My pepsi stove “breathes”, any ideas?

[Ken Walsh]

So being the curious, semi-enterprising type I made a little pepsi-can alcohol stove (open-jet type). Anyway, it seems to work so far, obviously need to do stand and windscreen optimization still.

The question is, my stove seems to breathe when operating, that is the flame hieght varies at about a once per second rate. Obviously there is some sort of pressure oscillation in the stove. Sometimes at the pressure peaks the flame separates so far from the nozzles as to nearly self extinguish. At the troughs the flames on the jets get very small. I’m guessing this isn’t what is suppose to be happening but I can’t quite figure out what might be doing it.

Anyone got any ideas? Or perhaps does someone know of a forum with a lot of dedicated stove makers some place?

Ken

[Robert Miller]

Ken,

It sounds as if you are building pressure between the walls.

Did you notch the bottom of the inner wall?

Did you glue the inner wall to the upper and lower sections?

[Douglas Frick]

>Anyone got any ideas?

Hmmm. Most of mine do this too. I just thought it was natural.

[Eric Noble]

I’ve made a number of stoves and they all seem to “breath”. It sounds like yours is more of a “heavy breather” than mine. I have only made one open jet style the other dozen have been closed jet.

[Ken Walsh]

Thanks for everyone’s input!

Yes, it seems as if for some reason the pressure in the inner/outer wall chamber is oscillating. I notched the inner wall in three places at the bottom with a hole punch and I did put a bead of JB weld along the top of the inner wall when assembling to prevent any vapor leaks up there. I didn’t bother with anything like that at the bottom since it is notched anyway. The design I used was the open jet stove on zenstoves.net and I pretty much did it straight up as the instructions state with the exception of adding the JB weld seal along the top (Pepsi-G stove suggests this).

I’m glad to hear this isn’t that uncommon. If it doesn’t effect the efficency it’s probably no big deal. It sounds like from various sources it almost doesn’t matter exactly how you burn your alcohol (open pan, open jet, closed jet, chimney, etc.) as long as you get the pot height and windscreen right.

Most of the time the breathing is pretty mild, but a few times the oscillations have been quite large – stove still kept itself lit though.

One theory I’ve got is that perhaps there aren’t enough jet holes and pressure builds so high that vapor manages to force its way back through the notches at the bottom into the central chamber and thus vents the outer chamber and the pressure plummets. Then more fuel vaporizes and the cycle continues. A poor analogy would be the way a nearly full 2 liter bottle glugs when you pour it as air rushing in and liquid pouring out compete and set up an oscillation. Current design has 24 holes made with #74 drill bit – maybe I’ll make one with 32 and see if there is a difference (Pepsi-G uses 32). Another difference with Pepsi-G is the notch sizes – and Pepsi-G specifies different notches for different types of cans so maybe that’s related.

Was cool to boil a pot of water in my sink with the little stove anyway!

Any other ideas or suggestions greatly appreciated!

Ken

[paul johnson]

Try asking John Austin aka Tinny over at MiniBullDesigns.com your question. I’m sure that he knows the answer to it and can tell you what to do to correct it.

[Ken Walsh]

So since I really can’t stand searching forums and finding a thread unresolved this post is for the archive…

It turns out it would appear my initial theory is correct, the problem is there is too much pressure in the sidewall and evenually the vapor bubbles back into the inner chamber. Following Paul’s advice I asked Tinny and he said he’d seen this before and believed it to be caused by having too much heat and or pressure as a result of having too little in the way of jets and described an oscillation mechanism similar to what I was hypothesizing.

I viewed the stove while pointing my head lamp into the center and sure enough as the flame heights reach their peak a bunch of vapor bubbles enter the center of the stove and then the pressure drops and the flame height drops. Then the process starts over.

A friends stove with more and larger holes doesn’t have the problem.

So, it sees like a “breathing” stove is the result of too few or too small holes for the jets. I may double the number of holes on mine as an experiment.

Ken

[Douglas Frick]

>So since I really can’t stand searching forums and finding a thread unresolved this post is for the archive…
[…]
>So, it sees like a “breathing” stove is the result of too few or too small holes for the jets. I may double the number of holes on mine as an experiment.

Thanks for following up on this.

[Ken Walsh]

Well I just doubled the number of holes and tested it out and sure enough the “breathing” effect stopped!

Ken

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