In the turbofan vs turbojet comparison, I will first tell you what a turbofan engine is. It is a gas turbine which is basically composed of an inlet, a fan, a low pressure compressor, a high pressure compressor, a gas generator (combustor), a high pressure turbine, low pressure turbine, and a nozzle. In this type of engine, a big portion of the turbine work is employed to supply power to the fan, which is lacking in the turbojet.
Except for the fan, the turbojet engine is made up of the same components. However, the turbofan is usually more economic and efficient than the turbojet in a limited realm of flight. The reason for this is that the thrust specific fuel consumption (fuel mass flow rate per unit thrust) is lower for turbofan as it shows a more economic convenience operation.
Technical Comparison
The turbofan can also accelerate a much larger mass of air to the lower velocity than a turbojet for a higher propulsive efficiency. The frontal area of a turbofan is very large compared to that of a turbojet. As a result, it has more drag and more weight. The fan diameter is also limited aerodinamically when compressibility effects take place.
The Pratt & Whitney F100 and the General Electric F110 are afterburning turbofan engines which are used in the F-15 Eagle and the F-16 Falcon aircraft respectively. In this kind of turbofan, the bypass stream is mixed with the core stream before passing through a common afterburner and exhaust nozzle.
Below, a diagram of a high bypass ratio turbofan
