Odd Metal jars

[Mark]

I've made a few of those shapes where the molecules "do a lot of calculations per second." It's almost as if they can sense confinement and another way out of the vessel. I wonder how it would behave if you capped one of the ends/escape routes, if it would still go bang or the flame front advance too slowly then to go exponetial? When I was about 9 my older brother told me I could catch a bee in my hand and it wouldn't sting me if I kept the light out. So several times I overcame my fear and cupped my hand quickly over the top of a dandelion and held a honeybee for several seconds, feeling it walking around, before shaking it from my closed hand. But then I got careless and let a crack of light in near my pinky finger and got stung as the bee tried to escape toward the light. While I didn't do the experiment enough times to actually prove this theory, it does seem very much like/analogous to the above apparatus you have built. ha
One thing I recall is putting/sandwiching a large washer in the front and at the "back bell" near the neck down of a plumbing pipe contrived typical pulsejet shape. In this way the combustion chamber/cylinder had a washer at either with an exhaust tube leading off in typical pulsejet fashion, vaguely resembling the top part of your apparatus. It too would gunshot when lit, which was kind of fun to marvel at and think about what was going on.
Another thing I tried was just misting/priming with methanol a typical pulsejet shape without capping or valving the front end and nothing inside. The flame front would make a slight whoop or weak pop as it traversed the length and that was it, methanol is snappy stuff. But if you ever so lightly held a sheet of paper over the front end capping it, you could get it to bark by lighting the tail end, the flame front sensing an obstruction and the reaction going fast enough to trick the duct into thinking the end was sealed solid. Or perhaps better said that the particles know beforehand what they are going to do. ha
Or maybe it's like the meter stick and the sheet of newspaper layed over it experiment where you strike it and the stick snaps in half instead of just rising off the table. Strange vague comparisons I know.
One thing that might have a slight chance is to pollute some of the air in the top chamber, perhaps slowing down the reaction or possible "flame dart core ignition" of the fuel/air mix so that a feedback/communication between the two vessels gets a chance to stabilize.
Neat stuff you are trying, I've always liked the discipline of odd metal jars.
http://www.physics.org/interact/physics ... index.html

[PyroJoe]

The little pipe between the two jars can be unthreaded and various lengths of pipe can be tested (without the second jar).
A 20" pipe makes a nice engine, though it does outrun the rate the alcohol can produce useable vapor.

[PyroJoe]

It is a little blurry, but here is a picture of the reynst setup, This was taken several weeks ago, and the gap is shown here about 150% open from where it is now.

[PyroJoe]

It has been some time since I posted the original pictures (page 12), here they are once more:

Cork gasket replaced with steel wool.

[PyroJoe]

Interesting bit about Thrust from Wikipedia:

The forward thrust is proportional to the mass of the airstream multiplied by the velocity of the airstream.

[larry cottrill]

Interesting bit about Thrust from Wikipedia:

The forward thrust is proportional to the mass of the airstream multiplied by the velocity of the airstream.

That is not exactly correct. Thrust is determined by the massflow of the airstream (say, kg/sec} multiplied by the relative velocity of the airstream (e.g. metres/sec). What we are concerned with is the mass passing a point in the duct (or engine) per unit time, and the velocity of that gas in passing that point. In other words, it's the velocity relative to the engine shell, not relative to the surrounding territory. It's the Zucrow rocket equation from 1946, though it was probably quantified much earlier by somebody.

Note that this simplified form of the equation assumes that all the thrown mass is accelerated from a standing start (relative to the engine), as in a rocket where everything is self-contained. The real question we have to answer is "How much can you increase the stream momentum in one second?" That is jet thrust.

L Cottrill

[PyroJoe]

Should we see this in UFLOW? A pulse of Mass Flow, with a corresponding Mach number alongside, traveling down the tail?

I was looking at Mikes Pockey Locky(2?) engine in UFLOW and noticed the attributes that stood out were a strong Mass Flow with a corresponding Mach Number pulse that matched nicely. It had a clean travel down the tail duct.

Even the Pressure pulse corresponded well.

I really should upgrade to NUDiS. UFLOW crashes so much. ha

[PyroJoe]

Wikipedia
on Deflagration:

"In free-air deflagrations, there is a continuous variation in deflagration effects relative to maximum flame velocity. When flame velocities are low, the effect of a deflagration is the release of heat. Some authors use the term flash fire to describe these low-speed deflagrations. At flame velocities near the speed of sound, the energy released is in the form of pressure and the results resemble a detonation. Between these extremes both heat and pressure are released"

[PyroJoe]

COMBUSTION IN POROUS MEDIA

BY
Prof. Dr. Mohammed Hamdan
&
Eng. NABEEL ABO SHABAN

"FLAME PROPAGATES WHEN THE RATE OF HEAT RELEASED FROM THE REACTION IS HIGER THAN THAT OF HEAT TRANSFER TO THE SURROUNDING MATERIAL"

[tufty]

Wikipedia on Deflagration:

I wouldn't trust wikipedia to tell me the sun will rise tomorrow morning.

[PyroJoe]

Tested 1/2 steel, 1/2 aluminum metal jars this eve. 2.59" I.D.x5" tall approx .43" opening. The steel bottom one runs longer and is more reliable. The aluminum bottom one will only run about 7 seconds max.

The weight savings is significant. Really light little things. The steel bottom one will begin to dance sometimes. I guess it is light enough the intake cycle pulls it a fraction of a mm off the table each time, then slams it back down with the pressure cycle.

For the most part it was a pressure fit of top over bottom. uneven heat often would expand one and the jar would pop open. Solved the problem by using 1/8" rivets, two arranged opposite each other.

Will test a 3" ID one soon. These are becoming light enough, that I may wish to build a suitable balsa boat to work with. My heavy steel 3"IDx6" moves a small toy car chassi but not very quick or far. This new type should have things zipping right along.

Joe

[Mark]

I am curious what raw materials you are using for the top and bottom bi-metalic wonder. It certainly is good food for thought, how the aluminum top works, perhaps wicking away heat better or not heating up as fast as an aluminum bottom would? Are you using something like a soup can and a Coke can or what? Seems it would be really fun to make one as light as possible, maybe even a flexing lid or bottom would be of some benefit on certain designs.
It's funny that your jar is lifting off the table ever so slightly. One would probably freak out if it lifted off by some negative pressure event/means or design. ha
I have some thin-walled titanium tubing, 1.75 inch diameter and .020ths which is fairly light, the three foot length has a strange feel/lightness to it. Maybe instead of steel and aluminum, a titanium and aluminum chimera would be something to consider. I have another length of 2.5 inch diameter titanium pipe a little thicker but still very light. I heated the sides with a torch and it turned a pretty rainbow color.
Long live odd metal jars.

[PyroJoe]

The aluminum is from a Monster energy drink can. The java type (yum). ha The steel is cut from the bottom of steel ether cans. It takes some work, but the java can be force fit over the ether cans.

[PyroJoe]

Here is the 3"X6" jar on a chassi. She travels about 8 to 10 feet per attempt. Still burning the coating from the inside of the jar. This may take over a dozen good runs to clear the smoke from the inside. I do think the steel is slower to transfer heat and prevents the fuel from creating a rich condition. Much as submerging the bottom of jars in water to cool the fuel pool.
Joe

[Mark]

I recall a fellow selling alcohol burners made from aluminum cans and he charged a bit more if you wanted them pre-sanded with fine sandpaper to get the coating off, which as you have mentioned tends to smoke until the paint and resin coating is all burnt off.
But if you buy laquer thinner it will yield silver cans without much effort. One funny thing though, if it is cold out the laquer thinner seems to be ineffectual. But if it is warm out, the coating will come off easily.
Here's an old dusty can of Red Bull I just got out of my garage, but I have never tried it, just picked up the can somewhere I guess. Anyway, with a paper towel and a dab of lacquer thinner, the paint and resin coating will come off easily, like magic. I just now swabbed a few spots/sections to illustrate with the Red Bull container. You can make beautiful silver cans. ha
The can I just did doesn't look super silver because I just took a second to wipe it and some of the dissolved paint and gum re-dried or perhaps there's a slight remaining resin on the can. I guess a clean second wipe with a new piece of paper towel and thinner would be in order to get the last bit of hazy/sicky residue off. I imagine you could clean a can in seconds flat though.
http://www.hotworldcustoms.com/images/p ... c-thin.jpg