A simple alcohol stove more fuel effecient than the Jim Wood Super Cat?

Rusty,

2 cups on 1 fluid ounce isn't particularly efficient. 3/4 fluid ounce is more common for 2 cups. Getting it down to 1/2 fluid ounce to boil 2 cups is pretty good and is less common. Finding a simple stove that is so efficient that it can boil 2 cups of water on 1/2 fl. oz. may be something you'll have to work at. I can get close to that level efficiency with my Caldera Cone set up, but I hesitate to call the Caldera Cone simple.

HJ
Adventures in Stoving

Well, first, I'm not the DIY alcohol stoves expert. So, be sure to take a look at a lot of designs.

Having said that, take a look at this photo.

In particular look at the homemade stove in the center of the photo. This is an open (the center is not sealed) top jet stove (jets on top). I prefer this style because it's easy to fuel, easy to light, and is reasonably efficient. I can get a boil on about 2 cups with a stove of this type with about 3/4 ounce of alcohol if I have a properly sized pot. You want to get a squat shaped pot, one that is wide but not tall, so that you don't have flame "spillage" which will cut your efficiency. See photo below. You don't want that.

The stove in the first photo was made for me by a friend. Let me see if I can get a design for you, but again I'd encourage you to look around on your own. Zen Stoves has a lot of designs available.

HJ
Adventures in Stoving

You can find stoves that are more fuel efficient, but there are likely other trade-offs: the stove will be heavier.more complicated so it traps more heat (like the Caldera Cone type design) and/or boiling time will be longer (like Sgt Rocks Ion stove). In my experience, The Ion stove was the most efficient if the wind shield was set up well. In moderate weather I could boil 16oz on just .3oz of fuel provided the windscreen was set up perfectly and I was willing to wait 14 for the boil to begin. Personally, I settled on the UL/Compact Caldera as my primary stove for the combination of ease of use, effectively in the face of mixed conditions, and acceptable fuel efficiency.

–Mark

You can find stoves that are more fuel efficient, but there are likely other trade-offs: the stove will be heavier.more complicated so it traps more heat (like the Caldera Cone type design) and/or boiling time will be longer (like Sgt Rocks Ion stove). In my experience, The Ion stove was the most efficient if the wind shield was set up well. In moderate weather I could boil 16oz on just .3oz of fuel provided the windscreen was set up perfectly and I was willing to wait 14 for the boil to begin. Personally, I settled on the UL/Compact Caldera as my primary stove for the combination of ease of use, effectively in the face of mixed conditions, and acceptable fuel efficiency.

–Mark

Hi, Mark,

Thanks for a good summation of the trade offs. I've kind of come down in a similar fashion and given up on some efficient but "fiddly" stoves.

HJ
Adventures in Stoving

It's only really sensible to discuss fuel efficiencies in terms of the entire cooking system. Trying to talk about efficiency of a burner alone will get you nowhere.

So, we need to consider how well the burner is matched to the pan, and how much heat is wasted up the side of the pan. We also need to consider the windscreen, and the fuel wasted during any priming phases.

If you have a burner that runs hot (for example, the Rusty's burner getting through 2oz of fuel in 5 minutes), you need to have a system that can extract that high power output. Generally, this means a large area to the base of the pan, or a heat exchanger (that's the principle behind the JetBoil et al; pulling out heat from the flame that would otherwise be lost up the side of the pan). If the burner is too powerful for the pan to usefully take heat from the flame, then energy will be lost, and the efficiency will be low.

If you have a low power burner that burns fuel slowly, there's a chance that the losses from your cooking system to the environment are such that efficiency drops, but Tom Beasley did some useful experiments on boil time vs burn rate for gas stoves that seem to indicate that you have to go pretty slow for this effect to be noticed, but it depends on the operating environment (temperature, wind).

Without a windscreen, the lazy flame from an alcohol burner is likely to be blown about by breezes, thus losing more energy, reducing the efficiency. A windscreen also reflects heat back to the burner, causing it to evaporate fuel faster, thus making it burn hotter and faster (more powerfully). This can reduce boil time, but can also reduce efficiency if it makes the burner too powerful for the burner/pan/windscreen system.

If a burner requires a priming phase that prevents the pan being placed over the heat, then we're wasting fuel again. That's one reason why I don't like priming burners, not to mention the additional faff required; I like 'fire-and-forget' burners I can simply light and stick the pan over. Some priming burners are also fire-and-forget.

We also need to consider the 'flame gap'; how far we hold the pan above the burner. This depends on the type of burner. The pan can sometimes be too close, which 'quenches' or puts out the flame before all the fuel has burnt, or it can be too far away. Quenching is noticeable by a sweet, sickly smell of partial combustion products (you can find out what an alcohol burner 'exhaust' should smell like by running the burner with no windshield and no pan; it should smell simply warm and moist). The optimum (for fuel efficiency) flame gap can only be determined by experimentation with the entire stove system, in my experience.

Then, when doing fuel consumption comparisons, we need to make sure we're not comparing apples and oranges. Methanol has an energy content of 18.8kJ/ml, whereas ethanol has an energy content of 24.7kJ/ml, 31% more than methanol. So, when reading other people's fuel use reports, we need to make sure we understand what fuel they're using.

Oh, and we need to check water volumes, too; US stovies generally use 2 cups (473ml), whereas non-US stovies may use the near equivalent of 500ml. This issue of measures may also have an impact on the fuel volumes; most refer to 'ounces', which I've always taken as shorthand for 'US customary fluid ounce', 29.6ml, rather than the imperial fluid ounce, 28.4ml. The US fluid ounce is a somewhat strange measure, since one US fluid ounce of water doesn't weigh one ounce; no doubt the origin is lost in the mists of time, but must be based on a liquid with a density less than water (wine, possibly, but at what %age alcohol…?), or on a simple 3D volume. To confuse matters further, US food labelling regulations use a different definition of the fluid ounce (exactly 30ml). Wiki has a useful entry, as usual.

I've settled on a system based on a caldera clone and a trangia-style burner made from 250ml red bull cans, with a conic inner wall that allows the burner jets to be made on the rim of the pressed dimple, giving a conic flame ring that focuses on the centre of a small pan. It's made and operates in a similar way to the one Jim suggested earlier. BTW, here's my attempt at a set of instructions for building a burner of this type.

The clone provides an efficient windshield, holding hot gas close to the pan to encourage heat transfer, as well as a pan support. This system allows me to routinely boil 500ml water with 15ml UK-spec 95/5 ethanol/methanol 'methylated spirits' (i.e. mostly ethanol). If I'm boiling more or less water, I can scale the amount of fuel I use and get a boil as expected.

Having spent a lot of time and effort playing with many stove designs, it's disheartening to find that one of the simplest is also just about as efficient; take a 250ml red bull can, and make a simple, open-cup burner by cutting a suitable height cup off the bottom; an inch, say. No priming, no vapour chamber, no fancy jets; just a simple puddle of burning alcohol. Obviously, it needs something to hold the pan above the burner to allow the fuel to burn.

It's interesting that both Rusty and Dan are using the same Cat Stove design, and yet one uses twice the fuel of the other (bear in mind my comments about comparing fuels). It would thus be very instructive to see the exact setups that both use, so we may be able to figure out just how this discrepancy arises, and where the energy is lost/is saved.

HJ, you might consider building a decision tree diagram for the alcohol stove design problem.

For instance, there are different starting points for this. For one stovie, fuel efficiency might be the top priority. For another, boil speed might be top. For yet another, it might be based on simplicity of a DIY construction or the weight of the burner. Fuel capacity might figure in. A lot depends on the diameter of the boiling pot.

Following fuel efficiency, it might depend slightly on the exact fuel, whether it is 190 proof Everclear, HEET, or whatever. Some of this may vary depending on the ambient conditions, e.g. if it is below freezing, or if the wind is at a certain speed.

In fact, HJ, you can probably start a whole new career around this. When you fill out an income tax return and you have to fill in the box that says "occupation," you can write Professional Stovie.

–B.G.–

Rusty,

Looks like a nicely done Super Cat.

The problem I've had with side burners is that the flames tend to go up the sides of the pot, thus wasting heat. If you look closely at the photo below, you can see the flame extends up around the edge of the pot directly in the center of the pot.

The great advantage of the Super Cat is it's incredible lightness. Mine weighs 7g if I recall correctly. If you can get a good stove+fuel+windscreen+pot combination, you've really got something. You just have to play with it. Jim Woods, on his site, appears to recommend slightly smaller holes than a standard hole punch in order to "tone down" the stove. If one can "tone down" the stove a bit, then the flames wouldn't shoot up the side of the pot, and the stove's efficiency would be higher.

HJ
Adventures in Stoving

Aluminum pots, got to have 5-6" dia. pot for efficiency.

Jim wrote: "The stove that Kevin is talking about, the one from 250ml Red Bull cans, is going to be pretty light."

Yes, it's also about 7g, so pretty similar to the Cat Stove. It cannot serve as a pan support like the Cat Stove can, but I use a caldera clone* to do that, and provide an efficient windshield that encourages heat transfer by holding the hot combustion gases close to the pan.

Here's my conic-walled burner:

* actually, I use a two-part Flissure clone, weighing 25g, that fits in the pan it supports, thus needing no caddy:

A clone is a little heavier than a simple windshield, but it makes up for it in stability, pan support and increased fuel efficiency.

The issue of how much fuel to carry is one of the benefits of alcohol fuels over gas stoves; you can carry just as much fuel as you need, and take a bottle sized to suit. With gas, you're limited to fixed-sized canisters (which, being steel, are heavy compared to a small plastic bottle). I played with the numbers a while back, and, to my surprise, found that a conventional canister-top gas burner never 'wins'. See this OM thread.

Rusty wrote: "I'll make one of the stoves based on your directions when I get time"

My OM article is simply my spin on the assembly of a 'classic' or 'Pepsi can' burner (aka trangia-style, open-reservoir, annular vapour chamber, low-pressure, jetted burner). There's nothing original in the design presented. The conic-walled vapour chamber burner above is more unusual. The conic wall is necessary to allow jets to be placed inside the dimple, thus forming a conic flame ring to concentrate the flame on the base of small pans.

Bob wrote: "HJ, you might consider building a decision tree diagram for the alcohol stove design problem."

It's certainly true that different people have different requirements, and approach the concept of 'efficiency' with different perspectives. For me, it's weight, and therefore fuel efficiency, but others like a quick boil. 'Light, strong, cheap; pick any two' comes to mind, only we might end up with more degrees of freedom: 'light, strong, cheap, fast, fuel efficient, easy to make'…

A decision tree would certainly be interesting. Especially if you added all the other fuel choices. It might get rather large…

>refilling is no more dangerous (perhaps less dangerous) than screwing on a burner and boiling a kettle of water.

Some extreme caution when refilling canisters,if the canister is totally full of liquid gas with no space for the liquid to expand to, this is a very dangerous situation, especially if you have a naked flame nearby.

Tony

Getting back on topic, witha a caldera cone and a small burner, it *is* possible to get 2 cups to boil from 40F water temp and 68F air temp with about 1/3ounce of fuel. I was also using a special aluminum pan with a 1/2" deep/wide radial ridges in the bottom. It takes a lot longer, ~13-15min after 6 runs.

You can see these in a picture on the thread entitled "SLX Denatured Alcohol vs HEET vs Green (Klean Strip) Denatured Alcohol" Both the stoves *can* do it but the can stove requires a narrower opening to slow down the burning…maintaing the about 45 degree angle on the sides.

SLOW seems to be watch word for efficiency. But at lower ambient temps, perhaps a bit faster would be better. I have my doubts the water would have ever boiled at 32F air temp and 32F water temp. I would have used an ounce of fuel and almost an hour to boil 2 cups, if it did boil. The radiative effect from the pan/cone may have increased beyond the flames ability to replace the lost heat. I could actually hold my hand on the top of the pot. But, I would call these stoves a failure, only because of the very slow boiling. At, 1/3ounce? That is good efficiency for alcohol. This seems to be the best case for fuel efficiency. SLX was used for the testing …other fuels may vary a bit…

I can do only slightly better with the SVEA. Around 3 grams(just over .1 ounce) after 10 runs on low(measured start and finish, no priming.) The Coleman F1 does a bit better at about 3 grams (just under .1 ounce) after 10 runs, but is very fussy at this low of a temp setting. Both of these waste a lot of heat, though and have the potential for doing being much better since I could *not* hold my hand on the top of the pot. Both boiled in about 4 minutes.

Roughly, holding my hand on top is a guide to how much waste heat is being generated.

Note that this corresponds roughly (within a fairly broad margin) to the heat of combustion for the three types of fuel: Gas, White Gas, Alcohol. For some reason, the alcohol did not perform as well as it should have in ALL the tests. Probably about 50 stoves (brass and can type) were tested. Theory says I should have been able to get a best case boil of 2 cups (~500ml) with about .25ounce(~7.5grams) of alcohol. I could never do that. I am guessing that I am hitting the radiative heat loss wall near the low end of heating the water. Heating quicker wastes more heat, but prevents so much heat loss. Heating slower increases rediative heat loss, but increases efficiency. Soo, again, the ultra small burners were failures due to the entire *system*, not so much because of the heat generated.

Rather than fret about it, I believe that the pots we use for camping are probably in need of a redesign. We discused this a few years ago on the backpackinglight forum on googel. A caldera cone works well, but wrapping it in fiberglass insulation would help and not weigh that much. A larger heating area on the bottom would also allow for faster heating, as well as increased efficiency. A heat exchanger on the bottom and lower sides of the pot will also help. But this is another subject.

> Nice burner and nice fissure clone.

Thanks ;-)

> 28g for the clone? That's very light and more than made up for in stability and efficiency.

That's made using 0.15mm (6 thou) Al foil; a big roasting tray, but others have used the Al flashing (seems to be 0.0092" (0.234mm)) that seems readily available in the US. Obviously, it's the classic 'light, strong, cheap' trade-off.

> What kind of fuel consumption, with what kind of fuel, can you get when heating 500ml of 20C water to 100C in a plain (non heat exchanger) covered pot?

That system (conic burner, Flissure clone, Alpkit MyTiMug) will boil 500ml of water at 20C with 15ml of UK-spec 95/5 ethanol/methanol 'meths'/methylated spirits/denatured alcohol (the UK has a fairly strict spec for meths, as to what the denaturant can be, and how much of it is added), in about 8 minutes. That's in a sheltered location (e.g. tent porch, which is where I cook).

> That's a very sophisticated set up for a DIY set up. I'm very impressed.

There have been 120+ users of my clone generator script over the years. There are plenty of examples on the associated OM thread. It's pretty easy to build: change the pan & burner parameters in the file, print the template, cut out with scissors, and punch the vent holes.

> The conic interior walls of the burner look like they'd be a lot of work and a bit of a trick, yes?

Each burner takes me about 15 minutes from start to finish. The conic wall is actually just as easy to make as a parallel wall; I use dividers to score the two outline lines, and the same fold and snap method to break the cone out. I have some pictures of the first one I made on an OM gallery. These days, I have a simple template made from the side wall of a can, unrolled, with the critical points pricked; I place it over the unrolled can wall, pr*ck (Nanny won't let me post the real word…) the holes, score the lines with dividers and ruler, and then assemble it with the same overlapping tabs method as per my 'classic' article. Like the clone, I have a PostScript design script for the burner.

> A very interesting article you wrote on OM. What would happen if you started with a 450g canister rather than a 230g canister? What would happen if you only boiled 1 liter per day (500ml morning, 500ml evening) which is a little closer to my actual solo consumption.

The gas vs meths consumption one? Derek Goffin's comment about the canister's contribution to each 'burn' gives you a clue; divide the weight of the canister by the number of burns you get from it, and add that to the amount of fuel per burn. That gives you the total fuel & container mass per burn. The amount of water you boil per burn is largely irrelevant, as the same energy is required for either fuel. Think of it as 'longer days'; it's a scaling factor.