To further increase efficiency of jet aircraft engines, turbo fans were developed these work just like a turbo jet but a fan is added to the compressor section

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On  a turbojet thrust is generated mainly from the exhaust, on a turbo fan thrust is generated by both the exhaust and the fan.

The ratio of thrust produced by the fan vs. exhaust is called the bypass ratio. if this ratio is aprox. 4:1 or less then the engine is referred to as a low bypass turbo fan.

www.globalsecurity.org/military/systems/aircraft/images/yf-22-01_300.jpg

 The F-22 uses low bypass turbofans - older fighter aircraft use turbo jets.
 
 

*Whenever there is a page number underneath a diagram the picture is from
A&P Technician Powerplant Textbook published by Jeppesen Sanderson Inc., 1997