Turbofans are one of the most common types of aircraft engines. They are characterized by the use of a ducted fan to blow air around the combination chamber. Upon entering a turbofan, some of the air will enter the combustion chamber where it’s mixed with fuel and ignited, and some of the air will bypass the combustion chamber where it’s used for cooling, additional thrust and noise suppression.
While all turbofans feature a ducted fan that moves air around the combustion chamber and core, there are different types of turbofans. Many commercial airplanes and some military airplanes, for instance, are powered by 2-spool turbofans.
What Is a 2-Spool Turbofan?
A 2-spool turbofan is a type of turbofan that features two rotating shafts or “spools.” There’s a low-pressure spool and a high-pressure spool. During use, both spools turn while engaging their respective components.
How 2-Spool Turbofans Work
Like all turbofans, 2-spool turbofans are designed to burn a mixture of fuel and air while moving some of the air around the combustion chamber. 2-spool turbofans simply have two separate spools.
The low-pressure spool powers the ducted fan and the low-pressure compressor. It typically spins at a slower speed and handles a greater volume of air than the high-pressure spool.
The high-pressure spool, on the other hand, powers the high-pressure compressor. It spins more quickly and is designed to squeeze and compress the air before it enters the combustion chamber. By doing so, more air can enter the combustion chamber, resulting in a stronger combustion process.
Why Airplanes Use 2-Spool Turbofans
While some commercial airplanes use a single-spool turbofan — or even 3-spool turbofans — most use 2-spool turbofans. 2-spool turbofans offer several advantages over their single-spool counterparts. They are typically more efficient, for instance. Compressors work best at specific speeds. With 2-spool turbofans, each spool can spin independently of the other, resulting in improved fuel efficiency.
2-spool engines are also very responsive to throttle changes. They react more quickly to changes in throttle than single-spool turbofans.
Another reason so many airplanes use 2-spool turbofans is ease of maintenance. They are easier to maintain and repair than 3-spool turbofans.
In Conclusion
2-spool turbofan engines strike a balance between performance, efficiency and maintainability. By separating the low- and high-pressure systems onto two independent shafts, these engines optimize airflow and fuel combustion, improving both thrust and responsiveness. Their widespread use across commercial and military aviation reflects the practical benefits of their design.
