The standard propulsion system seen on commercial aircraft is a twin turbofan gas turbine engine assembly. Airbus and Boeing utilize this dual engine system on most of their aircraft. The fuel-efficient assembly is widely used in high-speed transport and has helped propel the aerospace industry to what it is today (pun intended).
Standard gas turbine engine functionality is powered by a specific set of turbomachinery including a compressor, a combustion area, and a turbine unit. Turbofan engines add an additional fan in front of the engine, and an additional fan turbine behind it. Let’s examine how a turbofan engine works.
Turbofan engines have two separate shafts— one houses a fan and fan turbine, and the other houses a core compressor and core turbine. This system is called a two-spool engine because of its dual shaft arrangement. The fan serves two main functions that are critical to turbofan fuel efficiency. Its multi-blade construction increases the velocity of the incoming air stream and directs some air into the core compressor. Air that flows from the fan and around the engine instead of into the core compressor is called bypass air. Because the velocity is increased, this airflow provides additional thrust on essentially the same amount of fuel.
The core turbine is the driving unit of the engine. The turbine is made up of two types of airfoil blades: high-speed rotating blades called rotors, and stationary blades called stators. This configuration keeps airflow from deviating around the axis. The power turbine utilizes hot air flow from the burner to power the compressor.
The core compressor increases the pressure of air that is routed into the assembly. The compressor is powered by the rotation of the turbine and is located on the same shaft. The compressor pressurizes air flow using a centrifugal or axial flow rotating method. It is most common for a commercial jet to use a multistage axial compressor, which directs air in parallel to the axis of rotation of the shaft through a series of airfoil cascades. The compressor, like the power turbine, uses rotors and stators to increase pressure and direct airflow.