What is a pressure jet?

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steve
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Post by steve » Mon Jul 05, 2004 2:36 pm

It runs!
I ran it for about 5 minutes on acetelyne. It produces virtually no thrust but it has great throttle range and started without too much difficulty
It was definately worth the $15 I spent for the materials. Thanks for your help Mark!
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Post by Mike Everman » Mon Jul 05, 2004 3:12 pm

Very nice, Steve! Congratulations to you and Mark!
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Post by Mark » Mon Jul 05, 2004 4:44 pm

I'm surprised you built it so quickly and also in the speed in which you got it to run. Acetylene is very forgiving, I'm glad you had some on hand. Did you experience any of that billowing black soot snow storm from an occasional flame-out? Wouldn't hydrogen be fun too, it is the most forgiving fuel to run rich or lean. There is a small Lockwood sketch that I got in a booklet I bought from Lockwood Jr. and it was said to go 400 cps which would be interesting to hear. It had to run on hydrogen, but I bet acetylene might work.
One time I thought it would be interesting to introduce oxygen after starting my little Logan on acetylene. In less than a second after introducing oxygen to the acetylene flow and whining engine, I had eaten a hole straight through the opposite side of my side port, like butter.
It's an interesting sound to hear the little Logan run isn't it? Mine puts out more thrust out the side port. I like to tweak the acetylene or MAPP gas flow and modulate the amplitude, like a rheostat or volume control.
Good job!
Mark

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Post by Mark » Mon Jul 05, 2004 6:01 pm

It might be fun to make a Logan out of a straight 1 inch diameter copper pipe, crimping the sides to form the exhaust tube. You could pinch the head shut, the only real problem to solve would be to connect a side port. Some of the common copper fittings have side ports, and with a flared exhaust tube of a smaller diameter you can pull the exhaust tube through the fitting and lock it in place with an air tight seal as the flare seats against the walls of the larger fitting.
For those of you who haven't tried copper tubing for anything, I really like the beautiful colors the copper tints the flame.
Mark

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Post by Mark » Tue Jul 06, 2004 3:45 am

One thing to wonder about with copper tubing as a pulsejet, is that it acts like a catalyst in some respects like platinum wire or platinum in a car catalytic converter. If you take a fine coil or homemade filament of platinum wire and heat it briefly, you can insert it into a jar of methanol and vapor; it will brighten and get red hot until the vapor ignites in a whoosh. Fine copper wire will stay a dull red if given methanol vapor and air too. But eventually after a few minutes, the copper filament melts, platinum having a much higher melting point. If you turn the lights out you can better see your fine copper filament glowing in a jar with some methanol in it. You should place the preheated coil just above the surface of the methanol. I've read that you can melt down your car catalytic converter if you your exhaust has some unburned fuel in it from improper combustion in the engine.
So perhaps the entire surface of a copper tube would become a spark plug of sorts, or rapidly igniting any charge of fuel/air. At any rate it would spew a gamut of blue and green photos out the tail end. It might melt but it would be fun to try I think, perhaps it could be cooled somewhat with a water jacket or something similar.
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Post by steve » Tue Jul 06, 2004 11:32 pm

I knew it was too good to be true:
today I spent an hour and a half trying to start the little engine with no success. for some reason the spark plug is not igniting the fuel/air mixture. I think that this is because the mixture is blown out the tail and has no reason to travel in the opposite direction towards the spark plug.

could you tell me the starting procedure that you use when running on acetelyne. keep in mind that I do not have any methanol at my disposal

thanx!
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Post by Mike Everman » Tue Jul 06, 2004 11:47 pm

I'd take the cap off and see if you baked your plug. did you open up the spark gap to way big?
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Post by Mark » Wed Jul 07, 2004 12:11 am

There could be a problem with your sparking mechanism. I have found this baby, (see attachment), works really well for igniting almost anything, if you can afford it, it is the best spark I have found that will run longer than you can run it, hours on end, if that's what you like. A hot spark is a good thing. Another factor is the mixture. If you have an imperfect rich or lean mix, no amount of spark will help you out. If you have a too hot of spark, often you can fry the electrodes and create too much resistance and a weak spark.
A strange desperate attempt at starting can be had by employing both a spark plug buzzing, and get this, a propane torch running and the cone of fire directed at the tail end to ignite the acetylene. In this way you can prevent a cloud of explosive gas collecting about the experimenting area and also it often will "catch the wave" if you puff in air at the side port. I can guarantee you if you puff in air at the side port and have acetylene flowing, that a cone of fire from a propane torch near but not directly heating the exhaust tail end will crack bang with excitement. Acetylene is poppy stuff. I used this method with MAPP gas, it worked for me. A flame at the tail off-set so as not to upset or pollute the intake of fresh air up the tail, you don't want it focused right at the hole! and then with a sparking device running a spark plug in the combustion chamber you are covering all bases. If you waste 10 hours with a bad ignition system, one might start to see how valuable a hardened and perfect mechanism this is, for boneheads like me who refuse to give up testing after hours of failure. A buzz coil is your best, best friend in this field.
Mark
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Post by Mark » Wed Jul 07, 2004 12:41 am

Mike may be right here too, you might want to take your spark plug out if you can get at it or if it isn't welded permanently in. I have from time to time taken a plug out and held it against a spinning wire wheel, (my grinder has a stone on one side and a wire wheel on the other), to buff off the corrosion or soot which might have deposited on my plug. I have read that it is advantageous to also run the current in the opposite direction through your plug from time to time to prevent a build up of oxidation, I don't know if it is true, but it might be.
One time I completely ate up a spark plug, I may have formed too much ozone and with heat you can imagine O3 is highly corrosive. There is only one thing more reactive and that is fluorine gas. I ran a plug inside a small tube for a period of time without fueling, just air and spark, and my plug was really tarnished from this, it was quite a surprise. Strange things happen when you don't expect it.
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Post by steve » Wed Jul 07, 2004 1:42 am

I took the cap off etc. and checked the plug/ignition system and everything works fine. (by the way I'm using the design from bruce simpson's website and it does work, contrary to what some people have posted. hehe) Mark- your starting method sounds like a good idea and I will try it as soon as I get some more free time. as always, thanx!
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Post by Mark » Wed Jul 07, 2004 2:48 am

My brother has made a transistor ignition for me too that runs well, yet I think the simple magnetic make/break points and coil is still the most reliable and hardly anything to fail. After all a Model T had a buzz coil for each spark plug and it went for some long time before giving out. And even thought the buzz coil patent is over a hundred years old, it is still a strong contender.
I have used every ignition method that I could think of except for initiation by laser or divine intervention.
Mark

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Post by Mike Everman » Wed Jul 07, 2004 2:54 am

I've used "happy thoughts" with little success. I keep trying though.
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Post by Mark » Wed Jul 07, 2004 3:02 am

Yes, but have you tried Al Frankin's platitude or affirmation, "I'm good enough, I'm smart enough, and doggoneit, people like me." ?
Sometimes I put on a pink cardigan sweater and try to accept the fact that I cannot change some things like Stewart Smalley of Saturday Night Live fame.
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Post by Mark » Wed Jul 07, 2004 8:40 am

steve wrote:I knew it was too good to be true:
today I spent an hour and a half trying to start the little engine with no success. for some reason the spark plug is not igniting the fuel/air mixture. I think that this is because the mixture is blown out the tail and has no reason to travel in the opposite direction towards the spark plug.

could you tell me the starting procedure that you use when running on acetelyne. keep in mind that I do not have any methanol at my disposal

thanx!
I have to say I have had that happen to me so many times, "I knew it was too good to be true", something comes along the next day and my jet or jam jar chimera won't start or do what it use to do. A few times vibration will have loosened the threading, the weather and humidity have changed, (I've got a gauge now to record the day's humidity), or a multitude of other variables.
To start my Logan I put in in a vice at that strange angle, tail up and gently puff in air in/near the side port using a line from an air compressor. Sometimes it helps to angle the air in at a certain distance or to create the right tubulence, not too intense, but just right.The only other variables I can think of is if your acetylene gas feed is too fast or too slow or that the steel fuel feed line/needle has shifted and is intruding into the side port or angling differently, it's best if it is flush 90 degrees with the inside walls, just as it is best if your side port is threaded so it bites into the combustion tube but does not block or dampen the delicate flow of fuel/air resonance inside the combustion chamber. With a tail ignition going too, you can pretty much puff fresh air in the side port and that mixing will be good enough for the tail to help set up a resonance.
On a few occasions, I noticed with galvanized pipe, I have melted the zinc coating, for after a red hot run, on the end of my 3 inch diameter jet I was able to lift out a thin soft pliable ring of zinc from the tip of the exhaust that had collected there like sludge. Previously I had ground the tail end to get rid of any lip when the pipe was cut/threaded/folded inward, so I know this ring/deposit was newly formed. Maybe a little raised zinc residue lip has formed inside your sectioned exhaust tube somewhere. Sneaky little things can happen, snug up your jet and just ask what variable might have changed, (on your no moving parts engine).
I just have to laugh, pulsejets are so stealthy just when you think you have got a good understanding of how to start them. They are shifty little creatures and at times hard to grasp.
I know you will get it going again, puffing in air in the side port may help initiate ignition in the combustion chamber. I used a fine needle of air and held it at an angle an inch or two away from the side port entrance. With MAPP gas you can keep this up, a popping and choking madness until the pipe heats up and the fuel is more perky. Acetylene usually doesn't need a warm up though.
Not only have you copied my troglodyte Logan, but perhaps also some of the same disappointments I have had. It is just a primitive toy that works from time to time.
Mark

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Post by steve » Wed Jul 07, 2004 9:42 pm

sucess!
using the blowtorch and spark method it lit without too much trouble.
I then tested the throtleability and was shocked at just how good it was. It continued to run when I turned the acetlyne up as high as it would go while spitting blue and flames almost two inches past the intake. Then I reduced the throttle to a point about 1/16 of a turn form off and the engine continued to run while making a very faint humming noise. It was so quiet that I thought it had stopped running. when I looked into the intake all I saw was a tiny yellow flame about 3mm long that was aparently the explosion keeping the thing resonating. Did your engine perform like this as well? I made a slight modifacation to the fuel injector: it protrudes about halfway into the intake tube rather then being flush with the walls.
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