What is a jet engine?

A jet engine is an engine design that draws air in at the front of the engine, compresses it, mixes it with the fuel, burns it, and generates combustion gases.  By powerfully exhausting the hot and high pressure combustion gasses rearward, energy to push the engine forward (thrust) is created.

What is the turbofan engine, used to HF120?

The turbofan engine is one type of jet engine.
The incoming air is separated into two different paths. One is where air flows into an outer channel of the engine, and then is directly exhausted without being combusted. In the other, air flows into an inner core and is mixed with fuel and combusted before it is exhausted. Because the turbofan engine can separate and control the use of air, it is relatively fuel efficient. Therefore, the turbofan engine is widely used for large passenger aircrafts and business jets which require fuel efficiency. HF120 is applying the turbofan engine structure.

How the Turbofan Engine works

Watch the animation below which shows how the turbofan engine works in 3D.