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Staged combustion chambers.

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: psycix » Fri Sep 11, 2009 1:13 pm

jagerbond, though your idea requires airtight projectiles, it might help igniting high mixes, as extremely high mixes make it hard to jump a spark.
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Unread postAuthor: Hubb » Fri Sep 11, 2009 1:24 pm

psycix wrote:...extremely high mixes make it hard to jump a spark.


Yes and no. Larda runs his 200x hybrid using the following system:

Larda wrote:Because of the high pre-ignition pressure i cant use a normal spark gap, instead i use a thin wire that is connected to a relatively low voltage power source witch makes it possible to ignite the fuel-air mixture.
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Unread postAuthor: psycix » Fri Sep 11, 2009 1:54 pm

I know, he has to run that system because it is nearly impossible to jump a spark at 200x mix. His system simply glows, it doesnt spark.
And jagerbond's system is just an alternative.
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Unread postAuthor: Technician1002 » Fri Sep 11, 2009 1:57 pm

I wonder if an RC glow plug will hold the pressure. :?:
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Unread postAuthor: psycix » Fri Sep 11, 2009 2:01 pm

With good threads, I guess so. They are able to take a good punishment from the engine cycle for prolonged periods.
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Unread postAuthor: Hubb » Thu Sep 17, 2009 10:02 am

Besides the one post JSR linked to, has anyone else ever tried a staged combustion type launcher? This topic has led me to do more research into these devises (the V3 and ram accelerators) and I feel that it is quite possible to accomplish as it is intended.

From my research, I see a V3 design being much easier to accomplish than a ram accelerator. I have been gathering the data and making diagrams of what I believe will work. I'll send this data to inonickname first for him to view. If he sees fit, he can post it here for others to see.
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 17, 2009 11:08 am

Hubb wrote:I have been gathering the data and making diagrams of what I believe will work.


Do you predict though the gain in performance will be worth the effort compared to say a hybrid (or whatever it is you call those combustions with a burst disk and a pressurised chamber these days ;) )?
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Unread postAuthor: Hubb » Thu Sep 17, 2009 11:13 am

I got a chuckle out of that.

To answer the question - no, not initially. I do however predict that as this type of combustion launcher proceeds in this hobby, it will get better and better, eventually leading to a 1x combustion outperforming a hybrid made to the same sizes.

Now, I can definitely foresee a hybrid being built as this will have tremendous amounts of increase, again, if built right.
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 17, 2009 11:26 am

Personally I think that if the worthwhile potential were there we would see analogs in the powder-burning world, which to my knowledge don't exist.

Even the great Gerald Bullwho built some of the most extreme cannons ever used a single powder charge.
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Unread postAuthor: Hubb » Thu Sep 17, 2009 12:12 pm

Having a powder charge and having a flammable gas charge are apples and oranges. Similar, but not the same.

If a V3 type launcher were to be built using powder charges, my prediction would be that the initial charge would go as intended, but the additional chambers would be turned into a bomb.

But say it is designed with an initial powder charge and each additional chamber is charged with flammable fuel. I would tend to think that the projectile would have an initial velocity faster than the burn rate of the gas charges and, therefore, would be as if the gas charges are not even there. The round would just blow right by them.

Now, in a completely flammable fuel design, the initial velocity would be much lower than the speed of the flame front of the fuel. As the projectile passes, it ignites the additional changes, which produce another initial velocity added to the first one - and so on and so on - each one gaining an increase in velocity up to and beyond what a single chamber powder gun would produce. In a ram accelerator, this is exactly the case and those things have reached hyper velocities in hybrid charged hydrogen/oxygen chambers at only 5x.
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Unread postAuthor: Technician1002 » Thu Sep 17, 2009 12:47 pm

I believe the step velocity and step pressure diagram for the V3 showed the charges were timed to prevent the column of gas in the barrel from dropping in pressure from expansion and cooling from expansion. It would work in steps but the final result would more resemble a rocket in maintaining a constant high acceleration force for the length of the launch but without the burden of carrying the weight of the fuel.

Due to the burn rate of the fuel, in order to have combustion well started as the projectile passed, the ignition was electronically timed.

In a ram accelerator, compression heating of the gas to very high temperatures and using a light gas is the combination that gives them very high energy and efficient energy transfer from a large slower mass to a smaller mass.
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Unread postAuthor: Moonbogg » Thu Sep 17, 2009 5:05 pm

I am doubting a staged combustion will work much at all and heres the reason. The pressure from the second or third combustions will be weak because it will just head back down the barrel towards the initial chamber. So you would probably only get about half the potential force from those additional chambers. You would need a way to close off the barrel behind each new combustion for it to do much.
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 18, 2009 1:37 am

Bored out to 31cm and firing the Peenemünder Pfeilgeschoss out to an incredible 151 kilometres, the K5 Glatt obtained performance levels far in excess of what the V-3 ever achieved, using a shorter barrel and firing a heavier projectile.

Granted, powder and gas burning launchers might not be completely analogous, but I think that it would be better to devote more attention to perfecting the projectile as was done with the K5 to optimise performance. As MrC discovered recently, the importance of projectile design is often ignored and the effect on performance can be dramatic.

Just my €0.02 of course ;)
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Unread postAuthor: Technician1002 » Fri Sep 18, 2009 1:48 am

Moonbogg wrote:I am doubting a staged combustion will work much at all and heres the reason. The pressure from the second or third combustions will be weak because it will just head back down the barrel towards the initial chamber.


The theory is the pressure drops as gas expands and cools. This limits the pratical length of a barrel as the restriction to flow by the barrel provides a pressure gradient along the length of a long barrel. The staged combustion is to keep the pressure high in the vicinity of the projectile for a longer distance. The acceleration would in theory be like a staged rocket sled where it didn't carry the propellant, but the propellant was tossed into the rocket nozzle as it traveled along the length building speed the entire way.

The fact that blast goes the other way is proof positive that the blast is increasing the pressure at the location of the blast much above the existing pressure. It could be enough to both stop the forward mass of gas from the chamber (possibly sonic or above in speed) stop it and reverse the flow. The pressure required to do that also gives the projectile an additional push. :D
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Unread postAuthor: Pookydarts » Fri Sep 18, 2009 2:31 am

How about jaegers idea with the 'o' ring above and below the chamber extended up the barrel multiple times like inonicknames idea by making a 'rocket' length projectile more than half the length of the barrel with four or five 'o' rings and (at 1x) ignite the whole bloody lot simultaneously so that there is pressure 'waiting' to jump into the barrel/expansion chamber and augment the ordinarily decreasing pressure behind the projectile.

[Edit:] Hey! That might work in a pneumatic! :idea:

Or just make an expansion chamber 100x the volume of the barrel so the pressure decrease is minimised? :wink:
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