underwater operation of pulse jets

[nimblemotors]

Hello, can a pulsejet be operated under water?

[metiz]

no

[nimblemotors]

no

why not?
One can supply the intake air from above the waterline.
however, I can understand that the combusion in air must only expell against ambient air pressure,
but can't you pipe the exhaust back out of the water.
Hmm, can you creating combustion with sea water rather than air,
there must be something that can ignite in sea water.

[metiz]

you can run the engine underwater if the exhaust and intake are above the surface. you an't run it with the tailpipe and cc flooded. if you modify the engine for underwater running (SHOULD be possible, water is just a very dense gas), you run into the problem that no ambient air can enter the cc. you'd have to force feed it.

All that said, you'd need a tremendous amount of power to get water to move in the same style as air. pressure will be so high that you might end up with a pde

[Rossco]

(hey all, just dropping in to see what's happening)

This one tweaked my interest.
Yes... the whole thing past the intake can be submerged although the exhaust opening can not be to far under the surface due to back pressure. The intake can handle a fair amount of steam/splashed water although it can get a mouthful quickly and cut out.

can't you pipe the exhaust back out of the water

Yes, check out Eric's drum boiler.

can you creating combustion with sea water rather than air

I smell something.... overunity-ish coming.
But yes. Other than explosives and alkali metals, Steam. Look up cavitation, steam condensing rapidly and 'underwater jet'.

I have submerged a TP180 style engine on a boat resulting in a lot of fun and games albeit at walking pace.
Observations:
It makes a hell of a cool 'rooster tail'.
It reduces thrust to nearly nothing.
A combination of thermal stress and pressure will open the cc like a flower in short time.

Rossco

[nimblemotors]

I'm interested in propelling a boat using submerged hull like a submarine below the boat attached via pylons (see SWATH)
To reduce the hull friction, I want to heat up the water around the hull so it boils
and the bubbles work like ball bearings. To do this you need a lot of heat, and what better than a pulse jet.
If the exhaust comes out in the water it should stop the noise problem.
OK, so I understand the water pressure will cause the pulse jet to not work under water, but what if we can use the water
pressure to compression the charge, well looking into this, I have learned about PDE, or pulse detenation, which uses the higher pressure,
but otherwise is similiar to a pulse jet.

So now I have this idea, create a combustion chamber that will explode the air and gas under the pressure of the water,
effectively like a piston engine where the water is the piston.
The air fuel is injected and explodes and forces the water out of the exhaust followed by the spent fuel, then the water rushes
back into the chamber to create the pressure for the next explosion.
The key is to get the incoming water from ahead and the exiting water behind so it propels the boat forward.
This seems simple using passages and valves that don't have to be exposed to the full heat of the explosion.
The heat of the combusion chamber then heats the water around the tube and significantly reduces the hull friction.

If this can work as described it could be an VERY simple and efficient way to propel a boat.
It seems something worth trying.

Jack

[Mike Everman]

You're havin some fun now. I've got a patent around here somewhere along these lines. Guy made one that looked like an ouboard motor. or at least he patented it. I never saw actual hardware.
Ever seen a putt-putt boat? What you are talking about only it's a flash boiler that every time the water comes back up the tube and hits the heated part, which certainly could be a pulsejet wall or section. The neat part is the bubble of air in there does not change, other than the brief addition of steam.
I've been drawing a man-sized one for the bathtub race in July. Don't know if I can finish it, considering my workload, but it is the most simple thing in the world for propulsion with water. An elbo, two legs and a cap.

I like where you're headed with this. The gates will be a fun design to work like you want...

[nimblemotors]

you know, a patent is for something THAT WORKS. you can't patent an IDEA.
this seems to have been lost with all these patents I've seen. you must describe the thing that works,
not how you THINK it MIGHT work.

not sure what you mean by a putt-putt boat. Half the importance is the hull friction reduction, otherwise it would be inefficient wasted heat.
I'd really like to see what someone has already done, haven't found anything yet via google search.
so you are saying the explosion will just turn the water into steam, and not exit the tube?
I am thinking that the exiting of the exhaust jet will trigger a popit intake valve to open to insert the next packet of air and fuel.
I should do a diaghram..there was one kinda similar but using a piston in the PDE forum.

You're havin some fun now. I've got a patent around here somewhere along these lines. Guy made one that looked like an ouboard motor. or at least he patented it. I never saw actual hardware.
Ever seen a putt-putt boat? What you are talking about only it's a flash boiler that every time the water comes back up the tube and hits the heated part, which certainly could be a pulsejet wall or section. The neat part is the bubble of air in there does not change, other than the brief addition of steam.
I've been drawing a man-sized one for the bathtub race in July. Don't know if I can finish it, considering my workload, but it is the most simple thing in the world for propulsion with water. An elbo, two legs and a cap.

I like where you're headed with this. The gates will be a fun design to work like you want...

[Mike Everman]

Oh, these days you can patent a rock. No proof of function required. Think the one I should dig out and post for you was back when you actually had to show it work, but maybe not that old. 50's ish. Of my 11 and 5 pending, I have never once had to defend whether whatever it is actually works. I do agree with you that it should not be so, and that we inventors should put up or shut up. The patent office would be far smaller.

So you are after bubble drag reduction and propulsion, hmmm, cool.

[Mike Everman]

There's lots on the net about putt putts, and here in the off topic forum. I'm not saying it's what you want, but check em out just for the sheer simplicity factor.

[nimblemotors]

yes there is plenty about them, just had to look, thanks! very cool! It is a different mechanism, but similiar in effect I think.
I would impress my kids if I got my model boat to work this way, if nothing else! I do plan to build a real 50ft yacht for ocean going,
so I'm serious about building a real-world efficient propulsion system for it.

As described how they work, a vaccum exists after the conversion to steam pushes the water out,
it could then suck in the next charge once an intake valve was opened as I describe earlier.
I do think the incoming water should come from ahead to improve efficiency, so the jet should leave the tube, the length would have to be tuned like the pulse jet
to make this happen for a given combustion size, so I suspect it must be adjustable for different power levels, i.e. throttle.

There's lots on the net about putt putts, and here in the off topic forum. I'm not saying it's what you want, but check em out just for the sheer simplicity factor.

[nimblemotors]

some interesting reading here.

http://www.artformfunction.com/projects ... /index.htm

[sockmonkey]

Have a look at this. http://www.newscientist.com/article/dn3 ... ngine.html
For reducing friction I'd probably just go with compressed air.

[makulit]

I would have thought an underwater pulse jet would work just like an underwater ramjet (sort of). One possible underwater ramjet design would be http://www.freepatentsonline.com/2461797.pdf designed by Fritz Zwicky. For a pulsejet you would need to be able to convert a certain amount of water to steam very quickly, but because of the huge expansion between water and steam, the certain amount would be a smallish percent. I imagine a valveless underwater pulsejet could work well if you could make steam quickly enough and keep it steam until it left the exhaust end. That being said, you would probably have to get the steam production timed to correspond to the natural frequency of the engine, but that might happen naturally with the pressure changes in the engine (like water hammer maybe). Just saying.

[Mark]

Have a look at this. http://www.newscientist.com/article/dn3 ... ngine.html
For reducing friction I'd probably just go with compressed air.

From the above article.
"Shock waves created as the steam condenses are focused by the chamber to blast water out of the back."


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