Jet engine

A jet engine is a type of reaction engine that generates movement through jet propulsion. This process involves discharging a fast-moving jet of heated gas to create thrust. While the term can include rockets or water jets, it usually refers to air-breathing internal combustion engines. These engines are vital for modern aviation and long-distance travel. They allow aircraft to fly much faster and more efficiently than older propeller engines.

Most air-breathing jet engines operate using the Brayton thermodynamic cycle. This cycle is a step-by-step process of energy conversion. First, a rotating air compressor pulls in air and squeezes it tightly. Next, fuel is mixed with this compressed air and ignited in a combustion chamber. This burning process makes the air extremely hot and causes it to expand rapidly. Finally, the expanding air rushes through a propelling nozzle at the back of the engine. This high-speed exhaust creates the thrust that pushes the aircraft forward.

Engine designers use different configurations depending on the speed of the vehicle. Early jet aircraft relied on turbojet engines, which were less efficient for subsonic flight. Most modern subsonic planes now use high-bypass turbofan engines. These engines are more complex but offer much greater fuel efficiency. For very high-speed applications, engineers use ramjets or scramjets. These specialized engines do not use a mechanical compressor. Instead, they use the ram effect caused by the vehicle's own high speed to compress the incoming air.

The history of jet propulsion spans many centuries and different cultures. A very early demonstration was the aeolipile in 1st-century Egypt. This device used steam to spin a sphere on its axis. Later, traditional Chinese rocket propulsion provided theoretical roots for these principles. In 1633, an Ottoman soldier named Lagâri Hasan Çelebi reportedly flew using a cone-shaped rocket. In 1791, John Barber in England patented a stationary turbine. However, it took many more years to create a self-sustaining gas turbine. The first successful one was built by Ægidius Elling in 1903.

The 20th century brought the breakthrough of practical aircraft engines. Frank Whittle submitted his ideas for a turbojet in England in 1930. At the same time, Hans von Ohain worked on similar designs in Germany. In 1939, Ohain’s team flew the He 178, the world's first jet plane. During World War II, the German Junkers Jumo 004 became the first jet engine used in service. It powered the Messerschmitt Me 262 fighter. Soon after, the British Gloster Meteor also entered service.

Engine technology has seen massive improvements in both power and reliability. In the 1950s, engines like the de Havilland Ghost were common. By the 1990s, the General Electric GE90 turbofan represented a massive leap in power. Reliability has grown significantly over these decades. In the mid-20th century, there were 40 in-flight shutdowns per 100,000 engine flight hours. By the late 1990s, that number dropped to less than one per 100,000 hours. This reliability, plus better fuel economy, made routine transatlantic flights possible.

Today, jet engine technology is used in many different fields beyond passenger planes. Some engines power cruise missiles or unmanned aerial vehicles. They are also used in rockets for spaceflight and military missiles. Engineers even use jet designs to power high-speed cars like the ThrustSSC. In industrial settings, gas turbines can generate up to 50,000 shaft horsepower. These machines can power water pumps, oil pumps, or electrical generators. Even helicopters use related gas turbine forms known as turboshafts.