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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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Hybrid design ideas

Unread postAuthor: Alanstone » Mon Nov 19, 2012 8:12 am

I would like to draw you attention to this patent: http://www.google.com/patents/us5921765

I am sure that this patent must have already been studied by those of you who are interested in hybrid design. It got me thinking as I have always considered the complex and cumbersome manner of hybrid refueling to be one the big reasons why more people don¡¯t build them. (That and burst disk and ammo reloading)

As I understand it, one of the problems with using N2O as an oxidizer is the amount of energy required to ignite the mix. Could this be improved by adding O2? I thinking a nytrox diving mix, mixed with butane. This offers the pressure of N2O of around X48 as a hybrid mix.

I am not sure whether the ignition problem can be overcome so I started to think along another line to generate a high compression hybrid mix. What if one were to use a CO2 shock to compress an air/butane mix? The idea is that you compress an air/butane mix using CO2 (X58). When combustion takes place the CO2 shock is reset. (sear type catch and release).

I also would like to add another idea. A valveless chamber where the ammo is the valve. Now this has been done aplenty with o-rings and so forth but what I propose is pressing the ammo into a washer with an interference fit. Obviously this would take some prototyping but I offer a HGDT scenario:

Chamber data:
Dia ¨C 2.4 cm
Length ¨C 3 cm

Transition data:
Disk failure ¨C 3500 psi

Propellant:
Butane
Mix ¨C 58

Barrel data:
Bore ¨C 1.25 cm
Length ¨C 120 cm

Projectile data:
Mass ¨C 7gm
Dia ¨C 1.2

Result:
Muzzle energy ¨C 597 J
Muzzle velosity ¨C 413 m/s

There is a lot I don¡¯t know. These are just rough ideas. Auto ignition, DDT and stoimetric mixes being some of them. Please be so kind as to offer your thoughts on these idea. I haven¡¯t done any diagrams as I am still teaching myself acad. If you want my ideas in diagrams I will do my best to accommodate you although, to me, they are self explanatory.
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Re: Hybrid design ideas

Unread postAuthor: jackssmirkingrevenge » Mon Nov 19, 2012 9:01 am

I hadn't seen that patent, interesting thoughts.

Alanstone wrote:As I understand it, one of the problems with using N2O as an oxidizer is the amount of energy required to ignite the mix. Could this be improved by adding O2? I thinking a nytrox diving mix, mixed with butane. This offers the pressure of N2O of around X48 as a hybrid mix.


If you're using oxygen, might as well go directly for an oxygen/fuel mix. I would avoid working with oxygen like the plague though, because of the inherent dangers.

What if one were to use a CO2 shock to compress an air/butane mix? The idea is that you compress an air/butane mix using CO2 (X58). When combustion takes place the CO2 shock is reset. (sear type catch and release).


You mean a piston driven by CO<sub>2</sub> suddently compressing a chamber containing a stoichiometric air:butane mix?

I doubt you could get it to autoignite, butane needs 405°C which you're unlikely to achieve. Have a look at fire pistons: http://en.wikipedia.org/wiki/Fire_piston

You might as well use diesel fuel.

I also would like to add another idea. A valveless chamber where the ammo is the valve. Now this has been done aplenty with o-rings and so forth but what I propose is pressing the ammo into a washer with an interference fit.


If you're using say lead projectile, they can be swaged into a cone to form a seal, here's some experiments I had made: http://www.spudfiles.com/forums/viewtop ... tml#309515
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Unread postAuthor: Alanstone » Mon Nov 19, 2012 4:09 pm

Quote: JSK
You mean a piston driven by CO 2 suddenly compressing a chamber containing a stoichiometric air/butane mix?
I doubt you could get it to auto ignite; butane needs 405°C which you're unlikely to achieve. Have a look at fire pistons: http://en.wikipedia.org/wiki/Fire_piston
You might as well use diesel fuel.

It’s not the “suddenly” that is important here although auto ignition has its advantages, negating DDT of course (it would be pretty cool to exclude the ignition side of things) the idea of the CO2 is to compress the mix rather than having to run to a compressor or spend time pumping up my chamber. I don’t mind paying in CO2 for that privilege. Back to the point in turn: Does an increase in pressure of an air/butane mix lower the ignition point? (From what I have read on spudfiles it seems harder to ignite a mix the more it’s compressed). In a N2O/ butane mix the ignition energy at 150 psi is more than 2500 J. At 600 psi its 6J. (if I remember what I read correctly). I haven’t found the answer yet but I really hope to find I can compress it enough to ignite it with a taser circuit.

The idea behind the O2 in the N2O/butane mix is to lower the ignition point to where our standard ignition methods would work while having the benefit of the 720 psi offered by N2O. Working with clean oxygen, like you said, is just unviable. It’s always in the fore front of my mind that the components to a design should be commercially available as far as possible and that is why I mentioned nytrox. Nitrox is an N2O/O2 mix developed for scuba diving at different mix ratios. I was thinking that you could choose a “safe” ratio as an oxidizer to add to the butane. Gaining the N2O pressure/liquid as a bonus of course.




With regard to the ammo washer idea: what if the “washer” acted as a piece of rifled barrel and set up the spin of the projectile. This way the ammo is spinning when it enters the smooth bore barrel. You determine the release pressure and the initial spin.

English is my second language so I ask that you excuse any gramatical errors I may make.
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Unread postAuthor: mobile chernobyl » Mon Nov 19, 2012 8:25 pm

What energy are you planning on using to re-compress the CO2 shock? You're going to be robbing a lot of the combustion energy if you're using that.

The "washer" interference idea is a good one as well - one that I almost pursued for a senior design project to meet my mechanical engineering degree's req's. I was going to incorporate that idea to make a semi auto hybrid more feasible.

Washer is a great idea, I was actually going to make it more akin to an "inverse obturating ring" that would be sandwiched in between the chamber and barrel using the barrels threads as the compression force to keep it in place.

It's still mainly a pipe dream right now, until I graduate and get a Bridgeport and lathe of my own lol.
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Unread postAuthor: Alanstone » Tue Nov 20, 2012 4:21 am

@JSR: Thanks for the links and the reply Jack. You have put and incredible amount of work out for the spudding community over the years. You work on the cartridge design is very good. I was really hoping that the ideas I shared could help you in some way in your designs. I don’t have a tool to my name so I will thrash this design out then have it manufactured. I can draw in acad now but the 3d is beyond me. Going to see if I can get sketchup under my belt for that. Jack what software do you use to do you sketches with?

@ mobile chernobyl: thank you for you interest and reply. I am planning on using the combustion energy to reset the shock. My thoughts were that even although this would use and waste energy it wouldn’t matter as the chamber pressure would be designed to accommodate it. Just add moar power! The initial combustion will take place at the CO2 pressure. Once that is overcome the piston will move back and catch again. The ball will only release when the fit between washer and ball is overcome anyway. It may even be a good thing that the chamber expands as the combustion takes place I don’t know.

Also your thoughts on how the pressure of the combustion is used to sandwich the washer is along my line of thinking. I am planning a hollow bolt which creates the initial seal using the initial mix pressure to sandwich the washer against the reducer metal into which the barrel is screwed. The bolt also locates and centralizes the ammo. Once the gun has fired the bolt releases and the spent washer drops through a slot in the bottom and the next one drops in. the bolt is moved back by an external spring allowing the new round to enter.

Do you have any knowledge with regard to the N2O/butane idea? If that can work the CO2 shock isn’t needed. I am ignorant with regard to gasses too. Does the N2O molecule need energy to split first so the oxygen can be used in the combustion or does it act like air as an oxidizer and only need energy it ignite the mix? Also is it a benefit if the mix gets ignited as a liquid or a drawback? If anyone can share light on that I will be grateful.
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 20, 2012 9:47 am

Alanstone wrote:It’s not the “suddenly” that is important here although auto ignition has its advantages, negating DDT of course (it would be pretty cool to exclude the ignition side of things) the idea of the CO2 is to compress the mix rather than having to run to a compressor or spend time pumping up my chamber. I don’t mind paying in CO2 for that privilege.


If I understood well, you want to create a sort of in internal combustion engine where instead of the cylinder compression energy coming from a flywheel, it will be driven by CO<sub>2</sub> in some sort of piston arrangement, but it will still rely on a spark for ignition.

I thought of something similar manually operated: http://www.spudfiles.com/forums/self-co ... ter,0.html

Image

The thought was that a single stroke could both dispense correct amounts of air and fuel and simultaenous compress them. Since you start of with a stoichiometric mix, no matter what pressure you go to it will always give you a good ratio.

Back to the point in turn: Does an increase in pressure of an air/butane mix lower the ignition point? (From what I have read on spudfiles it seems harder to ignite a mix the more it’s compressed).


A compressed mix means the air and fuel molecules are closer together. This means that if a spark needs to travel across 5mm at atmospheric pressure for good ignition, if you're working at 10 bar the molecules are now packed together 10 times more densely, so the ideal spark gap is not 0.5mm

In a N2O/ butane mix the ignition energy at 150 psi is more than 2500 J. At 600 psi its 6J. (if I remember what I read correctly). I haven’t found the answer yet but I really hope to find I can compress it enough to ignite it with a taser circuit.


Even with a simple lighter piezo you can ignite 15-16x reliably.

With regard to the ammo washer idea: what if the “washer” acted as a piece of rifled barrel and set up the spin of the projectile. This way the ammo is spinning when it enters the smooth bore barrel. You determine the release pressure and the initial spin.


I don't quite get this, perhaps it's a language problem... diagram perhaps?

English is my second language so I ask that you excuse any gramatical errors I may make.


Don't worry, it's better than some of the native speakers on this forum ;) what is your first language?

Thanks for the links and the reply Jack. You have put and incredible amount of work out for the spudding community over the years. You work on the cartridge design is very good. I was really hoping that the ideas I shared could help you in some way in your designs. I don’t have a tool to my name so I will thrash this design out then have it manufactured.


Epoxy castings are a cheap way of achieving complex designs without the need for specialised tools, but they need some thought and patience.

If you need some small custom parts machined the forum can help: http://www.spudfiles.com/forums/the-off ... 23135.html

I can draw in acad now but the 3d is beyond me. Going to see if I can get sketchup under my belt for that. Jack what software do you use to do you sketches with?


I spent most of my life using MS paint and Jasc animation shop, these days I have the option of using solidworks. 3D is not easy, it requires a different way of thinking, but practice and you'll get the hang of it. I recommed skipping sketchup and going straight to a "proper" program as the skills do not really translate.

Do you have any knowledge with regard to the N2O/butane idea? If that can work the CO2 shock isn’t needed. I am ignorant with regard to gasses too. Does the N2O molecule need energy to split first so the oxygen can be used in the combustion or does it act like air as an oxidizer and only need energy it ignite the mix? Also is it a benefit if the mix gets ignited as a liquid or a drawback? If anyone can share light on that I will be grateful.


Nitrous oxide needs to decompose in order to provide oxygen, and this requires heat, which is why for example in racing engines it is used to enhance the combustion that is already happening as opposed to being the main source.
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Unread postAuthor: Alanstone » Wed Nov 21, 2012 4:34 am

Quote:

Epoxy castings are a cheap way of achieving complex designs.

I have seen your work in epoxy and it is seems you can almost do anying with it. Because I have not considered the idea I get a bit nervous considering building something out of epoxy that should handle 3000 psi and maybe a 1.5 times safety factor while lasting a life time. Can that be done with epoxy? If so then this grasshopper is ready to learn master!

Quote:

If I understood well, you want to create a sort of in internal combustion engine where instead of the cylinder compression energy coming from a flywheel, it will be driven by CO 2 in some sort of piston arrangement.


Yes Jack you understood what I meant with regard to compressing the mix. After reading through the link you provided I realise I still have a lot of thinking to do.

Quote:

A compressed mix means the air and fuel molecules are closer together. This means that if a spark needs to travel across 5mm at atmospheric pressure for good ignition, if you're working at 10 bar the molecules are now packed together 10 times more densely, so the ideal spark gap is not 0.5mm

Did you mean that the spark gap gets smaller and therefore at 10 bar a 5mm spark gap would be 0.5mm? If not then what would the theoretical spark gap be at 10 bar?

Quote:

I don't quite get this, perhaps it's a language problem... diagram perhaps?

My first language is Afrikaans as I am South African. It is closer to dutch that any other language. BTB and I would kind of know what we are on about if he wrote in Dutch and I in Afrikaans. J

I did a drawing of my thoughts so far and have attached it. The ball and washer assembly would be replaced by a rifled piece of tube and projectile.
The lead projectile would be swaged into the small piece of rifled tube to produce burst disk pressure. Once the release pressure has been achieved the projectile will move down the rifled piece picking up the spin until it enters the barrel. The rifled tube could then be later be used again. (Sorry about the pic quality. Gets better when you zoom in. Also the design is far from complete, I just put enough detail to give you some idea of where my mind is at.)
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 22, 2012 2:29 am

Alanstone wrote:I have seen your work in epoxy and it is seems you can almost do anying with it. Because I have not considered the idea I get a bit nervous considering building something out of epoxy that should handle 3000 psi and maybe a 1.5 times safety factor while lasting a life time. Can that be done with epoxy? If so then this grasshopper is ready to learn master!


I have had quite a few failures along the way, but most of the time it was down to my own under-engineering, like using the thin aluminium tube from a printer cartridge as a hybrid chamber :roll:

The one problem I see with epoxy in hybrids is heat which tends to soften most material. Thus for an auto you would need to think about cooling, but otherwise with enough epoxy, 3000 psi is not an issue.

Image

Mostly epoxy and can hold 4500 psi safely ;)

After reading through the link you provided I realise I still have a lot of thinking to do.


If this is your first project, it's definitely quite an ambitious one.

Did you mean that the spark gap gets smaller and therefore at 10 bar a 5mm spark gap would be 0.5mm? If not then what would the theoretical spark gap be at 10 bar?


What I mean is that for a given energy source, the spark gap needs to get smaller as pressure goes up. For example, if a piezo cigarette lighter ignitor is fine for a normal combustion cannot with a 5mm spark gap, if you had to try it in a 11x hybrid (pressurised to 10 bar) it wouldn't work with the same gap - this is because there are now ten times more fuel and air molecules between the gap, so it is the equivalent of the spark trying to jump a 50mm gap at atmospheric pressure. This obviously it cannot do, so you have to compensate by making the spark gap smaller. For most of my high mix hybrids, the gap is usually around the width of a sheet of paper.

A good analogy is to look at the spark gap on a gas cooker which works and atmospheric pressure, and a spark plug which has to ignite a pressurised fuel air mix.

My first language is Afrikaans as I am South African. It is closer to dutch that any other language. BTB and I would kind of know what we are on about if he wrote in Dutch and I in Afrikaans.


Cool, I'm guessing then this project is inspired by restrictive gun laws?

I did a drawing of my thoughts so far and have attached it. The ball and washer assembly would be replaced by a rifled piece of tube and projectile.
The lead projectile would be swaged into the small piece of rifled tube to produce burst disk pressure. Once the release pressure has been achieved the projectile will move down the rifled piece picking up the spin until it enters the barrel. The rifled tube could then be later be used again. (Sorry about the pic quality. Gets better when you zoom in. Also the design is far from complete, I just put enough detail to give you some idea of where my mind is at.)


I can see what you're trying to do, the physics is sound but translating it in practice is going to need a lot of thought and effort. Is it something you want to do for the sake of it, or is there some sort of performance target you have in mind?
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Unread postAuthor: Alanstone » Thu Nov 22, 2012 2:35 pm

You are right there is still much thought that needs to go into this. The gun laws have a lot to do with it and although its not that difficult to legally own a weapon here now it has become much more difficult than it has ever been. I believe that in my country and in many others we are moving toward a disarmed society.

I stumbled across spudfiles last year December and the site and the people on the site stole my heart. I have developed a passion for this and it occupies most of my waking thought. Will I manage to build what I am aiming for? I don't know. But what I do know is that I have learned to draw with a cad program and am now learning about surface finishes, tolerances, oring groove design, threads and how to design and detail drawings. This all from the internet using my blackberry as my only connection. I am a clinical hypnotherapist and this is very far from what I have been studying for the last 12 years but its like I can't stop myself.

I want to keep on learning and understanding and putting into practice until I have done something I can feel proud of. I believe if I keep working at it, it will continue to take shape.

What I am aiming for:
A semi auto capable of a high muzzle energy.
Easy to refuel and easy to reload.

The compression of the mix need a lot of thought. Compressing a 1X mix to a high X mix without having to have access to specialized compressors or prolonged effort is something worth working toward for the good of hybrid design in general I believe. To find an alternative to burst disks allowing for semi or even auto functioning hybrids is also needed in hybrid design.

I think once there is options to these ideas the designing and building of hybrids will get the interest it deserves on this site.

There is an immense amount of brain power between the members on the site and the designs that have already been built have been absolutely astounding. This hasn't translated into the interest that hybrids deserve though.
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Unread postAuthor: Heimo » Thu Nov 22, 2012 3:18 pm

Alanstone wrote:You are right there is still much thought that needs to go into this. The gun laws have a lot to do with it and although its not that difficult to legally own a weapon here now it has become much more difficult than it has ever been. I believe that in my country and in many others we are moving toward a disarmed society.



exactly the reason I have grown a lot more cautious with this hobby, the laws around here...

for example I know that owning a .177 calibre airgun is legal without a licence, but for a .22 airgun you need a licence, this is why if I am going to make more "air-guns" <cough>hybrids<cough> it is going to be in the sub 5mm calibre range and then if they ever find it, I can claim it to be a air gun...(obviously it will look the part )

also I am fairly sure regular size normal potato cannons are considered firearms over here, but I have not herd of anyone getting busted with one, but I am being careful non the less...l
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Unread postAuthor: Alanstone » Thu Nov 22, 2012 3:35 pm

By "over here" do you mean RSA Heimo?
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Unread postAuthor: Heimo » Thu Nov 22, 2012 3:38 pm

Alanstone wrote:By "over here" do you mean RSA Heimo?


that is correct...
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 23, 2012 2:42 am

Quite a few members from SA have been through here, with the same ideas. )DEMON(, sumisukyo and spitfire spring to mind. And Heimo of course :)

Alanstone wrote:I stumbled across spudfiles last year December and the site and the people on the site stole my heart. I have developed a passion for this and it occupies most of my waking thought. Will I manage to build what I am aiming for? I don't know. But what I do know is that I have learned to draw with a cad program and am now learning about surface finishes, tolerances, oring groove design, threads and how to design and detail drawings. This all from the internet using my blackberry as my only connection.


Hehe welcome to spudfiles, it's not a forum, it's a way of life! I suppose most members here cannot look at a piece of tubing without wondering what they could shoot out of it. My advice though is to start small. Make a simple piece of shít mini combustion cannon, get a feel for it, then move on to bigger things.

I am a clinical hypnotherapist and this is very far from what I have been studying for the last 12 years but its like I can't stop myself.


Should have gone for engineering ;)

I want to keep on learning and understanding and putting into practice until I have done something I can feel proud of. I believe if I keep working at it, it will continue to take shape.


I think something like this would make a great first project:

http://www.spudfiles.com/forums/mini-hy ... 21655.html

It can be made for a minimum financial outlay using easy to find parts, and will give you a feel for hybrid power, use, parameters etc.

What I am aiming for:
A semi auto capable of a high muzzle energy.
Easy to refuel and easy to reload.


Cartridges.

http://www.spudfiles.com/forums/bach-bo ... 16882.html

I think these are the best solution. Hundreds of years of firearm development have so far proved this to be the case.
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Unread postAuthor: Alanstone » Sat Nov 24, 2012 1:17 am

@JSR: thanks for the reply. I am studying the links you sent me. About the patent I mentioned? The fuel mix the author mentions is a liquid fuel mix which he intends to ignite with a spark plug. My questions are: how does he do that without a catalyst and/or the required heat to convert the N2O? Or is it that the spark plug generates that amount of heat? Or is the liquefied fuel mix subject to different criteria for ignition? Do you know?

@Heimo: with regard to the 5.5 ammo I hear you. The second important criteria to that law is that it may not be above 6 ft*lb, is it even worth making a hybrid to accommodate the law then?
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Unread postAuthor: Heimo » Sat Nov 24, 2012 6:05 am

Alanstone wrote:
@Heimo: with regard to the 5.5 ammo I hear you. The second important criteria to that law is that it may not be above 6 ft*lb, is it even worth making a hybrid to accommodate the law then?


well hehe thing about hybrids they are only as powerful as you want them to be at a given time, meaning their power is easily adjustable if you adapt your mixes thus it can be legal if it needs to be at a given time... :D

the hybrid I am still dreaming about is something that is pump action and with every stroke of the pump, the correct amount of fuel is automatically injected for that given volume of air then for example you can have low mixes and high mixes with minimal effort other the amount of pumping involed
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