What is a key difference between turbojet and turbofan engines?

What is a key difference between turbojet and turbofan engines?

• A. Turbofan adds a front fan driven by the turbine.
• B. Turbojet cannot operate at high altitude.
• C. Turbofan has no exhaust.
• D. Turbojet uses electric propulsion.

Answer: (A)

The main idea is how thrust is produced differently in turbojets and turbofans. A turbofan includes a large front fan driven by the turbine, so air is split: some goes into the engine core for combustion, but most bypasses the core and flows through a bypass duct. This bypass air provides a lot of thrust at lower exhaust speeds, which improves propulsive efficiency and reduces noise. A turbojet, on the other hand, directs nearly all the air through the core to be combusted, producing thrust from the high-velocity exhaust with little or no bypass flow. So the key distinguishing feature is the front fan in turbofans that creates the bypass stream. The other statements are not accurate: turbojets and turbofans both have exhaust, turbofans do not rely on electric propulsion, and turbojets can operate at high altitude just like turbofans (though efficiency and performance differ).

The main idea is how thrust is produced differently in turbojets and turbofans. A turbofan includes a large front fan driven by the turbine, so air is split: some goes into the engine core for combustion, but most bypasses the core and flows through a bypass duct. This bypass air provides a lot of thrust at lower exhaust speeds, which improves propulsive efficiency and reduces noise. A turbojet, on the other hand, directs nearly all the air through the core to be combusted, producing thrust from the high-velocity exhaust with little or no bypass flow.

So the key distinguishing feature is the front fan in turbofans that creates the bypass stream. The other statements are not accurate: turbojets and turbofans both have exhaust, turbofans do not rely on electric propulsion, and turbojets can operate at high altitude just like turbofans (though efficiency and performance differ).