Expert: Marc Ebelini - 5/23/2004

Question
Respected Sir,
What are the predominant features of the Turbo Fan Engines, that makes them significantly more fule efficient than Turbo Jet Engines?

Answer
Adding the larger ducted fan in front of the turbine allowed the engines to ingest more air at lower speed for quicker takeoffs making them more fuel efficient. Jet engines are not at their best at low altittutes, the fan also improves this condition. The additional stage is like adding a supercharger to recipercating engine. I will assume you understand the purpose of doing that. If not, let me give you a brief explaination. The intake pressure on a running engine is less that the ambient pressure, approximately 29.92 mm due to the piston drawing in outside air like a vacumm pump. Adding a compressor (supercharger) to push air into the intake causes the engine to develop more power because more fuel can be added to the engine keeping the same fuel/air ratio. Adding fuel without adding the additional air would just flood the engine because the proper fuel/air ratio would not be maintained.