How does this work?

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Post by Mark » Sat Feb 07, 2004 2:55 am

I'd have to agree, you would want to start small and even then remember if anything can go wrong, it will. If you have ever listened to sounds/screams of the astronauts sitting in their rocket on the launch pad fried in the cabin atmosphere of pure oxygen, one little spark, (and this brainstorm of design marvels had a lot of people on the committee), you have to wonder what dangers might lurk with pressurized vessels. They went back to using regular air in the cabin.
Metal embrittlement sometimes occurs if the metal gets too cold. What if you sprang a leak, would you or your surroundings burst into flames? How would you stop the leak? There are a host of things you might want to consider before using your own pipe bomb design. And sometimes it will work a hundred times before a bunch of little things all combine/add to form a different outcome. What can go wrong could become a matter of life or death. "God is in the details." (Einstein out of context)
I don't know if methanol would react with the metal in the container, with aluminum, methanol can generate hydrogen or rust the system, methanol is corrosive to iron and steel, and it is not allowed to be stored in aluminum. Maybe after some use, the threading on your pipe would become weaker, chipped and rusting? I have a terrible time with galvanized pipe rusting from methanol. You might make a homemade zip gun!
If you drop a chunk of magnesium in methanol, it will fizz like an Alka Seltzer and produce hydrogen. I remember doing this. Maybe you could just put some methanol and magnesium in a tank a screw on a fitting! Calculating the pressure might be tricky though but you could have a really peppy pressurized fuel system, if you are feeling lucky!!! I bet hydrogen and methanol would make for a good pulsejet fuel. But then there would also be magnesium methoxide formed, kind of poisonous and I don't know if your fitting would cake or clog or something adverse. There are just lots of things to think very hard about before risking your life. You don't want to be mentioned in the Darwin Awards.

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Post by cbromano » Sat Feb 07, 2004 8:28 am

Look- no offence to anyone, but saying I’m a future Darwin award winner is a bit harsh. I had no intention of just throwing together a piece of crap pipe bomb. My lack of knowledge of building pressure vessels aside, I still believe it would be a decent idea. To increase efficiency, fuel injectors using liquid fuel, appear to be the way to go. Due to their precision delivery. Fuel injectors require a pressure behind them by means of a pump. By pressurizing the fuel using another substance with a lower vapor pressure, a simple, constant pressure is maintained.

As for safety, I planned on doing more then just screwing pipe together and filling it up. I also was thinking of testing it by over-pressurizing it with water, but I would just use a long, vertical, length of pipe filled with water to test it.

Brittleness caused by temperature would not be that big of a factor, mainly because not that much gas will be produced to fill the pipe.

To be honest I didn’t think about corrosion of the galvanized pipe. Would there be a simple liner to cover the exposed pipe? I am thinking along the lines of rubber or plastic. I also think that the entire setup would not have to last that long. Pipe is cheap- at first signs of deterioration, replace the whole setup.

Lastly, no air would be present in the system to ignite like Apollo 1. Any leaks could be handled by keeping the tank submersed in water. The propane would bubble out the top and the methanol would just turn into an aqueous solution. This would also kill any chance of a fiery stream of combustible material.

Sorry to vent, I’m not all that well rested at the moment and probably not thinking straight. I might be wrong on a lot of things but to me something that is so simple and cheep cannot be that bad. The bits of pluming would be about 5 bucks and that is really attractive to me. Not to mention anyone could make a tank like this using cheap bits found at a hardware store. CO2 or nitrogen is hard to find when you only need very small amounts, a lot of people already have propane for their grills.

CB Romano
I don't wish to know everything.
I just wish not to be ignorant.

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Post by Viv » Sat Feb 07, 2004 2:28 pm

Good engineering is about how it fails as well as how it works, when it goes horribly wrong what happens, who dies.

Yes I take your referance to the darwin awards as well put but you are designing something that can only fail badly, ok put it under water but if the vessel splits it will lift all the water out in one go! so I am afraid it will still get you.

As to the Darwin awards I always think of the guy who stuck a JATO rocket pack on the back of his car, I can imagine the excitement of it all, finding it, fitting it doing the test run, and then the sudden dread as he realised it was a solid rocket with no off switch.

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Post by Mark » Sat Feb 07, 2004 3:25 pm

A pipe of that thickness would probably hold quite a bit of pressure. The threading is kind of coarse, maybe with pipe sealant or teflon tape you could get a good seal for your ~ 100psi of propane. It might slowly leak though, but it would "probably" be safe. It's just like pulsejets though, you can say this and that will happen, but until you really try it, you are just making an estimated guess.
I can't see anything wrong with the concept, yet it is wonderous the extent of things that have been designed and some completey charming malfunction occurs that you would have had to been psychic to know about in advance.
I think of flurocarbon refrigerant prototype gas was it, the next morning the one guy says to his friend if he used the gas or took it out of the compressor unit and he said no. Where had their gas gone? It had polymerized into a waxy substance, our friend Teflon.
Would the zinc coating in the galvanized pipe react with the propane or methanol releasing gases causing an overpressurization? The other day I was just toying with guar gum. They had in the past used it as a diet aid because it swells and creates a sensation of fullness. On my containers it says keep away from children. One fellow mixed some in a glass and drank it, it gelled in his esophagus suddenly, and he died and it was taken off the market for that use. The plant lives in a very dry climate, it uses the million chained polymer to pull and hold water. Anyway I had put a tablespoon in some warm water and it jelled instantly into a solid mass. I put a lid on it and forgot about it, the next day the metal lid had bowed way out and it was fortunate I released the pressure, it was sitting next to my computer. That's how to make bomb without really trying.
Magnesium will burn in CO2 and mixtures of Mg and liquid CO2 are more powerful than some military explosives. Mg will even burn with nitrogen. Gold won't dissolve in hydrochloric acid or nitric acid but mixed together it will attack gold. Maybe methanol and propane together could do something neither would by itself, if mixed in larger concentrations of a 50/50 mix. I just don't know myself, but I would keep it in the back of my mind.

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Post by Mike Everman » Sat Feb 07, 2004 5:27 pm

I'm pretty sure that in all of space and time, no being has ever said, or will ever say again, "The other day I was just toying with guar gum" as an anecdote to a discussion about pressurizing methanol with propane!

I don't see anything wrong with the idea, I'd tend to use a propane cannister rather than pipe fittings, but that's me. I don't much like a mix, but rather love the idea of a bit of propane to pressurize jet fuel, gasolene or meth. Just enough to maintain pressure, but under the vapor pressure of the propane, so no liquid mixing.

We propel aerosols with hydrocarbons in our every-day lives, but I still think a chemist should be consulted for any combination, to include the vessel material. Using an inert, non-reactive gas is of course the safest way to go if you don't want to ask a chem type.

No one thought you'd be dumb about it, CB, and I'm not talking about you here, but:

It does bring up an interesting point for the off-topic, which is "how do you know who you're talking to?" The rediculous handles people use, and lack of personal info; at least location in the world and perhaps age and profession make for a lot of wasted breath and time. I'd sure like to know if I'm lecturing a world authority in propulsion like a pseudo intellectual buffoon, or talking to a well spoken 8-year old that would have trouble squeezing the handle of a fire extinguisher!!! <GRN>
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Post by Bruno Ogorelec » Sun Feb 08, 2004 10:01 am

Mike Everman wrote:It does bring up an interesting point for the off-topic, which is "how do you know who you're talking to?" The rediculous handles people use, and lack of personal info; at least location in the world and perhaps age and profession make for a lot of wasted breath and time.
Hear! Hear! In the previous incarnation of this forum, I railed a lot against people who refuse to be what they are. This is completely, utterly unnecessary. I ahve been a public person -- very active on the Internet -- for eight years now, with my name, telephone number and even address on full display. With just a few basic precaustions, I have never had the slightest problem because of that. After eight years, it can't be just accedent. I always feel uneasy, talking to anonymous people. I wish everyone would stop that annoying habit.

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Post by sparks » Tue Feb 10, 2004 3:46 am

Finding small CO2 bottles is easy, at least in Sweden.
There was this very popular machine for making sodawater and other carbonated drinks some ten or fifteen years ago.
Many still use them, and because of that there are still many places where one can change the refillable CO2 bottles.
First the bottles was made of steel but now theres mostly Al-bottles about 30 cm tall and 5 cm wide weighing ~1.2kg full and 0.9kg empty.
Pretty useful (i made a beercanlauncher to send back the empty cans my neighbor used to leave everywhere).
The threads on the selfclosing valve are for some strange reason the same as many toilettes has on their inletvalve.....

My name is Peter by the way.

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