7 replies to this topic

[dave]

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Edited by phildunford, 15 December 2010 - 09:16 PM.
user request

[dave]

whoa ! pressed the wrong button,

as i was saying this has been purely an academic excercise looking at three different mixtures :-

i tried to go for a high emmision rate rather than longevity
all are relatively small, tube id = 1" , compressed with 6mm core in centre

1) colophony and ammonium chloride - cheap and easy to prepare, effective,

2) cinnamic acid (ca) - needed a lot of playing about before getting a smoking mixture
much denser smoke than colophony mix above

3) terephthalic acid (ta) - easier to formulate than cinnamic acid and again denser than colophony mix above,
probably as dense as cinnamic acid

the ca and ta were i think developed to find a less toxic smoke screening agent to hexchloroethane compositions used by the military.
i think the ta is preffered in america, wheras over here i think its the ca thats preffered and is also used as a cs gas simulant.

some flaming on the ca composition but this has now been sorted out
also the ca and ta comps seem to show "pulsating burning"...........maybe similar to a whistle mechanism ? anybody know why
might be a pressure effect ?

wind conditions were unfortunately not the same on each day..........






dave

[dave]

heres the 3 rd video



dave

[Mumbles]

Are you sure the "strobing" isn't just chuffing, which happens with excess ash or build up of other solids. I know this sort of thing can be an issue with chemicals that sublime. They tend to recondense over time around the nozzle, especially after burning a bit. The terephthalic acid one definitely looks like chuffing or ash or something like that. The CA smoke has a very regular rhythm to it, so I really don't know.

I really don't know how to test to see what it is though. Maybe cut open a case after the burn to see how much solid material is still left inside?

Edited by Mumbles, 13 December 2010 - 03:17 AM.

[dave]

Are you sure the "strobing" isn't just chuffing, which happens with excess ash or build up of other solids. I know this sort of thing can be an issue with chemicals that sublime. They tend to recondense over time around the nozzle, especially after burning a bit. The terephthalic acid one definitely looks like chuffing or ash or something like that. The CA smoke has a very regular rhythm to it, so I really don't know.

I really don't know how to test to see what it is though. Maybe cut open a case after the burn to see how much solid material is still left inside?

hi mumbles,

"chuffing".......chuff chuff..........great word

you could well be correct.............there will be a solid ish ash formed after burning, as with most smokes, so you could be right.
i'm open to other explanations.

chuff chuff.........chuff chuff......................you've tickled my fancy ah ah.....................chuff chuff chuff chuff

dave

[BrightStar]

"chuffing".......chuff chuff..........great word

Just how much of that smoke have you inhaled Dave

You mention 1" id with a 6mm core. Could I ask was this a core all the way through or just at the top? How long were these units? I'm quite interested in the burn rates etc.

[dave]

brightstar,

the tubes were 1" id, 4" in length, with 6mm core through the entire length.
but there were clay plugs at each end (also with the core hole)..the bottom core hole was simply blocked with a further small amount of clay.

the amount of composition was 30g in each case, so it did not totally fill the tube, there was a small air space for some cooling of the smoke.
the ta one was granulated with nc in acetone to aid compaction.

they were not heavily compacted ( 3 ton arbour press) but this was more than sufficient to maintain core channel integrity.
burn times you can estimate from the vids.

if you want long burn times, use colophony+ ammonium chloride as an end burner (credit to spectrum for info provided on these colophony compositions, he's the expert)
the ca composition was a bugger to get smoking, the ta no trouble, just like a coloured smoke with dye.

dave

[dave]

well, how about this, as mumbles suggested...........

Chuff: A form of unstable combustion marked by brief bursts of thrust separated by periods of no thrust. Typically, the bursts come faster and become longer as burning proceeds, until stable burning results. The sound of chuffing is similar to that of a steam locomotive starting up. It generally occurs in a composite motor that is ignited too low in the grain.

chuffing would seem to occur with some rocket propellants, interesting, what an unusual phenomena, i had not come across it before.
sounds like some sort of pressure effect.

dave