The Silver Bullet Sapporo Bottle Stove

[matt kirk]

Background: My goal is to develop a multi-use system to heat water and carry water that is simple (minimal parts to tinker with in set-up), fairly quick (boils 1 pint within 10 minutes or less), and as lightweight as possible for summertime fastpacking excursions. Another requirement is that it can't snag on the mesh shoulder strap pockets I use to carry my bottles.

The "cooking" I do is really just heating water (no more than a pint at a time). I've been happy with the 1 pint aluminum beer "stadium bottles" as 1 ounce water bottles and "pots" for my fastpack gear setup. Maybe I'm too rough on my gear, but I've found the bigger Monster/Rock Star containers too flimsy.

I've been experimenting mainly with alcohol and Esbit fuels. This most recent design is meant for solid fuel tablets (Esbits), but could probably be adapted to other fuel types. I was intrigued by the shape and sturdiness of Sapporo 650mL steel cans and thought one could be fused (JB Weld) to an aluminum bottle to create an efficient "Caldera Cone" set-up. So that's basically what I did. Pictures w/some descriptions below:

After consuming the contents of the Sapporo can, the only three tools I needed were a can opener, a hole punch and a pair of scissors. The Coors Light bottle pictured obviously has some miles on it. The black is stove paint, which was sprayed on as an attempt to speed boil time.

Here's a picture of the 3 oz. setup. My esbit supply is currently running low, I only had half a tablet for this initial burn. This little tablet stand was fashioned from the removed steel bottom of the Sapporo can.

The bottom ridge of the Coors Light bottle is approx. 7/8" above the base of the stove. Based on the experiment performed by AYCE (http://thru-hiker.com/articles/esbit_stove_height.php) I wanted to get as much of the bottle in the "cone" and as close to the hot spot of the tablet's flame as possible without snuffing it out.

Sorry that I wasn't more scientific with this initial burn. All I can tell you is that half a tablet brought 1 pint of cold tap water very close to a rolling boil. I noticed more fumes coming out of the top holes than I usually observe with Esbits. Is this due to not getting enough oxygen? Any feedback appreciated. Thanks.

[Caleb Boyle]

Matt,

To me this looks like uncharted territory. I'm amazed at how you can simplify items so ingeniously! You've combined drinking bottle, pot, stove, and windscreen into one 3-ounce item. You said you used half an esbit tablet– Is this as in half of 14 grams? If so, this system seems pretty fuel efficient as well.

Does it fit well into your shoulder strap pocket? I guess the only downside I can see (other than the small size of the water bottle) would be having to use aluminum on a consistent basis.

Caleb

[matt kirk]

Hey Caleb,

Thanks for the compliment. Because of it's smooth surface and taper, the SBSBS fits very nicely into the shoulder strap pockets. I look forward to picking up more fuel tablets later this week to further test and refine the design. I've got another Sapporo can and Coors Light bottle on stand-by.

Because the aluminum bottle is lined, I think the greater drawback is from consuming the BPA that's bound to be in the bottle's liner material. I read another post (David I think it was) mentioning repeated cycles in the dishwasher could reduce the amount of BPA that gets in you. I don't have access to a dishwasher, but have used these bottles to boil water many times. Perhaps this use reduces ingestion of BPA…?

[Caleb Boyle]

Hey Matt et al,
So I was googling and came up with this article– http://www.sciencedaily.com/releases/2008/01/080130092108.htm

Maybe there's some way to remove the coating, but it doesn't sound like boiling water should be around BPA much. I guess this is why repeatedly running it through a dishwasher could release BPA.

[matt kirk]

I got hold of some Esbit tablets and conducted a 2nd test boil of this stove this evening. The tablet kept getting snuffed out, so I added a 2nd row of air intake holes (pictures below). I was disappointed to learn that it took almost 20 minutes to achieve a vigorous rolling boil with a pint of water from the tap. Also noticeable was the abundance of fumes. I imagine that the bottom of the aluminum bottle is too close to the tablet and there is not enough oxygen inside the stove.

[matt kirk]

Oh yeah, any idea what's up with the formation of Esbit stalactites in the last picture…?

[Bob Gross]

I don't know exactly why Esbit forms that way. I was using Esbit for the last three days, and sometimes my pot had boiled early, so I blew the remaining Esbit tablet out. Ten minutes later, I noticed the hairy whiskers growing out from the surface. Then I noticed that I could re-light the whiskers about ten times faster than an intact tablet, so I'm not complaining.

–B.G.–

[Dustin Short]

I'm postulating here since I don't know the actual chemical make up of Esbit but I thought it was a gelled petrol product…so on that assumption lighting the tablets converts them from a solid to a gas. As a gas the fuel ignites and produces the flame for heating. This process is far from 100% efficient so some of the gaseous fuel never burns. Usually it's dissipated by the hot air/gas and lost to the environment, but if conditions are right it may condense and solidify on your bottle (or the original tablet).

The new 'crystals' also probably have more surface area which is by BG is seeing faster re-light times.

For teh OP, basically it looks like you're not getting enough air/oxygen to your heated tablets so they fuel is not combusting fully. I don't know how efficient esbit is in this regard (ie at standard pressure and temp what amount of fuel is not burned under ideal conditions) but there may be room for improvement in your design to ensure as much fuel burns as possible. This would decrease the amount of esbit needed to boil a given amount of water. The same principle is behind why pressurized alcohol stoves tend to have better efficiency than unpressurized versions.

[Franco Darioli]

A few years ago i played with some of those cans trying to make a windscreen and a "pot" with them.
I gave up because the stainless steel was not good at all as a pot (using alcohol…) and i did have problems with getting the right amount of oxygen to the flame.
My project was somewhat inspired by the Swiss Army Vulcano stove, so maybe have a look at that for some ideas.
Franco

[Bob Gross]

"so on that assumption lighting the tablets converts them from a solid to a gas."

I don't think that is a safe assumption. From what I can see, lighting the solid starts it first melting to a liquid, and the liquid burns with a flame. I don't think there is any direct solid-to-gas conversion.

"The new 'crystals' also probably have more surface area which is by BG is seeing faster re-light times."

Well, yes, but I've never seen these crystals before. I don't know whether I just didn't see them before, or if the manufacturing process has changed slightly.

"For teh OP, basically it looks like you're not getting enough air/oxygen to your heated tablets so they fuel is not combusting fully. I don't know how efficient esbit is in this regard (ie at standard pressure and temp what amount of fuel is not burned under ideal conditions) but there may be room for improvement in your design to ensure as much fuel burns as possible."

My guess is that Esbit is burned fairly completely when the conditions are mild and there is plenty of airflow, but when conditions are cold, then the extra residue is left behind. This shows up on the Esbit burner and on the underside of the pot if it had cold water in it.

–B.G.–

[Roger Caffin]

'The main component of Esbit tablets is hexamine (hexamethylenetetramine). Some fuel tablets (US Defence) use 1,3,5-Trioxane as another ingredient.'

'Combustion can create formaldehyde, ammonia, nitrogen oxide, hydrogen cyanide and ingestion may cause nausea, vomiting, gastrointestinal disturbances, and kidney damage. When burned, the chemical oxidation of the fuel yields noxious fumes, requiring foods being cooked to be contained in a receptacle such as a pot or pan, and burned tablets will leave a sticky dark residue on the bottom of pots. If they are stored or used under damp conditions then they can break up while burning and shed burning fragments.'

source Wikipedia

The white whiskers are most likely recondensed hexamine.

Cheers

[Bob Gross]

"The white whiskers are most likely recondensed hexamine."

That must be the same as the white whiskers on my chin. I'll have to explain this to my healthcare professionals.

–B.G.–

[Roger Caffin]

> That must be the same as the white whiskers on my chin.
You could see how easily they light?

cheers

[matt kirk]

Thanks for your insight on this fuel residue on the interior of the stove.

After a disappointing performance on the 2nd boil, I decided to go ahead and make a 2nd version of the stove, this time paying closer attention to AYCE's study (as mentioned in OP) and raising the base of the bottle to 1.5" above the base of the stove. This raises the overall height of this system to 9". I also carefully used a wood dowel to hammer out the concave bottom of the bottle. Finally, I added a third row of vent holes at the point where heat/fumes exit. All three modifications were done in an effort to boost performance (pictures below).

Comparison of heights (version 2 of stove design on the left).

The added room height, ventilation and flattened bottle base did seem to make a significant difference in performance.

The 2nd version seems to burn hotter (as evidenced by the greater surface area of annealing occurring along the side wall).

The 2nd version achieved a rolling boil with a pint of tap water in just about 13.5 minutes compared to nearly 20 minutes for the 1st version. Also, there was far less residue from the tablet coating the bottom of the bottle. Perhaps this indicates a more efficient burn? All three modifications seemed to help boost performance. I would still like to get the boil time down further. Perhaps I should try alcohol fuel? I also wonder what effect adding a second row of air intake holes around the base of the stove would have. I'm hesitant to do so at the moment because there seems to be enough oxygen getting into the stove.

[Kevin Beeden]

I think you need to identify whether the fumes are from the Esbit tablet, or from the epoxy-phenolic lining of the Sapporo can burning off; I note the discoloration of the base of the can in the later pictures.

If it's Esbit fumes, then this would suggest you need more air intake holes to ensure complete combustion; more exit holes won't help.

Funny that Esbit is hexamine; my limited experience with them lead me to think they were much more pleasant than UK military hexamine tablets, which, in my recollection (childhood spent running around in nearby woods that were used for military training), were foul things that felt and smelt oily (more like a firelighter block), and covered everything with thick, black soot.

My experience of Esbit tabs (the 20x4g tabs like those pictured on the Wiki page) has been far more pleasant, being a dry, crystalline tablet with little smell and no soot.

Yet they both claim to be hexamethylene tetramine.

Esbit solid fuel info
MOD Hexamine MSDS

Well, the MOD tabs are listed as hexamine tetramine, not hexamethylene tetramine. My chemistry's not up to knowing if there's a difference…

[matt kirk]

Thanks for your thoughts. The 2nd version of this stove seems to be burning efficiently and I'm quite happy with the design.

The concern over the BPA in the can's liner remains. I plan to use this bottle stove on a long trek. I don't know how much I like the idea of using such a container. Is there any known way to get rid of the liner? I appreciate any insight on this matter. Thanks.

[Kevin Beeden]

I guess you have to ask yourself just what risk BPA might actually pose to your health*.

Yes, there was a well-publicised scare a few years back, and everyone went crazy-ape bonkers about it, but the media do have a track record of massive hyping of hazards, and little or no understanding of genuine risk assessment. This is made clear by statements such as "I don't care how much it costs, if it saves just one life, then it's worth it", which, of course, is utter, utter nonsense; we'd ban cars, alcohol, getting out of bed, stairs, and all other activities that result in deaths (pretty well everything we do).

We are surrounded by toxins. We ingest toxins deliberately, for pleasure and for therapeutic reasons. Whilst we might try to reduce the amount of toxic material we ingest, we need to take a balanced view of risks and benefits.

* and that's something only you can decide, by reviewing the evidence, determining how much you might ingest, etc. How much BPA will be contained in the thin coating of a single can? How much of this coating will be released into the pot contents during cooking (clue: Arrhenius), vs a can of soda sitting in a hot warehouse for months on end?

[Adam Kilpatrick]

Hey Matt

after getting a lot of use and experience with this stove, do you have any rough stats on how much fuel you use to boil said amount of water?

Cheers,

Adam

[Ben Smith]

I'm still a recent convert to meths and will enjoy my caldera cone set up for a while longer before making anything myself but I have to say this is really impressive.

[Dan Yeruski]

A variation of the design from a while back:

[Adam Kilpatrick]

I just got a couple of local aluminium screw cap bottles here.

Both are very close to the same weight and volume. The heaviest was 24.0681grams empty with cap, the other a few fractions below 24 grams (yep, in a lab). The cap itself is a bit over 2 grams. The cap rings I've yet to remove, would definitely get the heavier (nicer) bottle under 24grams haha. Filled to the bottom of the threading in the neck, 410ml (I figure that would be what I do in practise for boiling so that I don't boil over with a loose lid).

Hopefully test with 4g esbit tabs over the weekend, have to figure out some kind of stove, maybe a cat can or cut down beverage can (lots to choose from here). They feel quite strong. I've never handled a fosters can but I'm sure these would be just as durable as a ridgeline can if not more. The thickness of the can is a bit more than a typical Australian coke can is, and the cone to the cap section gives a huge amount of rigidity.

Cheers!

[Dan Yeruski]

Here it is with fire added:

[Adam Kilpatrick]

How much weight does the Sigg bottle windscreen add? What sort of fuel efficiency do you get with this?

Sorry if you mentioned it in the video, they are bit long for me to view right now.

Cheers!

[Author]

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