Turbojet Engines

Turbojet Engines

The term 'turbojet' is commoly used for a number of engines such as turbojet, turbofan, turboprop, and turboshaft, because all these types use a common principle (Yoon, 2001 6).


All 'turbojet' engines apply Newton's Third Law of Motion that says, "for every motion there is an equal and opposite reaction" (Hunecke, 1997 1). In simple terms, as a result of engine ejecting burnt mixture backwards a forward force is created on the engine thus on the aircraft. The greater the backward force (force with which the burnt mixture is thrown backwards) the greater the forward force (reactional force on the aircraft).

The internal processes of a gas turbine engine are based on the principles of the brayton cycle.


Turboprop engines have a propeller driven by a gas turbine. This type of engines provides small power output and are commonly used in small subsonic aircraft.

Mechanism (Wikipedia (2009c)4) Application (Commuter aircraft)
Turboprop_operation.png Dehav.dash8.750pix.jpg


Turbofan engines use ducted fans. Similar to propellers when the air flow bypasses the engine core, it is accelerated by the fan blades. The effect of gas ejection rarewards, similar to other jet engines, results in forwar force generation.

1. Efficient
2. Relatively quiet
3. Subsonic Speed

Thus, these engines are commonly used in commercial aircraft.

Mechanism (Wikipedia (2009a) 2) Application (Airbus A380 with four turbofans)
Turbofan3_Labelled.gif 1er_vol_de_l%27_A380.jpg


Turbojet engines compress the air taken in through inlet, heat, inject fuel to explode the mixture forming an expansion and then eject the mixture with great force through the backward nozzle.

1. High exhaust speed
2. Low frontal area
3. Relative simplicity

1. Noisy
2. Inefficient to use below Mach 2

Thus, these engines are not commonly used in commercial aircraft, however, in military aviation systems such as cruise missiles, these engines are used.

Mechanism (Wikipedia (2009b)3) Application (Babur cruise missile)
Turbojet_operation-_axial_flow.png BaburCruise.jpg


Turboshaft engines are similar to turbojet engines except they use heat energy produced at the combustion chamber to generate shaft power

1. sustained high power output
2. high reliability
3. small size
4. light weight

Thus, this type of engines are commonly used in helicopters.

Mechanism (Wikipedia (2009d)5) Application (helicopter - US Coast Guard)
Turboshaft_operation.png US_Coast_Guard_HH-65_Dolphin_Helicopter.JPG
1. HUNECKE K (1997). Jet engines: Fundamentals of theory, design and operation. Airlife (Shrewsbury, UK), 1997.
2. WIKIPEDIA (2009a). Turbofan. Retrieved from http://en.wikipedia.org/wiki/Turbofan on 11 March 2009.
3. WIKIPEDIA (2009b). Turbojet. Retrieved from http://en.wikipedia.org/wiki/Turbojet on 11 March 2009.
4. WIKIPEDIA (2009c). Turboprop. Retrieved from http://en.wikipedia.org/wiki/Turboprop on 11 March 2009.
5. WIKIPEDIA (2009d). Turboshaft. Retrieved from http://en.wikipedia.org/wiki/Turboshaft on 11 March 2009.
6. YOON J (2001). Jet engines types. Retrieved from http://www.aerospaceweb.org/question/propulsion/q0033.shtml on 18 March 2009.

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