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Various Crazy, (But Feasible and Logical), Optimizations

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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Various Crazy, (But Feasible and Logical), Optimizations

Unread postAuthor: mark.f » Fri Nov 24, 2006 10:03 am

I've been getting back into combustion launchers lately, but not the standards.

After my first combustion craze which ended in the Last Blast, I figured it's time to start anew.

No more "pretty launchers" for me. I have a feeling that my next launchers will, quite frankly, scare the piss out of any federal agent who sees them. My up and coming hybrid has sooo many ball valves, hosing, and fittings, it looks like something out of a WWII submarine. But I've still got a charred and coated wooden stand, so it balances out.

For the optimized combustion I've got in mind for later, (maybe MUCH later, as I haven't totalled costs yet), it'll look like a tornado in a hardware store. Because I'm not going for ANY looks, I'm simply concerned with power and optimizing combustion.

First off, I want to discuss the first line of optimization I plan to install which is reactant chilling.

The chamber will be insulated, (on the outside), and the air and propane that goes in it will be chilled to the maximum I can get propane to go without liquifying. I really want to see subzero reactant temperatures in this thing.

Why?

Because chilling the reactants, which are both gases, increases the molar count at 1 atmosphere, effectively "cramming" as many fuel and O<sub>2</sub> molecules into the chamber as possible. I already have a good idea how I'm going to accomplish this, but it may be a <I>tad</I> pricy, but I'm willing to do it.

Second line of optimization is ignition. Rather than dual, triple, or quadruple spark gaps, I plan to utilize an idea mentioned by D_Hall on the SpudTech forums on jet ignition. May sound too high-tech, but I believe, and he even said, that it is well within the realm of a hobbyist. All it does is protrude a long jet of flame through the chamber to ignite nearly the entire length at once. If I were just to have one, I would obviously run the jet down the center of the chamber, but I don't plan on having just one...

Third and final line of optimization is turbulence. Turbulence increases the chances of DDT, so I believe it'll be beneficial. Many of you are now probably going "WTF?!?!? He wants DDT???" but no. I believe that DDT is bad, but just riding the line is good. Obviously, as you approach DDT, it means that your flame front gets faster in a shorter amount of time. So, therefore, we can assume that turbulence increases flame front propogation rate, which is good.

For the turbulence part, I plan to have two fans. One will be used for just venting and mixing, and then the second will be switched on to create turbulence by trying to interfere with the first fan's flow. I will have to be careful to place the second one to where it does not simply cancel out the first one's flow, (they're going to be the same type), but I think I've got the idea. Also, multiple jets, (from the ignition), should create turbulence if placed properly.

I plan to have a short enough chamber of a sufficiently small enough diameter to avoid any DDT. 50 atmospheres all of a sudden doesn't seem like something I want in even a welded steel chamber.

That's about it except for the fuel. For the fuel, I want to "push it" even more by making the mixture slightly lean. This way, I'm 100% sure there are no extra fuel molecules to absorb the energy of the combustion, and also to speed up flame front velocity even more.


Now that I'm done describing these things, let me remind you that this is not a hybrid. I call it a "super-charged" combustion gun. Basically, I'm just trying to increase the efficiency of our guns. This way, the best C:B ratio for <I>this</I> launcher may not be the average 1:1, but maybe we can get away with an even shorter barrel while maintaining higher velocities. Most of this stuff was "swiped" from the automotive energy. Why do you think "turbo-chargers" on cars take in cold air to the cylinders, (well that's one)? Also, the hemispherical cylinder doesn't create a jet, but it helps direct the flame front into the rest of the mixture better. That's another. Turbulence is created in an engine just due to the pure speed of fuel injection, compression, and ignition.

That's it! Tell me what you think, and I'd like to hear some more ideas if you have em! Just remember, I'll hear everybody's. A half-year ago, I would have regarded someone telling me to cool the fuel and air in a spudgun as full of BS. So don't be scared!!! Also remember that this can't be out of PVC, (not because of pressure, but because of the cooling part), so be reasonable in what you expect me to contruct. Steel is not as easily machinable by the average hobbyist as PVC is.
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Unread postAuthor: Recruit » Fri Nov 24, 2006 2:35 pm

What is DDT? All that I can think of is a pesticide that was banned in reference to DDT.
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Unread postAuthor: mark.f » Fri Nov 24, 2006 3:28 pm

DDT is deflagration to detonation transistion, and it is what happens when a flame front speeds up past the local speed of sound.
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Unread postAuthor: ammosmoke » Fri Nov 24, 2006 4:15 pm

Diam! Sounds cool, how much better do you think it will be than a standard combustion?
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Unread postAuthor: Recruit » Fri Nov 24, 2006 5:15 pm

Ok thank you for the explanation. Sounds good but make sure you have a blast sheild between you and that gun the first few times you shoot it.
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Unread postAuthor: rna_duelers » Fri Nov 24, 2006 5:33 pm

Well the idea will work aslong as you spend the time and the cash.And as for the cooling of the air thats simple.

Got a vacume pump?Well if you do run a series of small pipes that pass through an air tight container that is half filled with water and then the air is pumped out which lowers the pressure in the chamber and making the water boil thus making the pipes freakin cold.And the more surface area you have the better the more efficient the cooling is.I also stole this idea,its what is used in alot of refridgeration systems.

Also you could make a small intercooler,much like on a turbocharged/supercharged engine.If you have acces to compressed. CO2 then you can make a very effective cooling system.By simply blasting the extremely cold CO2 as it turns from its liquid state to the gas state it gets very cold.

Why not go the whole hog and use a dry ice cooler,used in drag cars to make the air extremely cold im talking -40C which.This usualy has an increase of anywere from 30RWKW-50RWKW on a 4 cyclinder car over the conventional air to air cooler.

Definitely go for a steel chamber of some sort.See if you can get an high pressure vesel container like a large oxygen bottle or diving air tank.


Some food for though and the cooler you can get the air the better.But aslong as your not turning your fuel into a solid its all good,not sure what temperature is need to do that but.
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Unread postAuthor: boilingleadbath » Fri Nov 24, 2006 6:20 pm

Might your aims of turbulance be better acheived by inserting restrictions, a-la flame-front-accelerator?
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Unread postAuthor: joannaardway » Sat Nov 25, 2006 6:22 am

Interesting... I was thinking about "supercharged" combustions as well.... (mostly inspired by BigBang's Crusader)

I was thinking about "insulation" of combustion chambers for more power... However that's to keep the heat of combustion in, rather than what you're attempting.

I thought that spraying the inside of the chamber with heat reflecting paint would probably do the trick quite nicely. If you really want to supercharge, that's probably a good port of call for you.

I don't know by how much it would help, but keeping in that extra energy should increase muzzle velocities by a few percent - perhaps more.

Just an idea.
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Unread postAuthor: mark.f » Sat Nov 25, 2006 7:19 am

ammosmoke wrote:Diam! Sounds cool, how much better do you think it will be than a standard combustion?

I think it'll be about the same, but I think that this design can get slightly higher velocities out of shorter barrel lengths.

Recruit wrote:Ok thank you for the explanation. Sounds good but make sure you have a blast sheild between you and that gun the first few times you shoot it.

It's not gonna be that much more powerful! If I have to I can tie a string to the ignition switch for remote ignition.

rna_duelers wrote:Well the idea will work aslong as you spend the time and the cash.And as for the cooling of the air thats simple.


I was thinking more along the lines of some refrigerant, some bendable copper tubing, a small compressor, and an expansion valve for the main line. Then, you just repeat the same set-up for the air and run that line right next to the refrigerant line insulated in some rubber and foil. This'll cool the air in it's own line, and then get cooled even further by the refrigerant line. Hopefully I can find some small compressors that I can use for this stuff, and I can basically just use a needle valve or flow regulator for the expansion valve.

boilingleadbath wrote:Might your aims of turbulance be better acheived by inserting restrictions, a-la flame-front-accelerator?

I thought about that, but the design of sticking two fans right in the middle of the chamber seems to be able to generate good enough turbulence. I'll keep this in mind, though, if it doesn't pan out quite as well as I thought.

joannaardway wrote:I was thinking about "insulation" of combustion chambers for more power... However that's to keep the heat of combustion in, rather than what you're attempting.

I thought that spraying the inside of the chamber with heat reflecting paint would probably do the trick quite nicely. If you really want to supercharge, that's probably a good port of call for you.

I don't know by how much it would help, but keeping in that extra energy should increase muzzle velocities by a few percent - perhaps more.

I good thing hit me when I looked at some of BigBang's cannons which had the inside of the chamber spray-painted as well. Keeping the heat in the chamber would be good for performance, too. Thanks for the tip, and I think I'll step up the insulation factor a little better.
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Unread postAuthor: pyrogeek » Thu Dec 14, 2006 5:18 pm

Lean mixtures are kind of hard to ignite, aren't they? Well, I heard of this lean burn technology they can use on cars where each chamber has a second attatched which acts as the ignitor. I'm in a bit of a rush, so that probably sounded incoherant, so I made a simple drawing in MS Paint.

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