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Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: ramses » Fri Jun 15, 2012 10:14 am

Petitlu wrote:These are small pieces of Kleenex paper from the barrel ! :D

EDIT :
I just had an idea but I do not know if it's good! : face:

By putting a mano on the chamber, we could measure the peak pressure during combustion is not it?


That's pretty funny about the Kleenex!

It has been attempted, but the issue is that the propellent gasses cool off in gauge, even if there is a check valve. You really need to have a fairly long column of inert, cool gas before the check valve that will then get pushed through into the gauge. You could use water or oil, but its inertia could cause it to either under-estimate the pressure due to not flowing enough in the short time span, or over-estimate due to the water hammer effect
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Unread postAuthor: DYI » Fri Jun 15, 2012 10:21 am

You certainly could, but your pressure transducer would need sufficiently high sampling rate to make it work. Considering how slow the combustion process is here, something like 1kHz would probably be enough.

If you're asking about putting an actual pressure gauge on the chamber and watching it with the high speed camera, that won't work. The gauge mechanism is far too heavy to be of any use for that. Even without a camera, it's not difficult to perceive the gauge's response delay.
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Unread postAuthor: Petitlu » Fri Jun 15, 2012 11:57 am

ok...
If I leave the syringe in the chamber during the explosion the plunger goes up to 30ml.
it might be the result of the use syringe ...

With the piston diameter and weight, one can determine the force required to roll back to Xcm ..
The warmer is the coefficient of friction but I can try to measure this friction using a load cell attached to the piston, I shoot 3cm and I see that it took power, it would be good right?
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Unread postAuthor: boyce123 » Fri Jun 15, 2012 4:22 pm

just an idea (the manometer would work fine, but if you don't have one that will record peaks, this might be cheaper) but it could be possible to make a sealed piston, either at the back of the chamber, or a separate cup like object set down in the chamber. Either way it would have to be sealed, with no air able to escape, so the air inside the piston will get compressed to the same pressure as in the chamber. If there is a good enough seal, the piston should depress, and you could measure the volume change to measure the pressure change (use the blue mark-all impression substance to see how far it went down). It would be interesting to see the different variable's impacts on the pressure peak (see how much, or if the fan's added turbulence effects pressure, or if the increased flame propagation speed has any effect on the pressure peak.

EDIT: fail... :roll: my email took me to the bottom of page 3 in the post, sorry for reiterating what you just said...
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Unread postAuthor: Petitlu » Fri Jun 15, 2012 4:29 pm

No problem! :D
it is an idea to explore that's for sure!
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Unread postAuthor: DYI » Fri Jun 15, 2012 9:50 pm

just an idea ...


You still don't quite get it, do you? A pressure gauge which measures peaks will NOT work. Neither will any of your other ideas. The measuring equipment has significant mass.

In the case of the tube with the piston: depending on the parameters, the pressure in front of the piston could easily exceed 10 times the pressure pushing it. A gauge which measures maximum pressure will either undershoot (the pressure didn't act long enough) or overshoot (the momentum of the moving mechanism carried the needle past the actual pressure). A pressure gauge settles to the equilibrium which is the actual measured pressure due to dissipative effects. Take those away, and it would oscillate forever. You're reducing the dissipative effects by shortening the timescale, and it's this same principle which dooms all your measuring ideas.

Much as I know you guys love to ignore downers and congratulate the guy with the ideas that sound kind of plausible, it still won't work. Your readings are guaranteed to be erroneous.
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Unread postAuthor: boyce123 » Sat Jun 16, 2012 12:00 am

i never intended the system to be accurate, i designed it around the parameters that it would have some proportionality (either linear, geometric, or some variation, it would be possible to figure this out by putting it in a tank with a guage known to function accuratly) that could be observed to compare the intensity of various pressure bursts in relation to the change in different variables. If the system were to be truly accurate, the friction and mass of the piston (a plunger from a syringe) would have to be accounted for both with acceleration and deccelleration, nearly verbatum to what you were describing, DYI. Yet the accuracy you describe may be futile, as long as the device measures the same every time, then it will fulfil its intentions of a comparitive device (the only condition i see that would require accurate pressure measurements would be in scaling it up to a full sized effecient cannon, yet the pressure data probably will not scale up to an accurate full sized cannon, though it may be interesting to see the varience in pressure busts depending on burn effeciency, geometry or size). Although, if anyone is going to attempt so many varying pressure experiments, it may be worth it to invest in an accurate digital manometer. I know that the vernier instrument that i have used in my science class can get to relatively small time intervals, and its a pretty cheap and easy system to set up. The speed and accuracy would of course be dependent on how much money someone will spend, but a digital system will instantly give a graph back of pressure v time, and could even be set up to simultaneously measure temeraure... but i'm sure most that have taken high school chemistry know all this...

DYI: i have observed that people will generally accept a constructive critic. I've been reading some of your posts, i'm not sure if you realize this (you seem to have had some implication toward calling yourself a downer), but a slightly subjective tone comes out of your writing that isolates people, and that may be the reason why some people tend to ignore you (but more generally, downers). Further reasoning may lie in the subject matter, you implied that people that provide insight as to why a theory may fail get ignored, they generally get ignored because people that are reviewing an idea are thinking of ways to make it work, instead of trying to troubleshoot something that hasn't been tried.
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Unread postAuthor: Petitlu » Sat Jun 16, 2012 3:25 pm

I did a little test in the evening, I changed the spark plug, I put a motorcycle D10 long enough.
So I did a shot with a flash + ignition transformer and nickel, by cons I have another shot with an EGM (electronic gas lighter) and another with a piezo has multiple sparks and ... nothing! none of the two has worked ...
What is the difference of 0.7mm (measured with the hold spark plug) is too high?
the sparks were of course but they are stretched and they have less power ...
What do you think?

[youtube]http://www.youtube.com/watch?v=Cjo7g5f5cBc[/youtube]
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Unread postAuthor: DYI » Sat Jun 16, 2012 4:30 pm

i never intended the system to be accurate, i designed it around the parameters that it would have some proportionality...


Unfortunately, your system will not even have proportionality, owing to varying shapes of the pressure profiles. Only with pressure-time curves having the same shape will it be proportional.

I've been reading some of your posts, i'm not sure if you realize this...


While I typically strive for objectivity and helpfulness, friendliness is rarely taken into consideration :wink:



@petitlu: are you saying that you've been unable to get ignition with the EGM or piezo sparker with the motorcycle sparkplug?
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Unread postAuthor: Petitlu » Sat Jun 16, 2012 4:37 pm

Yes that's exactly it!
spacing of 0.7mm is too big for a piezo electronic and manual? :(
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Unread postAuthor: Petitlu » Sun Jun 24, 2012 3:31 pm

New tests with ignition as the direct discharge of a capacitor

[youtube]http://www.youtube.com/watch?v=p5KZv91JfCE[/youtube]
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Unread postAuthor: POLAND_SPUD » Sun Jun 24, 2012 4:13 pm

wow awesome colours :D
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Unread postAuthor: Petitlu » Sun Jun 24, 2012 4:20 pm

I think the green comes from the copper electrode, but I'm not sure ...
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Unread postAuthor: Fnord » Sun Jun 24, 2012 8:57 pm

Have you tried putting the electrode behind the fan in a capacitor test?
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Unread postAuthor: Petitlu » Mon Jun 25, 2012 1:08 am

Not because behind the fan, these are fixed electrodes and for this ignition I need movable electrodes.

I would have to pierce the bottom ...
But there are a plurality tests with different ignition with an Exterminator II
:D
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