Could a Valveless Pulse Jet Engine Eliminate the Need for Moving Parts?

[Phrak]

A pulse jet has only one moving part. Nice. But what if it didn't need any moving parts? Stupid idea, right?

Check out this stupid idea. They're all over the internet.

http://www.youtube.com/watch?v=5U-grFuXZ9U&feature=related"

 

[Phrak]

What, not inpressive? These things actually work.

 

[russ_watters]

"Valveless Pulse Jet" sounds like "ramjet" to me.

 

[Phrak]

Check it out. These jets will run on a static platform. There are a dozen other YouTube videos by various amatures.

https://www.youtube.com/watch?v=5U-grFuXZ9U



For the combustion cycle, see Wikipedia.

 

[sophiecentaur]

Brilliant! Like a ramjet but doesn't need supersonic speeds to operate - just a resonant inlet. I'm surprised the inlet doesn't face forwards. Does anyone know why?

 

[minger]

I did a bit of reading into it. It seems that for these size, the turbulence caused by the bend is preferable.

Neat idea, I'd love to see some good analysis on it.

 

[Phrak]

It appears that thrust is developed out of both nozzles, though in unequal amounts.

 

[sophiecentaur]

Smart!

 

[dr dodge]

those engines are interesting things
I have been thinking about making one of the simpler versions
good links:

http://www.aardvark.co.nz/pjet/valveless.htm
http://arc.uta.edu/publications/td_files/Dudley Smith.pdf

but no one uses them like these guys (and gals)

http://madagascarinstitute.com/

dr

 

[sophiecentaur]

The only snag with them would be that they will only work over a small range of powers, I expect and where would you use one? (Apart from just to prove it worked)

I suppose you could always use them to send bombs or boxes of sweets to a neighbouring country LOL.

From the movie, it seems that it works from a standing start, whereas the V1 pulse jet needed to be launched in order to get it going.

Actually, you could use two such engines on either end of a long rotating arm and get a rotary motion. (mind your head!)

 

[dr dodge]

the people at the madagascar inst have used them to power a merry go round
I was wanting to build one as a high temp source. being as O2 is completely consumed the main exhaust is pretty oxygen free. I was wanting to use it as my heat for melting aluminum cans into ingots. at 130+ db, it sure would get the neighbors attention lighting the bbq smoker pit with...lol
the plans i have are for one that builds about 2 lbs of thrust
lots of plans on the net

dr

 

[Phrak]

The only snag with them would be that they will only work over a small range of powers, I expect and where would you use one? (Apart from just to prove it worked)

I suppose you could always use them to send bombs or boxes of sweets to a neighbouring country LOL.

From the movie, it seems that it works from a standing start, whereas the V1 pulse jet needed to be launched in order to get it going.

Actually, you could use two such engines on either end of a long rotating arm and get a rotary motion. (mind your head!)

I'm impressed by the simplicity, although 120 decibels (exaggeration) is a drawback, and the fact that they will apparently melt if run continuously.

There are a few variables that can effect the power band/fuel consumption. Changing the frequency by varying the length of the longer tube, the re-ignition tube, is one of them.

 

[M Grandin]

The only snag with them would be that they will only work over a small range of powers, I expect and where would you use one? (Apart from just to prove it worked)

I suppose you could always use them to send bombs or boxes of sweets to a neighbouring country LOL.

From the movie, it seems that it works from a standing start, whereas the V1 pulse jet needed to be launched in order to get it going.

Actually, you could use two such engines on either end of a long rotating arm and get a rotary motion. (mind your head!)

V1 engines didn't need speed to work according to

http://www.youtube.com/watch?v=v8PF5DtX_Fg&NR=1

where authentic V1 engine is started. As if a since long dead mummy is awaken.

The late valveless pulse jet engines are said being used in some cruise missiles and drones.
But scientists and engineers are reputed not fully understand and master this technology.

 

[Phrak]

From one you tube video the V1 appears to have used a ramp and rocket assist takeoff. Can anyone confirm a rocket assist? It may be that forward airspeed effects engine tuning and thus power output. What I mean is that if the fuel is metered for cruse speed it may not have enough power for takeoff from a standing start without an inconveniently long launch ramp.

 

[M Grandin]

There is a detailed description of V1 technology and operating in seven parts (p1 - p7) in youtube. (Originally used as instruction for Nazi officers?)

In this video (p4) the launching technique is explained
http://www.youtube.com/watch?v=-XiRkk4zYtU&feature=related

In this video (p5) the V1 is launched
http://www.youtube.com/watch?v=Kcup3W6uy_E&NR=1

So the V1 engine is started before launching but has not thrust to accelerate
sufficiently fast without help from a pressure-driven piston in a cylinder in ramp.

 

[Danger]

From the movie, it seems that it works from a standing start, whereas the V1 pulse jet needed to be launched in order to get it going

With no offense to anyone, I'm simply too tired right now to read all of the posts in their entirety or look at any of the links at all. I promise to do so in the next day or so.
For now, though, I can definitely state that the quoted statement is in error. The V1 used a launching ramp to eliminate a runway and the wheels to utilize it. (The Natter used essentially the same ramp, but that was a whole different bird.)
While the war was still under way, instrumentation showed that something like 85% of the fresh intake charge for the next firing cycle of a pulse jet was sucked in through the tailpipe instead of the shutter-valve box in front. It didn't take long after that to work out that the dynamics within the chamber could be tuned to provide a variety of operational responses. The valveless version is based upon (maybe not the proper technical term) a "standing" shockwave, that is formed by the combustion pressure itself, sealing off the front of the chamber.