The Different Types of Jet Engines

Jet engine being tested

A jet engine is a reaction engine, discharging a jet that generates thrust using jet propulsion. In a broad definition, jet engines are combustion engines and typically feature a rotating air compressor powered by a turbine. Read on to find out more about the various types of jet engines used in aircraft today.

Turbojet

A turbojet engine is a gas turbine engine which functions by compressing air with an inlet and a compressor mixing fuel with compressed air. The mixture is then burned in the combustor and the hot, high-pressure air passes through a turbine and nozzle. The engine converts the internal energy in the fuel into kinetic energy in the exhaust, which creates the thrust. Turbojets are airbreathing jet engines, and the concept was developed by two engineers, independently from each other: Frank Whittle in the UK and Hans von Ohain in Germany during the 1930s. The turbojet was the first form of gas turbine engine for aviation but has now been largely replaced by other developments.

Ramjet

Ramjet engines are air-breathing designs similar to gas turbine engines. They work by using the engine’s forward motion to compress the incoming air without a compressor using an inlet or diffuser, which differs from gas turbine engines. Ramjets cannot produce thrust at zero airspeeds, so a ramjet engine cannot move aircraft from a standstill. Aircraft with a ramjet engine will require assisted take off to get it to the speed where it can produce thrust. Ramjets work best at supersonic speeds, around Mach 3 (2,300 mph) and up to Mach 6 (4,600 mph), and are considered to be the most simple type of airbreathing jet engine as they have no moving parts.

Scramjet

A scramjet is a variant of a ramjet engine, where the combustion takes place in supersonic airflow. Scramjet engines rely on high speed to compress the incoming air before the combustion but differ from a ramjet which decelerates the air to subsonic velocities, as the airflow in a scramjet is supersonic throughout. This allows aircraft with scramjet engines to operate at extremely high speeds. The Soviet Union performed the first successful flight test of a scramjet in 1991. In the 2000s, progress was made in developing hypersonic technology, with several tests from the USA, Australia and UK seeing scramjet flights reach Mach 10 speeds.

Turbojets on an F-15 fighter plane

Turbofan

Turbofan engines work similar to but are different from turbojet engines as they have an extra fan at the front of the engine, which then accelerates air into a duct, bypassing the core gas turbine engine. Turbofan engines are categorised as high or low-bypass, depending on the amount of air bypassing the core of the engine. Turbofans are the standard choice for medium and long-range airliners, as they are considered more efficient than turbojets when operating at subsonic speeds, which is also the reason they were invented; turbojets are generally too inefficient for subsonic flight. The large frontal area generates drag at high speed, however, so the fans are smaller or absent when turbofan engines are used in supersonic or military aircraft.

Pulsejet

A pulsejet engine is a jet engine where the combustion occurs in pulses. It can have no or few moving parts and is capable of running statically, unlike ramjet engines. There are two types of pulsejet engines which both use resonant combustion and use the combustion products to form a pulsating exhaust jet, providing thrust intermittently. The valved type uses a mechanical valve to control the flow, forcing the hot gas out the back of the engine through the tailpipe. Valveless pulsejet engines do not have any moving parts and use geometry to control the flow.

Take a look at some of our previous blog posts on jet engines, including the most powerful jet engines in the world, and browse through the industrial products available to buy from Textile Technologies, from exhaust wrap to fibreglass insulation.

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