How Does a Turbofan Engine Work?
How do Turbofan engines work, and what are their parts?
To understand how this engine works, first, we need to know each of its parts. It is broken up into four sections. The:
When air enters into an engine, it enters through the fan blades. This section is called the intake. From the intake, it goes to the compressor section. The compressor section comprises two types of blades broken up into stages. Moving blades are called variable guide vanes, and fixed blades, called stator vanes. As the air passes through several blades at each stage, the blades become slightly smaller, allowing the air to compress further until it reaches the diffuser section.
The diffuser slows down the air from the compressor section, allowing pressure to slowly increase, making it easier to ignite in the combustion section.
The combustion section comprises the combustion chamber, igniters, and fuel nozzles. This is where the air slowed down in the diffuser, is mixed with fuel, and ignited, emitting a flame. In a sense, a controlled explosion/ continous burn. From there, the air/gas mixture goes to the turbine section.
A typical turbofan engines turbine section consists of two stages. The first stage is the high-pressure turbine; the air is received and converted from thermal energy to mechanical energy. The second stage is the low-pressure turbine. This stage receives what is left from the high turbine and makes the fan, located in the inlet section, rotate through a shaft that connects the turbines. So, we can say that the turbines do not work without the fan, and the fan does not work without the turbines. Finally, after the turbine stage, there is an exhaust nozzle where the rest of the gas is released. The engine noise produced by an engine is highly dependent on the speed of the exit, so the cold diverted air mixes with the hot air. That’s why it is possible to keep the exit speed within a limit and thus surpass the noise problem. With a quieter exhaust nozzle and better fuel economy, the turbofan engines still dominate the aircraft propulsion market.
So, now that we know all the engine’s parts let’s understand a bit more about how a turbine engine works and its principle.
Let’s first discuss airflow. In the turbofan engine, the air is separated into two paths called Primary and Secondary airflow. (Fig.2)
The primary airflow path is the air that enters the engine’s core. Believe it or not, only 20% or so of air that passes through here is responsible for the engine’s power.
The secondary airflow, also known as the bypass air, is the air that goes outside the engine core. The bypass is responsible for moving a large mass of air backward, making it responsible for 80% to 90% of the engine's power.
Remember, an engine keeps the aircraft flying using one simple principle. That principle is Newton’s laws of motion. This is the same principle that makes a balloon move through the air.
Newton’s laws of motion state that with every action, this is an equal and opposite reaction. Just as the reaction force made by the air leaving the balloon can move the balloon, the reaction force made by the high-speed turbine makes the plane move forward. Basically, the engine displaces the large air mass to the back, causing the engine to move forward. This is transmitted to the aircraft's wings, making the aircraft move forward and upward.
Daniel Blassle Orlandi,
Aircraft engineering student.
Engines. (n.d.). Glenn Research Center. Retrieved January 10, 2022, from https://www.grc.nasa.gov/www/k-12/UEET/StudentSite/engines.html
Wheeler, R. (n.d.). File:Turbofan3 Unlabelled.gif. Wikimedia Commons. Retrieved January 10, 2022, from https://commons.wikimedia.org/wiki/File:Turbofan3_Unlabelled.gif