Succesfull school project

[PJ-Holland]

Hello,
this is the result of our earlier post, after a week testing on school we have an running engine.
it does'nt run on itself, but we think it is an succesful enging, but if you think you have the golden tip to get it work stand alone, please tell us.

Our results:

our testconditions are:
a propane tank, with an reducing valve of 0,05 BAR (0.72 PSI).
propane runs 1 : 6,5 so we reduced the compressor to about 0.6 bar.
a few movies:
http://pws.gieltjev.xp-losion.com/MOV02228.MPG
http://pws.gieltjev.xp-losion.com/MOV02230.MPG

at last our first try at home:
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[Anders Troberg]

Nice to see a jet as a school project!

My first impression is that the diameter of the intake looks a bit big. The sides of the combustion chamber looks like they are screwed in place, not welded. Is it completely tight, or may there be leaks? The reduction valve on the tank may also be the culprit.

But, I'm no expert, so don't make any modifications based on my suggestions until the big guys here have given their opinion.

Is it a variant of the Electra?

[Mark]

In the first clip, the pulsejet sounds like a real machine gun, which is kind of what a pulsejet is anyway. Just a bit more tweaking and it should be able to run/feed on its own. Every pulsejet is different, and your box shaped combustion chamber is not often seen. Interesting and somewhat unique.
Mark

[larry cottrill]

pj -

I would go farther in playing with the length. Your'e seemingly not really at resonance yet, and when you get there, you will be AMAZED at how different it is. I say, extend the tailpipe some more! If you think you're having fun now, just wait till you hit resonance and can shut the air off!

Incidentally, DON'T FORGET that it is easy to cripple your efforts by trying to force too much air. Try it for a while just like it is, but gradually reducing the air pressure in your line - you may hit just the right mix and have her going!

You're doing great, don't give up while you're only halfway there!

L Cottrill

[PJ-Holland]

Nice to see a jet as a school project!

My first impression is that the diameter of the intake looks a bit big. The sides of the combustion chamber looks like they are screwed in place, not welded. Is it completely tight, or may there be leaks? The reduction valve on the tank may also be the culprit.

But, I'm no expert, so don't make any modifications based on my suggestions until the big guys here have given their opinion.

Is it a variant of the Electra?

Hi, indeed, it is an variant of Electra, only in holland our "electrical boxes" are made of plastics, so we took an piece of pipe with an ID of 10.5. see our earlier post for the design. and it is welded, you can click on the big image.

pj -

I would go farther in playing with the length. Your'e seemingly not really at resonance yet, and when you get there, you will be AMAZED at how different it is. I say, extend the tailpipe some more! If you think you're having fun now, just wait till you hit resonance and can shut the air off!

Incidentally, DON'T FORGET that it is easy to cripple your efforts by trying to force too much air. Try it for a while just like it is, but gradually reducing the air pressure in your line - you may hit just the right mix and have her going!

You're doing great, don't give up while you're only halfway there!

L Cottrill

Thanks again for al your effort !
About lenghtening the tailpipe, if we move the piece of pipe about 1 cm it only makes flames, no pulsating effect. Maybe it works if we lenghten the tailpipe by itself (2x this lenght) or 3 quarter it will work, but we think this isn't bad for 3 students.

about the air:
we have tried to shut of the air or sparks slowly, but we cant shut of either of those, unfortunatly.

at last a nice fact:
it is made of 4 mm thick pipes and plates, and it has been so hot that te chamber became red :)

PJ-Holland

[hagent]

Hi PJ-Holland,

Nice project.

The first thing that struck me was there seems to be a large amount of propane coming back out through the intake. You may want to try and place the propane about 3/4 down the lenghth of the intake pipe, and try different positions. As Larry said you should not need alot of air to start. You may want to try and hold the air nozzel to find a sweet spot, even if it's 6 inches away from the intake.

What sort of propane injector are you using?

A good begginers injector would be to get 1/8 or 1/16th inch metal tubing and cut it at a 45 deg diagonal so that the cut end squash together. There are lots of examples on the forum. It would also be helpful to have flares on the end of the intake. After is resonates good when you find the length of your exhaust you can add a flare there too.

The PJ's that I have never start when I force enough air into them to create that gun shot bang. The mixture is too lean at least on mine to continue the cycle on it's own.

Good luck!

Cheers.

[Jim Berquist]

It did sounds like a WWII Bren machine gun.

Expert I are not. I did see the intake could be a bit smaller.

What did you do when it started to run backwards?

Just some thoughts:

Jim

[leo]

Hallo PJ-Holland.
I don’t want to disappoint you but your motor is not running in resonance.
I think its running on the sparkplug frequency when its sounds like a machinegun.
If it is not making this sound, it its acting like a blowtorch.
If you want to get it running you will have to lose the pressure regulator, its impossible to get enough propane in your PJ with only 0,05 bar, I need always something from a 0,5 to 5 bar.
But this is depended on the resistance in your injector system.
The machine gun sound looks like 25 HZ or so, when its would run properly it would be something like 250 HZ.
If you make your pipes much smaller it would start easier, maybe you can flatten the pipes to get a smaller size.
Please don’t give up to soon, PJ are sometimes very hard to start, especially if you don’t have the experience, its get easier after the first time.
( where I heard that one before?.)

Greets Leo.

[PJ-Holland]

We varied the sparkplug frequencies between 20-200 Hz. With no drastic differences in result. We are still not totally sure about our intake/exhaust proportions. Because when it was running we kept changing the exhaust length with an bigger peace of pipe that we slided over the normal exhaust. Until we found the right length on witch it runs the best. But we never tried to extend the exhaust that much. We will definitely keep that in mind. We are far from quitting with the pulse-jet, but right now we are a bit busy with school so we haven’t got much time to work on it.
Thanks for your efforts,

3 Students from holland

[Anders Troberg]

We varied the sparkplug frequencies between 20-200 Hz.

When it's running, you can turn off the spark plug. If it runs properly, it will self sustain without the spark.