Pulsejets & PDE's

[KJ_Lesnick]

I've heard of many kinds of ideas regarding PDWE's and pulse-jets including

• The V-1's pulse-jet which used shutters
• The Gluhareff Pressure Jet which used no moving parts
• The PDWE which used a deflagration-to-detonation process to blast air out the back and entrain air through the front to "pump the duct" and sustain the process

The PDE has been proposed in various forms for up to 70 years, and recently (past 30 years), there's been various efforts to make the concept work, and from what I remember the issues had to do with the following

• Producing a reliable means of producing an efficient deflagration to detonation process in a duct that is reasonably short
• Ensuring the fuel/air mixture escapes to the rear: This often involves shutters or proposals for carefully timed valves last I checked
• Producing a high cyclic rate: This is often limited by the use of shutters to about 250 detonations a second; the desire is for thousands of detonations a second

I'm curious if any of these have been overcome...

 

[ouroboros]

I think there was a patent for a rotary shutter combustor that should be applicable.

http://www.secretprojects.co.uk/forum/index.php/topic,7651.0.html

The idea was to replace conventional combustor cans with a big slotted wheel that lines up with the ducts such that as the main shaft rotates, you have periodic blocking of the ducts. The patent was for efficient turbofans, but nothing stopping you from running as a low bypass turbojet in essence.

 

[quellish]

• Producing a reliable means of producing an efficient deflagration to detonation process in a duct that is reasonably short
• Ensuring the fuel/air mixture escapes to the rear: This often involves shutters or proposals for carefully timed valves last I checked
• Producing a high cyclic rate: This is often limited by the use of shutters to about 250 detonations a second; the desire is for thousands of detonations a second

I'm curious if any of these have been overcome...

All of these have been overcome in various ways. Popular Science did a reasonably good article on it in 2003:
http://www.popsci.com/military-aviation-space/article/2003-08/after-combustion-detonation?nopaging=1
P&W and GE are discussed, and each has their own solutions to the above. In the 80s and 90s Adroit, Boeing, McDD, GD, and Lockheed were all working on PDEs. There are some very interesting patents from GD (Lockheed Ft. Worth/LMTAS when the patents were issued) that are the result of their work.


Look through the patents that reference this one, you will find some interesting stuff:
https://www.google.com/patents/US4741154

 

[KJ_Lesnick]

The idea was to replace conventional combustor cans with a big slotted wheel that lines up with the ducts such that as the main shaft rotates, you have periodic blocking of the ducts.

And this provides the means to get a detonation?

The patent was for efficient turbofans, but nothing stopping you from running as a low bypass turbojet in essence.

Would it be possible to use a small PDE to set in motion a larger one?

 

[ouroboros]

The idea was to replace conventional combustor cans with a big slotted wheel that lines up with the ducts such that as the main shaft rotates, you have periodic blocking of the ducts.

And this provides the means to get a detonation?

The patent was for efficient turbofans, but nothing stopping you from running as a low bypass turbojet in essence.

Would it be possible to use a small PDE to set in motion a larger one?

Ignition for detonation would have to be provided by other means (spark? as the slotted disk (somewhat blisk-esqe) is only providing a non-reciprocating shutter arrangement for higher frequencies (which is dependent on how well compressed air can flush the duct after the shutter slot opens for a particular duct). Technically, it is integrating both the combustion chamber and the high pressure turbine.

Why are you interested in a smaller PDE driving a larger one? Some sort of two stage arrangement where the first stage is going for maximum shaft work, and the second stage features fixed rear facing ducts for jet propulsion? Some sort of shared compressor/shutter blisk arrangement?

Though the mechanical complexity and friction of the shutter blisk is an issue. As opposed to something like the continuous rotating wave detonation engine, where the detonation wave is partially trapped in a toroidal chamber, the wave looping around and around in a transverse manner. Apparently self igniting too.

http://ftp.rta.nato.int/public//PubFullText/RTO/EN/RTO-EN-AVT-150///EN-AVT-150-08.pdf

http://www.nrl.navy.mil/content_images/11_FA2.pdf

 

[KJ_Lesnick]

Ignition for detonation would have to be provided by other means (spark? as the slotted disk (somewhat blisk-esqe) is only providing a non-reciprocating shutter arrangement for higher frequencies (which is dependent on how well compressed air can flush the duct after the shutter slot opens for a particular duct). Technically, it is integrating both the combustion chamber and the high pressure turbine.

So the fan compresses air to some degree but it also acts like a rapid shutter?

Why are you interested in a smaller PDE driving a larger one?

Well I figure a small one is easier to make work; you use the small one to make a big one light off.

As opposed to something like the rotating wave detonation engine

I never heard of this before...

 

[Richard N]

Pulsejets don't have to be complicated. TLAR practiced here:


https://www.youtube.com/watch?v=bCsg5pQimWI&feature=player_detailpage#t=0