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Author Topic: Vertical stove pipe, sparks and pipe length  (Read 314 times)

Online Marko_Mrko

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Vertical stove pipe, sparks and pipe length
« on: November 13, 2017, 02:34:59 pm »
Unpacked the Atuk Kanguk for the upcoming trip, noticed a few spark holes. Would love to prevent that. Here are my thoughts, let me know what you think.

Here's my current set-up:
- Alaskan Kanguk 12'x12' with vertical stove pipe
- KniCo Alaskan
- Pipe cap made from the original spark arrestor (cut out the arrestor part as it clogged a couple of times)
- Spark arrestor made from 1/4" chicken wire in the top part of the damper (pic below):


Since that pic, I've actually added a second layer of chicken wire.

Here's my illuminating thoughts to... spark... a discussion:
 
1) Tents with a vertical stove pipe have an increased risk of sparks (as sparks can fall straight down). By comparison, angled pipe diverts sparks away from the tent (as long as the wind does not change).

2) Short pipe length increases the risk of sparks as it decreases the distance between canvas and pipe end. In particular, we dug out a stove well on the last couple of trips - shortening the stove pipe even further. I'm pretty sure that's the culprit.

3) I wonder if the pipe cap increases the risk of sparks in a vertical pipe set-up, as the sparks bounce off the cap and fall down.

Right now, my plan is to :
1) Stop digging a stove well.
2) Add an extra length of pipe. I have an extra set of the telescoping pipes. Both the bottom part and the top part can be fitted onto the assembled 4-piece pipe set. I'll likely add a set of screws to attach the two parts (the fit is not perfect).



If anyone has any other ideas or thoughts, would be greatly appreciated.

Cheers
Marko

Offline kinguq

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Re: Vertical stove pipe, sparks and pipe length
« Reply #1 on: November 13, 2017, 03:03:13 pm »
I use a lavvu with a vertical centre stove pipe. Adding a baffle to my stove completely solved the spark issue: no more spark holes after 5 nights last year. And I don't use a spark arrester at all.

Adding the baffle also made the stove more efficient (i.e. more heat per unit wood) and a better cookstove. I would highly recommend it.

Otherwise your other points seem true too. The cap might increase sparks falling on the tent as you note.

Kinguq.

Offline Bkrgi

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Re: Vertical stove pipe, sparks and pipe length
« Reply #2 on: November 13, 2017, 04:29:31 pm »
I find my issue is not so much if any sparks from the wood but sparks from creosote build up in the pipe.
Any single wall pipe stays cool enough to accumulate some creosote then you stoke the fire and it gets going good burning/cleaning the pipe out some and that has been the source of my sparks
Spark screen in bottom of pipe has created issues and in the top creates more issues so I'm at the point that small burn holes are just part of life for vertical installs and seam seal or something to plug the little hole is what I do
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Offline memaquay

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Re: Vertical stove pipe, sparks and pipe length
« Reply #3 on: November 13, 2017, 05:12:46 pm »
The only time I ever ended up with spark holes was when someone burned paper in my stove.  They threw and old cigarette pack in the stove, which promptly caught fire and got sucked right up the stove pipe, then fell back on the tent.

With normal wood burning, I have yet to get spark holes, and I don't use a baffle or a spark arrestor.

Online into the wind

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Re: Vertical stove pipe, sparks and pipe length
« Reply #4 on: November 13, 2017, 07:07:10 pm »
My experience is the same as  memaquay. Stay away from paper on vertical set ups.

Offline Undersky

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Re: Vertical stove pipe, sparks and pipe length
« Reply #5 on: November 13, 2017, 08:57:35 pm »
Hi Marko-Marko,

I agree with those who have already commented.

Maybe just a couple of other ideas:

A longer pipe can give sparks more time to burn up or burn into smaller pieces on the way up the pipe, as well as more time to burn up, or cool as the sparks come out of the pipe and drift downward.

A sideways breeze may be more likely to take sparks away from your tent if those sparks are higher in the air for a longer time, as with a longer pipe.

A longer pipe can give you much better control over the stove burn, too. My dad used to say that "the pipe is the engine of the stove." A bigger engine gives you more options insofar as burning goes. Just fooling around in the back yard many winters back, on a windless night, we added 8 lengths of pipe to the stove and let 'er rip. The combustion air was definitely whistling as it blasted through the almost-closed draft. You could change the rate of burn on that set-up instantly - like a rheostat for heat!

Some have found that the in-pipe hardware cloth spark arrester, as shown in your picture, can serve to reduce your potential for exhaust flow volume. An in-pipe arrester also can allow more sparks to pass because the pressure of the out-flowing gasses is quite high so sparks are more likely to get pushed right through the arrester rather than getting hung up long enough to burn away. Finally, in order to burn up sparks likely need some fresh oxygen, which, unfortunately, they are not going to get inside the top of that pipe.

One solution for all three issues is to use a large surface area conical hardware cloth spark arrester placed over the top of the pipe. The surface area of this arrester would be many times the cross-sectional area of the pipe, so the flow rate per-square-area through the screen can be slower, the pressure per-square-area is lower. This type of arrester is out in the open where fresh combustion air is available to help burn up the sparks that get caught in the arrester.

Lastly, the "out on top" arrestor does not have to fit too snugly and can have a lop of wire on top so that when you check visually for potential clogging it can easily be lifted off with a stick or ski pole, brushed through the snow to clean, and replaced.

Sorry for the too-long post!

 

Offline chimpac

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Re: Vertical stove pipe, sparks and pipe length
« Reply #6 on: November 13, 2017, 09:28:58 pm »
The wood stove in my basement is connected to 40' of bare stainless steel 6" pipe. The draw is mean, the conventional Canadian tire stove whistles when it is hot. It operates with the draft control just cracked a bit and I have bent the chimney in at the top of the stove to let in some top air. It burns a full load of wood quite clean front to back but I have melted the inside baffle and grate that came with the stove. The stove and pipe operate in a masonry chimney enclosure that has 6' vertical openings on 3 floor levels. I have air flow stops at each level to stop all the hot air rushing to the attic.
I have used my tent stove under a tarp pitch when the chimney was so short that it only stuck out the top of the tarp 2" and I never had any spark holes in the fabric.
The answer to stopping sparks is using a baffle inside the stove or using some rocket stove features.
A small horizontal burn chamber connected to an inside riser pipe that takes the smoke and heat up close under the cook top. The smoke then gives up most of its heat and exits at the chimney port down low on the stove body.
 When the chimney port is low on the stove body the chimney will quit drawing if the fire cools to much. If I am not pushing in new wood often enough the draw quits and I have to light a little strip of waxed cardboard to get it going again. When the fire is kept hot enough I get a very hot cook top, a very smokeless clean burn and a chimney that does not get much hotter than steam.
« Last Edit: November 13, 2017, 09:50:40 pm by chimpac »

Offline Undersky

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Re: Vertical stove pipe, sparks and pipe length
« Reply #7 on: November 13, 2017, 10:29:30 pm »
Chimpac, the type of stoves about which you often speak positively has always intrigued me. Some of their configuration seems to be more "natural", if a stove or fire can be described this way, than most other stoves' set ups.

Three questions that you'll be able to respond to I am sure, based on your experience.

Do you think that a rocket-style stove will use more combustion air than a more conventional, almost-air-tight box stove of similar heat output?

What happens to exhaust gasses later evening, as you are heading to sleep, and your stove's burn slows to the point that exhaust gasses stop rising up out of the chimney?

Finally, by "...hotter than steam" do you mean hotter than +100C or +212F?

Thanks Chimpac

Offline chimpac

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Re: Vertical stove pipe, sparks and pipe length
« Reply #8 on: November 13, 2017, 11:44:24 pm »
The optimum volume of combustion air for a clean burning fire is the same no matter what stove. The level at which the combustion air hits the fire is critical, it controls the temperature and rate of burn. Any air coming in above the fire cools it, any air under the fire makes it burn faster and hotter.
A chute fed rocket stove will need the wood pushed in often, like every 15 min. If no wood is added fire just gets cooler and goes out, all smoke goes up the chimney, never comes out of the stove into the tent.
I do not limit the incoming combustion air but I direct all air to the side and under the fire. The temperature of the fire is controlled by the amount and diameter of the wood pushed in.
I can control the volume of the air entering the grate under the fire by adjusting the opening of my vertical sliding feed door.
 To get a longer burn, any good clean burning stove with a large combustion chamber can be fitted with a vertical cylinder heat exchanger that is fed with the chimney as the riser pipe going up inside to near the top inside of the exchanger cylinder. The smoke exit port cut in lower on the cylinder.
 I have not done this myself but I have seen it done on the internet for rocket stoves in homes. The problem is that you cannot have as hot a combustion chamber with a full load of wood as a chute fed combustion chamber.
Yes , when I say near steam temperature I mean 100C. or a few degrees above.
« Last Edit: November 14, 2017, 06:29:21 am by chimpac »

Online Marko_Mrko

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Re: Vertical stove pipe, sparks and pipe length
« Reply #9 on: November 14, 2017, 08:24:26 pm »
So I made a removable baffle (as per previous post - http://www.wintertrekking.com/community/index.php?topic=3258.0 - thanks @Mercer!)

Couple of differences:
- I have a KniCo Packer, so it was narrower
- I made it longer than the original post - Mercer's was 11x12" - I made mine 9"x18"



Here's the baffle inside the stove. The false bottom keeps the legs from collapsing inwards. That works nicely, I think (also, I was lazy and used the 8x24" sheet metal for the false bottom. Should have used the 12x24" and cut to size. It works fine though.)


First burn was spectacularly easy. Although the baffle is longer than the original instructions, I had no problems with the smoke going out the front. As the stove burns, the flames do lick up the sides a bit, and at the back. Look at those flames swirl and combust!


One issue I can see is that the flames are not directly burning my spark arrestor - previously, without the baffle, the flames incinerated all soot and cleaned the arrestor. Obviously this will not happen with the baffle. I'm hopeful that the hot gases perform the same function. We'll see, I'll keep checking and if it's an issue I'll remove the spark arrestor.

Also: first boil on the stove! Just as fast as before (about 15 minutes). The hottest part of the stove is still closest to the pipe (as illustrated by the excellent thermal pics in the original baffle topic).

Now about the sparks: THERE ARE NONE! I even tested with paper. No sparks. Hardwood, softwood, birch bark. NO SPARKS! Just wow. I'm keeping the spark arrestor for now, but... wow.

Thanks for all the help gents!!
Marko

PS.
For storage, the legs don't fold flat. Instead, I'm packing it upside down:



Offline HOOP

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Re: Vertical stove pipe, sparks and pipe length
« Reply #10 on: November 14, 2017, 09:17:47 pm »
Brilliantly simple design on the baffle!  Totally adjustable for tuning the draw.  I like it!
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Re: Vertical stove pipe, sparks and pipe length
« Reply #11 on: November 14, 2017, 09:31:35 pm »
Nice work on the stove improvements.

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Online Marko_Mrko

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Re: Vertical stove pipe, sparks and pipe length
« Reply #12 on: November 14, 2017, 11:20:44 pm »
Thanks guys.

Two updates:

1) Spark arrestor - definitely getting more soot. I don't think it will block, but it will need to be checked frequently. I took out the second layer of chicken wire.
 
Before:


After:



2) The legs of the baffle were embedding themselves along the side of the stove (along the folds of the sheet metal in the corners of the stove). I had to curve the corners to prevent this.



Cheers
M

Offline chimpac

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Re: Vertical stove pipe, sparks and pipe length
« Reply #13 on: November 15, 2017, 11:24:51 pm »
If you want a baffle to be more tight to the sides of the stove cut it a bit wider than the inside width of the stove.
Then bend the two long sides, creased at about 1" to 1.5", down or up 20 to 40 degrees so the sides spring tight against the side of the stove.
The legs can be cut from the same material but bent 90 degrees like angle iron and riveted to he baffle.