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Turbofans are the most efficient engines in the range of speeds from about 500 to 1,000 km/h (270 to 540 kn; 310 to 620 mph), the speed at which most commercial aircraft operate. [ 21 ] [ 22 ] In a turbojet (zero-bypass) engine, the high temperature and high pressure exhaust gas is accelerated when it undergoes expansion through a propelling ...
While these engines are capable of giving high thrust levels, they are most efficient at very high speeds (over Mach 1), due to the low-mass-flow, high speed nature of the jet exhaust. Modern turbofans are a development of the turbojet; they are basically turbojets that include a new section called the fan stage. Rather than using all their ...
This has the advantage of being more efficient than allowing valuable compressed air to escape, although fuel consumption at low speeds is relatively unimportant. Further increases in pressure ratio, demanded by government procurement agencies and commercial airlines for long-range aircraft, caused a bigger mismatch of flow areas/density ...
Turbofans are usually more efficient than turbojets at subsonic speeds, but at high speeds their large frontal area generates more drag. [21] Therefore, in supersonic flight, and in military and other aircraft where other considerations have a higher priority than fuel efficiency, fans tend to be smaller or absent.
The physical size of the gearbox was 17 inches (430 mm) in diameter, [2] or no more than half the gearbox size of the PW-Allison 578-DX propfan demonstrator engine that Pratt & Whitney worked jointly on with Allison in the 1980s. The gearbox consisted of 40 components, weighed 500 lb (230 kg), and shared a 3-U.S.-gallon (11-liter) oil tank with ...
A corollary of this is that, particularly in air breathing engines, it is more energy efficient to accelerate a large amount of air by a small amount, than it is to accelerate a small amount of air by a large amount, even though the thrust is the same. This is why turbofan engines are more efficient than simple jet engines at subsonic speeds.
In February 2012, GE announced studies on a more efficient derivative of the GE90, calling it the GE9X, to power both the -8 and -9 variants of the new Boeing 777X.It was to feature the same 128 in (325 cm) fan diameter as the GE90-115B with thrust decreased by 15,800 lbf (70 kN) to a new rating of 99,500 lbf (443 kN) per engine. [1]
The type of jet engine used to explain the conversion of fuel into thrust is the ramjet.It is simpler than the turbojet which is, in turn, simpler than the turbofan.It is valid to use the ramjet example because the ramjet, turbojet and turbofan core all use the same principle to produce thrust which is to accelerate the air passing through them.