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Spring-piston exhausted hybrid chamber

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: POLAND_SPUD » Fri Jun 25, 2010 1:44 am

back-flow
I don't think I get it ? Couldn't you use a check valve ?? sure a flow restriction could work to some extent but remember that it works in both ways

2x 3-way valves - If I could get the electronic timing circuits I'm thinking this
this will work...

you might also use an piloted valve and connect its pilot port directly to the chamber... provided that the valve switches when the pressure inside the chamber is, let say 30psi (when propane is injected) it should work quite well
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Unread postAuthor: CS » Fri Jun 25, 2010 11:57 pm

I'm just thinking as the check valve is closing, will this happen: "Movement of pressurized air in the direction opposite to which it was pushed out of the device. "
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Unread postAuthor: POLAND_SPUD » Sat Jun 26, 2010 3:39 am

Movement of pressurized air in the direction opposite to which it was pushed out of the device
lol if I understand you correctly you are wondering how much time it would take for a check valve to close ?

probably not much... there is bound to be some dead space between the check valve and the DCV so that should act as a buffer


Wouldn't it be a good idea to place the chamber inside the propane tank ?? I just realized that this will both cool the chamber and keep the propane warm
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Unread postAuthor: CS » Sat Jun 26, 2010 6:15 am

Right now I figure chamber volume in ratio with the dead space is 100:1, no worries?

I'm not thinking the effect would come in enough magnitude to cool the chamber, but what do I know?

For cooling the chamber I'm thinking a recirculating ice water chiller and copper tubing wound around the chamber. Would like something more portable though.
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Unread postAuthor: POLAND_SPUD » Sat Jun 26, 2010 6:55 am

I hope that a check valve + dead space + flow restriction should be enough to solve this
anyway I am going to use tubing that is rated fairly low (for example to 100-150 psi) so i think this will work as a safety burst disk

portable
yeah, that's why I want to use propane as the coolant... well not to mention that I don't feel like lugging around a large propane tank with me just to fire 20-40 shots

What is more since my design is valveless some propane will be lost before the next round gets stuck in the detent... I am hoping that this will be enough to both purge the chamebr and cool it down

ohh and finally I just realized that it might be a good idea to use a glowplug for ignition... it will make a lot of things easier... it's a lot simpler and I wouldn't have to worry about timing as it will ignite as soon as propane & air reaches the right mix (though it might not be perfect :? )
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Unread postAuthor: CS » Sun Jul 11, 2010 1:26 pm

Making progress, changed up the valve design. The piston will be able to move a 1/2" or so before opening. This transition will allow for propane/compressed air to be turned on/off from the pistons movement.

For fueling I'm thinking of using a pneumatic cylinder to meter the propane, then it'll be displaced like a syringe. The compressed air will just be regulated on/off setup. Propane of roughly 1/25th the proportion, has to be more precisely metered because after all I'll be using the same style regulator for the compressed air, and propane source. Also since the propane meter will be displaced I figure that will be all the more volume that doesn't diluted by compressed air, from a metering sense.


I hope that a check valve + dead space + flow restriction should be enough to solve this
anyway I am going to use tubing that is rated fairly low (for example to 100-150 psi) so i think this will work as a safety burst disk


The source pressure should never come close to equalizing with the chamber's pressure. If that happens won't gas have every tendency to circulate with the source?

The valves I have are 24vdc 8w, is it customary to use a variety of different types of batteries in a system? For instance I got some 18 volt whatever amp rechargeable batteries, for electric drill, could they be used with say AA batteries?

^If I can scrounge the bats, I've got some roller micro switches. Something like this,
Image
, attached to the chamber pistons movement to create the on/off phase for the switch->solenoid valve..
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Unread postAuthor: BigBang J » Mon Jul 12, 2010 12:25 pm

Is there a significant difference between venting the chamger before refueling and not venting the chamber before refueling?
I mean is there a big advantage to be gained, using 7x - 10x fueling?
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Unread postAuthor: Gun Freak » Mon Jul 12, 2010 12:26 pm

Yes, you have to get all of the combustion-product-thingys out of the chamber before you try to fire it again or it won't combust.
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Unread postAuthor: SpudBlaster15 » Mon Jul 12, 2010 1:26 pm

BigBang J wrote:Is there a significant difference between venting the chamger before refueling and not venting the chamber before refueling?


Venting is important if you're looking for consistent results. In theory, you can maintain the post combustion atmosphere and simply add an additional atmosphere of compressed air, but in reality, trapping a volume of non-reactive gases in the chamber is impractical. Atmospheric diffusion and mixing will always contribute a small (Unknown) quantity of oxidizer, which will throw off your fueling calculations enough to have a significant effect on launcher performance.

Additionally, the combustion products are comprised largely of gaseous H<sub>2</sub>O, which will condense and create potentially severe corrosion issues if left to build up and linger in the chamber.
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Unread postAuthor: pat123 » Mon Jul 12, 2010 1:48 pm

what about something like this? when the part of the chamber on the left side of the piston ignites it pushes the piston to the right venting that side and vice versa.
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Unread postAuthor: BigBang J » Mon Jul 12, 2010 10:54 pm

I don't see that as being very practical, if I am seeing this correctly, when the left chamber combusts it throws the piston al the way to the right side, so you would want to put a stop so that the piston doesn't pass your right side meter entrance. Also I would think that you would lose significant pressure due to the piston venting one chamber will cause the volume to of the chamber to double and the pressure to drop in half. Also I think you would have to install a check valve between the barrel and the right and left piston valves or you will have pressurized gasses from one side of the chamber trying to enter the other side when the chamber piston tries to exuast.

Thats what I see.
What do you guys think?
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Unread postAuthor: CS » Tue Jul 13, 2010 1:24 am

Pat, personally I wouldn't use that setup quite simply for the fact it'll compromise an inline design. Could be wrong, but I'd see your design have a wobble strafe with the flow directions opposing each other perpendicular to the barrel. I would say one chamber may not satisfy my RPM desires, but in that case I'll probably use metal components, and multiple rotating chambers and a single barrel (like this) What I am building now will allow me to observe the RPM/functionality, from that a design with say 6 chambers it'll mainly be a multiple of cost not complexity. If it means anything I see where your going with your diagram there, just the particulars don't hash out for my purpose, soup!

SB delineated why I'm displacing the chamber volume with this spring loaded piston. (To answer your first question BigBang)

I figure my buna orings will hold out for a while, but what material should I be using in a design that can handle the heat? PTFE,aflas,kalrez?
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Unread postAuthor: BigBang J » Tue Jul 13, 2010 7:01 pm

CS, I think the piston idea inside of the chaber to exhaust is a great idea! I am working on a design right now based off of your idea.
Thanks for the idea :)

Also what strength do ya'll think the spring would need to be for a 5x mix to compress the spring completely?
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Unread postAuthor: Hotwired » Tue Jul 13, 2010 7:17 pm

BigBang J wrote:Also what strength do ya'll think the spring would need to be for a 5x mix to compress the spring completely?


How long is a chain of paper dolls?

Roughly 75psi is the pressure of the gas, how much surface area is it working on?

Use that to find the force from the gas on the piston then find a spring which when compressed or almost compressed will produce an equalising force.


On another note you don't need a spring that powerful.

You only need to sweep the chamber after the pressure has dropped, that's all the resistance you really need to overcome with the spring.
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Unread postAuthor: BigBang J » Tue Jul 13, 2010 8:14 pm

Hotwired wrote:
BigBang J wrote:Also what strength do ya'll think the spring would need to be for a 5x mix to compress the spring completely?


How long is a chain of paper dolls?

Roughly 75psi is the pressure of the gas, how much surface area is it working on?

Use that to find the force from the gas on the piston then find a spring which when compressed or almost compressed will produce an equalising force.


On another note you don't need a spring that powerful.

You only need to sweep the chamber after the pressure has dropped, that's all the resistance you really need to overcome with the spring.


Yeas I know that the force does not need to be very strong, but I have not done any calculations for springs before as far as determining so much pressure on this surface area equals this and so I need a spring with a whatever rating of so many whatevers. :?

O!, and a chain of paper dolls is approximately, 55.376 Bicrons
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