|Quoting Ozair (Reply 1):|
hat are these? I have not heard the term before.
One of the newest and most exciting areas of pulse-jet development is the Pulse Detonation Engine (PDE).
While they work on similar principles to a regular pulsejet, the PDE has one very fundamental difference -- it detonates the air/fuel mixture rather than just allowing it to simply deflagrate (burn vigorously).
So How do They do it?
The exact details on many of the PDE designs currently being developed are rather sketchy -- mainly because they have the potential to be extremely valuable so most of companies researching in this field are not about to tell us what they're doing.
However, from the information that has been published, it appears as if most designs are using a two-stage ignition process to achieve detonation.
Once a fresh air-fuel charge has been drawn into the pipe, a much smaller amount of a very volatile fuel (such as hydrogen) and an oxidizer (such as oxygen) are injected into a trigger chamber at the closed end of the pipe. This mixture is then ignited by an intensely powerful electrical discharge and made to detonate by forcing it through some carefully designed passages which create high levels of turbulence in the burning mixture.
This tube is sometimes referred to as a DDT (Deflagration to Detonation Transition) tube and its job is to force the trigger charge to burn at a rate that creates a supersonic shockwave.
Once it detonates, the small charge in the trigger chamber creates a very powerful shockwave that then hits the main air/fuel charge in the engine's secondary combustion chamber.
It may sound odd that it is possible to compress the gas in a tube which has an open end -- but the incredible speed of the detonation shockwave means that the air/fuel simply doesn't have a chance to be pushed out of the tube before it is compressed.
As, or because it is highly compressed, the air-fuel is also detonated by the intense heat of the shockwave.
Now while this all sounds pretty simple in theory, there are clearly quite a number of practical problems to be overcome before a working PDE can be built.
Firstly there's the issue of valving.
The effective life of a traditional pulsejet tends to be measured in minutes rather than hours -- and that's even though they're only called on to handle the relatively low pressures generated by deflagration. If you tried to use the same fragile valves when detonating an air/fuel mixture they would instantly be destroyed.
To get around this problem, some of the existing PDE designs appear to use robust rotary valves -- but this often requires a sophisticated synchronization system to ensure that the externally driven valves open and close at exactly the right times.
Another alternative is to use a valveless setup and rely on a careful synchronization of the shockwaves produced to control the gas flows.
Other problems with PDEs at this stage of their development include being able to inject and detonate the trigger charge at exactly the right moment to produce detonation of the main air-fuel charge. Too early and there won't be enough air/fuel to provide a good blast -- to late and the air/fuel will have already started leaving the tailpipe.
Then there is the problem of structural integrity. What you're effectively doing with a PDE is repeatedly setting off a small charge of hi-explosive inside a metal tube. This obviously requires that a PDE be massively stronger than a pulsejet. It also means that the levels of noise and vibration are similarly far higher.
One of the key players in the development of PDEs is NASA and they have a small but quite useful web page on the subject.
CalTech have also published some excellent information on their own PDE research.
Info courtesy of aardvark.co.nz
|Quoting B744F (Reply 2):|
if it was black on black, you wouldn't have heard about it
The -117 was black on black, note WAS. You can't hide everything from the public. All u need is a few talkative officials, someone with a camera in an area more than famous for aliens, and a government that doesn't doubt it's exsistance.
Ozair, I'm advocating that it does exsist now. The program that is. Whether or not there are operational "SwitchBlades" is questionable, but reportedly people have seen such FSW aircraft, but most mistake them for the X-29. PDEs (pulse det. engines) are still not mature enough to be used in full and upmost confidence,but i'd say it wouldn't be far fetched to say the technology exsists today, and that experimental aircraft with such engines, or even a switchblade itself, has been built and/or being tested. Remember the patents were filed in 1999.