The Mythbusters made an episode were they did a test to see if a sewer explosion could send flying manhole covers. The did a small scale test were they made a combustion chamber with a looking window, simulating a sewer. On a first try they put the methane and ignited it and it combuted. On the seco...

It better and cheaper to use fuel that is already in gas, like propane or butane. Denatured alcohol has many additives that vary depending on the brand, so its inconsistent and if you used pure methanol or pure ethanol it would be too expensive.

You can also get adapt a syringe to a butane, propane or MAPP tank. I use a syringe for metering the fuel and it works great.

Would making a marx generator do the job of making the spark?

Looks very nice. I tried making one of those with this schematic:

Plan 2
http://www.personalarms.com/schematics.htm

But I could get the 1k to 200k transformer. Is there a way I could make my self the transformer?

The bottle is safer since it expands with the pressure. However a PVC chamber is rigid. Since none of the two was built for this usage you have to run the risk of a failure.

Here is how a bottle looks before exploding:
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That 3 million sue seems ridiculous, its like if I am shooting a potato to the street but a car passes and the potato hits the car, ricochets and hits my eye and I sue the driver.

Would it be a good idea to use hydrogen as a fuel for a cannon and if so like what percentage of hydrogen should there be in the CC.

Thats really bad. I glad most of the damage was repairable. Something similar happened to me but with hydrogen bubbles. I was pumbing hydrogen into a syringe with soappy water and when I ignited the buble my eye got spray with hot vapor and soap. Fortunately my eye just hurt for some minutes because...

This is my ignition setup: I made hole in the end cap and taped really well a long nose ligher. This works well in a spray n' pray. The flame won't burn the pvc if you light it quickly, plus if using deodorant the material build up won't let the flame burn anything.

I stuffed through the barrel a plastic bag then threw down a small rock. This works really well since the rock goes really fast and its really cheap since rock don't are free and you can recycle the bag

Thanks for the info I'll try that. EDIT: I tried it out, the syringe filling when horribly. When I filled it the syringe didn't fill properly, but I ended up with a small amount of liquid butane. I threw the liquid butane into the combustion chamber and lighted it after it turned into gas. The shot ...

I have an old empty butane tank from a long nose lighter. Would that work if I refilled it.

I made a "medium" spray n' pray cannon. Its not a a mini but not the normal size. The barrel uses 1in. pipe and the CB uses 2in. pipe. I was thinking of using the sering method for controling the fuel. The chamber has a volume of about 350mL. How much deodorant should I put in the chamber whith the ...