Which statement best describes a turbofan engine?

• A. A turbojet engine without a fan.
• B. A piston engine with a crankshaft.
• C. A fanlike turbojet engine designed to create additional thrust by diverting a secondary airflow around the combustion chamber.
• D. An electric propulsion system.

Answer: (C)

A turbofan works by combining a large front fan with the jet engine core. The fan pulls in a lot of air; some enters the core to be burned with fuel, but a large portion bypasses the core and flows around the outside. That bypassed air provides most of the thrust and does so more efficiently and quietly than a pure turbojet.

So the statement that describes a fanlike turbojet designed to create additional thrust by diverting a secondary airflow around the combustion chamber captures this dual-flow, two-path thrust mechanism. It differentiates turbofans from a turbojet (no big fan), from piston engines, and from electric propulsion.