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Ram Accelerator

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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Ram Accelerator

Unread postAuthor: Hubb » Fri Nov 30, 2007 6:48 pm

Over the past few days, I've been looking into a way to really accelerate a projectile(i.e. I want to break the sound barrier, too).

A ram accelerator is a combustion cannon that has several different chambers. A round is accelerated by the primary chamber then, as it passes through the additional chambers, the gasses from the primary chamber ignite these additional chambers. This creates thrust to constantly accelerate the projectile.

Image
This image should explain it better.

I posted this in the combustion section but I don't see why, with a little creativity, this could not be applied to hybrid's as well, to get the round moving.

Any thoughts?
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Unread postAuthor: windshrike » Fri Nov 30, 2007 6:58 pm

It should work; even if the second chamber detonates so the gases are in front of the projectile and the detonation doesn't follow it, that would still create a venturi effect and increase velocity.
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Unread postAuthor: Hubb » Fri Nov 30, 2007 7:37 pm

The sub-caliber round should generate shock waves and vacuums and such to cause the gasses to ignite behind the projectile.

Now, I did say sub-caliber. From the research, the round should be stabilized with either guiderails or fins and should be shaped like a bullet. And, the individual chambers are separated by diaphragms (or burst discs). It is not limited by just one extra chamber. I was thinking more like five extra chambers along the barrel.

I mentioned hybrid in the first post. I don't see why all the chambers couldn't be charged hybrid style (which is what originally was intended).

I also thought about going with a railgun, but that's for another day.
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Unread postAuthor: Maniac » Fri Nov 30, 2007 8:16 pm

i see one problem keeping all the gasses from becoming liquids i would suggest a tee with a chamber fan in the ram accelerator chamber.

also how large are you thinking this gun is. and what woul you use for blast ventts just angled holes in the pipe?
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Unread postAuthor: Hubb » Fri Nov 30, 2007 8:24 pm

Of course there would be a fan. The main chamber would be set up like an advanced combustion, but suited for hybrid combustion (which is probably where it is going anyway).

As far as the size, the bigger the better, right :D . Seriously, I probably wouldn't want to go no bigger than a 1.5" barrel. Being a sub-caliber cannon, the round would probably be around 1" diameter, give or take. I wouldn't know on the chamber size. I'll have to do more research and some math to see what I can come up with.

Blast vents would be nothing more than angled holes.
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Unread postAuthor: LikimysCrotchus5 » Sat Dec 01, 2007 1:05 am

I think that this is a "simple yet affective" idea that can be easily done to a combustion and hybrid for better performance. I could see that though the burst disk will cause a decrease in velocity as it tries to pass through it. But this could be easily avoided by using aluminum foil because it is very penetrable.
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Unread postAuthor: Hubb » Sat Dec 01, 2007 1:10 am

That is the general idea, using something that could easily be penetrated by the projectile, which needs to be pointed anyway.

To add; in the original post, I stated I really wanted to accelerate a projectile (mach). I've never seen it done with a combustion, and believe it would be possible if these principles are applied (which is why it was posted in the combustion section).

I wonder if it would be possible to reach mach 2 with the right sized hybrid?
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Unread postAuthor: LikimysCrotchus5 » Sat Dec 01, 2007 1:22 am

Yea i think it is but it depends much on the configuration and the consistency of the hybrid. I think maybe Fnord's piston hybrid may be able to with this design.

Now what i was thinking was that you could apply this same principle with a hybrid but if you were to use a hybrid mix (2x mix in a ram accelerator) you can achieve much greater lengths. And you could always use different mixes.

But what would be a problem using this with mixed in the accelerator is that you would need a burst disk that is strong and able to hold back pressure so this would decrease the velociy of the projectile. But if it were to very penetrable but can withstand a great deat of pressure, then mach 2 should be achievable.
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Unread postAuthor: Hubb » Sat Dec 01, 2007 1:29 am

As far as hybrids are concerned, what I was thinking was putting, say, a 4x mix in the main chamber. Throughout the ram accelerator (barrel portion) each chamber would hold a 2x mix. There should be no problem with the round penetrating a burst disc to reach the remaining chambers, especially since it will increase its velocity after each chamber.

Through physics, yes, the round will be slowed down by penetrating the discs, but I wouldn't think it would affect it much, due to it gaining the velocity back (and then some) when it passes through the chamber.
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Unread postAuthor: Ragnarok » Sat Dec 01, 2007 10:24 am

hubb017 wrote:To add; in the original post, I stated I really wanted to accelerate a projectile (mach). I've never seen it done with a combustion, and believe it would be possible if these principles are applied (which is why it was posted in the combustion section).

I wonder if it would be possible to reach mach 2 with the right sized hybrid?

1: BigBang's Crusader recorded muzzle velocities of right about 1700 fps from an advanced atmospheric MAPP combustion launcher with golf balls.
2: Killjoy's FEAR hybrid has recorded velocities of 2700 fps

Of course, those numbers are a little debated, but it's not impossible that they actually did that. So I have to say you probably can achieve some pretty neat velocities.
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Unread postAuthor: bigbob12345 » Sat Dec 01, 2007 10:35 am

Sounds good to me I think it would work amazingly
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Unread postAuthor: jackssmirkingrevenge » Sat Dec 01, 2007 10:38 am

As far as I can tell simple using a bigger chamber will have the same effect.
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Unread postAuthor: boilingleadbath » Sat Dec 01, 2007 3:45 pm

From the wikipedia article:

Ramjets try to exploit the <b>very high dynamic pressure</b> within the streamtube approaching the air intake lip. A reasonably efficient intake will recover much of the freestream stagnation pressure, to support the combustion and expansion processes. Most ramjets operate at supersonic flight speeds and use one or more conical (or oblique) <b>shock waves</b>, terminated by a <b>strong normal shock</b>, to decelerate the airflow to a subsonic velocity at intake exit. Further diffusion is then required to get the air velocity down to level suitable for the combustor.

...inefficient (less than 600 seconds) until the airspeed exceeds 1000 km/h (600 mph)

Ramjets top speed is limited by disassociation to about Mach 5.5.

...optimized for one designed speed and altitude


Seems like a promising venture (mach 5.5 is a significant improvement over the limits of hybrid spudguns, IIRC), but one that could be very difficult to implement.
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Unread postAuthor: Hubb » Sat Dec 01, 2007 6:35 pm

jackssmirkingrevenge wrote:As far as I can tell simple using a bigger chamber will have the same effect.

In a ram accelerator, the round will gain speed significantly throughout the length of the barrel until it exits the muzzle. By using a standard configuration, the round may gain some speed while traveling the barrel but it will not be like that of a ram accelerator.



boilingleadbath wrote:Seems like a promising venture (mach 5.5 is a significant improvement over the limits of hybrid spudguns, IIRC), but one that could be very difficult to implement.

This design would be very difficult to implement. I've looked into it further and it would appear tests have never been conducted on a launcher that does not begin the round at supersonic levels.

If built, it would definately be something that would take some time and effort and may not even work for our applications, but imagine a potato flying mach5.5!!
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Unread postAuthor: jimmy101 » Sun Dec 02, 2007 11:05 am

Hubb077, you might want to consider replacing the "ram" chamber with just an evacuated chamber.

As you know, one problem with a mach round is getting the gases moving at mach speeds. Gases really don't like do that if they are rubbing against something that is stationary, i.e., the barrel.

Mach speed in the combustion chamber will be significantly above mach speed in air at normal temperature since mach speed is a function of gas temperature. In the combustion chamber, mach speed will be significantly greater than 1100 FPS. GasEq will estimate mach speed in a combustion chamber, I get roughly 3,000 FPS for propane + air at 1x. However, gas flowing at a couple thousand feet per second through 2" or so diameter pipe is going to be extremely turbulent, resulting in pretty significant back pressure.

The other gas you have to worry about is the air (or fuel + air) in the barrel in front of the round. This gas also has to be accelerated to the speed of the round. But, this gas does not have the advantage of being heated to high temperature, therefore mach speed will be a lot lower in the barrel in front of the round. At high projectile speeds you will get heating of the gases in front of the ammo but you may not get enough to get the mach speed up enough to make much of a difference.

One way to avoid the problem of having to accelerate the gases in front of the round is to simply not have any gases there. Put a burst disk in front of the round (or at the end of the "ram" chamber) and one at the muzzle. Evacuate the air in the barrel. When the projectile breaks the first disk the vacuum in the barrel sucks the projectile forward and there are no gases in front of the projectile that need to be accelerated. When the shell reaches the muzzle it bursts the muzzle's burst disk. Only when the muzzle's burst disk is ruptured do you have the problem of accelerating the air in front of the ammo to mach (or greater) speed.
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