Introduction: Build a Low Tech CFV Stove

The most popular alcohol fuel based DIY backpacking and camping stoves utilize aluminum beverage cans to provide a laminar or pressurized vapor fed flame. However, they have limited fuel storage and thermal generating capacity, durability and adaptability. Most require an extraneous pot stand or holder and have additional construction, storage, startup and usage needs.

While high tech CFV (Capillary Force Vaporizer) burners represent an advance in technology they are unfortunately too high tech to be offered to DIY stove builders as a solution.

Fortunately a low tech CFV stove can overcome the limitations and disadvantages of both the high tech CFV stove and the alcohol fueled beverage can stove by using low temperature evaporation of alcohol fuel fed to the flame at the perimeter by an encompassing pad wick made of almost any absorbent material. In fact, it might (except for the flame) be mor properly called a Capillary Force Evaporator stove.

While being easy to construct and simple to use it can be made to meet virtually any fuel storage, thermal generation capacity or durability requirement in addition to making replenishment of fuel during operation possible and startup hassles a thing of the past.

A basic low tech DIY CFV stove can be built quickly in an emergency to meet most any fuel or thermal need but with more time and materials it can be adapted and built to accommodate virtually any backpacking, camping or other need.

Step 1: Gather the Materials and Tools

You'll need some aluminum sheet. This can come from most any source to meet whatever requirements you have for durability.

To construct the test stoves I used aluminum flashing, since it is about the minimum thickness that can be secured with 1/8" pop rivets. Brass, stainless or aluminum machine screws can be used in place of aluminum or stainless pop rivets. I used aluminum pop rivets since I will most likely not be taking the stove apart. In the event I do need to take it apart, aluminum rivets are the easiest to remove. You'll need a pop rivet gun if you go with pop rivets as well as 1/8" by 1/8" pop rivets plus the length of the thickness of the stove you want to build - usually 1/4" long rivets will allow adequate space for fuel. Be careful not to over compress them as I have done.

Next you'll need some aluminum door screen. The dimensions of both the aluminum sheet and the aluminum screen as well as the number of pieces is the same. You will dimensions big enough to cut circles about 1/16" to 1/8" greater than the pot you plan to boil water in. For a frying pan you will want dimensions that are half the diameter of the frying pan. I used kitchen shears to cut both the screen and sheet.

You will need a straight edge,ruler,scribing compass,a power drill and 1/8" bit and some absorbent material. I used regular kitchen paper towels but cotton or fiberglass cloth would certainly be more durability. The choice of absorbent material is yours with the exception of synthetics and plastics, which melt. Update: I've now tried fiberglass angle hair, mat and asbestos cloth and I'm not really happy with either. The hair is extremely absorbent and for that reason the fuel can not be added before the pot is placed on the stove else half will spill. The fibers of the mat are too straight and stiff and will come loose and break into splinters. I have tried to seal them on the edges and sides with a blow torch but the glass can break and expose the fibers again. Asbestos cloth is best so I imagine fiberglass cloth would work at least as well.

I recommend alcohol fuel only since oil, mineral spirits and kerosene need to be heated inside a closed vessel until they become pressurized or they will burn incompletely and produce excessive carbon monoxide and soot.

Step 2: Decide How Big to Make Your Stove

Cutting Diameter

You want the diameter or perimeter of your stove to be a bit larger than the pot you are going to use. Your pot does not have to be round either. You can use a tea tin that is square if you want and only cut the stove slightly larger so your tea tin pot will sit on top of the stove with minimum protrusion of the stove and maximum setback of 1/8" of the pot from the edge of the stove to give not more than 1/8" clearance.

The first stoves I built were for 12 oz and 24 oz soda cans. I used the outside dimensions of the bottom foot since there is a taper from the foot of the cans running up to the sides for the flame to follow. Since these dimensions were 2-3/16" and 2-1/2" I added 1/8" to get a cutting diameter of 2-5/16" for the 12 oz can and 2-5/8" for the 24 oz. can.

For this instructable I decided to build a stove able to boil 1 liter of water in a 404 x 700 bean can and to boil 2 liters of water in a 602 x 602 coffee can

To meet these specifications i chose a diameter of 4-1/4" plus 1/8" to support the bean can using only a flat surface or the coffee can and to support the coffee can using the bean can for support.

Thickness, or Height

I used a bit of math and chemistry to help guide me in selecting the thickness or height but once you have calculated the basic requirements you can use trail and error to fine tune.

To boil 2 liters or 4.41 lbs of water from 60 F I needed to add 152F to raise the temp to 212F.

I BTU is required to raise the temperature of 1 lb of water, 1 deg. F so I needed 4.41 lbs times 152F or 670.2 BTU.

91% Isopropyl alcohol contains 20.73 BTU/g, so I needed 32.33 grams of Isopropyl fuel to bring 2 liters of water to a boil from 60F.

As life would have it there are thermal and evaporative losses and in actual practice it takes 50 to 60 grams of fuel to boil 2 liters of water.

If I use a container to store the stove to retain any unused fuel then I can make the stove thick enough to hold excess fuel. However this has a tendency even with the weight of the pot to increase the burn rate so I am testing another method which is to use the top of the lid of the bottom can as a small fuel reservoir which the stove can tap via a string running through the center of the burner. In practice this helps but if the reservoir fuel gets hot enough to escape under pressure then if will increase the burn rate further and start producing yellow flames. This is somewhat less efficient but boils the water nonetheless.

Since isopropyl weighs 0.785 grams per cubic centimeter I'll need to make room for at least 4.66 cubic inches of Isopropyl fuel to boil 2 liters of water.

For a stove diameter of 4.375 I'll need a height of 0.31" or 3/8" thickness or height.

Since paper towel is only about 40 percent efficient I've used a piece of string to feed the burner from the reservoir in the top of the bottom of the bean can for the 2 liter boil.

Therefore, I'll need a 3/8" thick stack of compressed paper towels 4-3/8" in diameter .

Step 3: Cutting and Assembly

Next I used a layout compass to scribe a 4-3/8" diameter circle in two pieces of aluminum sheet for the top and bottom halves of the stove and then cut out the disks and drilled a 1/8" hole in the center

I then placed two uncut pieces of screen on each end of the stack of cut paper towel and then placed the two aluminum disks over the screen in a two slices of bread sandwich fashion.

Next I used a drywall screw to temporarily hold the assembly together by screwing it through the center of the assembly while compressed.

I then drilled three 1/8" holes equidistant from each other, about an inch from the center and installed the pop rivets through them to hold the assembly permanently together.

Last, I trimmed the screen to match the diameter of the aluminum disks and paper towel, removed the drywall screw from the center hole and inserted a one inch piece of string in its place.

Step 4: Usage

The 2 liter boil

An empty bean can is turned upside down and filled about halfway up the ridge with Isopropyl. If you want a larger reservoir then you can use a rubber mallet to bash the end of the can into a deeper depression than is provided by just the ridge of the bean can. I was able to fill this reservoir with 40 grams of fuel after the first stove turned out to hold only 20 grams of fuel.

Now the stove is either soaked in a dish filled with 91% isopropyl alcohol or if you have found a leak proof container for the stove the container is filled with isopropyl and the stove soaked in it.

Next the stove is placed on top of the bean can so the string can soak up the fuel as it is burned.

Next the coffee can is filled with 2 liters of water and the outside thoroughly dried. failure to dry the outside may contaminate the fuel.

Next the coffee can is centered on top of the stove.

The bottom of the coffee can will extend out over the stove and the bean can by about an inch.

1 liter boil

The coffee can is placed upside down, the stove is loaded with fuel, centered on top of the coffee can and the bean can filled with 1 liter of water and centered on top of the stove.

Comments

author
KennyB21 (author)2016-03-08

This is a very cool design... but I'll put my CAT stove and 1 ounce of HEET (fuel) up against it anytime. It boils two cups of water in a hair over 4 minutes. I tried like 6-7 different designs as a project for a website, and I learned that simplicity works by far the best in this particular case.

Buuuut I'm going to build one of these anyway... lol.

author
Cann0n (author)2016-01-16

I hope you aren't cooking foods in the cans. Most people think they are safe by just opening the lid. Wrong. The inside of the cans are lined in a plastic to prevent leaching of the metals into the foods and also as a way to control bacteria from forming. If you cook in the cans, this lining will melt and leach chemicals into your food. I used to cook in the can all the time... I definitely will never do it again after a doctor told me the side effects of the type of plastic used.

I like this design but I have to admit that the self-priming aluminum bottle styles remain my favorite simply because I can build them with a multi tool or pocket knife.

Sometimes it's cheaper to buy gear than it is to buy the tools and material to make a homemade one.

author
superdave5481 (author)2012-11-19

I think what you did here was great, but over explained. Gotta keep it simple for simple folks.

author
Michael_oz (author)2011-12-03

Just a word on Asbestos: Don't do it!
"The inhalation of asbestos fibers can cause serious illnesses, including malignant lung cancer, mesothelioma (a formerly rare cancer strongly associated with exposure to amphibole asbestos), and asbestosis (a type of pneumoconiosis)." (Wikipedia)

author
KittyF (author)2010-11-05

I'm confused too. Are you lighting the edge of your metal paper towel sandwich? what does the wick do, do you light that too? or is it just serving as a wick to bring more fuel into the paper towels?
What purpose does the screen serve? (just gratuitous curiosity, that one.)

And last, but not least, why turn you tuna can or any can upside down? why not just put a small reservoir of alcohol in the bottom of the can and leave it right side up?

sorry for all the questions, but I'd like to understand the concept a bit better. thanks, Kitty

author
Wasagi (author)2010-07-20

Nice!!!! Could you use two tops of cans to replace the aluminum sheets in the stove?

author
spark master (author)2009-07-15

Hi Please do a video, I am confused , the video would help. Is what you have described, basically a wick that you put in an open can of alcohol? the center wick, is that to go up to the screen paper towel sandwich? I do not flame only ask, I live near the ocean so I figure one day I may need stuff like this with the family, all the stuff I have read came down to , thus far, no matter the shape the type, they all work about the same. BUT, that doesn't mean some person can't make one that works easier and looks nicer and is a lot safer, (more stable). I have box full of svea brass stoves and a few pop can units I made. I Would like to make yours as well. Thank you very much for posting this one it looks rather nice and please do a video as you make one. spark master

author
mattias law (author)2009-03-23

sorry but im not quite clear here, too many calculations and stuff. but is this something that can be reused and see for the picture with the string poking out the top is that for putting the fuel in or for lighting it. this could be very good because i need something which is very small and compact

author
sypher (author)2008-11-03

I am sorry, but this looks far more complicated than a Penny Stove, in construction and function. Seem a lot like a roll of toilet paper in a paint can soaked in alcohol, I think those a called ghetto stoves. Interesting idea, and application. You could make this thing thicker? It would hold more fuel. Something else I just thought of, the tip of a flame is the hottest point, I noticed that the flame is half way up the side of the make shift pot.

author
seudo411 (author)2008-04-20

Great instructable, would it be possible to use a metal jar lid and another piece of circular metal to make a larger reservoir.

author
watermelon (author)seudo4112008-04-20

Also be sure to experiment away from anything that might catch fire and only with adult supervision. Too much alcohol, i.e., too large of a reservoir or a disfunctional design can be much harder to extinguish in the event of a mishap.

author
triggernum5 (author)watermelon2008-04-21

Its also good advice to avoid panicking in the event of a mishap.. Straight up alcohol fires are easy to extinguish, but can spread FAST! If something happens, take a step back, pick up something you've decided already will smother fires well, and calmly put out all visible flames.. The last thing you need is to spill more alcohol in a rush, assuming you were stupid enough to ignite while the main bottle wasn't secured.. After you get all visible flames out, its a good idea to darken the area id possible to detect rogue flames.. On top of that, start small.. You can usually scale this stuff up easy.. A 5mL test rig will burn more than enough, and is 'pretty' harmless..

author
watermelon (author)seudo4112008-04-20

The problem with any reservoir is keeping it thermally isolated. I've used a smaller metal lid to raise the pot above the absorbent material by about a quarter inch which seems to have reduced thermal transfer from the pot to the absorbent material when it heats up and the water starts to boil. You could possibly use a metal lid with a deeper lip to hold additional absorbent material and then use a smaller metal lid to separate the absorbent material and the pot but if it does not work and you have too much fuel watch out! The idea here, however, is to try and match the capacity of the reservoir with the amount of water you need to boil. For instance I can boil about 20 fl oz of water in a Heineken 24 fl oz aluminum can with the top cut out and keep it going to hard boil three large eggs with 1 fl oz to 2 fl oz of Isopropyl by using an upside down tuna can with a depressed bottom filled with absorbent material. Adjusting the reservoir capacity to match the maximum job you have in mind will then allow you to do other jobs using less fuel. For instance, I use the same set up to boil water for tea with only 3/4 fl oz which results in hot tea but an end to the flame as soon as the water is boiling. Unlike my electric pot which does not have a timer I can set it up to make tea most anywhere, light it, go away and do something else and return to find no flame and a waiting hot pot of tea.

author
killerjackalope (author)2008-02-10

We had a really old really insanse liquid fuel jet lighter that worked like this, a wick flame heated a special nozzle that went in to the fuel sponge... after a while it fired spurts of fuel and eventually stabilized to be blasting a massive flame out the side, we called it the crazy professor stove... once the jet self sustained it didn't burn fuel at the wick much so it became efficient and very fun... Same principles in very different actions... I wonder how big I could get this principle to work on... soon come's up with completely ridiculous jet engine idea

author

Yeah, I was thinking jet engine for a project too, after putting too much fuel in a beverage can pressure stove the jet vapors reaching 3 or 4 inches after the liquid stopped spurting through the jets. I thought it was going to blow. I was thinking maybe a jet turbine powered generator project as well after doing one for a small ram jet type engine. I was just looking for info or an instructable on how to balance turbine blades, like maybe if they were tires? If you want to collaborate that would be cool!

author

Hey I'm working on a new stove jet plan based on this, I'll see how it goes, if it's good and had the effect I have planned it'll be an interesting low tech way of delivering a high power flame to stuff, it should also work horizontally...

author

I'm looking forward to seeing it.

author

Ooh I never saw this reply, if you have a good plan aswell It might be interesting, unless you'd rather have an arms race instead, I already predicted the instructables war so the arms race is the next logical step...

author

One of these...?

2plugburn2.jpg
author

Hmmm an insane trans-continental collaboration of jet engining... That's very similar to the one's we had a few of but not as good or rare, we ended up with four or five of the original design ones, you can solder easily with them as they're designed around lighting a pipe... Have a look at one and see if you can give me an estimate ofr the size of the jet hole nozzle... It would really be appreciated as I'm going to instructables on make a petrol lighter, a jet lighter and maybe just a normal gas lighter...

author
MisterSlippy (author)2008-02-14

Nice instructible. Out of interest, if you made a longer wick and had the tuna can open-end up (with fuel in the bottom), would the stove draw its fuel up the wick?

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