PDA

View Full Version : Homemade Vesta stove maybe??



dropkick
2006-10-24, 02:16
TeeDee posted a thread (Forum thread link) (http://hikinghq.net/forum/showthread.php?t=1911) about a woodstove that a man in Africa came up with (link to Africa stove story) (http://news.bahai.org/story/360). He also gave a link with a homemade version of this stove (link homemade version) (www.instructables.com/id/EFYJNQ9JEZES9J4SSJ/)

I looked at the homemade version and saw that it wouldn't work because the airflow would have been backwards, cooling whatever you were cooking and possibly choking the fire.

After thinking about it I thought I had the problem solved with the addition of a 3rd wall (fig. 1). I gathered 3 cans and was out in my garage happily drilling holes and putting a prototype together when I looked and thought a little harder and saw my idea would have the same problem that the homemade version in the link above had. As soon as the air heated the airflow would want to reverse it's path (fig. 2)
http://img.villagephotos.com/p/2006-3/1165284/crapstove.jpg
I came up with a few more ideas: some bad (fig. 3) some a bit better (fig. 5) but I can't see were any of them would be much improvement over the very simple can with a grate and airholes in the base (fig. 4)

Maybe there is something I'm missing but I'm not seeing where you can get much improvement over this without a fan.

Any ideas?

Lanthar
2006-10-24, 10:10
Dropkick,

I'm not following your line of reasoning on WHY you think the airflow in the Vesta would cool the pot...

Even reading your post in the original thread really doesn't make any sense with fluid (air) flow dynamics...

Hot gases will rise at the point of combustion (the flame), expelling out the top... creating (essentially) a vacuum BELOW the combustion chamber drawing air IN from the sides...

Unless forced by external means, combustion gases will NOT migrate downwards through a flame... that's why downdraft (rather than inverted downdraft... I still don't understand why they don't simply call it updraft) gassifier stoves require a fan.

This is why one ALWAYS places cooking pots ABOVE the combustion area (regardless of the flame source).

EDIT - However, just to clarify, you are correct in that the guy who made the 'homemade' version did NOT make anything other than a simple double-wall raised floor fire can. He would actually have been better off punching the holes in the bottom rather than the sides of his 'firebox' (the inner can, if I'm not completely missing something). Even then, he wouldn't be replicating the Vesta, just making his stove a little more effecient.

EDIT2 - I read your comments on the Instuctables site, and I think I understand your viewpoint a little better. One thing you are forgetting is that immediately above the flame the combustion gases will be far hotter than the air coming in the side wall. Will it heat the air in the outer chamber? Yes. Will this preheated air have a tendency to rise? Yes. However, the tising tendency of the hotter combustion gases will by FAR outweight this tendency to rise and suck this heated air 'down' and into the combustion chamber. This is why double-wall raised floor (some call them partial gassifiers) are SO much more effecient than standard woodstoves. The air is preheated BEFORE it enters the combustion area. (True gassifiers go even further by differentiating primary and secondary combustion air... DWRF stoves simply have primary air)
"Nature abhors a vacuum" so, no, you couldn't simply expell all the air out of the outer chamber and snuff the fire, either.

dropkick
2006-10-25, 00:04
So your saying I was oversimplifying the airflow?

I'll agree with that, but I still feel that the stove is going to be pulling air in from the top as soon as it warms, due to the fact that the airflow through the walls is going to be fighting itself, trying to travel in 2 directions at the same time.

Will this still be more effecient than a single wall stove?

If it is which would be better, a triple wall, or double? (I vote for double)

I need to do some real world tests.


- As I look at my drawings I see that fig. 3 & 5 are the same (sometimes I'm not to bright).

Lanthar
2006-10-25, 11:04
So your saying I was oversimplifying the airflow?

I'll agree with that, but I still feel that the stove is going to be pulling air in from the top as soon as it warms, due to the fact that the airflow through the walls is going to be fighting itself, trying to travel in 2 directions at the same time.

You're kind of oversimplifying it... think of it as a matter of degrees...

Both the hot and warm air have a tendency to lift. However, the hot air has a much stronger tendency to lift , so it will overcome the warm air's tendency to lift and 'WIN'.

Will the two tendencies be fighting each other and result in a lower net airflow into the fire? Yes.

However, this lower airflow is compensated by the increased incoming air temperature.

One keys to this: Your 'holes' need to be big enough to result in ease of air entry. Otherwise you can 'choke' the stove. Note, it doesn't take many holes to get enough air entry space.

This tendency is why 'true' gassifier stoves include a secondary air inlet in the fire chamber.



Will this still be more effecient than a single wall stove?


Absolutely.


If it is which would be better, a triple wall, or double? (I vote for double)

I need to do some real world tests.

- As I look at my drawings I see that fig. 3 & 5 are the same (sometimes I'm not to bright).

I have a tendency to agree. Though the third wall will 'blunt' some of the liftiness of the warm air (resulting in more air flow into the burn chamber), However, it forces the cool air to have to navigate another wall (causing less air flow). I'm pretty sure the two would cancell each other out.

JAK
2006-11-22, 13:37
I agree that figure 4 is best. The draft needs total height and temperature difference to be generated, or a fan. However, I like the idea of using a double wall for insulation, and stuffing the double wall with stuff that will char so you can use it to start the next fire.

JAK
2006-11-22, 15:21
Here are more single pot stoves:
http://www.newdawnengineering.com/website/stove/singlestove/

This one has me interested:
http://www.newdawnengineering.com/website/stove/singlestove/tsotso/

With some modifications in both concept and design, I think you could have an outer cylinder of blue foam with aluminum tape on the inside, a combustion chamber on the bottom of a 12oz tin can with lots of holes drilled into the sides, and some sort of venturi section in the middle to mix and complete combustion before hitting the pot. Sort of a Tso-Tso/Rocket/Hobo hybrid. It might be 12" high and 4"diameter and 5oz including a 16oz aluminum pot. An inverted can on the very bottom might serve as a stand and a chamber you could fill with combustible material to make char to start your next fire. For travel it would not get much smaller, but it might break down to carry the bottom half with firestarting material inside, and the top half with the aluminum pot and a water bottle nested inside of it, with perhaps a fleece sock over the aluminum pot to contain the soot and act as more insulation to fill the 1/4" gap between the pot and the windscreen.

Kea
2006-11-23, 01:02
That stove should draft just fine. I am confused as to why you think it would do otherwise.

I do a LOT of work with fire, and I don't see why any of those would not draft properly. The question of fuel economy and cook time is a whole different affair.

TeeDee
2006-11-23, 16:10
Dropkick - hot air doesn't "lift". You needed stratified
temperatures for air movement (in the absense of something forcing
air movement, read fan). Air at a higher temperature (hotter air) is
less dense than air at a relative lower temperature (cooler air). The
more dense air weighs more and so settles lower displacing the hotter
air up. So hotter air doesn't "lift", it is lifted.

In considering the forces acting on the air in the sidewall chamber
you have 2 to consider:

1. the lower air pressure created under the firebox relative to the
atmospheric pressure at the inlet vents produces a net force pushing
the air through the vents, through the wall chamber into the space
under the firebox and hence up through the fire.

2. the temperature differential from the top to the bottom of the
wall chamber created by the temperature differential in the firebox
itself. In practice, the top chamber wall will start out hotter than
the bottom, but the differential will be mitigated by the conduction
of heat by the metal of the wall and by the air heated at the top
moving down and heating the chamber walls.

The pressure differential will push cooler ambient air into the
vents. The air will be warmed as it moves through the wall chamber.
Since the air above is cooler it is "sinking" under the gravitational
force and pushing on the warmer air lower in the chamber. Now ask the
question: where does the warmer, less dense air lower in the chamber
have to go? In the confines of the chamber, it cannot move up, it has
to move into the space under the firebox where it is drawn up through
the fuel into the flame zone.

So actually, in the case of the wall chamber, the temperature
differential is helping the movement of air into the space under the
firebox.

JAK
2006-11-23, 16:53
I think Kea is right that it will still draw air. Hot is still lighter than warm.

p.s. I haven't made a stove yet that didn't suck.

oops56
2006-11-23, 20:34
O K i just cant stand it any more here my idea take a 4-5-6 in. can and a can 6 in. or so tall some air hols around bottom grill up in 2 in. or so off bottom a side door near top now put a fan blade near the top so the up heat will turn it and blow air down on fire ??? what you think

SGT Rock
2006-11-24, 02:59
Sounds like it will work.

incognito
2006-11-24, 15:21
go up to the first post and clik on african stove story. Look at the first photo. The framed photo on the wall behind the guy shows a red circular object, I belive that to be the fan housing that operates the the stoves air circulation system. Nothing is ever said about it, but I belive it to be the fan housing. Look at all the photos carefully!!!!!!

What do you think?

SGT Rock
2006-11-24, 16:27
I see it. But following other links on the stove in Google I don't see anything about a fan in the stove. What I do see in some of the pictures is an assembly that goes on top to hold a pot which I think that is. Here is a link to a Vesto in operation - I don't see a fan or anywhere that it says anything about a fan in the operation: http://www.newdawnengineering.com/website/stove/singlestove/vesto/cookingvesto.php

Reading the description of one of the photos I belive that part is a replaceable bottom plate with grate for holding the fire http://www.newdawnengineering.com/largeimage.php?imagename=vesto2hres.jpg&returnpath=/website/stove/singlestove/vesto/index.php

A top view looking right through the stove shows the top deck, the folded strip pot stand, the fire grate and the replaceable insert at the bottom. The bottom of the stove is open so it has to rest on a flat surface of else be snuggled into the soil or sand to seal the air properly and prevent it from entering the lower part of the stove.

incognito
2006-11-24, 23:32
quote from stove article: "The Vesto has three types of secondary air inlets, allowing it to function as both a charcoal-producing gasifier and a charcoal burning, wood burning, or dung burning stove."

I think the red circular device is related to the charcoal producing gasifier and all the other information that we are able to read about is the charcoal burning, wood burning, or dung burning stove.The red device having depth to it, not being able to see it in any of the other photos.

If they were available here, I'd buy three of them!!!!!!!!

SGT Rock
2006-11-25, 00:28
It does have depth, but if you see the design and read this part:

http://www.newdawnengineering.com/website/stove/singlestove/vesto/vesto1lres.jpg


This picture shows the stove as it is sold and opened for use. The left lever controls the primary and lower secondary air supply and the right one controls the middle secondary air supply. Left is closed and right is open.

So the air intakes are on the side, no battery or wires shown. I don't think there is even a set up for a fan unless you want to use a vacume cleaner on reverse and put the air hose in the hole. But I doubt it since the primary design was supposed to support a third world country without any electricity in most areas.

I also watched this video and didn't see a fan anywhere: http://www.newdawnengineering.com/website/stove/singlestove/vesto/vesto-semi-gasifier.mpg

But it does show adjusting air flow to make charcoal and other functions just by opening and closing air vents.

And this one two: http://www.newdawnengineering.com/website/stove/singlestove/vesto/vestovortex.mpg

Which mentioned the secondary vents also being opened and showed what effect that had on the burn.

I also read the instructions which do not mention a fan: http://www.newdawnengineering.com/website/stove/singlestove/vesto/vesto.pdf


But the depth part I think can be explained by this:

http://www.newdawnengineering.com/largeimage.php?imagename=vesto2hres.jpg&returnpath=/website/stove/singlestove/vesto/index.php

Now look at the attached blow up of that image in question, don't they look like the same part? They do to me. And the red is apparently from the lighting they used in the photo.

incognito
2006-11-25, 13:38
Sarge------I'll have to watch the video, I changed my mind, I'll buy six if they sell them stateside.

Dropkick-----look at the second photo labled "Cutaway model of the Vesto stove showing the chambers that preheat the incoming air, boosting the stove's efficiency." I don't see a double wall between the outer wall and the central column that has the four rows of small holes. The air passes through the large holes in the outer wall directly across to the column. In another photo it showed a removable canister with many holes that fits down into that center column. Air entering from the sides going into the fuel cylinder/chamber. Sarge also shows the Red section being on the bottom of the stove and clearly shows the grass beneath indicating a column of air comes from the bottom and go all the way up and out the top. This shows that there should be an enormous amount of draft to burn really really hot. The hieght of the stove is such that the central column acting as a chimney will produce the natural updraft.

Just something to think about, it was just an observation.

You build them and I'll buy 6:elefant:

They sell them for 29.00. How can they manufacture them out of stainless steel for that price. Somebody, like the Rock should import and retail them here. I'll buy six!!!!!!!!!!

TeeDee
2006-11-25, 18:33
Incognito - go top this site:

http://www.newdawnengineering.com/website/stove/singlestove/vesto/

scroll all the way to the bottom. On the right is a link for the manual in pdf, MS Word, RTF or Wordperfect format. Download. The manual mentions nothing about a fan. A fan would defeat the whole purpose. The stove is designed to be used where electricity and batteries are not readily available. On page 2 you will see the red thing you mentioned. The bottom of the stove must be sealed to prevent air from entering the open bottom. On sand or dirt, you just push the stove into the ground slightly to seal the bottom. For hard surfaces such as concrete, you use the red thing to seal the bottom.

And you are totally right. I'm trying to find out about ordering one. I don't think I need 6, but one will really be nice. I'm glad this thread re-activated that link. Looking at the stove a second time, I'm even more impressed with it.

Take-a-knee
2006-11-25, 23:47
Maybe we (HQ posters) could do a group buy of those things. That would be a cool thing to have in case of an extended power outage. Not to mention it would probably work as well as a coleman stove once you got up to speed on it.

dropkick
2006-11-26, 09:14
Dropkick-----look at the second photo labled "Cutaway model of the Vesto stove showing the chambers that preheat the incoming air, boosting the stove's efficiency." I don't see a double wall between the outer wall and the central column that has the four rows of small holes. The air passes through the large holes in the outer wall directly across to the column. In another photo it showed a removable canister with many holes that fits down into that center column. Air entering from the sides going into the fuel cylinder/chamber. Sarge also shows the Red section being on the bottom of the stove and clearly shows the grass beneath indicating a column of air comes from the bottom and go all the way up and out the top. This shows that there should be an enormous amount of draft to burn really really hot. The hieght of the stove is such that the central column acting as a chimney will produce the natural updraft.

The way they have it cut and also the way they took the picture, make it tough to see the wall that I numbered as 2 in the Photo, but it's there if you look close. There are at least 3 walls.
http://img.villagephotos.com/p/2006-3/1165284/bwns_5851-460.jpg
P.S. According to the maker the bottom of the stove is supposed to sit on either a flat surface or in a pan of sand so air can't enter from the bottom.

SGT Rock
2006-11-26, 09:29
Something I was thinking about last night as I looked at this. If you need to add fuel to the fire as you go, you have to remove the pot. Add to that the complex build o three walls and baffles and vents for the stove - probably pushing the weight and pain to build factor beyond what you really may want in a backpacking stove.

As I looked through those articles I saw a stove called the Rocket Stove - it looked like that would be easier to scale down and make work. Have you looked at that thing yet?

Lanthar
2006-11-26, 22:50
Maybe we (HQ posters) could do a group buy of those things. That would be a cool thing to have in case of an extended power outage. Not to mention it would probably work as well as a coleman stove once you got up to speed on it.

I must say I'd be up for one if we can get a group buy deal.

dropkick
2006-11-27, 01:22
As I looked through those articles I saw a stove called the Rocket Stove - it looked like that would be easier to scale down and make work. Have you looked at that thing yet?

The rocket stove uses a bunch of sand/ashes/cement to insulate the pipe and funnel the heat towards the pot. From what I can see it's more of a fixed position stove.
Maybe it would still work well without the insulation? But would it be an improvement over the Hobo stove?

I thought about building one once on my property, but went with a dirt stove/oven instead (like a clay oven, but I didn't have any clay - simplified concept: a buried oven with added vents for pot cooking).

I think we are all getting too complicated with the unpowered woodstove concept. We don't live in Africa and have problems with finding fuel (well at least I don't - but I bet most of you don't either). So why worry about saving half a handful of wood boiling your water?

I have decided that I am going back to simple. For an emergency woodstove I'm either going to do a hobo from a coffee can with front and back vents (hmm.. would that be much different than the airflow of the Rocket?) or a hook together, flat panel, wood stove/portable pit.

I've just made up my mind as I wrote this. I'm going with a flat panel take apart stove (idea to be posted later).
Now the only thing I need to make up my mind about is whether I want to build a small hand operated bellows for occasional air/fire assists or do I want to go with the simple plastic tube hooked to a copper tube for blowing assist.

dropkick
2006-11-27, 02:29
And here it is: a tripod (more stable) portable fire pit.
Just set your pot on top.
http://img.villagephotos.com/p/2006-3/1165284/woodstoveidea.jpg
Pretty rough sketch, but I think I might have a fairly good idea here.
If I wanted to up it's fire burning ability, I could add a fire shelf of hardware cloth - so that air could reach the bottom of the fire


Here's some other ideas (including Nimblewill Nomad's "Little Dandy" - the portable pit that got me thinking about building one years ago - forgotten until your posts revived it)
http://zenstoves.net/Wood.htm (http://img.villagephotos.com/p/2006-3/1165284/woodstoveidea.jpg)

SGT Rock
2006-11-27, 05:07
Look at these: http://hikinghq.net/forum/showpost.php?p=7131&postcount=11

Based on what I came up with playing with this I would reccomend:

1. A way to close the hole when using alcohol.

2. Some more holes in the bottom for better air flow when using wood.

3. A set of crossbars or something to lift the pot up off the base when using wood - there was not enough air flow at the top of the stove when using the pot support tabs that are shown.

4. Alcohol burner should have two tops - one for fast boil and one for Ion like performance.

The weight for the stove came in at something like 3.6 ounces if I remember right. Here is the entire thread: http://hikinghq.net/forum/showthread.php?t=1162

dropkick
2006-11-27, 08:18
What happened to the Fireball? Ever get around to trying a ti model?
Quite a bit fancier than my plan.

And how about those cozies?

Have you looked at Garlington's stove and Risk's version. They sound kind of like what I was wondering about when I started this thread.
-I also wonder if their forced use of starter fluid could be solved with a blow tube?

links:
Risk's stove (www.imrisk.com/woodgas/ddstove.htm)
Ray Garlington's stove (www.garlington.biz/Ray/WoodGasStove/)

SGT Rock
2006-11-27, 08:57
What happened to the Fireball? Ever get around to trying a ti model?

Yes I did. I have it sitting at the house ready to play with some more later. Basically I couldn't keep the fire going like I wanted to - and after all the discussion I think it was because I didn't have a large enough air flow around the pot at the top - hence the recommendation for a crossbar for the top when using wood. I think it came in a little heavier than I expected too - something like 3.8 ounces or something.

Some other issues: The Ti breaks easier when bending. I broke off a couple of those pot support tabs while I was trying to make it. Also, drilling ti is a bitch. Cutting it isn't so bad, but all those holes I had in the prototype for air flow on the base and the four you need to start the hole for feeding wood were some of the hardest parts to do. If I were to end up selling those things it would take a lot of practice and patients to make the things because of the drilling and bending.



Quite a bit fancier than my plan.

Yes it is. BUT the aluminum version was actually pretty easy to make. And it folds down flat to fit inside the cozy with the stove. I think you can build something similar with three sides.


And how about those cozies?
They are good to go. My wife keeps waffling on making them though. She does the sewing parts. I have been using that one in the pic for a while and really like it.



Have you looked at Garlington's stove and Risk's version. They sound kind of like what I was wondering about when I started this thread.
-I also wonder if their forced use of starter fluid could be solved with a blow tube?

links:
Risk's stove (http://www.imrisk.com/woodgas/ddstove.htm)
Ray Garlington's stove (http://www.garlington.biz/Ray/WoodGasStove/)

Yep, I have looked at them. I would like to play with something like that, but haven't had the time yet. What I was trying to achieve with my stove was something that utilized the insulating properties of Ti to help make a good stove/stand - windscreen. The idea to make it burn wood came later as I was playing with the original idea. It didn't start off as a wood stove. Basically I was playing with the prototype and thought about some of the crappy experiences I have had keeping a pot sitting in a large campfire without spilling. I sort of said to myself "you know, if that was made of ti, you could put it in a fire and use it for a pot stand..." Then I went one step further and thought if I just put a base on it - then it could also hold a small fire too.

As to the tube, that is something I never found very useful. What I ended up liking better was to force air by fanning or blowing into the large opening on the side.

Lanthar
2006-11-27, 12:44
I think we are all getting too complicated with the unpowered woodstove concept. We don't live in Africa and have problems with finding fuel (well at least I don't - but I bet most of you don't either). So why worry about saving half a handful of wood boiling your water?

I have decided that I am going back to simple. For an emergency woodstove I'm either going to do a hobo from a coffee can with front and back vents (hmm.. would that be much different than the airflow of the Rocket?) or a hook together, flat panel, wood stove/portable pit.

That's very much my opinion... for homemade woodstoves simple, well ventilate, raised floor is your best option.

BTW, looking at your design, it reminds me of one that Bill Forshnell has done over at BPL.com... gotta find the link... AHA!
(http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/3262/index.html)

SGT Rock
2006-11-27, 13:23
Well really if I changed out the bottom plate for a grill (and that is probably a smart idea) I could get the weight down some more. BUT, I think it might be a smart idea to at least have an oven liner type shield under the stove so you can use it on tables and in shelters.

TeeDee
2006-11-27, 21:33
Maybe we (HQ posters) could do a group buy of those things. That would be a cool thing to have in case of an extended power outage. Not to mention it would probably work as well as a coleman stove once you got up to speed on it.

TAK - I would also buy one if a group buy can be arranged.

That's 3, maybe more if incognito buys in.

incognito
2006-11-27, 22:59
Someone needs to do the research!!!!!!

Get costs on purchasing 6, 9, 12,

Is there a distributor here in the states?

I'm in for three if the price is right!!!!!!!

oops56
2006-11-27, 23:23
count me in like i need more stoves:cool: :cool:

Redleg
2006-11-28, 00:06
Maybe we (HQ posters) could do a group buy of those things. That would be a cool thing to have in case of an extended power outage. Not to mention it would probably work as well as a coleman stove once you got up to speed on it.

I'm in for 2. That's 6 or so...
jaf

SGT Rock
2006-11-28, 04:20
I'd like to have one. It would be a good stove for taking car camping - better than some of the fire grates they have at some of the campsites.

Lanthar
2006-11-28, 13:55
I'd like to have one. It would be a good stove for taking car camping - better than some of the fire grates they have at some of the campsites.

That's basically why I want one... once we get some shipping prices, I may even want more than one (the boyscout troop could probably use a couple).

So, who wants to take up the challenge of contacting New Dawn (http://www.newdawnengineering.com/website/company/) (I doubt they want a ton of people saying 'I represent a goupr that wants X stoves')?

BTW - Did anyone else notice the Basintuthu Baking Stove (http://www.newdawnengineering.com/website/stove/bakingstove/) or the Two Burner Vesto (http://www.newdawnengineering.com/website/stove/coal/) on their Price List (http://www.newdawnengineering.com/website/prices/)?

BTW2 - Other interesting things from their Stoves - Products Page (http://www.newdawnengineering.com/website/stove/)
Paraffin Stove (http://www.newdawnengineering.com/website/stove/paraffin/)
Fire Cube - (Homemade) Biomass for Household Cooking (http://www.newdawnengineering.com/website/stove/firecube/)

TeeDee
2006-11-30, 18:35
I sent an email to new dawn engineering today to get information on shipping for the Vesta stoves.

I counted 9 stoves so far - is that correct and is there anybody else?

TeeDee
2006-12-01, 20:48
Here's my count:

TAK - 1
TD - 1
Lanthar - 1
Incognito - 3
opps56 - 1
Redleg - 2
Sgt Rock - 1

total: 10

Here's the reply to my email from new dawn engineering:

I gave the request to Thabsile but she is really busy I see so I will say
that we have Vesto stoves in stock.

The stove is available for $25 and there are accessories if you want them:

BBQ plate $9.50
Stove stand $3.00
BBQ plate stand $2.00

The whole set posted one by one will be close to $85. If you want to get 9
we can send them by post in pairs which are acceptable in terms of
dimensions and mass. Two together go cheaper than two singles.

The box with everything is 7.5 Kg.

You can pay for them by personal cheque if you like. That is the cheapest
method I have devised. You would post the cheque to:

Margaret Pemberton-Pigott
265 Glenridge Drive
Ontario N2J 3W5
Canada

She will clear the cheque in my bank account and I will post the stoves from
here.

I hope that is everything.

Best regards
Crispin Pemberton-Pigott
New Dawn Engineering
Matsapha
Swaziland

Okay they don't seem to be offering a group discount - maybe the total is just too small and they figure, probably correctly, that it would be a one shot affair.

At this point, it would probably be best if each person that desires to purchase stove(s), to use the above information and make the purchase individually.

To those that do pursue and purchase - enjoy your stove - from the information posted on their web site, they are nice stoves.

I will be sending my check off tomorrow.

TeeDee

Lanthar
2006-12-04, 11:25
Tee Dee, thanks for looking into that!

Redleg
2006-12-04, 22:35
Thanks for the hard work. OR: I must throw my humble appritiation to your expert, hard working, doubtless beautifull... Feet.

Um. Thank you.
jaf

JAK
2007-01-08, 21:24
TeeDee posted a thread http://img.villagephotos.com/p/2006-3/1165284/crapstove.jpg
I've been thinking about this some more and I am thinking configuration #5 might be the way to go. The outermost cylinder could be of blue foam with aluminum foil on the inside. The innermost cylinder could be ceramic, but it could also be of thin steel or titanium, with a grate on the very bottom but raised up off the bottom. The upper part of the void space between these two cylinders could be filled with dry twigs and bark which would insulate oly partially combust and the char could be used in the inner chamber in the next fire. During a fire fresh fuel could be fed to the center through the bottom vents, rocket stove style. The pot would sit up on top, but the blue foam and aluminum take outer cylinder could extend right up. The lid of the pot could also be insulated. The tricky parts would be the two horizontal parts. The bottom of the stove, and the part the pot sits on. If there were metal they would conduct heat to the ground and to the blue foam, probably melting it. Perhaps that ceramic insulation would be just the ticket. The one in the middle that the pot sits on could be removable so you could stuff in the debris to be charred in the side chamber, and remove it after the fire and stored in a char box, or perhaps left in the stove as a char box. The weight of the pot might rest on the outer cylinder at the top however, rather than on the inside stuff. Should be more stable that way.

I think that make 4 parts, that might be easily assembled and disassembled in some way. Let assume we have a pot 4" diameter x 4" high, for about 700ml. The blue foam pad would need to be about 4.5" inside diameter, and so about 5.25" outside diameter, and so 16.5" in circumference. The whole thing might sit 10.5" tall and 5.25" in diameter, hopefully not to tippy. Perhaps a wider pot might work better but this might be a good start anyways.

Outer Cylinder:
Blue Foam Pad & Aluminum Tape, 10.5" high x 16.5" circumference.

Middle Disk(s):
Ceramic Insulation, 0.5" thick, 5" outide diameter, 2" inside diameter.
Also covered in aluminum tape to stay clean and dry.

Inner Outer Cylinder:
Ceramic Insulation, 0.5" thick, 4" high x 16" circumference.

Inner Combustion Cylinder:
Thin walled steel tube. 5" high, 2" diameter snug fit into Middle Disk.

Bottom Disk:
Ceramic Insulation, 0.5" thick, 5" outide diameter, no center hole.
Perhaps covered in aluminum tape to stay clean and dry.

The Outer Cylinder would extend the full height from 10.5" to 0".
The Pot would extend down from 10.5" to 6.5" with 1/4" clearance on sides.
The Middle Disk would extend from 6.0" to 5.5" for a 1/2" clearance above.
2nd Middle Disk would extend from 1.5" to 1.0" for a 1/2" clearance below.
The Inner Combustion Cylinder would extend from 6" to 1".
The Bottom Disk would sit at 10" to 10.5", or perhaps slightly off ground.

You would burn very dry sticks and char in the inner chamber, which should probable have a grate on the bottom. Additional dry sticks could be dropped in from above or fed in from the side. One or two or tree 0.5" diameter holes through the Outer Cylinder would serve as ventilation and feed holes. There might also be a place in the very center for a tealight, which could be a tealight, or oil, or just empty to lift up the sticks a bit. It is intended that the debris between the Outer and Inner Cylinders smoke and char but not burn. Thus the 2nd Middle disk, with a small vent hole to the bottom of the Inner Cylinder. This "retort" would have a volume 4" high, 5" outside diameter, 2" inside diameter. Perhaps it would need additional 1/2" ceramic insulation on the outside to keep the blue foam from melting and to retain enough heat from the Inner Combustion Cylinder to dry out and char the debris it would contain. This 1/2" Inner Outer Cylinder could also serve as the ledge on which the Upper Middle Disk would rest.

JAK
2007-01-08, 22:21
Now the fun part:

Hobbo Rocket Vesta Stove that packs inside its pot, with room for fire starting kit.

When disassembled the Outer Cylinder might actually split into a top and bottom, and so the Upper Outer Cylinder and the Bottom Outer Cylinder and the Inner Outer Cyllinder should all roll up around the Inner Combustion Cylinder to form a cylinder 5.25" high with an area of 33"x0.375" + 16"x0.5" + 3.14in2 = 23.5in2 for a diameter of 5.5", so that plus the three 5"x0.5"disks should fit into a container 7" high and 5" diameter. Because of the 2" diameter hole in two of the disks in could be shortened to a 6" height. With a little fine tuning on the dimensions, reducing the thickness of the ceramic insulation or using a larger pot, it should be possible to get such a stove to nest into the pot it is designed for. I guess that would mean the ceramic disks would need to match the inside diameter of the pot, and the Inner Outer Cylinder would provide the extra gap, and exten right down to ground level. Also, the space inside of the Inner Combustion Cylinder, with a cap on each end, would be an excellent place to carry the char for the next fire, and perhaps some flint and steel and some tealights and a long candle also.

Assuming an average density of 6.25 lb per ft3, for a specific gravity of 0.1 compared to that of water,
such a stove for a 1 litre pot would weigh 100g, or 4 oz; and such a stove for a 500ml pot would weigh 2 oz.
This is typically about the same weight as the pot itself, which is not a bad target, as long as it burns wood.

What is the best way to deal with the handle? I think the handles that fold to the sides are best.
You would just need a small slit at the top of the Upper Outer Cylinder, a.k.a. wind screen.:biggrin:

JAK
2007-01-08, 22:31
Perhaps there might be room on the pot for a glass replacement lantern lens also, and the stove might be reconfigurable to support heating the mug while reading by candle light or lamp light. As I see it the Middle Disks would do in first with a snug fit on the bottom, and the Inner Cylinder / Firestarter Kit would nest into their center hole. The Inner Outer Cylinder is made of ceramic wool and it might compress a little in circumference to fit snuggly inside the pot without having to overlap itself. The Lantern Lens could fit inside of that, and the pot and Inner Outer Cylinder thickness could be matched to it. That leaves the Upper Outer Cylinder and Lower Outer Cylinder to wrap around the Inner Cylinder and inside the Lantern Lens. The closed cell foam and aluminum tape could be reduced to 1/4" or even 1/8" to facilitate this, perhaps with some fibreglass cloth between the blue foam and aluminum tape for additional rigidity and heat proofing. The Bottom disk and Pot Lid would go on top to provide additional protection for the Lantern Lens. Not sure of best pot lid. Most importantly it needs to be clean and not allow too much smoke to find its way in when heating with wood. A plastic snap on lid can sometimes be found which is ideal for packing, and might work fitted loosely or upside down when heating water.

This nesting strategy means that the Outer Cylinders and Inner Outer Cylinders are the same height as the Lantern Lens, and about 1/2" shorter than the Inner Cylinder if the Middle Disks are 1/4" thick, and perhaps 1" shorter than the Pot. This is OK because the Outer Cylinder can slide up the sides of the Inner Outer Cylinder, except that the Inner Outer Cylinder is to be somewhat compressible in circumference. The Middle Disks will provide some support however, and the Outer Cylinders can be made to be a snug with when they are assembled into a tight cylinder, and fitted one on top of the other. How that is best done is not determined yet. Some sort of adjustable or rubber bands, and some flaps covering the vertical and horizontal seams. Fixed rings would work, but they would be too big in diameter to fit in the pot. Thin wool socks maybe.

Lanthar
2007-01-09, 13:16
Jak,

Part of the problem with figure 5 (for wood) is that the air doesn't actually follow that path, it just builds up in there... as would any humidity from 'drying' the wood (aka the wood would just warm up but likely not dry the way you think it will.

What is helpful is to have holes in the top of the burn chamber which actually allow air that gets preheated to enter at the top increasing the effeciency of the burn and greatly decreasing soot.

Of course,with the inner chamber well insulated, any preheating of the air will likely be minimal anyway so you may not get a large effect from the extra warm /hot air. Also, using that area for packing with twigs now you risk actually lighting the twigs on fire (though if they don't they will dry as the mildly warm and air moves across them).

If I may, I'd like to propose a different location for the drying chamber (green arrow is pointing to it). This is essentially what you do for making charcloth. Realize that the horizontal black line is a 'cover' of some metal (I've attached a pic of how you would do this with three cans... a burn chamber can, a burn chamber support can, and the outer can... grey circles indicate the holes punched all around the sides...)

JAK
2007-01-09, 14:54
Jak,

Part of the problem with figure 5 (for wood) is that the air doesn't actually follow that path, it just builds up in there... as would any humidity from 'drying' the wood (aka the wood would just warm up but likely not dry the way you think it will.

What is helpful is to have holes in the top of the burn chamber which actually allow air that gets preheated to enter at the top increasing the effeciency of the burn and greatly decreasing soot.

Of course,with the inner chamber well insulated, any preheating of the air will likely be minimal anyway so you may not get a large effect from the extra warm /hot air. Also, using that area for packing with twigs now you risk actually lighting the twigs on fire (though if they don't they will dry as the mildly warm and air moves across them).

If I may, I'd like to propose a different location for the drying chamber (green arrow is pointing to it). This is essentially what you do for making charcloth. Realize that the horizontal black line is a 'cover' of some metal (I've attached a pic of how you would do this with three cans... a burn chamber can, a burn chamber support can, and the outer can... grey circles indicate the holes punched all around the sides...)Thanks Lanthar.

My thinking on keeping the holes on the bottom is to use the side chambers as a retort, to let the steam and volatile gases accumulate and be forced out into the inner combustion chamber by pressure, but to provide insufficient oxygen for combustion of the char. Also my plan has developed somewhat to have the inner combustion chamber a thinwall of steel or titanium to the retort, but the retort would be otherwise insulated on the top and bottom and outer wall with the ceramic wool. I like your idea of the retort on the bottom though. I am going to try the sides and then maybe the bottom also, or perhaps just the bottom. I will see if I can draw a picture.

Lanthar
2007-01-09, 17:45
Thanks Lanthar.

My thinking on keeping the holes on the bottom is to use the side chambers as a retort, to let the steam and volatile gases accumulate and be forced out into the inner combustion chamber by pressure, but to provide insufficient oxygen for combustion of the char. Also my plan has developed somewhat to have the inner combustion chamber a thinwall of steel or titanium to the retort, but the retort would be otherwise insulated on the top and bottom and outer wall with the ceramic wool. I like your idea of the retort on the bottom though. I am going to try the sides and then maybe the bottom also, or perhaps just the bottom. I will see if I can draw a picture.

Replied to you're pic in the other thread... it looks like it would work.

incognito
2007-01-10, 01:04
This is from post# 40 by JAK

and perhaps some flint and steel and some tealights and a long candle also.

JAK how do you propose to light your tinder(Char cloth) down at the bottom of the stove with with flint and steel? Charred wood???? have you found that it lights the same as charred cloth??? The only charred wood that I know off is Pinion Pine, that is said to be highly ignitable with a spark. I have not had any experience with it, only read it on the net. Of what value is charred wood to you in your fire making in regards to this wood burner you are describing?

These double walled stoves seem to me not to have the ability to provide sufficient air to easily ignite a half fast lay of fire starter. In my opinion the double wall thing that preheats air is insignificant to the performance of the stove. It's way over rated, adds to much weight to the stove. My zip stove has a burner section that is only 2+ inches deep, how much does the air heat up in that short a distance? Cold air has more oxygen than warm air anyway. Coal fired boilers are old technology, don't even go there:argh:

Sure, wouldn't it be nice to preheat the wood before you put it into the stove so it would light easier.

Look at the boil times for the regular Hobo stoves, in the range of 5 to 7 min. No fans, no double walls.

JAK
2007-01-10, 05:09
This is from post# 40 by JAK


JAK how do you propose to light your tinder(Char cloth) down at the bottom of the stove with with flint and steel? Charred wood???? have you found that it lights the same as charred cloth??? The only charred wood that I know off is Pinion Pine, that is said to be highly ignitable with a spark. I have not had any experience with it, only read it on the net. Of what value is charred wood to you in your fire making in regards to this wood burner you are describing?

These double walled stoves seem to me not to have the ability to provide sufficient air to easily ignite a half fast lay of fire starter. In my opinion the double wall thing that preheats air is insignificant to the performance of the stove. It's way over rated, adds to much weight to the stove. My zip stove has a burner section that is only 2+ inches deep, how much does the air heat up in that short a distance? Cold air has more oxygen than warm air anyway. Coal fired boilers are old technology, don't even go there:argh:

Sure, wouldn't it be nice to preheat the wood before you put it into the stove so it would light easier.

Look at the boil times for the regular Hobo stoves, in the range of 5 to 7 min. No fans, no double walls.Very good points. I'll answer some of them, but most you are too right.

"JAK how do you propose to light your tinder(Char cloth) down at the bottom of the stove with with flint and steel?"
- Most of the fuel here is excellent, paper birch and dead sticks snapped the lower part of a Spruce. Both light easily but like you say not with flint and steel. I usually light the birch bark with a small lighter, or light a long thin candle and use that to light the spruce sticks, but I would like to get some flint and steel and make some charred cloth or try something like charred moss.

"Of what value is charred wood to you in your fire making in regards to this wood burner you are describing?"
- My primary intention is to be able to heat a small amount of water using wood, but with with less smoke and in a reasonable time frame. Efficiency is not so important as how quickly I can make tea without too much smoke. I am hoping that if I have some charred wood to start with it might speed things up, and it will help complete the cumbustion of the volatile gases and smoke escaping from the fresh fuel once it heats up and begins to char inside the retort.

"In my opinion the double wall thing that preheats air is insignificant to the performance of the stove. It's way over rated, adds to much weight to the stove." "Look at the boil times for the regular Hobo stoves, in the range of 5 to 7 min. No fans, no double walls."
- You are probably right. I am hoping to keep the weight down by using ceramic wool instead of steel cans. See other thread where I provide an illustration. My intention is not to preheat the air but to contain the heat , and to reduce smoke by raising combustion temperature and forcing the smoke from the fresh fuel in the retort to pass through the burning charcoal obtained from the previous burn. However, it may be hard to beat a Hobbo Stove, which could also be made simply of inswool wrapped in muffler tape. The strategy with a hobbo stove, which is well proven like you say, is to simply start with fresh fuel in a bigger fire and a top down burn and in a short time, after the smoke, you will have a hot fire with less smoke, and warmer hands, and you can then make tea. I will have to try it both ways, and also the best place for my retort might be at the bottom of the hobbo stove like Lanthar suggested. See other thread.

http://hikinghq.net/forum/showthread.php?t=2082&page=2

Thanks.

Lanthar
2007-01-10, 13:45
These double walled stoves seem to me not to have the ability to provide sufficient air to easily ignite a half fast lay of fire starter.

"seems to" and "are" are two differenet phenomena... double wall stoves provide more than enough air flow when desigened correctly.


In my opinion the double wall thing that preheats air is insignificant to the performance of the stove. It's way over rated, adds to much weight to the stove. My zip stove has a burner section that is only 2+ inches deep, how much does the air heat up in that short a distance?

Opinion is only that. The point of the double wall designs is that it accomplishes high-burn-temps / complete combustion passively. Whereas a zip-type stove does this actively. You are correct, though, a 2 inch deep burn area probably won't allow for much significant preheating (though it's been shown that 3-4 inches is significant.


Cold air has more oxygen than warm air anyway. Coal fired boilers are old technology, don't even go there:argh:

COMPLETELY incorrect, cold air is DENSER than warm air. The ratio of oxygen to nitrogen stays the same. It's the MASS of oxygen that determines amount of combustion. Density (ergo) is important in closed systems (automobile engines) because the volume is fixed in the combustion chambers (limiting the amount of mass of air brought in) and the potential power output of a motor is directly related to the MASS of air in the combustion chambers (NOT as many car enthusiasts thin the volume). It's a thermodynamic cycle thing.

However in wood stoves density is not important... the mass of air (and since the ratio of oxygen to nitrogen doesn't change this is the same as saying the mass of oxygen) that enters the bottoms of the stove will be the same mass of air that exits the stove, it's just that heating will cause it to accelerate (because the volumetric flow rate increases as the density decreases). Hot air allows the combustion process to be more complete (aka cleaner)... higher mass flow of oxygen causes the combustion process to be more complete (within limits). Both double wall stoves and forced air stoves attempt to make the burns cleaner and hotter (aka more complete or more effecient). Both do so by increasing the mass flow rate of the incoming air. Forced air stoves increase it more, however the double wall stoves make up for it by preheating the air as well.


Coal fired boilers are old technology, don't even go there:argh:

Ah, but coal-gassification electrical power plants are CRAZY effecient and crazy clean burning... so don't knock coal.


Look at the boil times for the regular Hobo stoves, in the range of 5 to 7 min. No fans, no double walls.

That's why my opinion is that a simple raised floor hobo stove (you get a big boost in effeciency with a raised floor that allow air to pass more easily) is the sweet spot of benefits / cost ratio for most DIY wood-burning camp-stove builders.

One final note, JAK's insulated design is essentially skirting both of these techniques and going for a third (thermodynamically speaking) option... he's raising the temperature of the entire combustion chamber (by reducing heat loss) causing the combustion reaction to take place at a higher temperature thus resulting in a faster combustion reaction (aka more complete - more clean - more efficient).

JAK
2007-01-10, 15:26
More draft too, hopefully.

incognito
2007-01-13, 00:31
"seems to" and "are" are two differenet phenomena... double wall stoves provide more than enough air flow when desigened correctly.

Lanthar!!! How does a passive double walled stove get the outside air to go into the side or botom of the outside wall and then go up and over the middle wall and then downward to the bottom of the wall and then enter the burn chamber. In my statement
These double walled stoves seem to me not to have the ability to provide sufficient air to easily ignite a half fast lay of fire starter. my thoughts were in regards to air being able to travel in the confines of the double wall , going up and then down to make its way to the tinder/fuel at the botom of the burn chamber. The burn chamber is filled with tinder and fuel. What causes air flow in this passive system? My mention of my zip stove
My zip stove has a burner section that is only 2+ inches deep, how much does the air heat up in that short a distance? is made because it is the only double walled stove that I have personally used and am familiar with and can speak of with some first hand use. It's been infront of me, filled with fuel in a halfass way is hardpressed if not impossible to start without turning the fan on. Without the fan on it's a passive system, double walled.


Ah, but coal-gassification electrical power plants are CRAZY effecient and crazy clean burning... so don't knock coal.

Come on Lanthar!!! I was not knocking coal. The old coal fired boilers are said to have had the need to pre-heat the charge of coal and air to about the same as the boilers interior before introducing it into the boiler. That info was given to me by a member on Whiteblaze. My statement was directed at him in case he follows this forum. And then I said
Sure, wouldn't it be nice to preheat the wood before you put it into the stove so it would light easier.



Ah, but coal-gassification electrical power plants are CRAZY effecient and crazy clean burning... so don't knock coal.
I agree in total with highlighted words.

On this issue
COMPLETELY incorrect, cold air is DENSER than warm air. The ratio of oxygen to nitrogen stays the same. It's the MASS of oxygen that determines amount of combustion. Density (ergo) is important in closed systems (automobile engines) because the volume is fixed in the combustion chambers (limiting the amount of mass of air brought in) and the potential power output of a motor is directly related to the MASS of air in the combustion chambers (NOT as many car enthusiasts thin the volume). It's a thermodynamic cycle thing.

However in wood stoves density is not important... the mass of air (and since the ratio of oxygen to nitrogen doesn't change this is the same as saying the mass of oxygen) that enters the bottoms of the stove will be the same mass of air that exits the stove, it's just that heating will cause it to accelerate (because the volumetric flow rate increases as the density decreases). Hot air allows the combustion process to be more complete (aka cleaner)... higher mass flow of oxygen causes the combustion process to be more complete (within limits). Both double wall stoves and forced air stoves attempt to make the burns cleaner and hotter (aka more complete or more effecient). Both do so by increasing the mass flow rate of the incoming air. Forced air stoves increase it more, however the double wall stoves make up for it by preheating the air as well.

I have some information posted on WB that relates to your statement and when I retrieve it I will post it in this thread.


That's why my opinion is that a simple raised floor hobo stove (you get a big boost in effeciency with a raised floor that allow air to pass more easily) is the sweet spot of benefits / cost ratio for most DIY wood-burning camp-stove builders.

I respect your opinion( or should I say "opinion is only that!!) and I agree with your opinion

JAK
2007-01-14, 10:51
Stoves often burn better in cold air because the air is more dense and contains less moisture. Of course once you heat it up it will contain the same moisture, and it has to heat up sooner or later for combustion anyway. I think the advantage of preheating has more to do with heat recovery after complete combustion and for getting the fuel to be more volatile, if I am using that term correctly. The tricky part of stove design in my opinion is the timing issue. Ideally the fuel will heat up and mix with the air completely in the correct proportions, and then burn completely at the right temperature, then heat whatever it is you are heating, then perhaps you can recover whatever heat is still available for preheating air or fuel, then escape to the atmosphere with unavailable heat and useless biproducts. Unfortunately the fuel does not always want to finish one stage completely before moving on to the next. Also, as the stove design becomes more complex to facilitate the above it will often make gains in one area at the expense of another, and also steal some heat just to heat itself up, as well as weighing more, or being more bulky, or more fragile, or more expensive, or any number of other imperfections. This is why stove design is so much damn fun for everyone. Like women, there is no perfect stove, and they are almost as difficult to understand. They are generally much safer to fool around with however. ;)

Lanthar
2007-01-15, 15:01
Incog,

In reading your reply, I believe there is a mis-connection of terms. The zip stove, according to most of the wood-stove literature I've read, would actually be classified as a triple wall configuration (outer wall, inner wall, burn chamber... aka, the burn chamber is considered one of the walls). Realize that I've never played with one, but your description + the pics you've taken confirms this theory. Double wall hobo stoves would be composed of outer wall + burn chambers (the bushbuddy is like this, as are most passive gassification stoves). Single wall hobo stoves (a tin can with holes punched in it) are just a burn chamber.

I am not at all surprised that the zip stove won't burn without the fan on. There's no way air is going to naturally maneuver through those narrow twisting confines.

PS - I've built a couple "woodgas" stoves (aka double wall by the terminology I'm using) along the lines of Risk's WoodGas Stove (http://www.imrisk.com/woodgas/ddstove.htm) or Garlington's Wood Gas Stove (http://www.garlington.biz/Ray/WoodGasStove/) and they burn like hades... I have another one that I'm working on (simpler construction... all you need is a church key, some tin cans, a punch and some snips... when it's done it will look a lot like a crappy DIY bushbuddy (http://www.google.com/url?sa=t&ct=res&cd=1&url=http%3A%2F%2Fbushbuddy.ca%2F&ei=q9CrRanfDo64ggT-1O2oAg&usg=__8k8LX3fUDf0SM_XJphhPlvBlhkk=&sig2=3qJojOO9sN6WK1TexQSNhw) ;)... at least, from my understanding of the bushbuddy design), but haven't got a chance to finish it yet.

JAK
2007-01-15, 20:09
All those passages can be a real drag, aerodynamically speaking. I think the primary function of double wall is to provide insulation, which might be done better with a single walled ceramic insulation with less drag. In the rocket stove they try and keep the drag to a minimum, except where the air scrapes past the pot to provide heat transfer. Because of something called Reynold's Analogy the amount of friction loss is proportional to the heat transfer, so if you made the gap wider you would have to make the surface area greater for the same ammount of heat transfer. In theory the only advantage of a forced draft stove is to reduce the height of the stove below the pot, which is an honourable enough objective in its own right. Happy stove building.

incognito
2007-01-16, 01:15
Lanthar!!!!!!

TeeDee posted a thread (Forum thread link) (http://hikinghq.net/forum/showthread.php?t=1911) about a woodstove that a man in Africa came up with (link to Africa stove story) (http://news.bahai.org/story/360). He also gave a link with a homemade version of this stove (link homemade version) (www.instructables.com/id/EFYJNQ9JEZES9J4SSJ/)

I looked at the homemade version and saw that it wouldn't work because the airflow would have been backwards, cooling whatever you were cooking and possibly choking the fire.

After thinking about it I thought I had the problem solved with the addition of a 3rd wall (fig. 1). I gathered 3 cans and was out in my garage happily drilling holes and putting a prototype together when I looked and thought a little harder and saw my idea would have the same problem that the homemade version in the link above had. As soon as the air heated the airflow would want to reverse it's path (fig. 2)
http://img.villagephotos.com/p/2006-3/1165284/crapstove.jpg
I came up with a few more ideas: some bad (fig. 3) some a bit better (fig. 5) but I can't see were any of them would be much improvement over the very simple can with a grate and airholes in the base (fig. 4)

Maybe there is something I'm missing but I'm not seeing where you can get much improvement over this without a fan.

Any ideas?

Figs. 1 and 2 are like the zip stoves walls. This configuration is what I was refering to. The diff being the zips air comes from under the stove.

Lanthar!!!! some additional info regarding more oxygen in cold air than war. So why preheat air in a Zip type stove or a passive stove with similar walled construction.

Quoted from Whiteblaze.com

[quote=terrapin_too;292661] I'm surprised you're still trying to argue your case.

Not me, I'm just enjoying your thread and sharing some information.


Quote:
Do you own one of these, or are you just surmising?

Yes, I own one. I stated in one of my posts that I did. Read my posts in their entirety

Here is a photo of it and it is flanked by two "StarLyte" fuel cells setting on their sides with one fluid ounce of denatured in each all ablaze. Notice!!!!!nothing spills out, totaly spill proof.



Quote:
Where are you coming from, with this?

A friend of mine is into high performance engines, he talks my ears off about how he improves performance. He is the one that educated me to the importance of the air being cool when introduced to the fuel. Here is some information that supports my way of thinking and where I'm coming from:

Colder is Better
By Karl Brauer
Email | Blog

While reading through the last few columns of Tech Center, you may have noticed a trend relating to cold air. Specifically, colder is better. When discussing the function of drum and disc brakes, it was stated that disc brakes are superior because they dissipate heat more rapidly, thus keeping the brake system cool and providing improved stopping power. A similar statement was made in regard to turbocharging, in which an intercooler is used to cool the compressed air after it leaves the turbo and before it enters the intake manifold. Finally, in our column discussing the workings of nitrous oxide, a specific mention was made about the tremendous "cooling effect" nitrous oxide has on the intake charge and why this effect helps increase horsepower.

With all this cold air blowing around, it might sound like we should just pack our bags and move to Fairbanks, Alaska, so our cars can finally operate at peak efficiency. From a pure automotive performance standpoint, it's not a bad idea. But it's tough to enjoy serious automotive performance in such a snowy climate (not to mention the dreadful guy/girl ratio up there), so a less drastic alternative seems in order.

One of the more common methods of improving vehicle performance, with regards to cooler temperatures, involves directing cold, outside air into a vehicle's engine compartment. This differs from the use of intercoolers in the sense that an intercooler is a container, much like a radiator, that passes air through it to reduce the temperature. In a cold-air system (or fresh-air system as they are sometimes called) a passageway (or series of passageways) is used to provide a cooler, oxygen-rich air charge to the engine. In an ideal system, the air is funneled directly into the engine's intake system for maximum efficiency.

As with the intercoolers used on turbocharged vehicles, the cooler outside air offers a more dense mixture of oxygen and a more powerful explosion when combined with fuel. It's this promise of increased horsepower that compels many current street racers to either hack open their hoods or to purchase aftermarket hoods with a "scoop" already installed. This is somewhat laughable since the use of cool air for increased horsepower has become standard procedure for new cars and is already utilized on most models, whether performance oriented or not. Though it rarely involves a hole in the hood, close inspection of the lower grille or bumper area will often reveal an opening that feeds into a system of pipes and eventually stops at the intake manifold. There are exceptions, of course, like the current Camaro SS with a hood that bumps performance (both perceived and actual) with its gaping maw.

An interesting bonus to cold-air induction relates to its effect at higher speeds. Depending on the location of the initial opening and the efficiency of the system, it's completely possible to get a "ram" effect from the force of the incoming air. In other words, at higher speeds the incoming air will actually start to compress in the combustion chamber during the intake stroke, creating a supercharger-like effect. (This ram effect is the basis for the "Ram Air" nomenclature that has been used on performance Pontiacs since the late 1960s.) No, you're not going to see a 30-40 percent increase in power just by letting cold air into the engine compartment and driving 100 miles-per-hour. However, an effective cold-air system can improve quarter-mile times by as much as three-tenths of a second; not a bad result for just letting some cool air into the engine. And since cold-air systems involve no drain on the engine, unlike turbochargers and superchargers, they cause no reduction in gas mileage or increased engine wear. Except for the small cost to design and install the cold-air piping, it's about the closest thing to free horsepower you'll find on modern automobiles.
Like we said, colder is better.
http://www.edmunds.com/ownership/tec...9/article.html

Here is more information:

Mechanics
All cold air intakes operate on the principle of increasing the amount of oxygen available for combustion with fuel. Because cooler air has more density for a given volume, cold air intakes generally work by providing cooler air from outside the hot engine bay. http://www.answers.com/topic/cold-air-intake

A little more:

http://lists.osourcery.com/pipermail...er/008698.html cold air versus hot

As I find more I'll post them. I'm not wrong to give my opinion on the statements that are made by stove makers.

This information pertains to cold air being introduced to a fuel. Form your opinions, I have. No need to double wall a wood burning stove!!!!!!!!
It's OK to add a fan to supercharge it , I love that oxygen, never deny your stoves oxygen.............
__________________
"Nothing Ventured Nothing Gained"

JAK
2007-01-16, 01:43
Cold air is important in engines for thermodynamic efficiency, and specific power, but not for stove for purely thermal efficiency. Unless you are planning on getting some work out of your stove, through a turbine or something, I think your references are not very relevant to the subject. There is perhaps a case in a forced draft stove that cold air is easier to push, but its not a very strong case. Your opinion about double walls being unneccessary or undesirable might be right, but not for the reasons you provide. Double walls are primarily just a way to achieve higher combustion temperatures with a metal stove, and therefore more complete combustion, but not neccessarilly better draft if friction losses equal or exceed the increase in draft for a given flow rate. For a small wood stove for hiking the primary interest should be reduced smoke and boil time, not efficiency, though higher efficiency might go along with the two.

A fan will not supercharge a stove. The flow can be considered incompressible even with a fan. It will increase flow rate, which is perhaps what you meant. However, along with oxygen comes lots of nitrogen and whatever moisture is in the air, and so you really don't want much more air than you need. Too much air will reduce the combustion temperature, and that is a bad thing. especially in such a small stove. Once you have char I can see getting a lot more heat out of a small stove with a fan, but you will soon need to add more fuel, which begs the question as to how much water you want to heat up, and how much BTUs you need, and so how much fuel and air you really need. There is a good case for a simple hobo stove for a small wood stove because you can start with more fuel and get higher combustion temperatures that way. I think a simple hobo stove with ceramic insulation walls instead of metal should work even better. Worth a try.

JAK
2007-01-16, 02:40
Lets say we want to heat up 32oz of water by 100F, what the heck, lets say 150F. So we need about 300 BTU. Assuming 20% efficiency we need 1200 BTU. Assuming wood fuel at 25% moisture we will need 4oz of wood. We might try for higher efficiency, but I don't think we can get much better than 20% beginning to end if we are primarily interested in heating up water fast without too much mess. 4 oz of softwood would need a firebox about 3 inches in diameter and 4 inches high. In a rocket stove you would make it smaller in diameter and keep feeding fuel in from the side at the bottom so you don't have to heat up so much fuel at once. In a hobo stove you would load it all at once and try and get most of the moisture and volatile gases and smoke out of the way quickly before putting your pot on to boil. That might be the best approach for a small stove. I think 3" inside diameter might be enough though. That will leave some room for ceramic insulation and still have a very compact stove. However, I think 4" inside diameter would also be a very compact wood stove compared to what people are used to. I think the think to try is different sized cans and how they compare whether or not they are insulated. As far as air goes, for 4oz of wood you need about 60oz of air at about 0.5 oz per ft3, so 120 ft3. If you are able to burn most of the wood in 12 minutes, that would be about 10 cfm. Through a 3" diameter flue that would be an exit velocity of about 3.4 ft/sec, which is a bit quick. I think to get that with a natural draft you would want a fairly tall stove and air inlets of the same total area as the exit flue. I think this is where that grate really helps keep things moving. Also another reason not to put the pot on too soon. Now most of the heating might only take 6-7 minutes, but it might be 15 minutes start to finish, though it can be a very pleasant 15 minutes if you are not in a rush. There might be a case for doing smaller burns back to back in a smaller stove. I think it would be interesting to start really small, like 2" diameter and 2oz of wood, but well insulated, and then go from there.

Lanthar
2007-01-16, 10:43
JAK is bang on about cold air vs hot air really being an issue with with thermodynamic power of engines or more specifically the "size" of the compression cycle (aka total mass of air involved affects the ability to produce power during a compression cycle with the same size cylinders). In very vague terms, with an engine, if supercharging your engine doubles the power (due to cramming more air into the cylinders), then supercharging + intercooling will triple the power (as now you're cramming more air that is also denser into the cylinders). Note that, the article from edmunds implies(correctly, I might add) that adding mechanically induced air chargers (turbo or super) decreases the fuel efficiency of the engine.

Figs 2 & 3 show a triple wall construction... realize, that, if the spaces between the walls were fairly large (like in the vesta) rather than small (like in the zip) natural convection will be just fine as long as the stove is tall enough to induce a temperature-difference draft.

incognito
2007-01-16, 12:05
Here is more info concerning warm versus cold, the first link is from a Geek and the second from an interested soul.

From the Geek (http://www.whiteblaze.net/forum/showpost.php?p=292973&postcount=76)

Interested soul (http://www.whiteblaze.net/forum/showpost.php?p=296572&postcount=111)

After your finished with that read my update on the Modified Zip

ixeric
2007-01-19, 06:25
There is only one rep for the Vesto stove here in the states: http://www.thesustainablevillage.com

TeeDee
2007-01-19, 14:41
There is only one rep for the Vesto stove here in the states: http://www.thesustainablevillage.com

Did you find the Vesta on their web site??? I couldn't.

ixeric
2007-01-19, 23:00
I emailed them to inquire about a US distributor. I found the email on their site: sales@newdawn.sz

A nice Africaner named Crispin Pemberton-Pigott [crispinpigott@gmail.com] emailed me back with the info. Gotta love the name.

The site is for a company in Denver that sells a bunch of sustainable living type products.

P.S. after writing all this I realized what you're asking is if I found the stove on the sustainable village site. I did and bought one to experiment with. It's about $100 delivered. Anyway, you are looking up the wrong name -it's Vesto. Here's the link: http://www.sustainablevillage.com/servlet/display/product/detail/33190

Gingerman
2007-06-21, 23:01
[QUOTE=dropkick;15971]The rocket stove uses a bunch of sand/ashes/cement to insulate the pipe and funnel the heat towards the pot. From what I can see it's more of a fixed position stove.
Maybe it would still work well without the insulation? But would it be an improvement over the Hobo stove?

I've built a Rocket Stove, and it is an improvement over a hobo stove: much hotter, burns less fuel (wood) for the amount of heat, and produces little to no smoke.

The insulation is essential, and a lightweight insulation, like ashes or perlite (which I used) works best. Dirt or sand or heavy weight filler saps heat from the flue, and adversely affects the burn.

I've read the technical development papers about the stove, and the issue of insulation is very important.

A four inch diameter flue, made of something very very fireproof is the ideal size, with a four inch feed tube and a nine inch chimney. You need to allow about 2 inches between the top of the chimney and the pot.

This stove is bulky, though not heavy, and not good for backpacking, but for consistant cooking, with no time limit it can't be beat. Temperature is controlled by the amount of wood fed into the stove. Only the tips of the wood burns, so it needs to be pushed in from time to time. Refeeding the stove is no problem, and once going there is no smoke. You use twigs to fire it, up to about the size of your thumb.

There is a good introduction on YouTube, "Making a Rocket Stove," which shows a simple DIY version that takes about 1/2 hour to make. Great for car camping or in the back yard. You don't want the insutaltion to get wet.

I used 4 inch duct material, and it burned through in one firing. The fire is really hot.

This is a serious stove for family cooking, and is being produced world wide to help cure problems with burning wood in houses for cooking. These are made usually of brick or ceramic tile.

Berkana
2007-12-26, 21:20
TeeDee posted a thread (Forum thread link) (http://hikinghq.net/forum/showthread.php?t=1911) about a woodstove that a man in Africa came up with (link to Africa stove story) (http://news.bahai.org/story/360). He also gave a link with a homemade version of this stove (link homemade version) (www.instructables.com/id/EFYJNQ9JEZES9J4SSJ/)

I looked at the homemade version and saw that it wouldn't work because the airflow would have been backwards, cooling whatever you were cooking and possibly choking the fire.

After thinking about it I thought I had the problem solved with the addition of a 3rd wall (fig. 1). I gathered 3 cans and was out in my garage happily drilling holes and putting a prototype together when I looked and thought a little harder and saw my idea would have the same problem that the homemade version in the link above had. As soon as the air heated the airflow would want to reverse it's path (fig. 2)
http://img.villagephotos.com/p/2006-3/1165284/crapstove.jpg
I came up with a few more ideas: some bad (fig. 3) some a bit better (fig. 5) but I can't see were any of them would be much improvement over the very simple can with a grate and airholes in the base (fig. 4)

Maybe there is something I'm missing but I'm not seeing where you can get much improvement over this without a fan.

Any ideas?
The solution to the problems in the stove model shown in Figure 1 and 2 is to use a "gas wick", which is basically an inverted can, above the fire itself. The surface of the can gets extremely hot, and causes a strong upwards convection in the narrow area around it (hence the name; it acts like a wick, sucking combustible gasses upwards), which basically eliminates any down draft. With a gas wick in place, the updraft will be so strong around the air and gases elsewhere will be sucked downwards to get to the combustion zone. If the outer wall of the combustion area gets too hot and antagonizes the action of the gas wick, insulate it somewhat so it still pre-heats the air without creating a back-draft that overcomes the "wicking" action of the gas wick.

Wood gassification stoves mechanisms like the one I described above can burn wood with a blue flame, AND produce charcoal as a byproduct, resulting in one of the most efficient burns possible.

To see a pretty scholarly examination of this mechanism for building a very efficient wood stove for developing countries, see this:http://www.crest.org/discussiongroups/resources/stoves/Reed/T1.htm
A color drawing of this stove can be found near the bottom of this page:
http://zenstoves.net/Wood.htm

Berkana
2007-12-26, 21:38
I found another solution besides the up-draft two-stage wood gasifier stove I linked in my prior comment.

See this PDF file:
http://www.crest.org/discussiongroups/resources/stoves/midge/THE_COMPLETE_MIDGE.pdf

I believe the design presented in the PDF would probably benefit from the use of a gas wick as well.

The design is similar to your Figure 1 and 2, but has subtle important differences; it gassifies the wood by pyrolysis (burning without enough oxygen, causing the wood to break down into gasses), and then burns the wood gasses, which can be burned much more efficiently than wood itself simply because the gasses can be thoroughly mixed with air.

JAK
2007-12-31, 01:52
This is sort of addressed to Rock, but thought I would keep it in this thread. I understand the Rock was interested in using a small wood fire occassionally in addition to his alcohol stove, especially on the first few cold weeks. Wondering what sort of a setup he decided on if any. I've gone back to using the Kelly Kettle even in winter, but am still interested in getting more skillful with a simple hobbo stove. Wondering how small it can be made and still be useful. Also wondering how to manage it in such a way as to avoid getting other stuff to dirty. What minimal accessories might be most useful, such as insulating pad, reflector, hanger, whatever. Are you thinking about messing around with some of this before you go or while you are travelling?

Still no major breakthroughs here. Good fuel still burns well. Crappy wet fuel don't.

incognito
2008-01-10, 15:05
This is sort of addressed to Rock, but thought I would keep it in this thread. I understand the Rock was interested in using a small wood fire occassionally in addition to his alcohol stove, especially on the first few cold weeks. Wondering what sort of a setup he decided on if any. I've gone back to using the Kelly Kettle even in winter, but am still interested in getting more skillful with a simple hobbo stove. Wondering how small it can be made and still be useful. Also wondering how to manage it in such a way as to avoid getting other stuff to dirty. What minimal accessories might be most useful, such as insulating pad, reflector, hanger, whatever. Are you thinking about messing around with some of this before you go or while you are travelling?

Still no major breakthroughs here. Good fuel still burns well. Crappy wet fuel don't.


JAK, last I heard he was going to use a stainless steel mesh stove. (http://www.whiteblaze.net/forum/showpost.php?p=424356&postcount=57) Goes by the name of "Globe Stove" (http://www.whiteblaze.net/forum/showthread.php?t=25589)
.