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According to the webpage ”turbofan engine” from SKYbrary(n.d.) and ”turbofan engine” from NASA(n.d.), a turbofan engine, also known as a fanjet engine or bypass engine, is the latest form of jet engine that utilizes both high-speed exhaust gasses and bypass air, amplified by a duct fan which is propelled by a jet core to help an airplane soar through the sky.
The NASA website also states that a turbofan engine is made up of an inlet, a fan, a compressor, a burner, a core turbine, a fan turbine and finally, a nozzle. The turbofan engine takes in air from the front through the inlet, which is then compressed by the core compressor. The compressed air is then mixed with fuel and burned in the burner, producing hot exhaust that will pass through the core and fan turbines and out of the nozzle to produce a thrust that will propel the aircraft foward. Many present day aircrafts use turbofan engines for their high propulsive force and low fuel consumption.
While turbojet engines and turbofan engines are similar, the main difference between them lies in the fan at the front. While the change may seem minor, the advantages brought by it made the turbofan engine the more popular choice when compared to turbojet engines in commercial aircrafts as it is more fuel efficient and produces less sound.
One of the advantages of the turbofan engine is that it produces more thrust for the same amount of fuel used by a turbojet engine. The efficiency of an aircraft engine is determined by how much fuel is used to produce a certain amount of thrust. (Chopra, 2022).
During flight, the turbojet engine continuously takes in a large amount of the surrounding air, also known as the free stream air flow, through the inlet that is compressed in the compressor. The high-pressure air is then fed into the burner where it is mixed with fuel and burned to produce high-pressure exhaust which exits the engine through the nozzle, which further speeds up the exhaust. As the velocity of the resulting stream is greater than the free stream velocity, thrust is created and allows the aircraft to be propelled forward. For a turbojet engine, the total mass flow, also known as the core airflow, is nearly equal to the free stream mass flow, since very little fuel is added to the stream. (NASA, n.d.)
For the turbofan engine, some of the incoming air goes around the engine, in addition to the air taken in by the inlet like the ones in the turbojet engine. This is called the fan flow, which is slightly faster than the surrounding air. The turbofan gets its thrust from the combination of the core flow and the fan flow. As the total mass flow rate through the inlet is the sum of the core and fan flows, a turbofan generates more thrust for nearly the same amount of fuel used by the core (NASA, n.d.). Of the total thrust produced by a turbofan engine, fan flow encompasses 30 to 70 percent of the total exhaust gasses. (Chopra, 2022). Thus, allowing the turbofan to have higher fuel efficiency.
Another advantage of the turbofan engine is that it is quieter than the turbojet engine. Paraphrased using chatGPT, turbofan engines are naturally less noisy than turbojets when producing the same amount of thrust. Turbofan engines generate thrust by spinning a fan using a turbine engine, which speeds up a larger volume of air to a lower velocity compared to turbojets. In contrast, turbojets rely solely on the turbine engine to generate thrust.
Consequently, when producing the same level of thrust, the exhaust from a turbofan engine contains less energy (though more mass), resulting in reduced noise. This is why turbofan engines are commonly preferred for commercial aircraft, as they offer improved performance and lower noise levels. (Bartlet, 2016).
One disadvantage of turbofan engines is that they are difficult to produce. According to chatGPT, “turbofan engines are more difficult to produce compared to simpler turbojet engines because of their complexity, the need for advanced materials, the requirement for high efficiency and low emissions, and the intricate integration with aircraft systems. These challenges make them a critical and costly component of modern aviation, but they also contribute to the safety and performance of commercial and military aircraft.”(OpenAI,2023).
In conclusion, the turbofan engine is the upgraded version of the turbojet engine, tailormade to be more suitable for commercial flight while the turbojet engine has been improved in a different direction to support fighter jets or aircrafts with speed as a higher priority. Therefore, while the turbojet engine has its merits, the turbofan engine is undoubtedly superior when it comes to carrying commercial aircrafts as it is more fuel efficient and is less noisy to be around.
References
NASA(n.d.) Turbofan Engine. https://www.grc.nasa.gov/www/k-12/airplane/aturbf.html
SKYbrary(n.d.) Turbofan Engine. https://skybrary.aero/articles/turbofan-engine
Devansh Mehta (2022), How Do Turbofan Engines Work? Simple Flying. https://simpleflying.com/how-do-turbofan-engines-work/
Matt Claiborne (2023), The Difference Between Turbojet and Turbofan Engines. Aerocorner. The Difference Between Turbojet and Turbofan Engines - Aero Corner
Anil Chopra (2022).Large jet engines. Power with fuel efficiency. SP’s airbuz. https://www.spsairbuz.com/story/?id=1203&h=Large-Jet-Engines-Power-with-Fuel-Efficiency
MachineDesign(2016). What’s the Difference Between Turbine Engines? https://www.machinedesign.com/motors-drives/article/21832035/whats-the-difference-between-turbine-engines
Bartlet (2016). The effects of using noise reduction turbofan engine nozzle designs on a turbojet engine.
OpenAI(2023,September 24) ChatGPT response to “What makes turbofan engines much more difficult than jets in production?” https://chat.openai.com/c/b62c7bef-1b20-4118-830b-c5e49835d388
OpenAI(2023,September 24) ChatGPT response to “Paraphrase ‘Turbofan engines are inherently quieter than turbojets for a given level of thrust. A turbofan thrust is developed by
turning a fan with a turbine engine that accelerates a larger amount of air to a lower velocity than do turbojets. Turbojet thrust is developed solely by the turbine engine. Therefore, for a given thrust, the fanjet’s discharge contains less energy (but more mass) as it exits the engine, and so produces less noise. Turbofan engines are commonly used on commercial transports due to their advantage for higher performance and lower noise?’” https://chat.openai.com/c/b62c7bef-1b20-4118-830b-c5e49835d388
NASA(n.d.) Turbojet Thrust. https://www.grc.nasa.gov/www/k-12/airplane/turbth.html
NASA(n.d.) Turbofan Thrust. https://www.grc.nasa.gov/www/k-12/airplane/turbfan.html
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