turbojets

A turbojet engine is a gas turbine engine that produces thrust by accelerating a flow of air through a nozzle. It operates on the Brayton cycle and consists of an air inlet, a compressor, a combustion chamber, a turbine, and an exhaust nozzle. The core engine is optimized to deliver a high jet velocity, yielding high specific thrust.

In operation, air enters the intake and is compressed; fuel is injected and burned in the combustion chamber, raising gas temperature. The high-energy gas expands through the turbine, which drives the compressor, and the remaining energy is expelled rearward through the nozzle to produce thrust. The overall efficiency depends on flight speed; turbojets have high thrust at high speeds but relatively poor fuel efficiency at subsonic cruise compared with turbofans, due to lack of a bypass stream.

Most modern turbojets are axial-flow designs, with one or two spools, and may include afterburners for military use to boost thrust for short durations. They typically have a low bypass ratio, or none, distinguishing them from turbofan engines that route air around the core.

Historically, turbojets were developed in the 1930s–1940s by Frank Whittle in the United Kingdom and Hans von Ohain in Germany. They powered early jet aircraft such as the Gloster Meteor and Heinkel He 178. Civil aviation later favored turbofans, reducing the use of pure turbojets, though some high-speed military aircraft and certain missiles continue to use turbojet cores, and some early SSTs used afterburning turbojets, e.g., Concorde.

Advantages of turbojets include high thrust at supersonic speeds and simple design; disadvantages include poor fuel efficiency at subsonic speeds, high noise, and greater maintenance needs. They remain relevant in applications requiring high-speed propulsion or operation in environments where turbofan efficiency is less favorable.