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Hybrid ThorJack

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: DYI » Mon Apr 23, 2012 12:19 pm

Sorry to intrude on this thread, but something said earlier last page REALLY needs to be corrected:

RJB wrote:The burn rate of H2 is incomparably bigger than the butane´s is.

2 C4H10(g) + 13 O2(g) → 8 CO2(g) + 10 H2O(g) + energy that is lower than the powerful H2 combustion:
2 H2(g) + O2(g) → 2 H2O(l) + 572 kJ (286 kJ/mol)

H2 is the future....


There's just far too much wrong with that statement to let it go. I'll start from the beginning and work through.

1. "... burn rate... incomparably bigger..."
Who cares? Butane burns fast enough. Lower burn rate is to be valued - it makes detonation easier to avoid and allows the burn to be maintained long after the disk ruptures, achieving the more level projectile base pressure profile which is desired by any gun designer. The more constant the projectile base pressure, the less stress is exerted on the gun for the same ballistic performance.

2. "energy that is lower than the powerful H2 combustion"
That "lower" energy? It happens to be 5315 kJ, or 354kJ/mol of gas in the chamber (oxidiser must be counted).

3. The H<sub>2</sub>O produced in the hydrogen/oxygen burn will be gaseous, not liquid. The actual energy release in the reaction given is 484kJ, not 572. This gives 161kJ / mol of gas in the chamber.

Starting at atmospheric pressure, the highest pressure oxygen/hydrogen mix produces about 9.6 bar on ignition, and that's with ideal adiabatic conditions. Butane/oxygen mixes under the same conditions are capable of over 24 bar. The energy considerations above are not the whole reason for that, but RJB's statement is just downright wrong. Hydrogen is, by mass, a very energetic fuel. Measuring fuels in terms of energy per unit mass is rather useless when we do all our work in the gas phase, where molar energy content is what matters.

[/rant]

Carry on, everyone. :roll:
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Last edited by DYI on Mon Apr 23, 2012 12:33 pm, edited 1 time in total.
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Unread postAuthor: Petitlu » Mon Apr 23, 2012 12:23 pm

"Sorry to intrude on this thread, but something said earlier this page REALLY needs to be corrected: "

DYI No problem!
Thank you for this important correction !
:D
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Unread postAuthor: RJB INDUSTRIES » Mon Apr 23, 2012 1:16 pm

The tests I did, didn´t confirm this theory, I am going to load some videos of that and everyone will take their own conclusions.


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Unread postAuthor: DYI » Mon Apr 23, 2012 2:54 pm

Your tests are in error, and most people here are not sufficiently knowledgeable to take the correct conclusions from experimental results. If you post the details of the tests, I can probably find the problem for you.
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Unread postAuthor: RJB INDUSTRIES » Mon Apr 23, 2012 4:25 pm

"Your tests are in error" ?
How can you say that if you haven´t study or even see them?



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Unread postAuthor: DYI » Mon Apr 23, 2012 4:48 pm

Because they run entirely counter to tests I have seen and studied, to literature which is peer reviewed and has been independently verified and used in industry for decades, and to the opinion of all material I've read regarding hydrogen in fuel systems, which is that its high specific impulse is its only desirable quality from a performance standpoint.

I've been doing engineering design on launcher systems for about four years now, and I have read a considerable volume of literature on the topic at hand here. All of it points to the conclusion that there is a flaw in either your measuring equipment, your methodology, or your interpretation of the results, and it does so very strongly.
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Unread postAuthor: CpTn_lAw » Mon Apr 23, 2012 5:06 pm

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Unread postAuthor: Petitlu » Mon Apr 23, 2012 5:12 pm

Excellent !
:D :D :D
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Unread postAuthor: RJB INDUSTRIES » Mon Apr 23, 2012 5:16 pm

What a joke... :D

Are you enjoy doing engineering design?



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Unread postAuthor: Petitlu » Mon Apr 23, 2012 5:19 pm

Yes I like very much, I am a technician!
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Unread postAuthor: Petitlu » Tue Apr 24, 2012 5:26 pm

projectile home made ! :D

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Unread postAuthor: jackssmirkingrevenge » Wed Apr 25, 2012 12:00 am

It seems like it will try and scratch your barrel :)
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Unread postAuthor: Petitlu » Wed Apr 25, 2012 2:10 am

hmm ... you think?
there is little surface to the diameter of the barrel ...
I will change!
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 25, 2012 2:23 am

You need something to keep it centred while in the barrel (like the two front halves of the arrow sabot I made)
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Unread postAuthor: Petitlu » Wed Apr 25, 2012 2:34 am

This "heat shoe" is not balanced, it is done to get to 2m! :D

I will put a caoutchou washer on the point
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