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Slow BP Methods


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#1 LiamPyro

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Posted 28 July 2020 - 11:43 AM

Consider that there are two ways to make a slower black powder type fuel: The fuel can be ball milled as usual and the ratio adjusted to something like 60/30/10, or the fuel can be made with the usual 75/15/10 ratio but simply screen mixed. Both of these will burn slower than regular black powder, and its conceivable that two fuels could be made that would burn at the exactly the same rate with one being screen mixed and one ball milled. In terms of making rockets, I see both methods of making a slower fuel employed. However, it seems as though adjusting ratios and ball milling would be superior seeing as this allows for a higher percentage of charcoal/sulfur fuel, whereas screen mixed black powder is simply a less efficient version of meal. The fundamental difference is whether the burn rate is controlled via surplus fuel or by making a less homogenous mixture with a larger particle size. Thoughts?

Edited by LiamPyro, 28 July 2020 - 11:44 AM.


#2 SeaMonkey

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Posted 28 July 2020 - 10:32 PM

If residue would be a problem I suppose one would choose the method

which produces the least or most easily managed residue.

 

It may be possible to reduce the sulfur content as well.

 

I agree that a well milled product with very small particle sizes

will be more consistent and predictable.


Edited by SeaMonkey, 28 July 2020 - 10:34 PM.


#3 justvisiting

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Posted 29 July 2020 - 03:22 AM

Burn rate and thrust produced seem to be separate things, IMO. 



#4 LiamPyro

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Posted 29 July 2020 - 12:54 PM

Burn rate and thrust produced seem to be separate things, IMO. 


If this is the case, then two mixtures one of which is milled and the other screened could burn at the same rate, but it seems that the one with the higher fuel content (milled) would be more energy dense and thus produce more thrust.

#5 justvisiting

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Posted 29 July 2020 - 02:09 PM

There are so many interesting factors at play in your hypothetical scenario. You mention 60-30-10 and you mention thrust, so I guess we're talking about rockets ;) You're not likely to use 75-15-10 in a nozzled rocket (although I have, lots of times), and you're certainly not going to use 60-30-10 in a nozzleless rocket, even if all the charcoal was fine enough to react within the motor.

 

Usually, a 60-30-10 rocket has a coarse charcoal and a fine charcoal. The fine charcoal participates in the black powder reaction in the motor. Anything that blows out the rear and produces sparks is not part of that reaction. If black powder has unsufficiently milled charcoal particles in it, those particles can't be considered as fuel.

 

When I make my screen-mixed black powder variants, I 'supermill' the charcoal. I'm not getting intimacy of incorporation by using a wheel mill like commercial manufacturers do. I am however, guaranteeing that all the charcoal has maximum fuel value. If a charcoal had a higher ash content, then more would be needed to get a similar fuel value. Also, I think something that is often overlooked is the role of water in the commercial manufacture of black powder. Commercial black powder doesn't use fast charcoals like we do. They use stuff like maple or oak. Maybe the reason willow was so popular in the 'olden days' is because manufacturing methods were less than ideal, so a 'hotter' charcoal was needed. Just a guess.



#6 snapper

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Posted 29 July 2020 - 02:58 PM

willow was used because military/government contracts called for it, today they use the cheapest wood they can source. if you want to slow down your burn rate there are multiple ways this is possible with the easiest being to use a different wood for your charcoal such as pine or dogwood that reacts well but slower.



#7 dagabu

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Posted 29 July 2020 - 05:23 PM

If this is the case, then two mixtures one of which is milled and the other screened could burn at the same rate, but it seems that the one with the higher fuel content (milled) would be more energy dense and thus produce more thrust.

 

Interesting thoughts shared here but lets get back to "Rocket Science" and look at this through a different lens since I see all sorts of words being used instead of the thing that lifts rockets... thrust.

 

Thrust is:

 

rockth.gif

This means that you are looking at what mix and how fine of a mix would make less thrust?

 

Not 'slower' but less thrust? Or, are you burning this in the open? Is this for lift, burst, propulsion? 


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#8 dagabu

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Posted 29 July 2020 - 05:24 PM

If this is the case, then two mixtures one of which is milled and the other screened could burn at the same rate, but it seems that the one with the higher fuel content (milled) would be more energy dense and thus produce more thrust.

 

Burns at the same rate, more gas production = more usable thrust.  


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