Reynst Drum

[Mike Kirney]

This old steel drum is 34" tall and 23" across. I burned a 3" wide hole in the centre of the bottom with my torch and tried to get a little pile of burning pine to pulse, but with no luck. I upturned the drum and poured a few ounces of methanol onto the underside of the top. I put it back over the fire and there was a momentary "whooosh" of flame (too fast to for me to capture on film), but I think it was just enough to set up a mild pulsation. Check out the puffs of smoke:

http://home.ca.inter.net/mkirney/drum3.wmv

[Mike Kirney]

Tried the drum again, but with a few ounces of stale chainsaw fuel from last year. I didn't put the can over the fire like I said I would because the idea sort of scared me, and it was hard to build a decent fire with all those bricks taking up room. I think the hole in the top is too small because the fire kept going out, even when soaked with gasoline. I did manage to get a couple of exciting "whooshes" when I poured gas into the hole, but my digital handicam was no good in the dark. I'm going to re-read Hanks article in JetZILLA and look for clues there.

[Bruno Ogorelec]

Michael,

I think you should improve the sealing. I doubt you can induce the kadenacy breathing with the inevitably leaky boddom of the thing. Try sealing it with clay or something.

Bruno

[Mike Kirney]

I raked the ground as smooth as I could and I had dirt piled up all around the bottom during the nighttime test so the sealing was pretty good I think. When I placed the drum over the fire it would die down almost instantly, but when I removed it, it would flare right back up. To me, this says 'lack of oxygen'. I think I will try some methanol in an old baking tin to see if that makes a difference. If that doesn't work then I will enlarge the hole to 4" diameter, and if that doesn't work I think I will make some holes around the periphery like in Hank's JetZILLA article. I read his post last night that claimed Reynst made a 3.5 gallon pulse jar that could be heard 6.5 miles away. Mine is about 61 gallons so hopefully it will excite some interest at CFB Petawawa, which is about 20 km from my residence.

[Andrew Parker]

Mike,

I have wondered if there is any relationship between the cone of fire in the jam jar experiment and the quarter wave. If there is, perhaps the end correction formula for sound waves in tubes, d=0.61r, comes into play when determining the size of the orifice. I thought I might play at being a mathematician/engineer and develop a formula for determining orifice size. This is what I came up with:

ro=radius of orifice, ri=internal radius of cylinder, li=internal length of cylinder, lc=corrected length of cylinder, or, lc=li+0.61*ri

ro=0.61*ri^2/lc

So, with an internal radius of 11.5" and an internal length of 34", the corrected length would be 41" and the orifice radius would be not quite 2" for an opening of just about 4".

I don't know if it is relevant or correct, but it was fun trying to figure it out.


Andrew Parker

[Tom]

just an idea.
won't you need to weight the drum down, as when you finally get some combustion in there, is there a possibility that the expanding gas will lift the drum off the grond, even if by only a few mm?
T.

[Mike Kirney]

So, with an internal radius of 11.5" and an internal length of 34", the corrected length would be 41" and the orifice radius would be not quite 2" for an opening of just about 4".

I don't know if it is relevant or correct, but it was fun trying to figure it out.


Andrew Parker

Those dimensions I quoted were exterior, but the difference is negligible. I think a 4" opening would improve combustion. If using a flat pan of liquid fuel doesn't help things, enlarging the orifice is the next step.

[Mark]

just an idea.
won't you need to weight the drum down, as when you finally get some combustion in there, is there a possibility that the expanding gas will lift the drum off the grond, even if by only a few mm?
T.

I just did a straight tubed brass lamp with bamboo artwork on it about 2 feet tall and 4.5 inches wide. The hole was too small. It lifts off and never gets the chance to pulsate. The K-bang effect is how I would describe it. I wonder how a 55 gallon drum would do filled with methanol vapor?
The way I like to think of it is, if you condense your gaseous reactant into a liquid equivalent and visualize several tablespoons of high explosive. Like a tablespoon of liquid oxygen and anything flamable woud probably separate your hand from your arm.
I read of a man trying to weld a 55 gallon drum with flammable gas inside and it killed his son who was next to him. I wonder how many tablespoons that was? I once saw a balloon cooled with liquid nitrogen and it shriveled to a mere teaspoon of liquid and then it repressurized and became the balloon again.
Mark
Mark