Comparison of Three Alcohol Stoves

[Odd Man Out]

As previously reported, I have had fun making alcohol stove recently. (www.whiteblaze.net/forum/showthread.php?t=65331) I started with Penny stoves. (www.jureystudio.com/pennystove/index.html) It was suggested I make a Super Cat, so I did that using the template with rows of 15 and 10 holes. (zenstoves.net/Templates/TemplateSuperCat.GIF). Both stoves were made using only my Victorinox Tinker pocket knife, except that the top row of holes on the Super Cat were made with a hole punch. My punch couldn’t reach down the can far enough to make the second row so I used the reamer on the pocket knife (the two sets of holes look pretty much the same). The burner holes on the Penny are also cut by hand so I don’t know the diameter, but the blue flame looks much like the pictures on-line. I also had a BIOS-2 I bought a year and a half ago. (www.minibulldesign.com). I decided to test them side-by-side to see how they perform. Tests were done on my patio behind my house at 60 deg F with negligible wind. I used tap water from a 5 gal bucket and rinsed the pot with water after each test so all water was at the same initial temperature. I boiled 2 cups of water in 1.5 qt aluminum REI Chefware Nonstick pot. For the penny stove I made a tripod pot stand by bending a single piece of 1/8 inch steel rod. For each test I used 1.5 Tbs (0.75 oz) of Ethanol. This amount filled my Super Cat all the way up to the bottom of the lower row of holes. It also filled the penny stove up to the rim (without draining any fuel into the lower fuel cup). The super cat and BIOS sat on a piece of scrap lumber covered with Al foil. The Penny stove sat on another Penny stove as a base. I did not use a priming pan for either the Super Cat of Penny. The BIOS has an attached wick for priming. The pot was over the penny stove from the start. The pot was put on the BIOS and Super Cat only after priming. For each test I measured the time to prime, the time to boil, and the time to burnout. Here are the results in minutes:seconds
BIOS: 0:20 to prime, 6:00 to boil, 7:10 to burnout
Super Cat: 0:30 to prime, 5:00 to boil, 5:40 to burnout
Penny: 1:50 to prime, 7:00 to boil, 11:00 to burnout

Observations:

The Super Cat was the hottest, but least efficient (burned out soon after boiling 2 cups). I could not extend the boil time by adding more fuel as it was filled to capacity. The flame pattern was very wide, coming up the side of the 8 inch pot, making the Aluminum handle very hot. The flames also seemed to be more bothered by the slight breeze. It primed pretty quickly so I don’t think a priming pan would help much. This was my first attempt at a super cat. Are my holes too low, thus cutting down on fuel capacity? Would a different hole size/pattern give better performance? I know this design is very popular, but I wasn’t impressed with my first attempt.

The BIOS-2 performed very nicely. Priming wick worked very well. The flame pattern got wider as the stove heated up. An insulated base might get it to peak performance faster? It also burned out soon after boiling, but with its large fuel cup, longer burns are possible with adding more fuel.

The Penny Stove performed very well. Boil time was slower, but this might improved with some optimization. (pot stand height/priming pan). The stove was much more efficient, burning for 11:00 and keeping the water at a full boil for 4:00. Longer boils are possible with more fuel (fill the fuel cup before adding penny).

I know I am a novice, but learning a lot and having fun. Comments welcome.

[Skidsteer]

As previously reported, I have had fun making alcohol stove recently. (www.whiteblaze.net/forum/showthread.php?t=65331 (http://www.whiteblaze.net/forum/showthread.php?t=65331)) I started with Penny stoves. (www.jureystudio.com/pennystove/index.html (http://www.jureystudio.com/pennystove/index.html)) It was suggested I make a Super Cat, so I did that using the template with rows of 15 and 10 holes. (zenstoves.net/Templates/TemplateSuperCat.GIF). Both stoves were made using only my Victorinox Tinker pocket knife, except that the top row of holes on the Super Cat were made with a hole punch. My punch couldn’t reach down the can far enough to make the second row so I used the reamer on the pocket knife (the two sets of holes look pretty much the same). The burner holes on the Penny are also cut by hand so I don’t know the diameter, but the blue flame looks much like the pictures on-line. I also had a BIOS-2 I bought a year and a half ago. (www.minibulldesign.com (http://www.minibulldesign.com)). I decided to test them side-by-side to see how they perform. Tests were done on my patio behind my house at 60 deg F with negligible wind. I used tap water from a 5 gal bucket and rinsed the pot with water after each test so all water was at the same initial temperature. I boiled 2 cups of water in 1.5 qt aluminum REI Chefware Nonstick pot. For the penny stove I made a tripod pot stand by bending a single piece of 1/8 inch steel rod. For each test I used 1.5 Tbs (0.75 oz) of Ethanol. This amount filled my Super Cat all the way up to the bottom of the lower row of holes. It also filled the penny stove up to the rim (without draining any fuel into the lower fuel cup). The super cat and BIOS sat on a piece of scrap lumber covered with Al foil. The Penny stove sat on another Penny stove as a base. I did not use a priming pan for either the Super Cat of Penny. The BIOS has an attached wick for priming. The pot was over the penny stove from the start. The pot was put on the BIOS and Super Cat only after priming. For each test I measured the time to prime, the time to boil, and the time to burnout. Here are the results in minutes:seconds
BIOS: 0:20 to prime, 6:00 to boil, 7:10 to burnout
Super Cat: 0:30 to prime, 5:00 to boil, 5:40 to burnout
Penny: 1:50 to prime, 7:00 to boil, 11:00 to burnout

Observations:

The Super Cat was the hottest, but least efficient (burned out soon after boiling 2 cups). I could not extend the boil time by adding more fuel as it was filled to capacity. The flame pattern was very wide, coming up the side of the 8 inch pot, making the Aluminum handle very hot. The flames also seemed to be more bothered by the slight breeze. It primed pretty quickly so I don’t think a priming pan would help much. This was my first attempt at a super cat. Are my holes too low, thus cutting down on fuel capacity? Would a different hole size/pattern give better performance? I know this design is very popular, but I wasn’t impressed with my first attempt.

The BIOS-2 performed very nicely. Priming wick worked very well. The flame pattern got wider as the stove heated up. An insulated base might get it to peak performance faster? It also burned out soon after boiling, but with its large fuel cup, longer burns are possible with adding more fuel.

The Penny Stove performed very well. Boil time was slower, but this might improved with some optimization. (pot stand height/priming pan). The stove was much more efficient, burning for 11:00 and keeping the water at a full boil for 4:00. Longer boils are possible with more fuel (fill the fuel cup before adding penny).

I know I am a novice, but learning a lot and having fun. Comments welcome.


Do the test again and measure the amount of fuel used.

[Wil]

This was my first attempt at a super cat. Are my holes too low, thus cutting down on fuel capacity? Would a different hole size/pattern give better performance?My fancy feast stove holds about 2 oz. of fuel, with the bottom row of holes bottoming at 3/4" from the bottom of the can.

I use 3/16" holes, burns just a little slower and handles wind a little better than the holes punched by a typical 1/4" paper punch. My punch is a McGill Punchline 2" reach 3/16" ROUND 53600.

My top row hole tops are about 1/4" from the top of the can; if anything I err a hair higher. The second row tops at 1/2", again any error tends higher. I use 15 holes in each of the two rows, offset symmetrically.

Your test version boils a little quicker, but mine lasts a little longer, with the same amount of fuel. I believe less fuel actually boils a shade quicker and requires less priming time; so you're better off not using the extra capacity unless it's really needed.

In many ways the best version of the cat is a single row of 15 holes downset just a hair lower. Boils slower but for a much long time. I believe it may actually be delivering a lot more BTUs; it certainly allows for more "cooking" and fussing with the food.

My stove as defined above is trial and error to my liking, but it's very subjective. The real test would be total BTUs delivered to the water under some kind of defined real world relevant standard condition of temperature and wind. Difficult for us amateurs.

[vamelungeon]

Time doesn't make as much difference to me as fuel usage. I can't quite understand the RUSH to boil water, but I do understand being frugal with fuel. I'm usually tired and thirsty after hiking, but not in a hurry.

[Odd Man Out]

Thanks.

I may try the 15 hole single row super cat as per Wil's parameters. Using my reamer tool on my knife, I can make the holes any size, up to about 1/4 inch. It would be easy to make them too small and gradually enlarge with each test.

I agree with Vamelungeon that I prefer efficiency to speed. Not only in terms of fuel carried, but also my cooking style involves making a lot of stews (rice and lentils, e.g.) that can scorch if cooked too fast. I also like to heat up water for tea and clean-up. So long (vs fast) boil times work nice for me.

Measuring BTU wouldn't be too hard. Put one liter of water in the pot and measure the temperature increase (assuming it doesn't boil) in deg C (or deg F divided by 1.8). Because it takes one calorie to raise 1 mL (gram) of water 1 degree C, the temperature change will be the kilocalories of heat output delivered to the water (this ignores the heat absorbed by the pot and lost to air). Multiply this by 4, or multiply by 4.2 to get kilojoules. If you divide kilojoules by the time of the burn in seconds, you get kilowatts (power). It wouldn't be hard to test under different temperatures. Controlling wind is tougher.

[Odd Man Out]

oops - That should have read "...multiply by 4 to get BTU or 4.2 to get kilojoules..."

[4eyedbuzzard]

Odd Man Out,
You would also have to test using different pots as flame pattern and transfer will likely differ between different stoves. Simply measuring water temperature rise in one particular pot with different stoves leaves out the dynamics of how the pot and stove work together as a heat transfer system. One stove may prove to have more heat output with one pot, but a different stove may prove to have greater output with a different pot. Pot diameter, sidewall height, lid, etc, all change the dynamics of this open system. There are more variables than just the stove, number of holes, etc.

[amac]

You did a very fair test. Thank you for going through the effort and posting the details. Funny thing, I came to a very different conclusion from results.

[Grinder]

Skids,
I don't understand your comment.
Odd Man states he used 3/4 ounces of fuel for each stove.
???

[Spokes]

Test are fine to establish a baseline of performance but expect differences in the field. You'll be amazed how much altitude and weather affects burning rates and fuel consumption.

BTW, you'll save a lot of fuel if you measure it out every time you use the stove. A typical plastic 35mm film canister holds 1 oz and with practice you'll get to know exactly how much you need to cook your favorite meals.

I've seen way too many hikers waste fuel to over-filling and flare-ups.

Good luck!

[Odd Man Out]

Fun discussions!


Odd Man Out,
You would also have to test using different pots as flame pattern and transfer will likely differ between different stoves....There are more variables than just the stove, number of holes, etc.

Agreed. But it seems to prudent to focus on one particular variable at a time. And for this first test, I used just one pot to limit that variable. There is a smaller pot that came with that set. At some point I will repeat the test with the small pot to see if there is a difference. However, I don't expect that some results will be pot-dependent, such as the total burn time.


You did a very fair test. Thank you for going through the effort and posting the details. Funny thing, I came to a very different conclusion from results.

Thanks. I have thought about improving my test procedures. Next time I will measure alcohol with a volumetric pipette to cut down some measurement variability. I would like to measure water temperature continuously with digital thermometer output recorded by computer (guessing boil time is quite subjective). I've even thought of continuously measuring fuel consumption by putting the stove on a digital scale and monitoring mass decrease, but that won't work for a BIOS or Super Cat, since the pot of water sits on the stove. BTW, What are your conclusions?


Test are fine to establish a baseline of performance but expect differences in the field. You'll be amazed how much altitude and weather affects burning rates and fuel consumption...

Again, I agree. As above, one variable at at time. I have thought long and hard about all the variables to consider. Ultimately, it seems this is as much art as science (hence the "Zen" website). And of course personal preference and needs dictate each person's optimal system. But as a scientist, I really enjoy taking enormously complex problems, breaking them down to manageable parts, exploring each part, learning as much as possible, and then applying that knowledge to figure out something new and come up with optimal solutions to real problems. In general, I expect that the more I know and understand about how these critters work, the better I will be able to deal with all the uncontrollable variables one encounters on the trail. But I certainly agree that all the lab testing in the world can't substitute for 5 months of thru-hike experience. I see backpacking as a craft - the creative application of knowledge, skill, and experience to accomplish something useful.

[Skidsteer]

Skids,
I don't understand your comment.
Odd Man states he used 3/4 ounces of fuel for each stove.
???

I missed that on the first read.

[Wil]

I may try the 15 hole single row super cat ... I prefer efficiency to speed. Not only in terms of fuel carried, but also my cooking style involves making a lot of stews (rice and lentils, e.g.) that can scorch if cooked too fast... long (vs fast) boil times work nice for me.The 15 hole cat is _slightly_ more susceptible to the flame extinguishing if the pot is initially lowered too soon or too abruptly.

I lower my pot very slowly and gently with all cats. In fact I start lowering the pot 5-6 seconds into the initial 20-30 second burn that is normally wasted. You'll notice if you can see the flame that it turns from yellow to blue (hotter) as the pot gets within an inch or two of the stove, and as you lower it further the blue flame starts to come out of the jets.

I actually touchdown the pot offset to the side so nearly 1/2 the stove is still open for a few seconds, then shift it to the other half. All this takes the same amount of time as the normal initial burn, but it quickly heats up the sides of the stove (and to a much lesser extent the bottom of the pot), and partially pressurizes the stove. This helps the flame survive the shock of the top being completely covered. It also gets you some significant heating right from the getgo as opposed to the total 20-30 second yellow flame waste.

I lower my windscreen into place at this point. If you have to have the windscreen installed from the start, because it's too windy or the design requires it, just lowering the pot very slowly, even without the side-to-side, works well.

[rodonne1]

I'm about to make a Supercat, I'll let you know what my experiences are...

[rodonne1]

Does anyone one know if the can of Denatured alcohol in the paint department at Wal-Mart safe to use for cooking in a Supercat, I read somewhere that some brands of alcohol can be harmful to cook with...

[rodonne1]

I saw a video on Youtube of a guy making homemade stoves and he was using the exact same can of alcohol from Wal-Mart.

[Odd Man Out]

Ran another test tonight with a coke can penny stove. I wanted to refine my testing procedures, improve priming, and practice operation in wind. This time I used a graduated cylinder to fuel much more precisely. I cut back to 20 mL of fuel to save fuel and time. I used a digital thermometer to monitor the temperature every 30 seconds. I used a soup can lid as a priming pan. Using 1.0 mL was too much and caused overheating and a flare up of the stove. About 0.25 mL of the ethanol worked OK and the stove was primed and settled in in just under 1 minute. Outside in the wind, I had to be more aggressive with my priming to keep the stove going. To determine to heat output of the stove, in tested inside measuring temperature every 30 seconds. The plot of temp vs time showed that the temperature increase was very linear from the time the stove primed up to boil. Extrapolating the linear temperature rise up to the boiling temperature made determination of the time to boil more reliable (4.6 minutes for 2 cups). Total burn time was 5.75 minutes. I also found that heating 4 cups of water instead of two cups gave a linear temperature rise with half the slope, just as expected, since it takes twice as much heat energy to cause the same temperature rise. For the 2 cup trial, the linear temp increase was 17.9 deg C per min. I multiply this by 1 min/60 sec, 1 cal/gram-deg C, 2 cups, 237 mL/cup, 1 g/mL, and 4.18 J/cal, you get a stove output to the water of about 590 Joules/sec or 590 Watts. I got about 550 Watts for the 4 cup trial, which is reasonably close, given the crudeness of the measurements.

[sbhikes]

Time doesn't make as much difference to me as fuel usage. I can't quite understand the RUSH to boil water, but I do understand being frugal with fuel. I'm usually tired and thirsty after hiking, but not in a hurry.
I feel the same way. However, I will choose a stove that's easy to make over one that is more efficient, too.

[davesailer]

The cap from a narrow-necked Platypus bottle/bladder holds 1/4 ounce. This is crazy handy for measuring since I carry my alcohol in the pint-sized bladder. Using that I can squeeze out excess air and prevent leakage from or crushing of a bottle when changing altitude. And the "bottle" is soft anyway. Slips right into one of my pack pockets. And on long trips I carry fuel split between two bladders, so I can lose at most only half of my fuel if I get really stupid.

Boiling (or near-boiling) one cup of water takes a hair over 1/4 ounce. For two cups of really hot water, I use 3/8 ounce (one and a half caps).

I use a Sgt. Rock-style stove that I made myself. S-L-O-W and extremely frugal, just like me.

[Wil]

Does anyone one know if the can of Denatured alcohol in the paint department at Wal-Mart safe to use for cooking in a Supercat, I read somewhere that some brands of alcohol can be harmful to cook with...The issues are: proportion of ethanol to methanol (most are a mix), amount of water, amount and nature of other chemicals contained.

100% ethanol would be the holy grail, burns hot and clean (not sooty) and is relatively benign in terms of fumes and touch. Methanol (e.g. Yellow Heet) is OK; but doesn't burn as hot and the fumes are somewhat more toxic. Water is bad if much more than 4-5% (that much is practically unavoidable; alcohol actually absorbs water from the air so 100% is impossible), burns cold and sooty.

Other chemicals are significant for their potential toxicity; breathing the fumes and spilling on the skin.

You can look up a specific brand on the internet to get its Material Safety Data Sheet (MSDS). Will tell you about eth/meth/water/other chems. But the sheets are often out of date.

I have always taken some comfort if the label mentions use as a boat stove fuel. My johngaltish view of private enterprise is that they wouldn't be suggesting you poison yourself with a high proportion of methanol or added chemical toxic fumes in the limited ventilation of a tiny boat galley.

A whole different issue (not relevant to the hardware store denatureds), is isopropyl alcohol. "Rubbing alcohol" and Red Heet. Poor stuff for the stoves. Cold, and soot like you wouldn't believe. Some rubbing alcohol also contains oils and other stuff hurting its efficiency.

[Transient Being]

Did you have to use perlite as a wick in any of these stoves?

[Odd Man Out]

I have not put anything inside the stoves (perlite, fiberglass). I did just the other day get some fiberglass cord to use as a priming wick on the outside. The cord is about 2 mm's thick and about 10 mm wide. It cuts easily with a scissors, but tends to unravel. I glued it on around the perimeter of the bottom of the fuel cup with some Meeco's Gasketing Cement and Stove Sealer. It comes in a small plastic bottle for $4.49. It is a black, thin liquid glue. It dries pretty hard in a few hours and is rated to 2000 degrees. It seemed to work pretty well as an alternative to a priming pan. Plus it may add some insulating to the fuel cup. It certainly makes it easier to pick up a hot stove. But priming seems to be most critical in cold and wind, and the weather has been real nice recently, so it hasn't had a good test yet. This glue didn't adhere to the aluminum too well as the cord now will slide off the bottom. But the cord is coated with a film of hardened glue around the inside to it forms a stiff ring that holds its shape and stays on the stove well just by friction. I know most people us JB Weld, but I thought this stuff looked like it worth a try. The hardware store also had a silicone flexible caulking material that is rated for stove use. Might try that too someday.

[brooklynkayak]

Time doesn't make as much difference to me as fuel usage. I can't quite understand the RUSH to boil water, but I do understand being frugal with fuel. I'm usually tired and thirsty after hiking, but not in a hurry.

I also agree and I tend to use a slower cooking stove.
Slower cooking can be less efficient if you are dealing with strong winds that can't be fully blocked.