View Full Version : TPStove

2006-11-21, 10:17
OK. Here is my second prototype TPStove.
Not much to look at, but feel free to poop all over it.

Approximate weights using cheap scales (shown):
1. 4" x 4" Ground pad with tealight burner and cotton wick wrapped around brass screw: 0.25 oz
2. 4"H x 4"Dia TP Combustion Chamber with 4 thumbtacks: 2oz
3. 12.5"H x 4"Dia x 0.375"thick Wind Screen with 4 thumbtacks: 1.5oz
4. Beer Can (32oz shown but too snug of a fit): 1oz
Total weight excluding beer can: 3.75oz

This is the Wind Screen, inverted, with the TP Combustion Chamber installed with 1/2" space, friction fit.
I haven't lined the cardboard roll with muffler tape yet, so that it wan't burn.

This shows the tealight burner, cotton wick around brass screw.
Nice flame but only burned ~0.25oz in 30min, ~80 BTU/10min, still too slow, needs work.
The idea of the TP combustion chamber is to allow a hotter flame without smoke, and to create a draft.

http://i130.photobucket.com/albums/p243/JAK_45/TPStove_4.jpg http://i130.photobucket.com/albums/p243/JAK_45/TPStove_5.jpg
Photo 4 showing TP Chamber set down into Wind Screen. Photo 5 showing 32oz can is too snug for Wind Screen.

http://i130.photobucket.com/albums/p243/JAK_45/TPStove_6.jpg http://i130.photobucket.com/albums/p243/JAK_45/TPStove_7.jpg
Photo 6 showing 8oz minican sitting on TP Chamber. Photo 7 combustion happening down in the TP Chamber.

http://i130.photobucket.com/albums/p243/JAK_45/TPStove_8.jpg http://i130.photobucket.com/albums/p243/JAK_45/TPStove_9.jpg
Photo 8 showing 8oz minican set down in Wind Screen. Photo 9 showing minican raised up an extra 4". I pushed it down for test.

http://i130.photobucket.com/albums/p243/JAK_45/TPStove_10.jpg http://i130.photobucket.com/albums/p243/JAK_45/TPStove_11.jpg
Photo 10 showing air gap at base of Wind Screen. Photo 11 showing melting of plastic thumbtacks which cause pot to tip.

Plenty of room for improvement. If you have any poo, fling it now.

2006-11-21, 11:41
I was pleased with the weight, if I can get it to burn oil at 200 BTU/10 min. The pins need work. Besides melting they were to woobly in the TP roll. The dimensions need work to optimize for the size of pot I want. I think a mini one, 8" high for a 8oz mini can, might be fine with just a tealight, but I think I would want it to be more of a candle stove, for reading and simmering tea. I think I would like it to work with a 24 oz can. I would need a handle on the pot to get it in and out.

I think it would need to be a little more robust to burn wood fuel, but the combustion chamber idea is still a good one as an alternative to a battery and fan. The 'rocket stove' concept of Dr. Winarski (sp) is intended for wood fuel, larger stoves. One feature of it is that you constantly fees the sticks in, so the stove doesn't have to heat up all the fuel at once. This normally involves 1 or 2 1" diameter holes or tubes rather than the gap at the bottom. The holes need to be big enough to allow the fuel and the air to get into the combustion chamber. The chamber might need to be a little taller, or just push the TP chamber up and extra inch or two. Wood fuel takes up a bit more space, but it does radiate more heat because it has more surface. This is one reason why a kelly kettle works well, and why wider pots work better in such stoves, but the rocket stove idea still forks if the heat has nowhere to go but up and you have enough surface area to capture the heat. It does make for a taller stove however, which can get unstable.

Here is the link to "Design Principles for Wood Burning Cook Stoves":
It is the first under Download Publications. It has many ideas and concepts that I think apply to all camping stoves and not just wood cook stoves. I see there is also a publication on Designing a Clean-Burning, High-Efficiency, Dung Burning Stove - Lessons in cooking with cow patties. That might be more appropriate for my TP stove. Might be some good shit in there.

SGT Rock
2006-11-21, 12:14
Hey, thanks for that article. Some of these things it points out are stuff I have sort of figured out by trial and error over time:

1. Retained energy in the stove body helps to cook food.
Experiments by Baldwin have shown that retained energy is mostly lost. Leftover charcoal can heat food after the fire has been extinguished but retained energy in the stove body is usually too cold to effectively heat pots.
Note that retained energy in a stove can be advantageous if the stove is used for space heating.

I figured this and even had a sort of argument about it concerning the Etowah II which has a big old steel pot support that absorbs a good deal of heat energy. This is one reason I have been trying to re-design the Tipod to have less material to absorb any energy in the system.

Once the food has boiled, the fire can be extinguished. Placing the pot of food in an insulated cooking box most effectively uses the heat to accomplish the task of cooking. The haybox does all simmering without using extra fuel. This technique saves tremendous amounts of wood. And using a retained heat cooker saves time for the cook who lets the haybox do the simmering!

Sounds like a pot cozy! :D

I looked at that article. So the only question I can think of for now: Is your flame contacting your pot or are you using the heated air to transfer heat energy to your pot?

So maybe the next step is to figure out how to make a good, light, insulated windscreen. Seems like someone had a link to some sort of soldering cloth to protect wood while doing plumbing work.

2006-11-21, 14:06
The idea with the rocket stove concept is normally for the flame NOT to be contacting the pot, but for combustion to be completed before the flue gases come into contact with the pot. This improves efficiency on one hand with higher combustion temperatures and more complete combustion, but reduces efficiency on the other hand by requiring more surface area and heat transfer on the sides of the pot, so it needs a better wind screen, especially if you want to reach boiling.

So as you said a good light windscreen is essential, even more than usual, and more insulating. I think blue foam pad with aluminum tape on the inside is insulating enough and won't burn as the gases should be cool enough by then. I made that one of 12.5"x12.5" and it weighed in at 1.5oz with the aluminum tape on the inside and 4 thumbtacks as leg spacers. The TP Chamber is intended to deal with the highest temperatures. The blue foam might melt a bit next to the aluminum in a long burn, and it might char and change its properties a bit, but I think it will still hold together and contain some gases and remain insulative. It might get stiffer with use as it chars, but as long as it is sealed on the inside it shouldn't burn. That's the idea anyways. I am not so sure about the TP chamber made of toilet paper. For this to for right I would like the TP Chamber to get very hot, hot enough to melt and even burn aluminum, and char the cardboard and paper beyond the aluminum. A thin steel tube would be better, but not to thick as to be too heavy. I think 1" diameter is about right. It would need to be insulated beyond the steel tube, but a combustible material might be OK as long as no air gets in. It can char but still be insulative, but I don't know how long it would last.

The entire TP chamber wall could be insulative ceramic, such as a mix of sawdust and clay fired at high temperature, but it ends up at a specific gravity of about 0.35 which would be about 10 oz, way heavy. I was thinking it could be hollow and filled with combustible material like dry grass or dry moss or bark, which would char but still insulate, and then be used for the next fire. The combustion chamber could then be just thin steel, with a lid for adding fuel and removing char, and small pinhole vents to vent out volatile gases into the bottom of the combustion chamber. It would be tricky to manufacture. Perhaps a cylindrical tin with a lid just the right size, and then a holes cut in the lid and the bottom for a steel tube to be added and welded to the lid. The loose fit at the bottom would act as the vent.

Here is a link that explains how char is made for a flint and steel firestarting kit, which is where I got the idea from:

2006-11-21, 15:03
Here are some numbers:

To raise 16 oz of water from 50F to 175F = 125 BTU in 10 minutes.
Aiming for 50% efficiency = 250 BTU = 0.25 oz canola oil in 10 minutes.
Using an air to fuel ratio of 15:1, 4oz of gas in 10 minutes = 1.5 pounds/hour.
1.5 pounds/hour / 0.05 pounds/ft3 = 30 ft3/hr = 0.5 cfm

Air Density:

Using a cross section of 1 square inch for the combustion chamber and double that for the air gap around the pot, this works out to a velocity of 1.2 ft/sec in the chamber and 0.6 ft/sec up the pot, which seems about right, but might not be achievable with only a 4" chamber and 8" chimney. Might need 1 square inch for every 8oz of water in a stove that small (short). That would mean for 16oz, 2 square inches, which is a 1.6" diameter combustion chamber and I think about a 0.25" gap around the pot. Needs trial and error. You could go crazy and work out friction losses through a pipe and around corners and the amount ot draft created and the heat transfer into the pot and out the sides, if you were into that sort of thing, but you would still need lots of trial and error anyways.

With oil it needs to heat up quite a bit. For safety as well it is best not to have more that 0.5 oz of fuel in the burner. The other nice thing about a batch burn is that the burn rate tends to pick up as the fuel warms up, which is good because the draft also increases as the water heats up, and it also matched well to heat up the water faster as it gets hotter so as to lose less heat to the environment. I think a burn time of 10 min is a good target for 50F to 175F, using 0.25oz of oil for 16oz of water, and perhaps an extra 0.125oz and 5 more minutes to get boiling or close to it. I was thinking it might be better if this thing was all one unit, including the pot, so that any soot on the pot would be contained and the insulated wind screen would makes it all more rugged, though bulky. For a 16oz pot I thing it could all be about 4" diameter and 10" tall and fit where a Nalege Bottle might be carried. Anything more that 4" might be too cumbersome. Taller also provides a better draft, though tippy. For a larger stove you could split it into a bottom half and a top half, and carry one on each side, each perhaps 4" diameter, and 6" tall. It might also be used with an aluminum corked flask, and the top half could insulate it while it is being carried. The bottom half could carry fuel.

In the final analysis however I think a wood stove might be kept a little simpler, and lighter, and more compact, like that UL Bush Buddy, because efficiency is less of an issue, and soot is the real issue. The rocket stove does potentially reduce the soot issue, but at the expense of simplicity, and bulk, and the pleasure and warmth of actually seeing the flames. For a vegetable oil stove to work I think the combustion chamber does help, but it is hard to compete with the relative simplicity, and saftey, of and alcohol stove. I'll keep working on it though. I need a better Burner, and a better Chamber. I am happy with the Screen so far, even though it isn't collapsable. I could make it collapsable so I could sit on it, but then what would I sit on when I'm using it?

2006-11-21, 15:17

So, is the basic idea of the "combustion chamber" to make a smallish volume area that can heat up the air to where oil combustion is more complete?

as far as some SS tube... might try a bit of this
1" OD x 0.049" WALL x 0.902" ID T-304 TUBE (http://www.onlinemetals.com/merchant.cfm?pid=12933&step=4&showunits=inches)

If you don't care abotu seamless vs not... STAINLESS TUBE - ROUND (http://www.onlinemetals.com/merchant.cfm?id=18&step=2)

Oh, and I like the calcs...

On emore thing, can you post a pic of the burner sans flame? I'd like to see your wick setup.

2006-11-21, 15:39
Yes. I don't think the small volume is so essential as the small surface area that goes with it. At very high temperature radiant heat loss increases exponentially, so having less walls to radiate to, and walls that can get hot without losing heat, or burning, is what allows high combustion temperatures. Quite often a flame won't smoke until you but a cold pot of water near it. Then your done. The other part of it is to control the air flow so as to get enough air, but only enough air, plus mayber 50%, for complete cobustion. I think the rocket stove design manual also talks about turbulence in the chamber. Turbulent mixing generally improves combustion, except perhaps in the case of wick stove, an I am sort of bastardizing a rocket stove with a wick stove, which might not be good.

Thanks for the tube data. For my char making chamber idea I could use a tube within a tube, with some sort of removable bottom and fixed lid. So there would still be three main components: The Burner; the Chamber; The Windscreen. The Burner could be an alcohol stove, and oil wick stove, or a tin with some wood scraps, though for alcohol the Chamber isn't really neccessary. For the oil stove it is most important to insulate the fuel from the ground, so the ground pad I made is mostly with oil in mind. It gets very hot. It will melt through a blue foam pad without the aluminum tape, and perhaps even with it. We will see.

SGT Rock
2006-11-21, 16:14
OK, now maybe I am confused, But I swear I read in one of those reccomendations that you do have the flame touch the pot - and use the maxium space to be in contact with the pot with speed to the flame if possible, that using heated air to heat the pot was the worst way to do it:

Air is a poor heat transfer medium. It takes a lot of hot air to bring heat to the pot.

2006-11-22, 09:50
OK, now maybe I am confused also. :)

On page 7 they talk about improvements over an open fire, and say one improvement is: "fire hits the bottom of the pot, and sometimes the sides of the pot, exposing a lot of the pot to the hot gases".

Later on page 7, they talk about improving combustion, and one step is: "placing an insulated short chimney above the fire and helps to increase draft and gives smoke, air, and fire a place to combine, reducing emissions. This is a popular strategy used in many stoves including the Z stove, the Vesto, the Wood Gas Camp Stove, the Rocket Stove, the Tso Tso Stove, etc.
... Winarski developed the concept in the early 1980s creating a stove that cleaned up combustion and improved heat transfer efficiency."

But then on page 8 there is a picture and the flame does reach the pot, and I presume at times it does lick up the sides also. Hopefully it is a cleaner flame by then, so that combustion is more complete for more heat and less soot, and you should still get good heat transfer as long as there is enough area on the sides to finish the job, before heat is lost through the insulation or out with the exhaust gas. So you are right, but I think you only want the flame to 'just barely' reach the pot.

Lot's of very good information on page 8, like size of gap and height of contact with pot. "A 1.7kw fire with a channel gap of 6mm that forces ht flue gases to scrape against the pot for 15mm will be about 47% efficient." This is a gap of 1/4" and a pot height of 6". The 1.7kw fire is 5800 BTU/hour or almost 1000 BTU/10min, and enough to heat up 2 litres of water from 50F to 150F at 47% efficiency. I would scale it down to a 1 litre pot by sticking with the 1/4" gap and 6" height and 10min heating time, but reducing the heat to 500 BTU/10min, which is about 0.5oz of oil, or about 1oz of dry wood.

I made a small wood stove last night with 1oz of wood in a 12oz can, but couldn't get it to burn in 10 minutes. It heated up 8oz of water in about 40min, 12.5% efficiency. Definitely room for improvement. The rocket stove is intended as a domestic cook stove, but I think it scales nicely to a camp stove, if you can get the weight down a bit further, and keep it from tipping over.

SGT Rock
2006-11-22, 10:14
Just for a little clarification on the terms they may be using. Flame is an exaust gas of combustion. Flame is a plasma - which is an ionized gas.

A highly ionized gas. The fourth state of matter (it does matter). 99% of all matter in the universe is in a plasma state. Lightning, neon lights and fire are natural examples of plasma on Earth

So when they say "exaust gas" that could be a way of including the plasma, soot, and other gases like enols in the general term.

2006-11-22, 10:39
I think you are right. When they say flame, they mean flame, but when they say exhaust gases, they mean a combination which can include flame in addition to the usual suspects; mostly nitrogen, carbon dioxide, water vapour; and all the nasty stuff but hopefully not too much. The idea of the rocket stove, and some of the others with the insulated chimney before the pot, is to get most of the combustion out of the way before reaching the pot, and then to rely on insulation and a small gap, with enough draft forcing it, to get good heat transfer to the pot. The hot gases should be hotter as a result of the chimney, but it needs to be because you are relying more on convection and less on radiation. Another option might be just a taller better insulated hobo stove without the constriction in the middle between the fire and the pot. This would result in less mixing, but more radiation. You might get more smoke, but better heat transfer. The constriction, or pre-chimney, is intended primarily to complete combustion, not to increase draft. I don't believe there is anything special about the constriction that improves draft. It is the hieght and heat that creates the draft. The gap next to the pot reduces draft, but friction loss always goes hand in hand with convective heat transfer. They tend to be proportional because of something called Reynolds Analogy. In a sense, the fan and battery can be used to reduce the height of the stove while still maintaining good convective heat transfer, and not just to provide more air for a higher rate of combustion.

Later in the paper they talk about how critical that gap is for good heat transfer. I needs to be 1/4" or less for a small stove, for a pot 2 litres or smaller. If most of your heat transfer is to the bottom of the pot by radiation then the gap on the sides is less critical, and the wind screen is primarily just to keep the heat in the pot, not to transfer more to it. But if you rely too much on radiation I think you will get more smoke, especially when the pot is cold and the fuel is damp. Of course there is a continuum between a hobo stove, and a rocket stove, and you can supercharge either of them with a fan. In the end I think the primary trade-off is weight and bulk vs smoke, but you should be able to design and build both good and bad stoves of all types.

SGT Rock
2006-11-22, 10:57
Something to consider Jak - Titanium (especially the alloy) is more of an insulator than a concuctor. If you could make your stove from ti alloy it would help to insulate some. I have been thinking about reviving my knock-down stove idea and trying to figure on the dimensions - this article you sent will help me work out the math.

Also, I'm still looking for that link for that insulating flame proof wrap for doing plumbing solder work around wood. That stuff could be used to make a wrap for the stove and pot that would double as a cozy and as a stove insulator.

Anyone remember seeing that link?

2006-11-22, 11:04
I can't remember the link. In my next post I will show a bunch of photos from last nights experiment with 1oz of wood in a tall 12oz tin can. I made it like a hobo stove initially, without enough air flow. As one consequence it did sort of melt the blue foam a bit through the aluminum tape. Not much, but if the stove really fired up the way it should then I would need something other than blue foam in that area. Perhaps yellow fibreglass batt insulation, with aluminum foil on both sides to keep it together and keep it air tight.

Anyhow, here comes my mini-hobo experiment:

2006-11-22, 11:05
http://i130.photobucket.com/albums/p243/JAK_45/MiniHobo/MiniHobo_01.jpg http://i130.photobucket.com/albums/p243/JAK_45/MiniHobo/MiniHobo_02.jpg http://i130.photobucket.com/albums/p243/JAK_45/MiniHobo/MiniHobo_03.jpg http://i130.photobucket.com/albums/p243/JAK_45/MiniHobo/MiniHobo_04.jpg
The 12oz tin can weighs 1.5oz and came with a neat little spoon. Can't say I liked the Black Rice Congee, but whoever makes this stuff probably hates haggis, so I guess that makes us even. I made 2 holes at the bottom with a can opener, and 2 holes on the opposite side on the top, and stuffed it with 1 oz of birch bark and dry softwood sticks, for a total of about 400 BTU assuming 25% moisture. Later I added some beeswax to get it started and keep it going. The main problem was lack of draft.

http://i130.photobucket.com/albums/p243/JAK_45/MiniHobo/MiniHobo_05.jpg http://i130.photobucket.com/albums/p243/JAK_45/MiniHobo/MiniHobo_06.jpg http://i130.photobucket.com/albums/p243/JAK_45/MiniHobo/MiniHobo_07.jpg
http://i130.photobucket.com/albums/p243/JAK_45/MiniHobo/MiniHobo_08.jpg http://i130.photobucket.com/albums/p243/JAK_45/MiniHobo/MiniHobo_09.jpg http://i130.photobucket.com/albums/p243/JAK_45/MiniHobo/MiniHobo_10.jpg
The 8oz mini aluminum can started with cold water and a couple of ice cubes. Temperature outside last night was near freezing. The cubes were melted after 10 minutes when things really got going and I put the windscreen on. I also dripped about 1/5 of a 0.5oz beeswax candle, for another 100 BTU, so about 500 BTU in fuel in total.

http://i130.photobucket.com/albums/p243/JAK_45/MiniHobo/MiniHobo_11.jpg http://i130.photobucket.com/albums/p243/JAK_45/MiniHobo/MiniHobo_12.jpg
It took about 30-40 minutes to complete the experiment, which is a burn rate of only 125-150 BTU/10min. I wasn't able to measure the temperature. I am not sure what it goes up to. It felt like about 140-150F. So I transfered about 50-60BTU from 500 BTU of fuel, or 10-12% efficiency. There was a lot of char left over, which burned really hot if I took the pot off and let it breathe. Not a good design, except perhaps for making charcoal. I think just the tin can, with more holes on the bottom, and the blue foam windscreen, and a 16oz pot suspended down from the top. like a regular hobo but taller and more insulated, would have worked a lot better. Some sort of constriction in the middle might help the gases mix and burn for less soot, but probably not better performance. I think the tin can was about the right size for a single firing of 500 BTU. I think a simpler insulated hobo/rocket hybrid could be shortened down to 8" for a 8oz pot, but 12" seems about right for a 16oz pot. By hobo/rocket hybrid I am thinking the constriction could be reduced in height, and with a wider opening, so there is more heat transfer to the bottom of the pot with some soot on the bottom but not on the sides.

2006-11-22, 11:49
I think I will try a 8oz aluminum can as the wood container. It only weighs 0.25oz.
I suspect it will melt. These are the numbers and dimensions I am going to try next:

~5" high 16oz pot = 2.75" diameter, suspended into windscreen.
0.25" gap around pot = ~3.25" inside diameter wind screen.
0.375" thick blue foam = ~ 4" outside diameter wind screen.
~ 2" high constriction zone ~ 2" diameter opening.
~ 5" high primary combustion zone for 1oz on wood in a 8oz can.
Some sort of additional insulation between the fire can and wind screen.
This makes for a 4"dia stove about 12" high, perhaps in two or three parts.

Regarding wood stoves, they burn warm at first, and then very hot, unless you stoke them more constantly. In either case I think it makes sense to have no more than 1oz of wood or 0.5 oz on char in the stove at any time. This is about 400 BTU of fuel, and will deliver about 200 BTU of heat to water in a well designed stove. The challenge is to get the burn rate up to 400 BTU/10min and the heat transfer rate up to 200BTU/10min without a lot of smoke. Besides insulation, draft is required, which can be natural or forced. The draft is required not just to provide a higher rate of combustion air, but also to overcome the friction which is a natural consequence of the small spaces and turbulence required to achieve good combustion and good convective heat transfer. You should try and have smooth air flow, except where it is intended to create constriction and mixing for better combustion, or constriction for better heat transfer to the sides of the pot. I will try and achieve the required draft without a fan, by using a taller stove. This is the principle of the rocket stove. I think it might end up being slower. I would be pleased with a 10min heating time and a 15 minute boil time for 16oz if I could keep the stove weight under 4oz and the dimensions under 4"D x 12"H.

For a larger pot, which really needs to be wider, I might have to push the outside diameter of the top half to 5" or even 6". I think this is where a fan really has lots merit, so that the entire assembly can be closer to the ground, unless you add a stovepipe.

To add another twist, the idea of combining a lantern and stove has merit. This can be small, and does not have to be as quick, since you have plenty of time to simmer tea while reading, especially on winter nights. It is usually best if hung. The best fuel is usually oil or wax. This can be like a rocket stove, with a can over can setup. The trick is getting the light out without letting to much air in, or adding too much glass, which is heavy and breakable, or keeping plastic from melting while keeping the flame hot. If hiking solo, it is worth considering whether you should combine this lantern stove into your cooking stove also, rather than having the weight divided between two items.

SGT Rock
2006-11-23, 01:57
Here is the stuff I was thinking of: http://www.whiteblaze.net/forum/vbg/showimage.php?i=11900&catid=member&imageuser=6779

2006-11-23, 08:22
Very timely. My Blue Foam windscreen went China Syndrome on me last night. I tried to use it with some isopropyl alcohol that spread a little from the tealight. I heroically tried to salvage some toilet paper, but to no avail. It was a total loss. It all happened in my fireplace, which has glass door so I can use it as a flame hood.

2006-11-23, 10:52
Here is the stuff I was thinking of: http://www.whiteblaze.net/forum/vbg/showimage.php?i=11900&catid=member&imageuser=6779

Here's the thread link (http://www.whiteblaze.net/forum/showthread.php?t=16053&highlight=Light+alcohol+stove) to go with the photo, Sgt. Rock.

SGT Rock
2006-11-24, 12:26
I started sketching out a stove design trying to incorporate the ten design principles and hit a snag right away.

Working using the math for design principle two a chimney should be about 3 times as tall as the diameter of the burn chamber. I was planning for a 5" burn chamber so you could have some room to work with inside in order to build a fire that is large enough to do more than boil a pint of water. Unfortunately that means a 15" chimney. That doesn't even compute for the height of adding a pot skirt of the bottom legs so you can get the fire up off the ground for air flow. This means for a small 2.8" tall pot, I am going to have to build a stove that almost a foot and a half tall. Doesn't that seem sort of unnecessary for a camping stove?