“Cobalt” Beer Bottle Stove

Looks nice! Do you have a construction video too?

Thanks Herman, a construction video is in the thinking stage. I feel like I have to write a script. It's difficult to adlib. Seems like its too easy to repeat myself. I have alot more respect now for Jay Leno(dan laughs)

I didn't mention this in the video: no priming wick is necessary, thus making the stove more efficient than other beer bottle stoves. Another neat little thing that I added to the stove is a small wick in the center to aid in lighting the stove. I found that beer bottle stoves are difficult to light in cooler weather because the evaporation at the bottom of the stove is very low, not enough oxygen down there to get it lit. The little wick is attached to the bottom of the stove(inside). When fuel is poured into the stove the wick becomes saturated and capillary action brings fuel to the rim of the stove where there is plenty of oxygen. Light the wick and the flame travels downward and ignites the fuel. If you watch the video again you can see the wick sticking up and you can see I touch it with the match. No more burned finger hair also. That's another thing about lighting this type of stove. A match or lighter has to be poked down into the center of the stove to light it. When it ignites, the flame would reach up and zap your finger hairs into char. Not with the Cobalt stove though, the ignition wick keeps your fingers away from the center of the stove. The introduction of the internal wicks is a major improvement over the stoves currently on the market. I should have some stoves available by Tuesday of this coming week.

The design of the die thats used to form the rolled over edge looks just the opposite of the type of die thats used to roll the edge of a grommet. That's where I got the idea on how to roll the edge inward.

I use a table saw to cut the tops off the bottles. A chop saw(mitre saw) could work just as well. A lathe is not required for this task.

Here is a demo video of the ignition wick that really helps this type of stove light in cold weather. Click on the blank window and it will start.

The “Cobalt” stove is now Heineken pot compatible.

Boils 2 cups of water in 10 min. using less than 3/4 oz. fuel.

Let it go bill. Cool off.

Dan,

This is a very interesting modification. I will stay tuned.

>Boils 2 cups of water in 10 min. using less than 3/4 oz. fuel.<

It would be really helpful when your state this kind of information to give us the starting temp of the water. As you may be aware, the information as given is basically useless. If you got 2 cups of 80 F water to boil in 10 minutes I would say you better go back to the drawing board. If you got 2 cups of 32 F water to boil in 10 min. then bravo!

Also, what has been your experience with this stove in the wind.

Thanks,

-Mark

Hi Mark, when I design a stove I test them under what I call "Ideal Conditions" or "Optimum Conditions". Those are terms that existed when I started making stoves. I think Sgt. Rock is the one that I heard use them on Whiteblaze.net. The conditions being 70 degree water and air/room/atmosphere temperature and no wind. These are what I use on stoves that are bench tested.

I got 2 cups of 70 degree water to boil in 10 min. on less than 3/4 ounce of HEET. I firmly belive I could have gotten 32 degree water to boil on 3/4 ounce of fuel. You have to understand that the original "Cobalt" was modified to be used under the Heineken pot. It now becomes a different stove. I have a separate thread on my website devoted to it. I should have done the same here.

Side jet and top jet stoves are new to me. I'm in the learning process. My goal was to create a beer bottle stove that bloomed quickly without the aid of a primer pan or wick on the outside of the stove. Priming on the outside of the stove is not "User Friendly" I accomplished my goal.

I have not tested this stove in the "wind".

Mark , what is the air speed that stoves should be tested at? Give me a little something to go on when you say tested in the wind.

Dan,

Thanks for the info.- so doing the math:

2 cups=473 ml = 473 gm water and
70 F to 212 F is the same as 21.1 C to 100 C = 78.89 C degree change.
So 473 gms of water X 78.89 degrees C = 37.314 Kcals required

(Since I don't have a value for "less than 3/4 ounce" I will use 3/4 oz)
3/4 fl oz = 22.1 ml fuel used
methanol's density is 0.7918 gm/ml
So 22.1 ml X 0.7918 gm/ml = 17.5 gm of fuel used

17.5 gm x 4.7 Kcal/gm of methanol = 82.25K Kcal available in the alcohol used.

37.314 Kcals required / 82.25 Kcals used = 0.45 or about 45% efficient.

Which is not going to win any prizes but is fairly respectable.
(For comparison a Caldera Keg system gets closer to 60%. and the most efficient beer can alcohol stove I am aware is about 80% efficient)[NOTE: THIS IS AN ERROR, SEE MY 3RD POST DOWN BELOW}]

Concerning the wind- As you well know, wind has a huge effect on the performance of alcohol stoves. With 45% efficiency and the hard to heat beer can pot, I would think you will need to have a good wind screen before you market this stove. To my knowledge there is no standard for wind in stove testing circles (Is there? You would know better than me), but a light breeze (defined as 3-7 mph or 6-11 km/h on the Beaufort Scale) would be a reasonable design goal IMO.

-Mark

P.S. – Out of curiosity, with the beer can mod and top jets, what kind of bloom time do you get now? You should have better heat transfer, but then again with the insert you have more thermal mass.

I'm just curious how the wick holds up after repeated use. Doesn't it end up dry and brittle (and less 'wicky') over time?

RE: Wind tests. I don't know of a standard, but since *most* people would carry (and use) a windscreen, would it be best to test with a windscreen? It hardly seems fair to compare a windtest of something like a Caldera Cone stove to and un-screened alcohol burning stove…?

Allison,

Dan uses a metal wick for lighting the stove. I would assume this is some kind of braided wire affair. He also uses another kind of wick material between the inside and outside wall which I, like you, would be concerned with becoming brittle or charred over time.

As for the wind test- yes, any comparison for wind tolerance should be done with a windscreen. A windscreen may also improve the efficiency of his stove even without any wind.

-Mark

Hi Mark,

I got the same efficiency figures of 45% from Dans measurements, but the highest efficiency reading from a alcohol stove that I have measured is 70.3% and that was using my volcano stove a JetBoil 1.5l GCS flux ring pot and using 99.9% ethanol

fuel used 9.3g ethanol, 0.5l water, temp rise 80C

I am wondering what stove/pot/fuel combination was used to obtain 80% efficiency.

Unfortunately the efficiency equation does not take into account the actual mass of fuel used eg: if you use 20 g of fuel with 25 MJ/kg to heat 0.5l of water 80C and then used 10 g of fuel with 50MJ/kg to heat 0.5l of water 80C you will get the same efficiency figures but one used twice the mass fuel of the other. That is why I use g/80C/0.5l

Tony

Mark,

Glad to see some rigor in the analysis department.

I'm guessing the 80% number was achieved using some sort of kettle stove where the flame is enclosed by the water jacket.

Regarding the breeze. I did some testing using a fan and anemometer. Just a 5mph breeze can impose severe heat loss even on stoves with wind screens. When the stove I was testing failed to achieve a boil (temperature was in the 40's) I concluded it is best to seek a sheltered spot, wind screen or no wind screen.

H

I did a cold water test for you Mark. I boiled 2 cups of 32 degree water with 3/4 ounce of fuel.(HEET) How’s that for efficiency?

Everyone should use a windscreen in the field to conserve heat. I have a great little corrugated windscreen that reflects infra red heat waves back to the pot. The corrugations run virticle to the pot.

The fiberglass inside the double wall will not char or become brittle with age. I doubt the copper ignition wick will lose much cappilary abilitiy over 10 year periode.

I get a fast bloom time with the top jets. The body of the stove was reduced by 3/4″ and the potstand sticks up 3/4″ above the rim. The overall height of the stove remains the same.

The one video will show how wind will not blow out the flames during it’s operation.

I’m having fun learning how to edit a video, it’s a learning experience to the max.

Dan,

Thanks for the doing the test.- Ok once again with the new numbers:

2 cups=473 ml = 473 gm water and
32 F to 212 F is the same as 0 C to 100 C = 100 C degree change.
So 473 gms of water X 100 degrees C = 47.3 Kcals required

3/4 fl oz = 22.1 ml fuel used
methanol's density is 0.7918 gm/ml
So 22.1 ml X 0.7918 gm/ml = 17.5 gm of fuel used
17.5 gm x 4.7 Kcal/gm of methanol = 82.25K Kcal available in the alcohol used.

47.3 Kcals required / 82.25 Kcals used = 0.575 or about 58% efficient.

Which is quit good! Bravo!

How long did that take to heat the water from freeze to boil? Still the 10 min?

As to the internal fiberglass wick -why exactly won't it turn brittle and even char with repeated use like these wicks do in other stoves? Is there something special about the wicks you use?

Wind- Well it does seem to be wind tolerant which I think is a big plus and yes wind screens are a must. In fact as Herman notes site selection may be even more important.

Nice Stove, Dan.

-Mark

Tony,

Concerning that 80% efficiency….well ah..hmmm….
Ooops! I was misremembering some testing I did on the CFV (Capillary Forced Vaporization) stove I was playing with last March.(see the URL below)

I remembered that I could get consistent boils of 2 cups (473 mls) of 60 F (15.56 C) water with 13 ml of alcohol. My mistake was that I thought I remembered using methanol, but I used 91% isopropyl alcohol which has an energy content of 7.2 Kcal/gm , This is significantly more that the 4.7 Kcal/gm in methanol. So revise that 80% down to 54-55%. I should have gone back and checked. Sorry.

-Mark

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=12031&skip_to_post=92445#92445

P.S. – I still really like the CFV stove for it's simplicity and ability to burn isopropyl alcohol, but I found that if there is the slightest breeze it won't work at all. I even went about devising all sorts of elaborate wind diverters with multiple screens and interesting venting. Eventually I realized that although the stove only weighs 5 gm the windscreen was coming in at 70 or 80 gm which sort of negated the stove wt. Live and learn.;-)

Hi mark, Dan and merman,

I am finding this discussion about efficiency and wind very intersting and thought I would share some test results that I have.

I have recently obtained an old anemometer (see pic below) and using a fan I ran some tests with my BPL 550 Caldera Cone and a standard parallel windscreen both tests used using the 10-12 stove that was supplied with the CC stove. The fuel used Australian denatured alcohol 95% ethanol content.

These tests are not comprehensive and are the results of some initial testing to plan future tests. More test need to be done.

Results: No wind, heating 0.5l water 80C

BPL 550 Caldera Cone 12.46g/80C

Using a parallel WS and 10-12 stove 13.62g/80C

Note very small difference between different windshields with no wind.

Results: wind 7.2 kph

BPL 550 Caldera Cone 14.0 g/80C

Using a parallel WS and 10-12 stove 26.45g/80C

(note: the parallel windscreen has holes around the whole circumference and the CC has hole in only half of the circumference which the holes were placed down wind, I have not yet tested a parallel windscreen with hole only on one side)

I also did a test using the CC and my volcano stove and got results of 10.54g/80C. I think this shows that the flame from the 10-12 stove is to big for the small BPL 550 pot.

Tony

CC under test (note parallel WS on left)

Hi Tony

What's that red thing under the bench? Tool and cutter grinder?

Cheers

Hi Roger,

It is a very old Black and Decker engine valve grinder, the drive belts have perished and are not available, I have to do some modifications to take different belts.

In the early seventies I did my original apprentice training in engine reconditioning.

Tony

Hi Tony
" I think this shows that the flame from the 10-12 stove is to(o) big for the small BPL 550 pot."
Yes, me too. I really like using the CC with the 550ml pot but I have noticed that the flame is a bit too wide. Again I suspect that it has to do with using Ethanol and not Methanol. BTW I have not done "scientific" tests , but using about 14 ml of Ethanol (two capfuls of my alcohol bottle) the difference between wind and no wind is around a minute of extra boil time.
I did some experiments with a tea light type stove but that took too long to bring the water to boil.
Franco

Tony and Franco,

Thanks for your info and thoughts on windscreens.

Not to derail Dan's thread, but as Tony's experiments show- good wind screens are key to efficient heating and therefore fuel consumption/efficiency. The Caldera Cone, in my experience, is one of the best.

-Mark

Thanks a million mates, for the education on testing using scientific methods and for your time to do the calculations.

The CC really seems to be a well designed set-up. I have not seen a recent close up of the closure system. I'll have to go to their website and take a look. I like the ss bushbuddy also for wood use. The FeatherFire also seems to be pretty good, very well designed simmer device installed. I've done some testing of that one. Sgt. Rock makes a mean "Ion" with titanium pot support legs. I've made several of those.

"The fiberglass inside the double wall will not char or become brittle with age."

Dan,

I am still interested in your internal fiberglass wick -why exactly won't it turn brittle and even char with repeated use like these wicks do in other stoves? Is there something special about the wicks you use?

Thanks,

-Mark

Hi Mark, Yes it's special. It's designed for commercial applications. Designed to withstand 1700 degree temperatures. It is not wick material, it is cloth, 2" wide, with selveded edges along the 2' dimension.It's totaly different than what is used on Tinny's wick stoves. It does not come in contact with oxygen as does the wick material used on the bluefly stove made by Tinny, that's why he sells extra wick to his customers; You have to trim the wick, just like an oil lamp.

The wick material he uses on the outside as primer wick seem to last forever and not get brittle/fused together. Same with the stuff he uses to wrap Heineken pots. Those of you that wrap pots with fiberglass wick, look a the tiny fibers that stick out of the wick. Those fibers are coming off on your hands when you handle the pot. Be sure to wash your hands befor eating/handling your food and cleaning your nose or rubbing your eyes. Look at your pot up close in sun light, you'll see the fibers. They are loose, especially when it is new.

Hi Mark,

>good wind screens are key to efficient heating and therefore fuel consumption/efficiency. The Caldera Cone, in my experience, is one of the best.

I agree the CC stove is a very well designed stove but I think that a well designed normal parallel wind screen could handle wind just as effectively.

Tony