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).
Principle
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
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) |
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Turbofan
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.
Qualities
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) |
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Turbojet
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.
Qualities
1. High exhaust speed
2. Low frontal area
3. Relative simplicity
Drawbacks
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) |
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Turboshaft
Turboshaft engines are similar to turbojet engines except they use heat energy produced at the combustion chamber to generate shaft power
Qualities
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) |
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