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rocket stove cooker? Imagine I know zilch about rockets (but a bit about cooking with fire)  RSS feed

 
r ranson
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What I'm really interested in is experimenting with different fuel sources for cooking. I know how to cook over an open fire, I'm actually very good at it, but it's not very efficient if we are cooking for less than 12 people. It's even less efficient if we are only cooking one meal. The fuels I'm thinking of using are things like sunflower stalks, small branches, &c. Things that I've read used as traditional cooking fuel, but would burn too fast for an open fire. Then I saw someone with this kind of a stove:



Is this a rocket stove?

I know rocket mass heaters, but I'm not up on rocket cookstoves. This is a real thing, right?

I google around, and I see a lot of people are making stoves out of tin cans. I remember somewhere here, someone once said that metal and rocket stove burn chamber were not a good mix. Is this not a good mix long term, or not a good mix ever?

My friend works in a food place and has access to some rather large tin cans, which I thought would make a fun little stove, not for everyday use, but rather as a way of experimenting with the different cooking fuels. Once I can experiment with this style of cookstove, I can decide if it's worth building a proper one. This is a nifty video, but I have some issue with it, that maybe you can help me understand.



How come the flame keeps going backwards (out the hole we stick the wood)?
How long would a stove like this last? 1-hour total cooking time?

Pretend I know nothing about rocket stoves (because I have to sell the idea to people who know nothing about it), I'm confused by what google has to say, where does one start learning accurate information about rocket cookstoves? Am I even using the right words?

 
r ranson
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This video is very interesting, but again, I'm concerned about metal in the burn chamber. Would it be a concern if I'm burning it for less than an hour at a time, or would it be possible to use a big tin like this as the outside, but make the inside out of something like clay that wouldn't melt? I'm sure it's been done before, but I'm not sure where to start. If anyone knows, I bet they are here.



Edit to add: this is probably a stupid question, but please forgive me as I'm still learning. If I used clay for the inside of the stove, would the fire get hot enough to 'fire' the clay? Like I said, pretend I'm a complete n00b (person with zero experience). Could cob withstand this kind of heat? What kind of heat are we looking at?
 
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R Ranson, if you want to experiment, even tin cans can do. The metal thing applies to something which gonna run on a fairly regular basis for long period of time. Tin cans and cob surounding it is better, just in case the metal fails. If you cook a lot, it will. At a 1 hour, twice a day, the tin can could last a year i would think. There's people who would know better than me here or at donkey's.

The ecozoom you're showing here has a firebrick base, and a stainless or other heat resistant metal liner in the burn tunnel. Don't know how long that would last.

http://ecozoomstove.com/products/zoom-dura


But with a bit of wire, 20 firebrick splits, and perlite or vermiculite; you can make a durable rocket for not much, which gonna last.

May be check this drawing, to give you the idea of a 10cm heat riser, here coupled with a batch. But this hasn't been tested soo far.

http://www.permies.com/t/38889/a/20390/heatriseresteban.skp?download_attachment=true

You hold the four bricks with wire, and they're held on top of each other by slightly packed vermiculite. Only prob, you need a diamond blade on an angle grinder, to make the ledges on the bricks.

You can contain your stove, in barrels, big flower pots, anything you like, etc.

I did this last time i built a cooking one.

http://www.permies.com/t/35569/rocket-stoves/Range-retrofit

There's many other options.

http://www.rocketstove.org/index.php/institutional-stoves

http://www.ecologieforum.eu/viewtopic.php?f=3&t=4610


About the draft. It keeps drawing, because the pot is not straight above the heat riser, there's two or three spacers. And in the case of the institutional stove, a pot skirt is added, to heat even more the pot.

Hth.

.

 
r ranson
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Oh, thank you so much. I'll pick up those cans and start building. It will be my first time making cob too, so that will be interesting.

I can see this stove as something mostly used to boil water for tea while I'm out in the garden, or making a light meal in the summer when the kitchen is too hot to cook. Mostly, that would be less than half an hour of cooking time, occasionally up to an hour.

Thank you for taking the time to reply. I adore the range retrofit. Maybe one day... ah, a girl can dream.

I feel out of my depth with this, but I love cooking with fire and I'm fascinated with the idea of annual crops for cooking fuel. I can't see how an annual would work with a normal fire, so stove making time! They may not work with a stove either, in which case, I'll use twigs. The best way to learn is to try it, so that's the plan. Thank you so much for helping me build momentum.
 
Glenn Herbert
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A stove as small as this one is not going to get hot enough to degrade the tin cans quickly. A somewhat bigger stove might not last long, as it will be able to get significantly hotter.

Cob will work well as the inner core of the rocket stove, mixed in very straw-rich proportions for insulating value. The inner surfaces where the fire is hottest may become chemically altered to at least not melt in water, but the entrance of the firebox and probably the top of the riser will not get that hot.

The stove is smoking back because the fire is not big enough and hot enough, and the riser (vertical tin can) is not tall enough, to establish a strong draft.
 
Peter van den Berg
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There are a couple of things missing in that video. All around the combustion L-chamber there should be insulation material, gravel and sand won't insulate. There's also no shelf in the horizontal part to support the fuel and allow air to go underneath. Outside cooking is always prone to wind gusts, which is the reason why the flames are going in reverse. This could be alleviated by a wind screen and it would help a lot when the ratio horizontal to vertical is 1 to 3. This way, the draw of that little chimney is much stronger.
 
r ranson
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Thank you guys, this is great.

3 to 1, the 'chimney' should be three times as high as the firebox (place where I put the sticks) is long? This is good stuff.

How about the diameter of the sections? Does it matter if the horizontal is the same width as the upright?


It's going to be a few days before I get my tins. Oh well, it will give me time to source some clay. I'll probably have to get it from offsite, but I'll dig around and see if my soil has any to spare.

Trying to figure out how much clay I'll need, I dug out my copy of Hand-Sculpted House, to see if there were some general guides on the ratio of straw, sand, and clay. All I can find is "it depends," which is probably the best answer there is. What I did find was a nifty little write-up about cook stoves and how a large amount of sand in the clay prevents cracking.
 
Glenn Herbert
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The firebox and riser should be about the same in cross section for best results. A double-height big tin can shell would give enough size that you could get decent draft and real heat. A small one like the first picture would cook a couple of eggs or boil water for a cup of tea, but probably be pretty slow for a full meal sized task.

Cob inside a metal shell has very low strength requirements, essentially only needing to stay together in the original shape, so any soil with clay-like properties will probably be fine. For this purpose, any straw will burn out leaving insulating air spaces, so the quality is irrelevant. I have found that dried grass clippings work excellently here.
 
r ranson
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Good news, I found a lump of pottery clay from an earlier project. I've got sand, clay, hay (not straw, but if it burns out anyway, maybe it's okay), and silty soil. This is turning out to be a very affordable project.

How does this sound? One part clay, one part soil, and one part sand (by volume), mix together then add hay to feel.

 
r ranson
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I picked up my tins today. I have a few pressing jobs to finish, then I can play with my stove.

Question: how long should I leave the cob to dry after I assemble it?
 
Glenn Herbert
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I have found that cob, unlike pure pottery clay, can be fired while still damp without ill effect. In the case of a rigid sacrificial internal mold or form surrounded by cob, it is actually best to burn it out before the cob dries and shrinks. If burned out while the cob is pliable (but not so wet as to collapse on its own), the form is removed as the clay stiffens from the heat, and there are no stresses to split the clay as it shrinks in drying.
 
john lindsey
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How about biogas....the only problem that I see is that the plastic barrels cost way too much.
 
Len Ovens
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R Ranson wrote:



How come the flame keeps going backwards (out the hole we stick the wood)?
How long would a stove like this last? 1-hour total cooking time?


The big fail on this one is no fuel shelf. A fourth can smaller than the feed and squashed almost flat to make a shelf 1/2inch or so off the bottom for the fuel to sit on would give a hotter fire by giving air direct at the burning part of the fuel rather than encouraging the flame towards the fuel mouth.

The second video (with the squarish green can) shows a shelf. I think it could be a bit lower and still work well.

The rocket stove (as opposed to the RMH) is designed to be less efficient on purpose to get the hottest gas to the pot. The pot will also blacken because the pot is cold condensing anything it can out of the flue gas. People have tried taller rocket stoves and the optimum height seems to be shorter than the flue gases fully burned height... as measured in a fuel-use/time to cook scenario. Which generally is measured as time to boil x amount of water. (what gets the most heat to the pot for the amount of fuel used) I don't seem to have the link I had to the numbers... 4inch diam. riser 15inch high sounds familiar... different diameter needs different height. The ones I saw were all cob using the same mold to make lots (for a village). The riser form was a 4in. drain pipe in a 5 gallon plastic pail. Hmm, seems I posted it before: Old permies posting However the url I left there has a blank page so, I looked around and found this: rocket stove photo album. It gives some dimensions and instructions.

From the same site: Instruction book for rocket stove.

They have some things to say about building materials quality and mixes.

Just for completeness: home page with two rocket hobs and an oven.
 
Elmira Rose
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Not sure if this would be helpful but I've built a few of the tin can rocket stoves and cooked on them daily sometimes three meals a day. the quick and dirty one made out of clay, straw and tin lasted me about a year. I've made sturdier rockets out of 5 gallon metal buckets -got it from a natural food coop selling bulk maple syrup, Who gets to lick the bucket! Another source for metal 5g buckets is construction sights but you might want to burn out what was in it before hand. For the feed tube and riser I used stove pipe -got it from a scrap yard. I also bought vermiculite for the insulation and filled any cracks with clay. Lasted a couple of years of daily use and then I gave it to a friend. seemed like it could've lasted awhile longer.
Other folks on this forum probably know more about specifications but I just loosely followed the 3 to 1 rule. This I would say is not a hard and fast rule. I've seen and made stoves that break this rule but are good enough to get some water rolling with just a few sticks. I think good insulation is important. but in some situations if your riser is tall you can get away with poor insulation.
The information I'm presenting is based on real world experience. Like the time I was under an overpass waiting for freight to hop and it got chilly (winter in texas and it was snowing, what the Eff) and I got hungry and was sick of cold sardines. I decided to throw together a make shift shelter and build a rocket stove with some tin cans lying around. One hot meal ready to go on the fly! buckle up Sardine Sammy is blasting away on his rocket stove!
In summary tin can rocket stoves are awesome. quick, convenient (as in free), and once you get the hang of it shouldn't take you more than a few minutes to make.
Oh and by the way you definitely do not need all those electric tools in the videos. Try a multlitool and gloves. Or a knife you don't care about dulling or if you know how to sharpen knifes just use any old knife. gloves are key.
 
Shaz Jameson
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Just wanted to say, I am also a complete RMH n00b, and this thread was the first time I felt like, woah, I could do this too.
So thank you!
 
r ranson
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Shaz Jameson wrote:Just wanted to say, I am also a complete RMH n00b, and this thread was the first time I felt like, woah, I could do this too.
So thank you!


Glad to find another Rocket n00b out there. I felt a bit embarrassed asking because I'm so active in other parts of the forum. But you know, gosh darn it, I want to make a rocket stove. I got to start learning somewhere, and if there is anywhere on the internet that is welcoming of new people, it is here.

Cooking with fire is one of my passions, but I have so little experience cooking with a fire-powered stove. I've been seeking a complete and utter beginners guide to wood-fired stoves - something that lists what types exist, their pros and cons, then points us in a direction where we can learn more - but still looking. In the meantime, I've decided I'll just build one and see what happens.
 
Shaz Jameson
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I know what you mean.

As a (now-proud) n00b, I look at the very well put together Table of Contents on RMH and recognize that it is an absolute goldmine of information, but it's overwhelming and still not Instructables-level of beginners.

One option is of course to buy the book, though I'm not at the stage of wanting to retrofit my house. It's more like, let's see if I can boil water for my tea or have a small BBQ in the community garden.

Is there an instructables-level of beginner's RMH somewhere? If not, that would make a great article for somebody to write (nudge nudge) and would be a pretty good residual income stream.


So I went to look at the Wood Burning Stove page on permies.

It seems my best option would be this:

Although a lot has happened since this book was written, this book still has a lot of good information. It has explanations on how this type of wood burning stove works in general. Rocket Mass Heater Book


Then regarding your thoughts on the overview of wood burning, Paul writes:
Ernie and Erica's book "Art of Fire" goes into detail on all sorts of fire based inventions, and heaps of things most people never knew about fire. It covers the foundations of rocket mass heaters and the predecessor, the rocket stove. And the predecessor to that: the fox stove.


Is that the kind of thing you were looking for?
Again, forgive me if it's a stupid suggestion, this is really my first time searching through these fire-forums.

 
Len Ovens
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Shaz Jameson wrote:I know what you mean.

As a (now-proud) n00b, I look at the very well put together Table of Contents on RMH and recognize that it is an absolute goldmine of information, but it's overwhelming and still not Instructables-level of beginners.


I think, at least in these forums, we have tried to always call the RMH a "RMH" and not a rocket stove. This is because they are two different beasts. The RMH is much more complex and requires more knowledge to build or even plan. The RMH is built in place. The rocket stove, or as the title of the thread says "rocket stove cooker" is quite different. It does rely on some of the same principals as the RMH, but not all. The use of the rocket stove or something very close has been used almost since man started using fire. The RMH is quite new and even the principals it is based on are not that old (hundreds of years rather than thousands). The rocket stove is a fire with a chimney where the cooking is done on top of the chimney. There are simple versions and not so simple versions but from what I can tell by reading, getting more pot heating from a given amount of fuel is the hardest part requiring keeping maximum gas contact with the pot for as long as possible. Just setting a pot on top of the chimney will not be much more efficient than an open three stone fire though it can be much cleaner and generate less smoke (a great benefit all on it's own). However, in cooking, getting the most heat out of fuel is secondary to cooking properly. One of the oldest methods of getting the most out of ones fuel for cooking is the kind of cooking one does... the "stir fry" is one of the best where the food is cut very small and fried quickly. cooking a roast on a spit takes a lot of fuel.
 
Brian Van Dine
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I first became aware of rocket stoves for cooking before I became aware of rocket mass heaters. I have found a good resource for learning about the technical aspects of rocket stove design. There is a facility that is devoted to exploring sustainable technologies and rocket stoves for cooking are a primary focus. The resource is www.aprovecho.org. On the home page of this website you can download a PDF book of over 100 pages that details laboratory experiments they've run with different rocket stoves - they actually have built a lab with testing equipment! The PDF examines that various factors of rocket stove effectiveness and what they've discovered are key issues. They also produce videos and at least one video I found on Youtube by this group details how they make their rocket stove for cooking. They actually make their own fire brick, which implies they must have a ceramics kiln on site as well.

It would be nice to know how to construct a wood fired kiln in order to make one's own fire brick. Interestingly, I did do a little web surfing to try to find small wood fire kiln designs. I found some forums that primarily consisted of professional or amateur potters, understandably so, but there were also a couple of posts from folks who had homesteads and who made their own earthen vessels on site. Also, it seemed like most of the commenters weren't aware of rocket stoves, but one post did raise the question of whether rocket stove technology might work for kiln design. There appears to be a potential opportunity for some cross-over discussions which might eventually yield a design for a hybrid between rocket stove and kiln. Who knows?
 
Shaz Jameson
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Len Ovens wrote:

I think, at least in these forums, we have tried to always call the RMH a "RMH" and not a rocket stove. This is because they are two different beasts. The RMH is much more complex and requires more knowledge to build or even plan. The RMH is built in place. The rocket stove, or as the title of the thread says "rocket stove cooker" is quite different. It does rely on some of the same principals as the RMH, but not all. The use of the rocket stove or something very close has been used almost since man started using fire. The RMH is quite new and even the principals it is based on are not that old (hundreds of years rather than thousands).


Len, thanks for this, I really appreciate you laying out this difference, it makes it all fall into place a lot easier.
 
Julia Winter
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I went to the Aprovecho video gallery and found this video:


Some of it is making your own firebricks, but that requires a kiln. It's probably easier to find a few firebricks.
 
r ranson
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I finally started construction on my stove this evening.

I'm not going to tell you what I'm using for my fire tube because I'm confident it's not a good idea. It will 'burn out' very quickly. But, it should last a fire or two until the cob can harden and be strong.

I have my clay rehydrating, it will probably take a day or two, then I'll mix it with sand, dirt and hay/straw mixed.

Very excited!

Next is choosing the pot(s) I plan to use on this stove. I would like to shape the cob in such a way that these two pots can rest on it, and the fire can escape around the pot a little bit. Which isn't actually making sense as it's a picture in my brain and I have trouble translating pictures into words. But I think it will work. One pot is a shiny kettle, the other is a big cast iron dutch oven.
 
r ranson
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Not sure where to ask this question but since it's related to my stove, I'll ask it here, and maybe somewhere else later.

When I make up my cob for my stove, do I have to use it all right away or can I dry it to be re-wet later? Or is there a specific stage where I can stop (like before adding the hay) and dry the mix, then rewet it later and add the hay then?
 
Alan Bowen
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Julia Winter wrote:I went to the Aprovecho video gallery and found this video:


Some of it is making your own firebricks, but that requires a kiln. It's probably easier to find a few firebricks.


Julia, In the video he is making Insulated Firebricks. I wouldn't make that stove with plain hard firebricks.
You can make something to fire them in by using a Harbor Freight weed burner and some thrown together fire box with insulation wrapped around it.
 
Len Ovens
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R Ranson wrote:Not sure where to ask this question but since it's related to my stove, I'll ask it here, and maybe somewhere else later.

When I make up my cob for my stove, do I have to use it all right away or can I dry it to be re-wet later? Or is there a specific stage where I can stop (like before adding the hay) and dry the mix, then rewet it later and add the hay then?

Clay and sand can be dried/rewet... but it is a lot of work to get lumps out. Better to keep it in a plastic bag and keep it wet. I hope you are using straw rather than hay. Straw is strong, hay is weaker. I would not add the straw till just before use. I have read how long straw can sit while wet without starting to smell (smell means it is starting to degrade and will loose strength) Also fiber looses it's shape if you are using it to insulate if it stays wet too long.

Note, if you are only using the hay to make the cob lighter and more insulating (in place of sawdust) strength is less of a worry as you will be burning it out anyway by firing.
 
r ranson
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Thanks, that sounds like great.

I mixed in half the minimum amount of sand into the clay yesterday, will be adding more today. Still toying with adding soil to the mix, well, I say soil, it's more like depleted silt.

At the moment what I have for the 'straw' is grass clippings and hay left over from the animals (they don't like the coarse bits, so I gather that up for bedding, and in this case for making cob). Hopefully this will work. If not, I'll have learned something and need to try again. I suspect I am making every rocket stove mistake possible, so I'll probably be making a new one in the summer.


Once my grain harvest comes in, I'll keep the straw and use that for the next stove. See what difference it makes.

 
r ranson
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Would tow and boon from flax processing make a good 'straw' subsitute? It's pretty strong stuff, but the individual fibres of the tow are quite fine.
 
r ranson
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I have my stove together and most of the giant tin can filled with cob. We did a test firing and it looks great. Right from the second the match touched the paper, the fire was going in the right direction.

Tomorrow I'll make a proper shelf for in the firebox, then make some smoother cob to shape a shelf for the pot at the top of the stove. I figure there are only two or three posts I'll use on this, so why not use cob to shape where they sit? Any reason I shouldn't?
 
K Putnam
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Last year, I bought the EcoZoom with the cast iron top as an emergency preparedness measure. A bit spendy when you can make your own, but it works great and it is there if the power goes out following a big winter storm. The cooktop is a nice feature. It doesn't get super hot, but it can help keep pans and the edges of pans warm. I've made large pots of chili from start to finish on it in a big dutch oven. So, having a sturdy cooktop that holds heat rather than insulates against it might be nice.
 
Elmira Rose
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Check this guy out!
Rocket stoves can be as easy as mud pie.

He forgot his tea kettle for the top
 
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R Ranson, remember that for the pot rest, three or four legs are good, but you should leave as much as the CSA space, below and on the sides of the pot, so airflow doesn't get restricted. Below, raising it with pot legs. On the side, it's only when using a pot skirt.

Hth.

Max.
 
r ranson
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Cob is drying nicely. I've been lighting a small fire in it for about 20 min each day since the cob went in. I'm hoping to dry the cob from the inside out... if that makes any sense. I'm worried if the top drys too fast, the moisture trapped inside will make the cob rot.

As you can see from the photos, the pot I tried at first was a touch too big for a small fire and made lots of smoke. I think if I had the fire good and going, there would be enough room for the air to get out, but most of the time I'll be using a much smaller pot.

The cob looks pretty smooth. That's because I made the top layer with the pot rest, of cob with fine tow from flax processing. For the bulk of the cob I used straw and hay, heavy on the straw.
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alex Keenan
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I hear much about rocket stoves and outdoor cooking.
Having been a outdoor cook for a long time and loving history I see something missing from this whole conversation.

There really are two main techniques that technology falls into.

1) Low and slow such as dutch ovens, BBQ brisket, pot of beans, roasting roots in ashes, etc.
2) Hot and fast like the rocket stove, woks, grilling, griddles, etc..

Most of the time, when I see a rocket stove associated with cooking I see a pot with some liquid being heated to the boiling point.
Some times I may see a wok associated with a rocket stove.

The really impressive thing about the rocket stoves is the reduced amount of smoke generated. For people who cook over fire this is a major thing because of all the health problems related to inhaling smoke over a period of time.
The second impressive thing is that rocket stoves provide a better utilization of fuel so over time less fuel is required to prepare meals. This is important where fuel is limited.

This said for outdoor cooking you are mainly talking about heating a pot of liquid or using a hot and fast cooking method.

Now once you have a pot of something in liquid boiling you can shift to a low and slow by transferring said pot into a haybox.
This tends to work very well for legumes, soups, and stews. For water boils at around 212°F depending on elevation. So putting a simmering pot in a haybox can start you around this temp and minimum safe temperature for chicken is 165, and 160 for beef and pork.
I wish there were more effort to match rocket stove to haybox. For both have to be designed for the size of the pot being used.
To use rocket stove and haybox together you need to use the same pot so both systems have to be optimized around that pot size.


 
Satamax Antone
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R Ranson, it's not that your pot is too big, but the four legs too low. You see the space at the edge of the tube, on the perimeter; is too small

You have 4 gaps. And the total surface of those gaps should be at least equal to the CSA of the heat riser, 1.5 is better, due to the friction caused by the gas direction change.

CSA of each gap is "lengh of arc X height". You can't realy make the legs thiner. So you have to change the height. Myself, i would do it with rebar or something, laid flat across two of the rests.

Also, carefull that the lip on the outer casing doesn't restrict the gas flow either.
 
Hans Quistorff
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My observation is that to use the larger pot the legs should be on the sides instead of the corners. This would allow space for the exhaust gasses to escape and rise up along the sides of the pot.
The flow could be increased by cutting down the sides of the square can but that would increase the chance of a breeze blowing through from one side to the other.
Two pieces of rebar or angle iron inserted through the sides of the square can about the width of the core would eliminate the need for the legs and expose more surface to the heat.
 
Len Ovens
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R Ranson wrote:Cob is drying nicely. I've been lighting a small fire in it for about 20 min each day since the cob went in. I'm hoping to dry the cob from the inside out... if that makes any sense. I'm worried if the top drys too fast, the moisture trapped inside will make the cob rot.

If this is not a problem in cob homes with 2 foot thick walls with no fire to dry them, then I think you will have no problems here


As you can see from the photos, the pot I tried at first was a touch too big for a small fire and made lots of smoke. I think if I had the fire good and going, there would be enough room for the air to get out, but most of the time I'll be using a much smaller pot.


Also remember that your pot is less than the boiling point of water and it will cool the flu gas. The flu gas even if burning completely is made of CO2 and water. With no pot both will be invisible, but the pot will bring the temperature down and so some of what you are seeing may be steam too.

The rocket cooker does trade complete burn for efficiency. It is very clean burning, but not as clean as the RMH. Expect the bottom of your pots to be somewhat blackened. Still, it should be better than it is... see the comments above about pot spacing.
 
r ranson
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You have 4 gaps. And the total surface of those gaps should be at least equal to the CSA of the heat riser, 1.5 is better, due to the friction caused by the gas direction change.


Question: what is CSA? (remember, total newbie to rocket stoves)

I was wondering if it was too low. I only put an inch and a quarter above the pipe (and it shrunk to an inch overnight - clay might have been too wet). I'm going to try to get a stove circle from an old gas stove that will raise the pot up a bit more, should give us more airflow.

This is great feedback. I'm learning loads on this prototype.

Also remember that your pot is less than the boiling point of water and it will cool the flu gas. The flu gas even if burning completely is made of CO2 and water. With no pot both will be invisible, but the pot will bring the temperature down and so some of what you are seeing may be steam too.


It does not help that the wood was a bit wet, the fire just started, and the water in the pot cold. This is good to remember.

If this is not a problem in cob homes with 2 foot thick walls with no fire to dry them, then I think you will have no problems here


I hope so. I wondered this because cob walls usually breath and aren't surrounded in tin on most sides.
 
Satamax Antone
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CSA= cross sectional area
 
Len Ovens
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R Ranson wrote:
Also remember that your pot is less than the boiling point of water and it will cool the flu gas. The flu gas even if burning completely is made of CO2 and water. With no pot both will be invisible, but the pot will bring the temperature down and so some of what you are seeing may be steam too.


It does not help that the wood was a bit wet, the fire just started, and the water in the pot cold. This is good to remember.

Wood is a "Carbohydrate". This in general terms means it is made from Carbon and Hydrogen. When it burns or "oxidizes", both of these elements combine with Oxygen. The Carbon when fully burned makes Carbon dioxide and Hydrogen when burned makes H20 or water. Most carbohydrates are in strings like Ch3-ch2-...ch2-ch3 with any number of CH2 in the middle (most organic carbohydrates also have a CH2OH on one end like Alcohol). So for every Carbon atom there are at least two Hydrogen atoms which means that a burn puts out roughly the same number of water molecules as Carbon dioxide molecules. Then, of course, even dry wood has at least 10% water content as well. But the burn produced water is probably the major source of steam.
 
r ranson
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Today I cooked breakfast, well sausages. The rest of breakfast was foraged from the garden.

I started by getting the fire good and hot. Then I put the pan with the sausages on top, in the middle.

cob tin rocket stove


Smaller than the earlier pot, there wasn't any issue of the fire dying down or smoking/steaming.



The first thing I noticed is that this is a darn sight hotter than my electric hob. The second thing is that temperature control is an issue. On an open fire, I move the pots closer or away from the flame to control the temperature, or occasionally stoke or pull apart the fire if need be. It's difficult to adjust the fire in the rocket stove, although poking in more sticks quickly increases the heat, there is no easy way to decrease it. I thought this might be the case, that's why I made the pot rests so large. I took the pan so it was off center, and this way I had a hot spot for fast cooking and a cooler area of the pan for keeping warm.



We cooked two batches of sausages (the first ones tasted so good, we needed more), and each batch took one handful of twigs. I had the best luck mixing different kinds of wood.

This is a stove I would use for frying (which isn't that easy on an open fire), as well as stir fry, and things that need boiling.


For starting the fire, dry ornamental grasses worked best, with a bit of paper. It took hardly any fuel to get the fire started - unlike an open fire that tends to require a lot of kindling.

So you get an idea, this is the kind of fire cooking I'm comparing it too.

fire roasted goose, fire cooking


Lots of pots on the go, heat control via moving the pots. This is great for group cooking, but tends to be slow.


The rocket cooker did as I hoped, it cooked quickly and efficiently. Two batches of sausages took the same time as one batch on an open fire (with less fuel) or one batch on my electric hob.


As you predicted there was a lot of soot - especially after I moved the pot off center.



It looks like the cob pot rest will need to be replaced after a few dozen firings. That wouldn't be hard to do and will give me a chance to try different shapes and heights.

By the end of the second handful of twigs, the outside of the tin began to feel warm. After the fire was out, the cob still emitted a lot of heat. It actually seemed to increase in heat after the fire went out, but that might be partly the sun's fault as it was warmer on that side than the shady side. This gives me an idea for camping. Cook the meal and get the cob warm, then move the stove inside (fire out) the tent at night to help heat the tent. It would need to be a large tent and safety considerations would need to be met, but it might be worth investigating.



My biggest concern with this design is that it might be easy for fire to fall out of the feeding tube if I wasn't paying attention. I kept the ground in front of the stove very wet to prevent grass fire. This is something I need to take into account when I design my next stove.
Unlike the open fire, this stove took my full attention - I couldn't run in and get more sausages while it was lit, so I had to bribe someone else to do it for me.
If I continue to use this stove as the weather warms, I'll need to make a safer platform for it to cook on.
Otherwise, very happy.
 
I agree. Here's the link: http://stoves2.com
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