Air Intake & Fuel Delivery

Turbojets are the oldest kind of general purpose jet engines. Two engineers, Frank Whittle in the United Kingdom and Hans von Ohain in Germany, developed the concept independently during the late 1930s, although credit for the first turbojet is given to Whittle. more...

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Turbojets consist of an air inlet, an air compressor, a combustion chamber, a gas turbine (that drives the air compressor) and a nozzle. The air is compressed into the chamber, heated and expanded by the fuel combustion and then allowed to expand out through the turbine into the nozzle where it is accelerated to high speed to provide propulsion.

Turbojets are quite inefficient (if flown below about Mach 2) and very noisy. Most modern aircraft use turbofans instead for economic reasons.

History

On 27 August 1939 the Heinkel He 178 became the world's first aircraft to fly under turbojet power, thus becoming the first practical jet plane. The first two operational turbojet aircraft, the Messerschmitt Me 262 and the Gloster Meteor entered service towards the end of World War II in 1944.

A turbojet engine is used primarily to propel aircraft. Air is drawn into the rotating compressor via the intake and is compressed to a higher pressure before entering the combustion chamber. Fuel is mixed with the compressed air and ignited by a flame in the eddy of a flame holder. This combustion process significantly raises the temperature of the gas. Hot combustion products leaving the combustor expand through the turbine where power is extracted to drive the compressor. Although this expansion process reduces the turbine exit gas temperature and pressure, both parameters are usually still well above ambient conditions. The gas stream exiting the turbine expands to ambient pressure via the propelling nozzle, producing a high velocity jet in the exhaust plume. If the momentum of the exhaust stream exceeds the momentum of the intake stream, the impulse is positive, thus, there is a net forward thrust upon the airframe.

Early generation jet engines were pure turbojets with either an axial or centrifugal compressor. They were used because they were able to achieve very high altitudes and speeds, much higher than propeller engines, because of a better compression ratio. However they were not very fuel efficient. Modern jet engines are mainly turbofans, where a proportion of the air entering the intake bypasses the combustor; this proportion depends on the engine's bypass ratio. This makes turbofans much more efficient than turbojets.

Although ramjet engines are simpler in design as they have virtually no moving parts, they are incapable of operating at low flight speeds.

Air intake

Preceding the compressor is the air intake (or inlet). It is designed to be as efficient as possible at recovering the ram pressure of the air streamtube approaching the intake. The air leaving the intake then enters the compressor. The stators (stationary blades) guide the airflow of the compressed gases.

Read more at Wikipedia.org