A turbofan is a jet engine that uses a large front fan to generate thrust more efficiently and quietly than a basic turbojet.
Most airliners you’ve ever flown on are powered by turbofans. A turbofan engine pulls air in through a large fan at the front; some of that air enters the core to be compressed and burned, while the rest bypasses the core entirely, contributing to thrust. Understanding what a turbofan is comes down to how that fan splits the air.
How a Turbofan Engine Works
The core of a turbofan is a gas turbine, the same technology found in a turbojet. The big difference is the additional low-pressure fan mounted up front.
The fan spins, drawing air in. Part of that air passes through the compressor, combustion chamber, and turbine — that’s the core flow. The rest flows around the outside of the core, which is the bypass flow. Both streams create thrust, but the bypass air does most of the heavy lifting in modern designs.
- Front fan: a large, low-pressure fan that pulls in massive amounts of air.
- Compressor: squeezes the core air to high pressure before combustion.
- Combustor: burns fuel with the compressed air.
- Turbine: spun by the hot exhaust; a shaft links it back to the front fan.
- Exhaust nozzle: accelerates gases out the back to generate thrust.
NASA’s educational resources on turbofan engine basics explain that the fan and turbine are connected by a shaft, so what happens in the turbine drives what happens at the front of the engine.
What Is Bypass Ratio?
The bypass ratio is the amount of air that flows around the core compared to the air that flows through it. A high-bypass turbofan pushes most of its air around the outside of the engine.
High-bypass engines are what you’ll find on commercial jets. They are significantly more fuel-efficient than the turbojets used in older aircraft, and the slower-moving bypass air muffles some of the engine’s noise. Low-bypass designs, where more air goes straight through the core, are common on military fighter jets where raw speed matters more than fuel economy.
Turbofan vs Turbojet vs Turboprop
The practical difference between a turbofan and a regular turbojet comes down to that bypass flow. In a turbojet, all the air goes through the core; in a turbofan, a good portion skips the core entirely.
That bypass design is what makes the turbofan the workhorse of civil aviation. According to SKYbrary’s turbofan engine article, these engines dominate modern airliner fleets because they burn less fuel and produce less noise than their simpler predecessors. Turboprops, by contrast, use the turbine to spin a propeller rather than a ducted fan.
| Engine Type | Airflow Path | Typical Use |
|---|---|---|
| Turbofan | Part through core, part bypasses | Commercial airliners, business jets |
| Turbojet | All through the core | Older jets, high-speed military aircraft |
| Turboprop | Core drives a propeller | Regional and short-haul flights |
One important distinction: a turbofan is an aircraft jet engine, not the same thing as a consumer appliance or an automotive part. If you’re researching a turbo fan for your car’s cooling system rather than aircraft propulsion, the engineering is completely different. For the garage, you’d want a powerful electric fan that mounts behind your radiator — a roundup of the best turbo fan wheels can point you to tested options that move serious air without the jet-engine price tag.
FAQs
Why are turbofans so common on commercial aircraft?
Turbofans are the standard choice for airliners because they offer the best balance of fuel efficiency, thrust, and noise reduction. A high-bypass turbofan can move a large aircraft while burning less fuel than a comparable turbojet, which keeps ticket prices lower. The ducted fan also contains some of the noise, making modern airports quieter than in the turbojet era.
What’s the difference between a turbofan and a turbojet?
The key difference is airflow. A turbojet sends all its intake air through the core for compression and combustion. A turbofan splits the airflow: some goes through the core, but a significant portion bypasses it, creating thrust directly and increasing efficiency. That’s why a turbofan is sometimes called a bypass engine or fanjet.
What does a high-bypass turbofan mean?
High-bypass means the engine pushes a large volume of air around the core relative to what passes through it. This design prioritizes fuel efficiency and quieter operation, which is why airliners favor it. Low-bypass engines push more air through the core itself, producing higher exhaust speeds suited for supersonic military aircraft.
References & Sources
- NASA Glenn Research Center. “Turbofan Engine.” Provides the basic diagram and function of the turbofan engine.
- SKYbrary. “Turbofan Engine.” Explains the turbofan’s role in commercial aviation and its efficiency benefits.