turbine is the component that is mainly responsible for introducing air into the turbine.
The importance of air inlet in gas turbine systems is based on its role in supplying air or oxygen to the components and processes of the gas turbine, that require it.
Various types of gas turbines have various designs and applications of air inlets. In turbofan gas turbine engine, for example, the air inlet supplies oxygen for burning fuel in the combustor, and part of this inlet air is used to accelerate the rotation of the turbine, as well as to cool the system.
Incoming air of a gas turbine is subjected to processes like compression, fuel mixing, ignition and expansion; all of which enable it to play its role effectively as a working fluid for the turbine.
Another important process with respect to gas turbine air inlet is cooling; also called inlet air cooling.
This process is simply the reduction of inlet air temperature as the air enters the compressor, which helps to increase energy efficiency of the entire system by raising the density of air that interacts with the movable parts of the turbine. It can also help to mitigate the risk of thermal fatigue or any similar form of damage to aerodynamic parts.
Inlet air cooling methods for gas turbines include; chilling and evaporative methods, which employ different mechanisms to reduce inlet air temperature .
For inlet air chilling, it can be achieved by thermal energy transfer between the incoming air and a circulating coolant in a heat exchanger.
On the other hand, evaporative inlet air cooling involves the spraying of atomized water into the inlet section of the turbine, so that the incoming air is cooled as this water evaporates. Because it depends on atomized water, evaporative cooling can also be called inlet air fogging.
Inlet air cooling is especially important for gas turbines that are being used under environmental conditions of high temperature.
Air inlets in gas turbines also need to be equipped with a filtration system that removes particulate matter and other contaminants from incoming air, to protect the turbine from problems like corrosion, fouling and erosion .
The function of a compressor in gas turbines is to reduce the volume of incoming air, thereby increasing its pressure before the air is fed to the combustor .
This function increases the efficiency of the turbine because it improves combustion rate and fluid stream-pressure, so that smaller amounts of air and fuel can be used to generate significant amount of power.
The components of gas turbine compressors include inlet and outlet air valves, pump, and rows of both stationary and rotary blades that are airfoil-shaped and help to accelerate the flow-rate of air as its the compressor. These components work together to compress and pressurize incoming air.
The two main types of compressors in gas turbines are axial and centrifugal compressors, which are classified based on aerodynamic flow interaction between incoming air and the rows of fans in the compressor.
In total, three types of gas turbine compressors can be distinguished, which include centrifugal, axial, and mixed compressors.
Centrifugal compressor is arguably the most-used type in gas turbines for aircrafts and power plants, due to the effectiveness of gas pressurization and acceleration by this type of compressor.
3). Combustor (as one of the Parts of Gas Turbine Engines)
Combustor in a gas turbine is the component that contains and facilitates the combustion of air and fuel mixture, to produce thermal energy and high-pressure gas.
Basically, combustors are used to control the process of fuel combustion in the engine.
The function combustion in gas turbines is a core one, which includes heat production, and generation of fluid kinetic energy that is converted to mechanical energy in the turbine rotor.
Components that are used in a gas turbine combustor include; air inlet, fuel injector, casing, dome, swirler, and exhaust; which introduce air and fuel, protect the system, create turbulence for air-fuel mixing, and emit hot pressurized gases respectively.
The three types of gas turbine combustors are; annular, turbo-annular, and multiple-chamber combustors; which are distinguished based on design and operational details .
One of the key factors that determine performance for a combustor in a gas turbine is the ratio of air-fuel mixing, which differs with type and composition of fuel, as well as with engine scale and design .
Many gas turbine combustors are adaptable and can work with different energy resources or fuels .
Three main sections of a gas turbine are the inlet, engine core, and exhaust, which introduce air, carry out combustion, and emit gaseous effluents respectively.
The turbine itself is part of the engine core (or core engine), alongside the compressor and combustor. This is because these three components are responsible for the main function of mechanical energy production in the gas turbine system.
The turbine in gas engines is very similar to steam turbines, and generally comprises of rows of airfoil-shaped blades mounted on a rotary shaft . These blades capture kinetic energy, velocity and impulsive force from pressurized gas streams, and use them to create rotary mechanical energy.
The mechanical energy produced by the turbine can be used to start a generator, using the effect of electromagnetic induction on moving conductors in magnetic fields.
5). Fuel Nozzle (as one of the Parts of Gas Turbine Engines)
A gas turbine nozzle is any tube-like component with an aperture through which fluid is injected ejected at relatively-high pressure.
The function of gas turbine nozzle is to facilitate fluid transfer in components and processes where high-pressure fluid entry or exit is required.
Nozzles are named according to specific use, so that those used to eject exhaust gases are called exhaust nozzles, while those used to inject fuel into the combustor are called fuel nozzles.
Fuel nozzles are an essential component of gas turbines, because their function is needed in order to achieve thorough mixing of air and fuel, so that the mixture can be ignited and burnt to yield thermal energy and pressurized gas.
The fuel nozzle(s) is attached to a fuel feeder tank from which they supply fuel in thin sprays that allow for atomic mixing with air (oxygen) in the combustor.
Types of fuel nozzles used in gas turbines are simplex and duplex nozzles; where the simplex nozzles are equipped with a single orifice for fluid flow, and the duplex nozzles are equipped with multiple orifices that can be classified as primary and secondary (orifices) based on position and relative importance. Other lesser-known types of fuel nozzles for gas turbines are; fan-spray, spill-return and dual-orifice .
The duplex fuel nozzle is generally more efficient and effective for delivering atomized fluid over a wide area. It is therefore more commonly used, especially in large and/or complex gas turbines.
The exhaust in a gas turbine is a component that is primarily responsible for ejecting used gases from the engine core.
Exhausts of gas turbine engines are used to regulate the engine's functioning by reducing internal fluid pressure and temperature as gases are emitted from the system.
Gas turbine exhaust is also useful for evaluating the performance of the turbine. One of the exhaust parameters used in this regard is the exhaust spread.
Gas turbine exhaust spread is a measure of the difference in minimum and maximum temperature of gases from the core engine that exit through the exhaust terminal. Also called exhaust temperature spread, it assesses the width of the operating-temperature range of the system.
Exhaust spread is indicative of the fuel and energy efficiencies of the turbine, which in turn indicate its working condition and reliability. An excessively-high exhaust spread suggests that combustion is uneven, and may be caused by engine faults.
The composition of gases from a typical gas turbine exhaust includes carbon dioxide, and nitrogen oxide, alongside small quantities of other gases like sulfuric oxide, whose chemical makeup and relative volume depend on the fuel being used.
Gas turbine exhausts can be connected to a heat recovery system to create a form of cogeneration unit that captures waste heat from the system, which could be reused as part of measures to conserve fuel .
7). Auxiliary Systems (as Parts of Gas Turbine Engines)
Auxiliary systems in gas turbines comprise of all components that are not main components, and which perform functions that are of secondary importance to the overall working of the gas turbine engine.
While the main components include compressor, combustor and turbine; auxiliary components of a gas turbine include; fuel filter, scavenge pump, fuel control, inlet fogging nozzle(s) or water injectors, oil lubrication system, ignition unit and exhaust silencer.
Although their role is secondary, some auxiliary components of gas turbines like filtration and fluid injection components can consume significant amount of energy, especially in large turbines where these components operate in significant volumetric scale.
Parts of gas turbine engines are;
1. Air Inlet
5. Fuel Nozzle
7. Auxiliary Systems
1). Abinaya, R.; Dharamaraj, R.; Soundarya, B.; Balakrishnan, S.; Dakshinamurthy, B.; Rajeshwari, P. (2020). "Flow conditions analysis of Gas Turbine Combustor." IOP Conference Series Materials Science and Engineering 995(1):012043. Available at: https://doi.org/10.1088/1757-899X/995/1/012043. (Accessed 8 March 2023).
2). Hashim, M. A.; Khalid, A.; Salleh, H.; Sunar, N. M. (2017). "Effects of Fuel and Nozzle Characteristics on Micro Gas Turbine System: A Review." IOP Conference Series Materials Science and Engineering 226(1):012006. Available at: https://doi.org/10.1088/1757-899X/226/1/012006. (Accessed 8 March 2023).
3). Khosravy; M. (2013). "Review of the New Combustion Technologies in Modern Gas Turbines." Progress in Gas Turbine Performance. Available at: https://doi.org/10.5772/54403. (Accessed 8 March 2023).
4). Lefebvre, A. H. (2000). "Fifty years of gas turbine fuel injection." Atomization and Sprays 10(3-5):251-276. Available at: https://doi.org/10.1615/AtomizSpr.v10.i3-5.40. (Accessed 8 March 2023).
5). Moradi, A.; Salehi, G. R.; Manesh, M. H. K. (2021). "Performance Analysis of Gas Turbine Inlet Air Cooling Plant with Hybrid Indirect Evaporative Cooling and Absorption Chiller System." International Journal of Thermodynamics 24(3):248-259. Available at: https://doi.org/10.5541/ijot.840496. (Accessed 8 March 2023).
6). Mousa, F.; Hashem, H. H. (1989). "Gas turbine exhaust gas heat recovery at South Baghdad (Iraq) power plant" Heat Recovery Systems and CHP, Volume 9, Issue 6, 1989, Pages 547-552. Available at: https://doi.org/10.1016/0890-4332(89)90019-7. (Accessed 8 March 2023).
7). Philips, J.; Simas, P. (2004). "Gas turbine fuel nozzle refurbishment." Hydrocarbon Processing 83(1):72-74. (Accessed 8 March 2023).
8). Sadrehaghighi, I. (2022). "Components of an Axial Gas Turbine Engine." Available at: https://doi.org/10.13140/RG.2.2.19447.50088/7. (Accessed 8 March 2023).
9). Santos, A. P.; Andrade, C. R. (2012). "Analysis of Gas Turbine Performance with Inlet Air Cooling Techniques Applied to Brazilian Sites." Journal of Aerospace Technology and Management 4(3):341-354. Available at: https://doi.org/10.5028/jatm.2012.04032012. (Accessed 8 March 2023).
10). Soares, C. (2015). "Gas Turbine Major Components and Modules." Gas Turbines (Second Edition). Available at: https://www.researchgate.net/publication/282598128_Gas_Turbine_Major_Components_and_Modules. (Accessed 8 March 2023).
11). Wilcox, M.; Kurz, R.; Brun, K. (2012). "Technology Review of Modern Gas Turbine Inlet Filtration Systems." International Journal of Rotating Machinery 2012(12). Available at: https://doi.org/10.1155/2012/128134. (Accessed 8 March 2023).