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Hybrid design ideas

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: Alanstone » Sun Nov 25, 2012 12:25 am

@Heimo: I like your pump action idea. One of the ideas I am working on having the combustion chamber act as part of an accumulator. By having a stoichiometric mixture of gas flow into the combustion chamber then have the combusted gases pump up a chamber. The chamber will supply the valve assy the same way compressed air does for a pneumatic gun. I am drawing furiously and hope to have a few ideas out in the next few days.

@JSR: Jack please be so kind to check this link out.
http://72.41.12.125/microflame/torches.cfm

They are lighting these things with spark wheels. Am I missing something? If I understand right then I am seeing a stoichiometric supply of N20 and butane that's easily ignited somehow. Could it be?
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 26, 2012 4:00 am

Alanstone wrote:@JSR: Jack please be so kind to check this link out.
http://72.41.12.125/microflame/torches.cfm

They are lighting these things with spark wheels. Am I missing something? If I understand right then I am seeing a stoichiometric supply of N20 and butane that's easily ignited somehow. Could it be?


I'm not sure how these work exactly, you're feeding butane and nitrous oxide but would it work in a vacuum? I suspect that the butane combined with the atmospheric oxygen ignites first, and this then gives the heat which decomposes the nitrous oxide to enhance the flame.

From here:

Oxygen is the original oxidizer gas used with the Microflame torch, But early on they encountered problems shipping it through the mail, so they switched to 'Micronox' gas and larger diameter tips. This stuff didn't work out very well for me, and it was very annoying having to change out the little cylinders every 5 minutes.
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Unread postAuthor: Alanstone » Mon Nov 26, 2012 4:46 am

@JSR:

I want the N2O for the pressure it offers more than anything else. Its also great that it compresses to a liquid and offers additional O2. Ijahman used an air butane mix and prepared it as an ignitable mix for his gatling by adding butane through a "faucet" until it was ignitable. Thus he had a stoichiometric mix on tap. If it were possible I propose that N2O is added to the mix to provide pressure. A rich butane air mix then adding N2O until its ignitable. That way you have a high X mix on tap. If its high enough I think it would overcome what gases are left in the chamber after the previous combustion or the air already in the chamber on the first combustion. Do you think I am wasting my time with this idea? If so have you any thoughts on pressurizing an air butane mix in the chamber?
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 26, 2012 5:58 am

Alanstone wrote:Do you think I am wasting my time with this idea? If so have you any thoughts on pressurizing an air butane mix in the chamber?


I think the theory is sound, but actually implementing it is not as simple as you might be imagining. I suggest you do some research into N<sub>2</sub>O use as a liquid rocket propellant.

Here's the wiki page: http://en.wikipedia.org/wiki/Nitrous_oxide_fuel_blend

Upon use, the propellant is heated or passed over a catalyst bed and the Nitrous oxide decompose into oxygen-rich gasses.


I'm sure it can be done, but not by simply injecting nitrous and butane into a chamber.

Personally, I think a simple butane/air mix provides more than enough power for your purposes. If you have a large calibre, say 0.5" or 0.75", even a relatively low mix of 5x-10x will give you a lot of power.

What firearm does your final project look like? I'll use some local examples ;)

Image

Image

Image

Have you thought about the calibre and what you're going to use as ammunition?
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Unread postAuthor: Alanstone » Tue Nov 27, 2012 10:08 pm

Firstly Jack, I want to thank you for taking the time to reply to my threads and for the effort you put in. You have made me feel welcome here.

The gun will look similar to the design in my "pneumatic ideas" thread. I am drawing a new setup for the air/ butane mixing which I will hopefully post soon. For now the barrel will be fridge tubing (burst pressure 86 bar) with an id of 8.39mm and the ammo no. 00 buckshot (id 8.38 mm). That's cutting it close but if it doesn't clear I will go for no. 0 buckshot (id 8.13 mm).

I will continue to find out more about the N2O. Being able to feed mix into the chamber at 720 psi is an idea hard to give up. But I will heed your advice for now and focus on butane / air mix.

With regard to the drawing I posted: this is obviously not a final design but I wanted to ask you something about it before I continue. The idea is that the pump piston is a predetermined distance from the pump wall. This allows a set amount of butane to be pumped into the pump section (this will also be adjustable to find the right distance. Upon pulling the plunger back air is drawn into the pump creating a stoichiometric mix. This mix is then pumped into the chamber on the return stroke. Assuming proper ratios between the chamber and pump, orings and what not, what is your guess on the pressure I could hope to obtain in this manner. the chamber?
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 29, 2012 2:25 am

Alanstone wrote:Firstly Jack, I want to thank you for taking the time to reply to my threads and for the effort you put in. You have made me feel welcome here.


Think nothing of it, we all had a leg up along the way and legitimate questions from the genuinely enthusiastic deserve answers in my view.

The gun will look similar to the design in my "pneumatic ideas" thread. I am drawing a new setup for the air/ butane mixing which I will hopefully post soon. For now the barrel will be fridge tubing (burst pressure 86 bar) with an id of 8.39mm and the ammo no. 00 buckshot (id 8.38 mm). That's cutting it close but if it doesn't clear I will go for no. 0 buckshot (id 8.13 mm).


8mm with a long barrel and 15-20x mix behind it will be pretty devastating, you can expect supersonic velocities easily.

With regard to the drawing I posted: this is obviously not a final design but I wanted to ask you something about it before I continue. The idea is that the pump piston is a predetermined distance from the pump wall. This allows a set amount of butane to be pumped into the pump section (this will also be adjustable to find the right distance. Upon pulling the plunger back air is drawn into the pump creating a stoichiometric mix. This mix is then pumped into the chamber on the return stroke. Assuming proper ratios between the chamber and pump, orings and what not, what is your guess on the pressure I could hope to obtain in this manner. the chamber?


Is the pump manual? If so, do you plan on pushing it directly (like a pump action shotgun) or with some sort of lever?

If you're resting it on a hard surface, even pushing directly 300 psi should relatively easy to achieve, assuming you don't make your piston too wide. Remember a thin long tube is better than a short fat one in this case.
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Unread postAuthor: Alanstone » Thu Nov 29, 2012 2:39 am

I have a dismantled springer pellet gun ( a chinese AT 11). Since you mentioned a lever perhaps I could use the parts off that somehow to compress the mix. I will look into it. 300 psi is nothing to sneeze at. That's a 20X mix right there!
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 29, 2012 6:09 am

It would be interest to make a springer hybrid... shock heating might not be enough for the mixture to autoignite, but you could have the piston motion close an ignition circuit...
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Unread postAuthor: Alanstone » Fri Apr 26, 2013 12:44 pm

Both CO2 and N2O are sensitive to temperature. (N2O much more so). For instance CO2 at 70 degrees Fahrenheit has a pressure of 856 psi. At 300 degrees Fahrenheit the pressure is 5076 psi. At 600 degrees Fahrenheit the pressure is 13658 psi.

N2O at 70 degrees Fahrenheit has a pressure of 762 psi. At 260 Fahrenheit the pressure is 5229 psi. At 340 degrees Fahrenheit the pressure is 10767 psi. At 500 degrees Fahrenheit the pressure is 46995 psi. And then, of course as Poland mentioned somewhere, it decomposes into a monofuel at 315 degrees Celsius. But let’s for a moment forget N20 as it seems to have demons in its closet.

C02 however is much more stable.

HGDT reports that a butane / air mix reaches over 1800 degrees Celsius in the combustion chamber. Surely this can be used to increase the temperature of a quantity of CO2.

So there would be two chambers. The first is a butane /air mix and the second is CO2. The heat generated by the first raises the temperature of the second to provide the pressure wanted as it fires, then mixes, into the second.

Here is a very basic pic of the idea. Am I missing something obvious with regard to the concept? Or does this idea have merit?
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Unread postAuthor: Alanstone » Fri Apr 26, 2013 1:05 pm

please excuse the double post. I thought that it may make more sense if I added a second pic of the design in the open position.
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 26, 2013 1:31 pm

Interesting concept, the theory sounds fine on the face of it but how much you would actually gain in performance would have to be seen.

A simpler way to achieve it would be to charge the chamber with 20% oxygen, 4% propane and 76% CO<sub>2</sub>...
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Unread postAuthor: Alanstone » Wed May 01, 2013 5:50 am

To JSR: "A simpler way to achieve it would be to charge the chamber with 20% oxygen, 4% propane and 76% CO2..."

Very elegant! Yes that is!

What you suggest would simplify the piston and chamber design, for sure. On the other hand it would probably be a pretty complex feed setup. An oxygen source and regulator, a propane source and regulator, a metering setup of some kind and a CO2 source and regulator. (Unless, of course, this becomes a cartridge design. Which, at these pressures, seem more reasonable perhaps, especially when encased by a big fat breech).

What I keep in mind is a small bullpup configuration (500 -800mm total length including suppressor) painted in bright toy colours (and looking oh so very much like a water blaster) lying inconspicuously on the back seat next to the baby seat of a favorite vehicle of choice.

Heimo spoke earlier of a pump action design and that is what I have had mostly in mind if a chamber design works here. When considering this then the ideal is: One pump equals a reload and fire. However, to get to any worthwhile mix there is a lot of pumping to be done. (Or my old idea of having CO2 do the work.) One could get around that by using compressed air, sure. I would like to get around that too if possible and that's why I have been coming up with wacky ideas with regard to focusing on the heat generated from the combustion rather than the pressure generated by the combustion. In other words, a second stage.

I really don't know how to calculate what I proposed in the drawings earlier but I am going to wing it here just as to detail my thinking a bit more.

Both chambers are 3cm dia x 1.5cm long (around 9.6 cm3 vol excluding piston). The chamber on the right is a 3x butane\air mix (45 psi) for instance. This is achieved by a single pump of a mixed volume of butane and air from a 16mm id tube that is about 140mm long. It will take around 6kg to achieve. The butane and air is mixed and correctly proportioned when sucking the air and butane into the tube of the pump as being detailed elsewhere on the site when using a venturi nozzle. The chamber on the left is CO2 (at 180 psi say) which is about 4 times the pressure of the pre combustion butane/air mix. ( This done to diminish the temperature). On the butane/air side the piston is unbalanced slightly, and held in check, while on the CO2 side the piston is balanced.

The butane/air mix is ignited which pushes the piston back and allows the combustion gases to mix with the CO2. The butane/air combustion generates (theoretically) 1970 degrees Celsius. As it mixes with the CO2 the CO2 increases in temperature and pressure. The CO2 side of the piston hasn’t cleared the barrel yet. As the piston moves back further, it then opens up to the barrel. The piston can be designed to generate the maximum chamber pressure before the piston clears the barrel.

(Now for a lot of assumption on my behalf. I wish I knew how to calculate this and I will keep on trying to work out how but I’ve got a feeling the math on this one isn’t for sissies. Palmer pursuit has a ” psi CO2 temp calculator” where you can plug in a temperature and it gives you the pressure. This is for bottled CO2 however but it does give an indication of how silly CO2 gets at high temperatures. Google “psi CO2 temp calculator” if you want to use it as I don’t know how to place the link. I downloaded an excel spreadsheet that does the same for N2O from somewhere and if you want that I can post it here for you, and like I said before N2O is waaaaaaay meaner than CO2)

Lets say that if the CO2 in the left chamber is 4 times the initial pressure of the pre combustion air/butane mix in the right chamber, the temperature of the CO2 and the post combustion mix will be a quarter of 1970 degrees Celsius generated by the combustion. (This said, only because I have no real clue as to how this really works). This will give 492.5 degrees Celsius or 918.5 Fahrenheit. This will provide a pressure of 25435 psi if the CO2 which initially was at bottle pressure (which it’s not but that’s not a bad thing because the chamber design could never handle 25435psi = 1788 kg/cm squared. On a 3cm diameter face that’s around 12640 kg). Wikipedia states that the 5.56 NATO round delivers 62366 psi. Bear this in mind because unless I am way off track, in my opinion, I believe this concept in the right configuration could deliver such pressures. It’s all about delivering the heat to the CO2 or N2O. N2O, of course, having a few more tricks up its sleeve (such as a massive release of energy on decomposition and then also becoming a mono fuel which can combust producing even more energy). All this is assumption on my behalf of course and I may have missed the boat completely in my understanding.

Now I know that what I have said above has many, many holes in it (must have) and I apologise for my ignorance with regard to this. However I am sure you can see the potential I see here. Obviously the gains will never be as high as it seems in the above example but there is obviously something warrantable here.

Now perhaps this is not something that is best approached in a chamber but rather in a cartridge. Butane/air or oxygen mix behind a burst disk (acting as a percussion cap I suppose) and then CO2 or N2O behind the swaged ammo. (Very much like standard modern day ammo, I am embarrassed to say.) The butane/air side could be filled and plugged in a pump. Then a second stage could do the same for the CO2 or N2O then plugged with swaged ammo. If one were to go this route it would be business as usual with regard to weapon design (breech, magazine, etc..) as it would mimic modern day weaponry except of course… no solid propellant. And also something you can produce right at home in your “bat cave”. And with a rifled barrel, one could actually use any caliber bullet as the bullet itself, is not regulated in sale.

I know there is a huge amount of knowledge behind the pseudonyms on this site. Please help me in my understanding.
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Unread postAuthor: jackssmirkingrevenge » Wed May 01, 2013 6:37 am

I understand the fascination with exploring this possibility, and you could genuinely be on to something here, but my suggestion would be to build yourself a regular hybrid first, you will be quite impressed with the power of a regular one I'm sure.

This is not a polite TL;DR btw :) but I am confident that a cartridge roughly the size of a 3" shotgun shell, with a swaged projectile say around half inch calibre, and filled to a high regular mix (say 30-40x) will give you at least as much power as a 9mm handgun from a two foot barrel.

Heimo spoke earlier of a pump action design


Cartridges would allow for a straight blowback mechanism, simple and reliable and easily capable of full auto fire.

You could basically then create a hybrid version of this or any other simple subachinegun design like the Sten or M3.
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Unread postAuthor: Alanstone » Wed May 01, 2013 8:59 am

Well no matter what I build its going to cost money and time. More money than time because I will have to outsource everything. So in that case why not work on something that offers the spudding community something new to work with? It keeps things alive and interesting I would think. A 50x mix requires an initial pressure containment of around 750 psi. Doing it the way I propose should have much lower initial pressures. More for less! Always a bargain!

I mean a person doesn't have to create anything illegal. Scale this idea down and you might have an awesome source of energy for a .177 cal. I mean what would it be like to have brass flying from you homemade pellet gun. Kaching! Kaching! Yeah baby!
Now that tickles my fancy! Your idea of mixing oxy, butane and CO2 together into the cartridge or chamber makes it seem much simpler. :)
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Unread postAuthor: jackssmirkingrevenge » Thu May 02, 2013 1:14 am

Alanstone wrote:Well no matter what I build its going to cost money and time. More money than time because I will have to outsource everything. So in that case why not work on something that offers the spudding community something new to work with? It keeps things alive and interesting I would think. A 50x mix requires an initial pressure containment of around 750 psi. Doing it the way I propose should have much lower initial pressures. More for less! Always a bargain!


Fair enough but it's smacking of "free energy" to me... you're not adding energy to the mixture after all - I'm not sure the increased energy absorbed by carbon dioxide vs nitrogen would necessarily lead to moar power. Still, it would be great if you could try it.

I would definitely do a side-by-side comparison of a chamber with air + fuel and then CO<sub>2</sub> + O<sub>2</sub> before investing in a fully functional setup.

I mean a person doesn't have to create anything illegal. Scale this idea down and you might have an awesome source of energy for a .177 cal. I mean what would it be like to have brass flying from you homemade pellet gun. Kaching! Kaching! Yeah baby!


That is aspiration I can agree with. I'm ashamed I never followed up on this now that I have machine tools.

[youtube]http://www.youtube.com/watch?v=cB1JzDdWlMc[/youtube]
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