Discuss about the Impacts of Turbofan Engine in the Aviation Industry.
Turbofan engine is among the most common type of gas turbine engine used today (Hall, 2015). The first turbofan engine was manufactured by Rolls-Royce Limited in 1950s. The engine had a by-pass ratio is 0.25. In 1960s, Volvo Flygmotor and Pratt & Whitney also started manufacturing turbofan engines. Today, these engines are manufactured by different manufacturers, including General Electric, CFM International LEAP, Engine Alliance, and International Aero Engines, among others (Lucintel, 2012). The main motive of developing turbofan engine was to overcome the two main disadvantages of its predecessor, turbojet engine. The disadvantages were: poor fuel efficiency at lower altitudes and poor runway performance. Turbofan engine has successfully overcome these drawbacks of turbojet engine. Therefore turbofan engine was developed so as to replace turbojet engine. Since its invention, turbofan engine has greatly revolutionized the aviation industry by enabling quieter flights and lower fuel consumption by aircrafts. The purpose of this report is to discuss various elements of turbofan engine, including its components, operation, advantages and disadvantages.
The basic operation of a turbofan engine is similar to that of other turbine engines, where air is drawn into the engine, compressed, mixed with fuel, ignited and exhausted to create thrust that propels the aircraft. The main components of turbofan engines are: fan, compressor, combustor, turbine and nozzle/mixer, as shown in Figure 1 below (Cutler, 2016). These components are similar to those of a turbojet except the fan. In other words, a turbofan engine has similar components to those of a turbojet engine only that the former has a fan.
Figure 1: Components of a turbofan engine
The fan draws in large amounts of air into the turbofan engine. The air passes through two parts. Some of it flows into the core of the engine where it will be combusted whereas some of the air (called bypass air) is directed via a duct outside the engine core (Chmiel, (n.d.)). The bypass air has three main functions: it generates additional thrust; blankets the exhaust air leaving the engine thus making the engine to produce less noise; and cools the engine. Bypass ratio is the ratio of quantity of air passing outside the core of the engine to the air passing through the engine’s core (Hall, 2015). According to DutchOps.com (2012), turbofan engines can be classified into two groups based on their bypass ratios: low and high bypass ratio turbofan engine. The air flows through the axial flow compressor, which uses its spinning blades to accelerate the speed of the air and compress it. Stators, which are positioned between compressor blades, converts rotational energy of the air into static pressure thus increasing overall air pressure. In addition, the stators straighten the air flow making it ready to move into the succeeding set of spinning blades. The air then enters the combustor where it mixes with fuel and gets ignited. The combustor comprises of several parts, as shown in Figure 2 below (Cutler, 2016).
Figure 2: Parts of turbofan engine combustor
The diffuser is used for slowing down air entering the combustor from the compressor, which helps in easing the ignition. Swirler and dome are used for increasing air turbulence for easy mixing with the fuel. The fuel injector supply fuel that mixes with the air to create the desired fuel/air mixture. The actual combustion occurs in the liner, which comprises of various inlets for allowing entry of air at different points within the combustion zone. The igniter is used for lighting the fire to start the actual combustion process.
After leaving the combustor, the high-speed and hot air passes over the blades of the turbine. The blades draw energy from the air, rotating the turbine and engine shaft that is fixed to it. The same shaft is also connected to compressor and fan hence when the turbine rotates, the compressor and fan also keep on drawing in more air.
The nozzle is where the high speed air from the turbine gets exhausted at the back of the engine thus creating a thrust that pushes the airplane forward. This is in accordance with third law of Isaac Newton, which states that for every action force creates an equal reaction force that acts in the opposite direction.
There are several advantages of a turbofan engine. Some of these advantages are as follows:
A turbofan engine has a higher fuel efficiency. The engine burns less fuel than most of the other gas turbine engine thus saving fuel costs. In addition, this also reduces the amount of harmful emissions that the engine releases to the atmosphere (Whitfield, 2016).
A turbofan engine generates very high thrust compared to other turbine gas engines. The high thrust results from the air passing through the engine’s core and the bypass air (Stratos Jet Charters, Inc., 2010). With the other gas turbine engines, thrust is only generated by air flowing through the engine’s core. However, turbofan engine generates thrust from the air flowing through the engine’s core and the extra thrust from the bypass air flowing through the bypass duct.
A turbofan engine is quitter than majority of gas turbine engines. There are two factors contributing to this quietness. First, it is the bypass air that masks the exhaust air leaving the engine thus making the engine quieter. Second, it is the blades’ tips that are confined inside the turbofan engine casing thus controlling noise levels and preventing noise from leaving the engine casing. These two elements make the aero-acoustic properties of turbofan engines to be greater than most gas turbine engines.
A turbofan engine is more efficient to control especially when the airplane is flying at low altitudes. This does not only help the pilots to be in more control of the airplane but also improves the overall safety of the persons onboard.
A turbofan engine can fly at greater speeds than other conventional airplane engines. One of the factors enabling this is the design of the turbofan engine blades. The blade tips of a turbofan engine are designed to exceed the drag divergence speed. This capability of exceeding the drag divergence speed makes it possible to the turbofan engine to accelerate at very high speeds than most turbine gas engines.
A turbofan engine produces zero or very minimal vibrations. This has two benefits: it increases the comfort of the cabin crew and passengers, and also increases the longevity of aircraft components (Shields and Carmel, 2013). With less vibrations, it means that the airplane flies smoothly with minimal upheaval. Also, there are less interactions between various components of the airplane components thus reducing the likelihood of wear and tear that could otherwise cause damages and reduce the lifespan of these components. Therefore if maintained properly, turbofan engines are more durable than other gas turbine engines.
Another major advantage of turbofan engines is that they have the capacity to facilitate short takeoff distance. The turbofan engine’s fan draws large amounts of air into the engine thus generating adequate thrust quickly to propel the aircraft. Therefore airplanes using turbofan engines do not require longer runway distances to takeoff as they can generate sufficient thrust within a very short distance.
Despite the many advantages, turbofan engines also have some disadvantages. The key disadvantages are as discussed below
The frontal area of a turbofan engine is usually larger and this is mainly because of the large size of the fan. The large frontal area helps in drawing in more air into the engine. However, this large front area usually translates into more weight. In general, turbofan engines are usually heavier than their predecessors – turbojet engines.
One advantage is that the efficiency of a turbofan engine is greater when the airplane is flying at a lower altitude. However, this becomes a disadvantage when the airplane is moving at a higher altitude. The less efficiency at greater altitudes means that the airplane may be difficult to control and it is likely to start consuming more fuel.
Conclusion
Turbofan engines have had significant impacts in the aviation industry. The engines comprises of five main parts: fan, compressor, combustor, turbine and nozzle. They generate great thrust through air flowing pass the engine’s core and bypass air passing through bypass duct. These engines have reduced noise levels of airplane engines, increased fuel efficiencies, reduced fuel costs for many airlines, minimized carbon emissions, and increased fuel speeds. Considering its advantages, many airlines and aircraft owners/operators prefer turbofan engines than any other gas turbine engine. With the current innovative technologies, it is expected that turbofan engines will continue improving the aviation industry in different ways.
Chmiel, M. (n.d.). How a turbofan engine works. Retrieved April 3, 2017, from https://homepages.wmich.edu/~msw8680/myppt.pdf
Cutler, C. (2016). How Does A Turbofan Engine Work? Retrieved April 3, 2017, from https://www.boldmethod.com/learn-to-fly/aircraft-systems/how-does-a-jet-engine-work/
DutchOps.com. (2012). Engine Types. Retrieved April 3, 2017, from https://www.dutchops.com/Portfolio_Marcel/Articles/Engines/Engine_Types.htm
Hall, N. (2015). The Turbofan Engine. Retrieved April 3, 2017, from https://www.grc.nasa.gov/www/k-12/airplane/aturbf.html
Lucintel. (2012). Global Commercial Aero Turbofan Engine Market, Supply Chain and Opportunities: 2011-2017. Irving, TX: Lucintel.
Shields, M. and Carmel, J. (2013). Turbofan Engine Technology Upgrades – How Should Suppliers React? Retrieved April 3, 2017.
Stratos Jet Charters, Inc. (2010). Jet Charter Engine Basics: Why Turbofan Trumps Turbojets. Retrieved April 3, 2017, from https://www.stratosjets.com/2010/06/28/aircraft-engines-101-the-advantages-of-the-turbofan-engine-compared-to-the-turbojet-for-jet-charters/
Whitfield, B. (2016). Turbofan Engine: How It Works. Retrieved April 3, 2017, from https://www.flyingmag.com/how-it-works-turbofan-engine
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