Turbofan

A turbofan or fanjet is a type of airbreathing jet engine that helps airplanes fly. The word "turbofan" comes from an older engine called a turbojet with an added fan to help it work better.

A turbofan engine has a gas turbine engine that adds energy to the air by burning fuel. It also has a ducted fan powered by this turbine. The fan pushes air rearwards to move the plane forward. Unlike a turbojet, where all the air goes through the combustion chamber, in a turbofan some air moves around the main engine parts. This makes the engine more efficient.

The amount of air that moves around the engine compared to the air that goes through the middle is called the bypass ratio. Engines with more air moving around are called high-bypass turbofans, and these are used in most commercial airplanes. Engines with less air moving around are called low-bypass turbofans, and these are often used in fighter jets. Modern turbofans usually have a large fan or several smaller fans to work even better.

Principles

The turbofan was made to use less fuel than older jet engines. It does this by pushing more air. It moves a lot of air at a slower speed, instead of a small amount of air really fast. This is done by adding a ducted fan.

Frank Whittle thought about how planes could fly in 1936. He described how turbofans work. Regular jet engines push air out really fast to make the plane go, but this isn’t very good for slower speeds. Turbofans use a fan to push a lot of air around the main engine. This makes most of the push come from the fan, not the hot air from the engine, saving fuel.

Turbofans work better for slower speeds because they move a lot of air at a slower speed. This is more efficient. The amount of air that goes around the engine compared to the air that goes through it is called the bypass ratio. Most planes today use high-bypass turbofans. These fans push much more air than the engine itself.

History

Early turbojet engines used a lot of fuel because the technology wasn’t very good.

The first turbofan engine was tested in Germany in 1943, but development stopped because of World War II. Later, the British tested their own design. As technology got better, engines became more efficient. The first turbofan used in airplanes was the Rolls-Royce Conway, which came out in the 1950s. In the 1960s, turbofan engines were used in civilian airplanes like the Tupolev Tu-124. The General Electric CF700 was an early small turbofan used in business jets and even helped train astronauts for Project Apollo.

Common types

Turbofans are a type of jet engine used in many modern airplanes. They mix parts of older turbojet engines with a big fan to work better. There are mainly three types of turbofans: low-bypass, afterburning, and high-bypass.

Low-bypass turbofans are often used in military jet fighters. They can make a lot of power quickly but use fuel fast. Afterburning turbofans add a special part that gives even more power for short times, like when taking off or fighting. High-bypass turbofans are used in airplanes that carry people because they save fuel and are quieter. These engines have a large fan that pushes a lot of air backward, helping the plane go faster and farther.

Turbofan configurations

Turbofan engines come in many different designs. They all have a central part called a spool. This spool includes a fan or compressor and a turbine that spins on the same shaft.

One common design has the fan on a slower-spinning shaft and the compressor on a faster-spinning shaft. This is called a two-spool setup.

Another design uses three spools. It has an extra middle spool for better performance. Some engines use a special geared fan. This lets the fan and turbine spin at their best speeds. Most civilian engines use this setup, while military engines usually stick to simpler two-spool designs.

Main article: Geared turbofan

Overall performance

Turbofan engines can use less fuel by squeezing the air more as it enters and heating the air inside. This needs special materials to stand up to the heat and pressure.

There are two ways to make a turbofan engine stronger: the "hot route," which heats the air more inside the engine, and the "cold route," which lets more air flow through. Both need more fuel. The cold route can be done by adding parts to the engine, making the engine work better at squeezing air, or making the engine a little bigger.

To deal with this extra power, the fan at the front of the engine must also change. For airplanes, letting more air through the fan helps keep noise down and makes the engine stronger.

Improvements

Aerodynamics helps us understand how air moves around the fan and blades of a turbofan engine. Modern engines can handle air moving at different speeds, keeping it flowing smoothly to create thrust. Engineers measure temperatures in easier-to-reach places instead of the very hot parts inside.

Engine blades must stay strong at high temperatures. They are made from special materials and have cooling systems. Fan blades have grown very large—they can carry as much weight as nine double-decker buses and move a volume of air equal to a squash court every second. New design techniques make these blades stronger while using fewer materials. This saves cost and improves efficiency.

Future engines aim to use less fuel and make less noise. Engineers are testing new designs, such as fans with fewer blades and lighter materials. Advances in technology and materials science continue to improve jet engines, making them more efficient and friendly to the environment.

Main article: Turbofan

Manufacturers

Commercial turbofans in production

Several big companies make turbofan engines for airplanes. These engines help power the jets you see flying in the sky. Companies like Pratt & Whitney, Rolls-Royce Holdings, and General Electric are some of the largest makers. They design and build these engines to be safe, strong, and efficient for long flights.

Extreme bypass jet engines

In the 1970s, Rolls-Royce/SNECMA tested a special type of engine called a turbofan. This engine had adjustable fan blades. It was designed to help very quiet aircraft take off and land from city-centre airports.

Later, a new engine called a propfan was developed. Unlike regular turbofans, propfans have blades outside the engine duct. They look like turboprops but have wider blades. Both General Electric and Pratt & Whitney/Allison showed these engines in the 1980s. However, they were not used because they made too much noise and because jet fuel was cheaper. The only propfan engine used on an actual airplane was the Progress D-27, made in the U.S.S.R.

Terminology

A turbofan engine has several important parts and ideas. The bypass is the part that moves air around the main engine. The core is the center where fuel burns to make hot gas. The bypass ratio shows how much air goes around the core compared to how much goes through it.

Other words explain how the engine works. Net thrust is the force that pushes the airplane forward. Propulsive efficiency shows how well the engine uses energy. Specific fuel consumption tells us how much fuel the engine uses to make thrust. Learning these words helps us understand how turbofan engines power airplanes.

Afterburner

Flex temp

IEPR

Overall pressure ratio

Propulsive efficiency

Specific fuel consumption

Stagnation pressure

Static pressure

Specific thrust

Thermal efficiency