Turbofan

A turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft propulsion. It is a very important part of how airplanes fly. The word "turbofan" comes from the older turbojet engine technology and the added fan stage that helps it work better.

A turbofan engine has a gas turbine engine that adds energy to the air by burning fuel, and a ducted fan that is powered by this turbine. The fan pushes air rearwards to help the plane move forward. Unlike a turbojet, where all the air goes through the combustion chamber, in a turbofan some of the 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 and more power from the jet itself 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 make the engine work even better.

Principles

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

Frank Whittle thought about how planes could fly as fast as 500 miles per hour in 1936. He described how turbofans work, even though he didn’t use that name. Regular jet engines push air out really fast to make the plane go, but this isn’t very good for slower speeds. Turbofans fix this by using a fan to push a lot of air around the main engine. This makes most of the push come from this fan instead of 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 than moving a little air really fast. 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, where the fan pushes much more air than the engine itself.

History

Early turbojet engines were not very fuel-efficient because of the technology and materials available at the time.

The first turbofan engine was tested in Germany in 1943, but development stopped because of World War II. Later, the British tested their own turbofan design. As technology improved, 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 combine features from older turbojet engines with a large fan to improve efficiency. There are mainly three types of turbofans: low-bypass, afterburning, and high-bypass.

Low-bypass turbofans are often used in military jet fighters. They produce a lot of thrust quickly but use fuel fast. Afterburning turbofans add a special combustor that boosts thrust even more for short bursts, like during takeoff or combat. High-bypass turbofans are common in commercial airliners because they are more fuel-efficient and quieter. These engines have a large fan that pushes a lot of air rearwards, making the plane go faster and farther.

Turbofan configurations

Turbofan engines come in many different designs. They all have a central part called a spool, which 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, known as a two-spool setup.

Another design uses three spools, with an extra middle spool for better performance. Some engines use a special geared fan to let 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 become more fuel efficient by increasing the pressure of air as it enters the engine and raising the temperature of the air inside the engine. This needs better materials to handle the higher temperatures and pressures.

There are two ways to increase the thrust of a turbofan engine: the "hot route," which involves raising the temperature inside the engine, and the "cold route," which involves increasing the amount of air flowing through the engine. Both methods need more fuel to work. The cold route can be achieved by adding stages to the engine or improving how the engine compresses air, or by making the engine slightly larger.

To handle the extra power from these changes, the fan at the front of the engine also needs to be adjusted. For airplanes, increasing the amount of air moving through the fan helps keep noise levels down while also increasing thrust.

Improvements

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

Engine blades must withstand extremely high temperatures, so they are made from special materials and designed with cooling systems to stay strong. Fan blades have grown huge—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 allow these blades to be stronger while using fewer materials, saving cost and improving 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, to achieve these goals. Advances in technology and materials science continue to push the limits of what jet engines can do, making them more efficient and environmentally friendly.

Main article: Turbofan

Manufacturers

Commercial turbofans in production

Several major companies make turbofan engines used in commercial airplanes today. These engines help power many of the jets you see in the sky. Companies like Pratt & Whitney, Rolls-Royce Holdings, and General Electric are some of the biggest manufacturers. They design and build these engines to be safe, powerful, and efficient for flying long distances.

Extreme bypass jet engines

In the 1970s, Rolls-Royce/SNECMA tested a special type of engine called a turbofan with adjustable fan blades. This 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, making them look like turboprops but with wider blades. Both General Electric and Pratt & Whitney/Allison showed these engines in the 1980s, but they were not used because of 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 of the engine that moves air around the main engine core. The core is the central part of the engine where fuel is burned to create hot gas. The bypass ratio measures how much air flows around the core compared to how much flows through it.

Other terms describe how the engine works. Net thrust is the force that pushes the airplane forward. Propulsive efficiency shows how well the engine uses energy to create this force. Specific fuel consumption tells us how much fuel the engine uses to create a certain amount of thrust. Understanding these terms helps us learn how turbofan engines power modern airplanes.

Afterburner

Flex temp

IEPR

Overall pressure ratio

Propulsive efficiency

Specific fuel consumption

Stagnation pressure

Static pressure

Specific thrust

Thermal efficiency