7 Types of Gas Turbines Explained
Types of gas turbines are; turbofan, turbojet, turboshaft, turboprop, aeroderivative, heavy-frame, and integrated gas turbines.
They can be classified broadly into aircraft gas turbines and land-based gas turbines.
It must be noted that the aircraft gas turbines may be also called gas turbine engines, due to their function as a thrust-generator and propulsion component, in these aircrafts.
This article discusses the types of gas turbines, as follows;
-Aircraft Gas Turbine Types
Types of gas turbines used in aircrafts are; turbofan, turbojet, turboshaft and turboprop turbines.
1). Turbofan (as one of the Types of Gas Turbines)
As the name implies, turbofan is a technological system that is derived by combining a turbine with a mechanical fan.
Turbofan is a gas turbine engine used in aircrafts to produce thrust force by the rotary action of a fan which decreases fluid pressure in the engine.
The function of the turbofan is mainly to accelerate the flow of air through the gas turbine assembly, and to thereby magnify the mechanical energy and thrust force produced by the engine [1]. This thrust force is what propels the aircraft.
The energy efficiency of a turbofan is a measure of the extent to which wastage is minimized as kinetic energy of air from the inlet is converted to mechanical energy that rotates the fan.
It must be noted that the fan in this type of gas turbine assembly, is different from the rotor of the main turbine core, although they are connected.
Part of the rotary torque of the fan comes from the turbine. In turn, low-pressure air that is forced in by the fan helps accelerate the turbine, while some of it mixes directly with the jet exhaust stream.
While they are very similar, turbofans differ from turbojets, which represent another type of gas turbine system used in aircrafts.
The difference between turbojet and turbofan systems is the presence of additional fluid volume and velocity in the turbofan due to the presence of the fan component. Turbojets are an earlier, less-advanced variant of the turbofan, and derive all their thrust force from the rotary dynamics of high-pressure fluids in the main turbine core.
Turbine core here refers to the turbine shaft and its enclosure, including the compressor and casing.
Turbofans are used where high thrust and acceleration are needed, as in large jetliners.
2). Turbojet
A turbojet gas turbine assembly is a type of aircraft engine design, that comprises of gas turbine, compressor, combustion chamber and propulsion nozzle, which work together to create sufficient thrust force to propel the aircraft into its path of flight.
The main function of a turbojet engine is to use high-pressure fluid streams produced from air-fuel combustion, to induce mechanical rotation, fluid expansion, fluid expulsion, and thrust force [3].
Fuels like kerosene can be used in the combustor of a turbojet engine.
Because all its thrust comes from the engine core, turbojets are less powerful and less efficient than turbofans, which are a modified and advanced version of the turbojet.
3). Turboshaft (as one of the Types of Gas Turbines)
Turboshaft is a type of gas turbine engine used in aircrafts, to produce enormous amounts of torque or rotary mechanical energy, which is transferred to a rigid linear component or shaft.
The turboshaft engine can be described as a turbojet to which a large shaft is connected. It is required and used in aircrafts that depend on shaft rotation for their propulsion. Examples of such include helicopters [2].
Turboshaft engines can be incorporated into aircrafts that are already equipped with another type of engine, in order to enhance the performance of such aircrafts. Their overall energy output is generally less than that of turbojet and turbofan systems, due to the connection and energy transmission mechanism between the turbine core and the shaft.
4). Turboprop
A turboprop gas turbine engine is a modified turbojet that has a propeller with a hear box connected to the turbine core.
Turboprops are used for aircrafts that depend on engine-connected rotary propellers to provide thrust force. This differs from the turboshaft in that it transmits both fluid pressure and torque from the engine to the propeller, while turboshaft engines transmit only torque to the shaft.
-Land-based Gas Turbine Types
Land-based gas turbine types are; aeroderivative, heavy-frame, and integrated gas turbines.
5). Aeroderivative Gas Turbine (as one of the Types of Gas Turbines)
As the name implies, aeroderivative gas turbines are designed based on similar operational objectives as aircraft gas turbine engines like turbofan and turbojet.
Aeroderivative gas turbines are used for electricity generation at a smaller scale than heavy industrial turbines, and they make a better choice than the latter where portability, flexibility and relative simplicity are all priorities.
The difference between aeroderivative and industrial gas turbines is in their design, scale of operation, and performance.
Aeroderivative gas turbines are designed to be much lighter than industrial turbines. They are generally smaller and operate at a smaller scale, with lower mechanical energy and electricity output.
While industrial gas turbines often have energy capacities above 500 MW, aeroderivative turbine capacities rarely exceed 50 MW, although some are able to produce more than 100 MW of power.
6). Heavy Frame Gas Turbine
Heavy frame or heavy duty gas turbine is a type of land-based gas turbine that is designed to generate electricity in large-scale and is used in power plants.
The heavy duty gas turbine differs from aeroderivative gas turbine by being much larger and heavier. Its power capacity is generally above 70 MW, and could exceed 700 MW.
In terms of energy efficiency, aeroderivative gas turbines tend to be more efficient than heavy duty industrial turbines. They (aeroderivative turbines) are also easier and less-expensive to maintain.
Heavy duty gas turbines are more elaborate and complex in their constitution, and are more likely to work with various types of fuels, than aeroderivative turbines.
7). Integrated Gas Turbine (as one of the Types of Gas Turbines)
The integrated gas turbine is simply any turbine that combines the desirable characteristics of aeroderivative and heavy frame types.
Such turbines are usually developed in a bid to adapt to certain conditions of use, and/or to meet performance goals.
Conclusion
Types of gas turbines are;
1. Turbofan
2. Turbojet
3. Turboshaft
4. Turboprop
5. Aeroderivative Gas Turbine
6. Heavy Frame Gas Turbine
7. Integrated Gas Turbine
References
1). Farahani, S. D.; Alibeigi, M.; Sabzehali, M. R. (2021). "Energy and Exergy Analysis and Optimization of Turbofan Engine-TF30-P414." Iranian (Iranica) Journal of Energy & Environment, 12(4), 307-317. Available at: https://doi.org/10.5829/ijee.2021.12.04.04. (Accessed 7 March 2023).
2). Nkoi, B.; Pilidis, P.; Nikolaidis, T. (2013). "Performance assessment of simple and modified cycle turboshaft gas turbines." Propulsion and Power Research 2(2):96–106. Available at: https://doi.org/10.1016/j.jppr.2013.04.009. (Accessed 7 March 2023).
3). Virdi, P. S.; Khan, M. S.; Pereira, N.; DSilva, R. (2017). "Design and Fabrication of Major Components of Turbojet Engine." Emerging Trends in Mechanical Engineering, ETIME-2017. Available at: https://doi.org/10.5923/j.ep.20170705.02. (Accessed 7 March 2023).
