What is the Difference Between Turbojet and Turbofan?

[Nguyen]

Below are the differences between turbojet and turbofan engines: 1. Different power sources; Turbofan engine: Power comes from the fan and gas expansion work; Turbojet engine: Power source is gas expansion work; 2. Different structural components; Turbojet engine: Compressor + combustion chamber + turbine. Turbofan engine: Fan + bypass duct + compressor + combustion chamber + turbine. Here is some basic knowledge about turbojet engines: The shaft and fan in a turbojet are used to compress air. The compressed air is mixed with fuel in the combustion chamber and burned, then the expanded high-temperature and high-pressure air is ejected from the rear to provide jet thrust. As it passes through the turbine, it causes the turbine to rotate. The turbine is connected to the compressor fan via the same shaft, providing the power for air compression, thus completing the cycle.

[DeFrancisco]

I've been repairing aircraft for over a decade. The main difference between turbojet and turbofan engines lies in their intake and exhaust structures. Turbojet engines are older designs where all incoming air is compressed and combusted in the core before being expelled at high velocity through the exhaust nozzle, generating thrust solely from this hot gas stream. These engines perform well at high altitudes and speeds, but have terrifying fuel consumption and deafening noise levels. Turbofans are much smarter - they add a large fan at the front that splits incoming air into two paths: one goes through the core for combustion, while the other bypasses through the outer duct. This bypass airflow is cooler and quieter, contributing about 70% of total thrust, making turbofans more fuel-efficient and environmentally friendly - which is why modern airliners all use them. However, turbojets haven't been phased out completely, as fighter jets still rely on them when maximum speed performance is required.

[StLila]

When I taught students at flight school, I always used car analogies: turbojets are like pure electric vehicles, relying solely on the core motor for power; turbofans are like hybrids, utilizing both electric motors and retaining the efficiency of internal combustion engines. Turbojet engines have a simple structure with only one pathway—all incoming air is processed by the compressor and combustion chamber. Turbofans, on the other hand, add a high-speed auxiliary route—the bypass duct—allowing some air to bypass the scorching core area and directly propel the aircraft. This design reduces fuel consumption by 30-40%, especially showing significant advantages at low speeds. Nowadays, except for supersonic aircraft still using turbojets, all commercial airliners have switched to turbofans—after all, with fuel prices so high, saving fuel means saving money.

[Geoffrey]

As a frequent flyer on business trips, the most noticeable difference is the engine noise. Those old turbojet-powered aircraft are deafening during runway acceleration, relying solely on hot gas expulsion for thrust. Modern turbofan airliners are much quieter during takeoff because the large front fan diverts the airflow - nearly half bypasses the core through the outer duct for direct propulsion, with only a small portion entering the high-temperature core. This design also significantly reduces fuel consumption, saving us a lot on ticket costs. While turbojets have a slight edge in top speed, fuel efficiency is king for civil aviation. Even military transport aircraft are now adopting high-bypass turbofan engines.