What is the difference between a turbofan and a turbojet engine?

What is the difference between a turbofan and a turbojet engine?

• A. A turbofan relies primarily on exhaust jet thrust with less bypass air.
• B. A turbofan uses a large bypass fan to boost thrust.
• C. A turbofan has a large bypass fan that creates additional thrust with higher efficiency and lower noise.
• D. A turbojet is always quieter.

Answer: (C)

Turbofan engines generate most of their thrust from a large amount of air that bypasses the engine core, pushed by a big fan. This bypass air adds thrust directly and does so with the jet exhaust moving more slowly, which raises propulsive efficiency and lowers overall fuel burn. The result is higher efficiency and noticeably quieter operation, especially at takeoff and during subsonic flight. A turbojet, by contrast, relies mainly on the high-speed exhaust from the engine core and has little bypass air, leading to lower efficiency and higher noise. The statement that a turbofan has a large bypass fan that creates additional thrust with higher efficiency and lower noise captures this key difference. The other points describe turbojets or oversimplify the comparison, which is why they aren’t as accurate.

Turbofan engines generate most of their thrust from a large amount of air that bypasses the engine core, pushed by a big fan. This bypass air adds thrust directly and does so with the jet exhaust moving more slowly, which raises propulsive efficiency and lowers overall fuel burn. The result is higher efficiency and noticeably quieter operation, especially at takeoff and during subsonic flight. A turbojet, by contrast, relies mainly on the high-speed exhaust from the engine core and has little bypass air, leading to lower efficiency and higher noise. The statement that a turbofan has a large bypass fan that creates additional thrust with higher efficiency and lower noise captures this key difference. The other points describe turbojets or oversimplify the comparison, which is why they aren’t as accurate.