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Two-stage hybrid

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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Two-stage hybrid

Unread postAuthor: hectmarr » Thu Aug 15, 2019 5:51 pm

I am working on this idea. It is a combustion chamber "A", with a mixture of butane-air, at 80 psi, and a combustion chamber "B", the same, with a mixture at 80 psi.
The chamber "A", explodes when the trigger is pressed, and the energy of the expanded gases, compresses the combustion chamber mixture "B", which is the one that breaks the rupture disc, (orange color), and Boost the ammo. The ignition on the camera "B", occurs automatically, when the contact "C", are touched.
The idea is to compress the chamber mixture "B" to more than 80 psi, to obtain more energy. This shell, on the side of the rupture disc, is previously compressed to keep the piston balanced in the center of the whole assembly. The idea is to increase the power, by increasing compression in the "B" chamber, without needing a more complicated air pump. The hybrid is inflated to 80 psi, and would only increase the amount of air in the two chambers. I estimate that the pressure of the chamber on the side of the rupture disc reaches quite more than 80 psi.
 
Will it be possible to work? I have thought that the burned gases that are in chamber "A" serve to dampen the recoil of the piston when chamber "B" explodes. It is clear that they cannot be burned due to an increase in temperature due to compression, since they have already done so.
The idea of achieving self-ignition by compression in the chamber on the side of the rupture disk, the one that drives the projectile, I have abandoned it because for it to work, a minimum level of compression is necessary, which is too high for what I want to build . With the automatic ignition system, you can shoot at any pressure.
I would like to hear opinions. :shock:
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Re: Two-stage hybrid

Unread postAuthor: Moonbogg » Fri Aug 16, 2019 5:45 pm

Predicting it's behavior would be complicated and difficult, but I can see this possibly working. It's funny to see this because I had a similar idea except I thought about using a hand crank to compress the chamber B side. A gear reduction and a worm gear or ACME thread with a piston to compress the gas. This way you fuel the cannon like a standard, atmospheric pressure combustion, then turn the handle to compress it and you end up with a hybrid without needing to mess with pumps. I think just using a pump would be way easier, lol, but that was my idea and it's similar to yours.
All I can say is go for it. I'd prepare for that piston to slam and knock the crap out of your chamber. Maybe the combustion pressure in chamber A will dampen it, but figuring all that out is quite a task. I'd honestly just get a higher pressure bike pump and use the whole chamber for a higher mix instead of relying on a hybrid combustion to super compress another hybrid mix. Maybe it will be awesome and work really well, but it's too complicated for me to attempt it.
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Re: Two-stage hybrid

Unread postAuthor: hectmarr » Fri Aug 16, 2019 6:34 pm

Moonbogg wrote:Predicting it's behavior would be complicated and difficult, but I can see this possibly working. It's funny to see this because I had a similar idea except I thought about using a hand crank to compress the chamber B side. A gear reduction and a worm gear or ACME thread with a piston to compress the gas. This way you fuel the cannon like a standard, atmospheric pressure combustion, then turn the handle to compress it and you end up with a hybrid without needing to mess with pumps. I think just using a pump would be way easier, lol, but that was my idea and it's similar to yours.
All I can say is go for it. I'd prepare for that piston to slam and knock the crap out of your chamber. Maybe the combustion pressure in chamber A will dampen it, but figuring all that out is quite a task. I'd honestly just get a higher pressure bike pump and use the whole chamber for a higher mix instead of relying on a hybrid combustion to super compress another hybrid mix. Maybe it will be awesome and work really well, but it's too complicated for me to attempt it.

The idea of using an endless screw, works, no doubt. The problem of loading the mixture at atmospheric pressure, like a normal combustion weapon, is that the combustion chamber must be very bulky.
I use a 50 ml camera, for example, and mix at 10X. In this case the total volume of compressed mixture is 50 ml x 10 bar, about 500 ml. In this case the camera is small, (50 ml). If these 500 ml are charged at atmospheric pressure, then compress by whatever method, the chamber must have 10 times the volume! about 500 ml This is not practical because it makes the weapon very large and ugly. It is for this reason that my idea is to compress the mixtures of the two cameras, to make everything more compact.

On the other hand, an air pump to compress at 20 or 30 bar, (compressing as a normal hybrid), are not cheap, (at least on these sides).
With this system, it seems to me, you can compress both cameras to 2X, but the shot will be many more "X". I am making some numbers, to estimate very roughly how much is the increase in compression in the "B" chamber.It is clear that the effort to compress with the pump, I will not, but the camera "A".

Let's say the area of the piston is 5 cm 2, for a diameter of 2.5 cm, 1 ", compressed to 3X.
When the mixture "A" explodes, the pressure increases 7 times, about 3bar x 7 times = 21 bar. The force exerted by the piston in chamber "B" will be 21 bar x 5 cm 2, about 105 kg ... and the pressure of the mixture would increase from 3 bar to 21X. Probably a lot less, but I don't think much.
You would compress at 3X and shoot at 21X, (or something less, I don't know).

To shoot at 8 or 9X, which is what I use, I may have to compress the two cameras, (which are actually only one, divided), at 2 or 3 bar maximum. You do it with a simple plastic bicycle pump.
It's just an idea, because I haven't thought about trying this in the present tense, in the near future, yes.

Taking only the concepts of the previous example, it is clear what can be expected from the "spawn" jajajajaj !! :bounce:
It is not complicated to build, and I say it because I have manufactured with tools and materials of the house, more complicated things. The problem is to approximate the best possible energies for common materials ... an error and PUM! Goodbye to Hectmarr, (or part of my face). :shock:
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Last edited by hectmarr on Tue Aug 27, 2019 10:18 am, edited 1 time in total.
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Re: Two-stage hybrid

Unread postAuthor: Moonbogg » Fri Aug 16, 2019 10:00 pm

That all makes sense. I can see the convenience of doing this to enable more power. It would be a real innovation in this hobby if you made something like this. I don't think I've ever heard of one before and certainly haven't seen one.
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Re: Two-stage hybrid

Unread postAuthor: D_Hall » Sat Aug 17, 2019 12:05 am

You almost certainly do not need the second ignition system. The piston moving to the left will adiabatically compress the mixture in chamber B and chamber B will ignite much as a diesel engine will. Voila.

That said... DANGER, WILL ROBINSON.

It is worth noting that you're playing around with a system very similar to a 2 stage light gas gun. I suspect you're aware of this given your naming of the concept. With this in mind I'll point out that a 2 stage light gas guns routinely achieve pressures on the order of 130,000 psi. I do not expect your gun to achieve such, but I would not be shocked to see pressures on the order of 1,000 psi out of your gun. Much depends on the details, mind you, but you're playing a very dangerous game.
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Re: Two-stage hybrid

Unread postAuthor: hectmarr » Sat Aug 17, 2019 1:38 am

I am aware of the danger involved in "playing" uncontrollably with not so low pressures and things that can be fragmented.
At first I considered the auto ignition of the mixture in the "B" chamber, it is a matter of trying, and trying to learn about this possibility. The other option is double on, as it is in the drawing.
The plan is to start with very little pressure, and see how it behaves, how it sounds, and analyze what is destroyed. I mean compressing 1X or 2X, to start.
In fact, the diagram lacks some elements, such as the spring to expel the burnt gases after firing, and the other piston. I will upload a more complete drawing as soon as I can sit down to do it.
I had no idea of the "two-stage light gas guns", I'm looking for information on the web.
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Re: Two-stage hybrid

Unread postAuthor: jackssmirkingrevenge » Sat Aug 17, 2019 9:55 am

The elusive two stage hybrid!

We spoke of it before but good to see that you are seriously contemplating it!

You almost certainly do not need the second ignition system. The piston moving to the left will adiabatically compress the mixture in chamber B and chamber B will ignite much as a diesel engine will. Voila.


Agreed. Very interesting to see what will come out of this, high supersonic velocities are definitely a possibility.
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Re: Two-stage hybrid

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Re: Two-stage hybrid

Unread postAuthor: hectmarr » Sat Aug 17, 2019 10:19 am

jackssmirkingrevenge wrote:The elusive two stage hybrid!

We spoke of it before but good to see that you are seriously contemplating it!

You almost certainly do not need the second ignition system. The piston moving to the left will adiabatically compress the mixture in chamber B and chamber B will ignite much as a diesel engine will. Voila.


Agreed. Very interesting to see what will come out of this, high supersonic velocities are definitely a possibility.


You are absolutely right, I had forgotten this two-stage cannon that has been discussed. :wink:
What I intend to do is the same as that, but for the first stage, mixture of butane and air. It is an adaptation of that idea with much less energy for obvious reasons.
I'll upload something else about this project.
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Re: Two-stage hybrid

Unread postAuthor: hectmarr » Sat Aug 17, 2019 4:06 pm

Enthusiastic about this project.
Here a schematic drawing of the elements of the future prototype.
The intermediate spring, between the two pistons, is for cleaning the two burnt gas chambers. When the cameras are compressed, the whole set of the two pistons and the spring, behave as one thing. When it is fired, chamber "B" is exposed to atmospheric pressure because the rupture disk is no longer there, and the spring sends the piston to the end, leaving that chamber with zero volume. The chamber "A" remains with the burned gases trapped in it, but when the burnt gas exhaust valve is pressed, the spring expands and the piston reaches the top, leaving the chamber clean. It is clear that when the hybrid is not compressed, the spring is expanded and the two pistons are attached to the ignition. On the contrary, when the hybrid is compressed, the spring is fully compressed. The function of the hollow rod is to maintain approximately the atmospheric pressure between the two pistons.
The burned gas elimination system is almost the same as I use in all the autonomous hybrids that I have built, and avoids the worst defect of this type of weapons, the "complication" of having to connect valves, disconnect it, and pump to clean and clean. be able to shoot again Sometimes it seems that they are operating an old submarine in an emergency situation jajaja :)
For the rest, I think of using the cartridge system, which contains the rupture disk, the ammunition and the seal o'ring.
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Re: Two-stage hybrid

Unread postAuthor: jackssmirkingrevenge » Sun Aug 18, 2019 8:36 am

Why did you retain the automatic ignition? Don't you think it will auto-ignite once a certain compression is achieved? The auto-ignition temperature of butane is almost twice that of diesel but I think that a hybrid-mix driven piston should have no problem achieving that...
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Re: Two-stage hybrid

Unread postAuthor: hectmarr » Sun Aug 18, 2019 10:07 am

jackssmirkingrevenge wrote:Why did you retain the automatic ignition? Don't you think it will auto-ignite once a certain compression is achieved? The auto-ignition temperature of butane is almost twice that of diesel but I think that a hybrid-mix driven piston should have no problem achieving that...

I think that autoignition has a minimum compression threshold. I do not like the idea of ​​being "bound" by this issue, to have to perform tests limited to this minimum amount of energy ... In other words, with the automatic ignition system, I can compress the hybrid, at 0, 5X, and it will work, (in the initial tests, surely). If I eliminate the possibility of having the electronic ignition in the combustion chamber "B", it would not work, with low test pressures.
On the other hand, by regulating the distance of the contacts "C", in the drawing, I can determine at will, the point that I want to turn on the camera "B". Longer, turn on later on the piston stroke, shorter, turn on earlier. This is to make it work safely. I imagine that if you pass the prototype the basic tests, you could turn off the ignition of the "B" chamber, and let the mixture self-inflate.
I am studying this issue and it seems that self-ignition occurs when the temperature of the butane-air mixture reaches 900 ºc, which surely corresponds to a fairly high pressure achieved very quickly.
 Tell me what you think of this strategy ... :roll:
Another important issue. I have noticed that the piston movements in hybrids, like the ones I have in my weapons of the "Autonomous Hybrid" series, have a lot of strength but relatively little displacement. The geometry of the chamber cylinder and piston are fundamental. I think it should be rather large in diameter, because variations in volume can occur with less longitudinal displacement.
Example:
If I consider a volume of 50 ml of combustion chamber, the internal diameter of the chamber is 2.5 cm, (area of 5 cm2), the length is 10 cm. If in this case, the piston can move 3 cm, the volume variation of the mixture is 30%.
If the 50 ml are in a combustion chamber of 5 cm, of internal diameter, (area of 20 cm2), the length of the chamber is 2.5 cm. The variation in volume in this case could reach 100%. I have to carefully determine this aspect. :?
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Re: Two-stage hybrid

Unread postAuthor: mrfoo » Sun Aug 18, 2019 10:21 am

a fairly high pressure achieved very quickly.

This is the principle a "fire piston" works by; its fuel, charcoal, auto-ignites slightly hotter than butane. Fire pistons work at a compression ratio of around 25:1, significantly higher than that of a diesel engine.

If you wanted to fire at a lower pressure, you could use diethyl ether as fuel. It's what model diesel engines ran on, and as an air-fuel mixture it has a significantly higher energy density than the equivalent mixture of butane.
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Re: Two-stage hybrid

Unread postAuthor: hectmarr » Sun Aug 18, 2019 10:39 am

mrfoo wrote:
a fairly high pressure achieved very quickly.

This is the principle a "fire piston" works by; its fuel, charcoal, auto-ignites slightly hotter than butane. Fire pistons work at a compression ratio of around 25:1, significantly higher than that of a diesel engine.

If you wanted to fire at a lower pressure, you could use diethyl ether as fuel. It's what model diesel engines ran on, and as an air-fuel mixture it has a significantly higher energy density than the equivalent mixture of butane.

25-1, quite a compression ratio. Very good data.
I am trying to use butane because it is easy to get, and it comes in small bottles that we use to crease the lighters. Diethyl ether works, as you tell me, but it is difficult to get, and more expensive. I have "played" with this fuel, in a small jet engine that I have built in the past. I used it because it boils at less than 50 ° C. The disadvantage is that it is very volatile and the vapors ignite with an almost "magical" facility.
Actually, self-ignition is not what I pursue. What I need is to pump at less pressure, but get a little higher firing energy.
Thanks for the idea, and the info.
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Re: Two-stage hybrid

Unread postAuthor: Moonbogg » Sun Aug 18, 2019 1:14 pm

I'm enjoying this thread. I like the input from a variety of people. Reminds me of the good old days when the forums were more active and people got excited about new ideas. I hope this things works. Might I suggest safety glasses, some thin leather gloves and perhaps a safety T-shirt...
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Re: Two-stage hybrid

Unread postAuthor: hectmarr » Sun Aug 18, 2019 2:43 pm

jajajaja :D yes! you're right. It would add a small bunker made of old wood, old cushions and some thick acrylic, (so that I can see what happens, which is the only interesting thing in all this).
Seriously speaking, I agree with you. I really enjoy, like you, the fact that those who are interested, help, in several aspects, because I really do not have enough knowledge of physics, mathematics and engineering to be able to leave a more complicated design round and secure.
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