Which statement correctly describes turbofan engines compared with turbojets?

Which statement correctly describes turbofan engines compared with turbojets?

• A. Turbofan uses a fan to bypass some airflow for higher thrust and efficiency; turbojet uses core exhaust; turbofan is more fuel-efficient and quieter.
• B. Turbojet uses a bypassed airflow to reduce noise.
• C. Turbofan is less fuel-efficient than turbojet.
• D. Both engines operate identically; no difference.

Answer: (A)

Turbofan engines gain thrust and efficiency by using a large fan to push a lot of air around the engine core (bypass air) instead of all the air going through the combustion process. This bypass air adds a substantial amount of thrust because there’s a big mass of air moving, but at a lower velocity than the core exhaust. By mixing both the bypass flow and the core exhaust, the engine delivers more total thrust for the same fuel flow and does it more efficiently. The slower, high-mass bypass flow also lowers the jet speed when it leaves the engine, which reduces noise. In contrast, a turbojet has no bypass; all air goes through the core and is expelled at high speed, giving less propulsive efficiency and more noise and fuel use for the same thrust. That’s why turbofan engines are generally described as more fuel-efficient and quieter than turbojets. The other statements don’t fit because turbojets don’t use bypass air, turbofans aren’t less fuel-efficient, and the engines don’t operate identically.

Turbofan engines gain thrust and efficiency by using a large fan to push a lot of air around the engine core (bypass air) instead of all the air going through the combustion process. This bypass air adds a substantial amount of thrust because there’s a big mass of air moving, but at a lower velocity than the core exhaust. By mixing both the bypass flow and the core exhaust, the engine delivers more total thrust for the same fuel flow and does it more efficiently. The slower, high-mass bypass flow also lowers the jet speed when it leaves the engine, which reduces noise. In contrast, a turbojet has no bypass; all air goes through the core and is expelled at high speed, giving less propulsive efficiency and more noise and fuel use for the same thrust. That’s why turbofan engines are generally described as more fuel-efficient and quieter than turbojets. The other statements don’t fit because turbojets don’t use bypass air, turbofans aren’t less fuel-efficient, and the engines don’t operate identically.