backfiring alchy stove
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Julian Dean
(hambone) - F

Locale: New Jersey
backfiring alchy stove on 02/13/2012 22:32:19 MST Print View

Ive done a little bit of tinkering around building a few alchy stoves, but they have always been by template or direction. the other day i started just messing around with a few old cans laying around and coming up with designs of my own. the one thing that im having trouble with is that most of the stoves are backfiring like old jalopys. what causes this to happen in the stove and how do i prevent it?

Kevin Beeden
(captain_paranoia) - F

Locale: UK
re: backfiring on 02/14/2012 05:50:50 MST Print View

A bit hard to say without seeing the stove design in question, but in chimney-style stoves, I've found that it's due to inadequate airflow through the burner, so the flame front moves back into the body of the burner. More, or larger intake holes may help.

One other common problem with chimney burners is too small a chimney opening, which causes 'flame lift-off', due to excessive chimney velocity, so the flame front rises above the hole, and often snuffs itself out.

For jetted burners with an open central fuel reservoir, too small an opening can prevent priming, as air cannot get into the reservoir to sustain the initial burn before the jets are established. Not a backfire problem, but a related issue.

John Donewar
(Newton) - MLife

Locale: Southeastern Louisiana
Re: backfiring alchy stove on 02/14/2012 11:18:54 MST Print View

Julian,

Can we see some pictures and have some construction details?

What kind of "alcohol" are you using for fuel?

Party On,

Newton

Jack Hoster
(OrlandoHanger) - F
Re: backfiring alchy stove on 02/14/2012 22:43:19 MST Print View

Backfiring Stoves? Video Please.

Julian Dean
(hambone) - F

Locale: New Jersey
re: backfire on 02/15/2012 13:26:59 MST Print View

im making basic chimney styles. im willing to bet the problem im having is that not enough air is getting to the flame to keep it going. i could probably punch a few more holes to help this out. is there such a thing as too many air intake holes? some of the designs ive seen have large numbers of holes.

im using kleen strip slx to fuel these things.

ill get some pictures up as soon as i can, probably not till later tonight

John Donewar
(Newton) - MLife

Locale: Southeastern Louisiana
Re: re: backfire on 02/15/2012 21:11:26 MST Print View

Julian,

"I'm making basic chimney styles".

What size is the opening in the top of your chimney type stove and how tall is your stove?

The info below is copied and pasted in part from Adventures In Stoving.

http://www.adventuresinstoving.blogspot.com/2011/12/diy-alcohol-stove-design.html

"There is a relationship between height and opening size, so lesson five: For a practical stove, the optimal ratio between height and opening size is approximately 1:1".

Here is a link to a thread on Zen Stoves concerning chimney type stoves.

http://zenstoves.net/ConstructionStep2-FuelPort.htm#Step2cChimney-LPSBStove

I hope some or all of this helps.

Party On,

Newton

Hikin' Jim
(hikin_jim) - MLife

Locale: Orange County, CA, USA
Re: Re: re: backfire on 02/16/2012 11:01:16 MST Print View

John Donewar wrote: > The info below is copied and pasted in part from Adventures In Stoving.
http://www.adventuresinstoving.blogspot.com/2011/12/diy-alcohol-stove-design.html
"There is a relationship between height and opening size, so lesson five: For a practical stove, the optimal ratio between height and opening size is approximately 1:1".
Hi, John,

That quote is mainly for open jet (semi-pressurized) type stoves. Chimney stoves can be a little shorter relative to the width of the opening because air is coming in via the ventilation ports and not just through the central opening.

Therefore, for chimney type stoves, the central opening should generally be a bit larger than the height of the stove. In other words instead of a 1:1 height to opening size ratio, you want something more like 1:1.1 or 1:1.2 (those are just made up numbers showing that you want something greater than one to one; don't take them as proven ratios!).

I think Kevin's assessment is dead on: backfiring is caused by insufficient air flow. The opening size, while important, is a secondary issue.

As I've experimented with the FeatherFire as well as another chimney stove with a simmer ring, I've noticed "burping" or "backfiring" going on as I decrease the airflow.

I think that insufficient air flow is the probable cause of the burping in Julian's stove.

HJ
Adventures In Stoving

Edited by hikin_jim on 02/16/2012 11:04:33 MST.

John Donewar
(Newton) - MLife

Locale: Southeastern Louisiana
Re: Re: Re: re: backfire on 02/16/2012 13:39:28 MST Print View

Hi Jim,

Thank you for clarifying that piece of information for all of us. ;-)

I was only trying to share what I thought would be helpful information from stove sites regarding Julian's question. It now seems obvious that I am no stove expert. LOL

"Therefore, for chimney type stoves, the central opening should generally be a bit larger than the height of the stove. In other words instead of a 1:1 height to opening size ratio, you want something more like 1:1.1 or 1:1.2 (those are just made up numbers showing that you want something greater than one to one; don't take them as proven ratios!)".

Please help me understand the info below copied and pasted from ZenStoves concerning the Mini Zen Chimney/Sideburner Stove.

http://zenstoves.net/ChimneyStove.htm

"Chimney Stove made from two 5.5oz V-8 Cans

(25mm top hole, 6 1/4" vents centered 1/2" from top , 3/8" top pressed flush with 1.5" bottom)..."


Is this a different type of stove than what Julian is building?

If I am reading and understanding this correctly the Zen stove is 1.5" tall and the opening is 25mm or approximately 1". How does that correalte to the specs that you posted? Am I comparing apples and oranges?

Party On,

Newton

Edited by Newton on 02/16/2012 13:40:19 MST.

Hikin' Jim
(hikin_jim) - MLife

Locale: Orange County, CA, USA
Re: Re: Re: Re: re: backfire on 02/17/2012 01:18:50 MST Print View

Oh, heck. I wrote that backwards, didn't I? Cr@p!

What I meant is that if you have a chimney type stove, the stove can be taller for a given opening size than with a semi-pressurized stove. With a semi-pressurized stove, you want about 1:1 height to opening width. With a chimney type, you can increase the height without depriving the stove of air because you're bringing in air via the ports. I wrote it all totally backwards in my first response [severely embarrassed look]. Ack! It's a little tough to increase the opening beyond the width of the can. :)

The Zen stoves site sounds reasonable in terms of the proportions they're describing.

Sorry to have muddied the waters,

HJ
Adventures In Stoving