# Tag Info

26

The regular way to burn fuel is not to use an afterburner. The afterburner is an option added downstream of a regular engine to increase its thrust temporarily. It is an interesting alternative to fitting the aircraft with a larger engine. However the additional thrust it delivers is very expensive. The normal way to burn fuel involves a combustion chamber ...

13

Another NASA article shows you the diagram you need. You can see the two places fuel can be injected, before and after the turbine. As you say there are two separate phases to add fuel to airstream

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— airliners.net; cropped In the photo above (taken in 2011, four years before the Pearl 15 first ran), that feature can also be seen; that engine is in the same family that includes the Pearl 15, the BR700 family. — flickr.com; click image for a closer look In the high-resolution Pearl 15 photo above, that feature is seen to protrude slightly above the ...

9

Indeed, exhaust gases can be expanded beyond Mach 1, and doing so will result in higher thrust from higher propulsion efficiency. The problem is that pressurised gas is expanded by constricting the cross-section area when lower than M1, and expanding it when higher than M1. So in order to achieve full expansion to ambient pressure $p_0$ at supersonic exhaust ...

8

The basic answer is yes. Fuel is burned in the main section to make thrust (and drive a fan in that kind of engine), and keep the compression/combustion cycle going, and to work properly (not melt itself), most of the air that got compressed by the compressor section is used to control the flame boundaries within the burner can and cool the engine. Maybe ...

8

It means the time the engine has been operating at the indicated Exhaust Gas Temperature (EGT). These are limitation graphs for startup and running to prevent thermally damaging the hot section of the engine during a hot start. It’s the chief vulnerability of a jet or other aviation gas turbine engine - they’re pretty robust and reliable, but don’t ever, ...

7

It means duration (time [spent] at). As an example, above are three durations at which the engine was run at 800°C: t1: troubleshooting will be needed (0–90 s) t2: depending on the model, engine to be returned for inspection of the nozzle (45–90 s) t3: engine to be returned for intermediate maintenance (over 90 s)

7

So first, both measurements are made by accelerometers, and accelerometers are by definition sensitive to acceleration. So the original units are either G or m/s^2. They are converted to different units for analysis and display. So, what units are most convenient for analysis? It depends on the frequency range. If we have a sinusoidal vibration with ...

6

Choked nozzle Whether flying supersonic or subsonic, a jet engine's intake, compressor, and diffuser, all slow down the air to slow subsonic velocity so combustion can take place. When the temperature rises sharply, part of this energy is converted to velocity. Because of the high combustion temperature, the speed of sound is much higher, so the mass flow on ...

5

There's the fact that the hot gases from combustion are actually cooled in the combustion chamber. The turbine cooling isn't sufficient enough to maintain the appropriate temperature for the turbine blade(~1700 C). The above figure(shamelessly taken from Aircraft Propulsion) clearly depicts the cooling mechanism in the combustion chamber(CC). 12% of air ...

4

There's been patent wars regarding this invention. What you show is not just a twist, but also a varying sweep. According to Rolls-Royce's patent from 1996, which was the subject of one of the lawsuits, a basic summary is as follows: This feature produces a distinct mid-height bias to the airflow distribution across the span of a blade, with the result that ...

4

Military Power is the maximum rated thrust from the core engine, that is, without afterburner. The Throttle Angle can vary within a few degrees when the engine is at Military Power due to tolerances in the fuel control system. On a chart this variability (70-75 degrees) shows as a strip or band marking the minimum and maximum values of throttle angle. ...

4

TLDR: Pretty much impossible with current technology as I understand the question. I think you are focusing on the wrong part of the problem. Turboprop vs turbofan is pocket change compared to the amount of rocket fuel required to get to orbit. Let's put some numbers to it. I'm assuming the following mission 1) Deorbit from low earth orbit, 2) landing (...

3

Briefly: inside a jet engine's core or within its fan shroud, huge quantities of air get sucked through while their flow directions get rapidly changed up. This causes parcels of air to bounce off the walls of the engine passages and off their neighbors, a process that generates random (roaring) noise. In addition, in the center of the engine's core, ...

2

Listed under Benefits on the Wiki page link edited into your question: The benefit of this setup is increased specific impulse over that of a rocket. For the same carried mass of propellant as a rocket motor, the overall output of the air turborocket is much higher.Emphasis added Since most "jet fighters" use jet engines (or low-bypass turbo fans)...

2

it's really two questions- 1) Compressible flow in ducts The first part of the question addresses how to accelerate a flow in ducts to supersonic speeds. In simple terms, for compressible flow in a pipe with varying diameter: when subsonic, it accelerates along the pipe, when the diameter of the pipe reduces when supersonic, it accelerates along the pipe, ...

2

I'm in aircraft engineering school right now, and i can tell you blisks are definitely in use. For example the Rolls-Royce Trent 500 turbofan, or the Allison Model 250. (The latter of which we have a cut-open version of, on a dolly here) This is the turbine section as blisk (edit: corrected from fan) And this is the compressor stages as blisk vvv If you ...

2

Why do jet engine fan blades have a twisted shape? Your question is about fan blade twist, but actually the answer is valid for nearly all rotating blades. If a blade weren't twisted, the angle of attack would be very different from its root to its tip. Twist equalizes the angle of attack along the length. I say equalize for simplification, the angle may ...

2

The F-4 Phantom throttles have an idle position and a military power position. This diagram shows nozzle position and diameter, as well as RPM at military power, otherwise known as the "military band". The reason the lines flatten out is that above that the throttles control the activation of the afterburners, but do not change the RPM of the ...

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So does it mean there are two separate phases to add fuel to airstream, first (compulsory) for the normal operation and the second (optional) for the afterburner? Yes. The key difference is that the regular burner is between the compressor and the turbine, but the afterburner is the last item at the back of the engine. That means that the regular burner has ...

2

Your source about the flame temperature is valid for a stoichiometric mixture. This means all oxygen molecules will be matched by carbon and hydrogen such that theoretically a complete conversion into H₂O and CO₂ can take place. Real gas turbines, however, operate with a fairly large amount of excess air, which is why they produce comparably large amounts of ...

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The gas is not cooled prior to turbine inlet entry. Any attempt to cool down the gas, with decreasing efficiently of the engine. Most modern engines have turbine inlet temperatures of approximately 3600° F. This is far too hot for conventional alloys used to make the stator of rotor buckets to maintain acceptable yield strengths, so engineers have been ...

1

The F-35 Lightning has an approach to VTOL that is similar to what you are requesting. There is a propeller (strictly speaking, a ducted fan) pointed straight up in the middle of the fuselage and has doors that open above and below it. It is powered by the jet engine and used during vertical takeoff and landing.

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