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Slow burn slightly pressurised alcohol stove
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Techno Tinker
(TechnoTinker) - F

Locale: New Sarum
Slow burn slightly pressurised alcohol stove on 06/21/2011 10:14:48 MDT Print View

Greetings all!

I've lurked on the sidelines for a l o n g time, now I've actually got something to say.

Like many I've spent hours playing with alcohol stove systems; side burners, pennys, cola-can, copies of "commercial" ones etc. Some have been failures, some match the "best of breed", but now I seem to have come up with something a bit different. But I'm not sure it's useful! It certainly doesn't meet my original criteria, but what it does - it does well.

In brief: it's a aluminium bottle stove, with internal jets. It needs a pot stand and a tin-foil wind-shield.

I've repeated these burns so many times with very similar results:
(Burning outdoors - not a workshop bench)
25cc fuel (UK standard "methylated spirits"),
450cc water at no higher than 55F in a lidded stainless container.
Total burn time in excess of 22 minutes - sometimes as much as 25.
Rolling boil achieved after 12 minutes - sometimes 10 minutes - and then bubbling boil sustained until the end of the fuel, so good for actually cooking rather than just a cuppa.

It doesn't "bloom" the way a side-burner or cola can does - the jets mix in with the initial flame and then come together when the priming fuel is spent in a swirling single flame.

It's obviously not going to be of use for those who might want a quick brew, pack away and then off, but the length of time it runs for, and the fuel economy may have some use. It won't win any "boil-off" contests.

Can the regulars see a use for something like this (in which case I'll write up the instructions, do the youtube vid. etc.) or should I get back to experimenting?


Regards,

TechnoTinker

James Cavan
(JamesCavan) - F

Locale: UK
Sounds Interesting on 06/21/2011 10:21:30 MDT Print View

Hi

It sounds like a interesting twist on a good design, got any photo's to give us a better idea of the design?

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Slow burn slightly pressurised alcohol stove on 06/21/2011 10:33:24 MDT Print View

I'm no expert, but there are alcohol stoves that require 1/2 ounce of alcohol to boil 16 ounces of water - that's not very specific because I don't say what the temperature of the water was and maybe it's not a rolling boil, but anyway...

so 25 cc of alcohol should boil should boil 800 cc of water to have the same efficiency

Techno Tinker
(TechnoTinker) - F

Locale: New Sarum
Photos as requested and reply on 06/21/2011 11:15:15 MDT Print View

Hello Mr Cavan:

Here are some quick shots to show the beast:Complete systemburner and stand from abovedetail of burner in stand Note the different sizes of holes - went through several bottles optimising those!pot standThe Pot stand is a stainless cutlery drainer through which a couple of tent-pegs are placed. The height was gradually reduced until it worked well - then of course another one after I'd gone too far!

Mr Adams - yes, I've seen some remarkable claims for stoves, and many seem to be unsupportable outside the workshop, hence - after a deal of inside testing - I took it all outside to test in the breeze. There's also a deal of confusion in stove tests between UK and US "ounces", cups - and indeed the types of fuel available each side of the Atlantic. I hoped that by specifying cc that others might be able to get a clearer understanding of what this one is doing.
It certainly makes the H = m * s * t equations rather easier to work! The starting temperature and the mass of the water used has to be a "must" in making comparisons.

What I find interesting about this particular bottle stove variation is the longevity of the boil - this isn't a quick flash up to 100C and die away - but could possibly be useful for meals - I'm thinking of the UK rat-pack meals where one can cook up in the sachet, and then use the water for a brew - and a clean-up. When I have more time I'll see just how much water can be brought to the boil in total by a single 25cc fuel load.

Regards,

TechnoTinker

Kevin Beeden
(captain_paranoia) - F

Locale: UK
looks familiar... on 06/21/2011 12:01:23 MDT Print View

Looks rather like the 'inverted conic' burners I build, and the 'Lynx' can burners discussed somewhere in the huge OM How to Make Meths Stoves Q&A thread. I know we discussed adding internal jets to a bottle burner like this.

One issue with this design is that the threaded part of the bottle sits on the pressed dimple of the bottle, and so when the fuel level falls below this point, there's nothing to stop the vapour leaking into the centre of the burner, so the jets tend to die away, so the burner reverts to an open-pot style. Not really a big issue, and, if used carefully, can add a nice 'boil and simmer' function.

The 'Lynx' deodorant burner uses the same principle of an inner jet ring, but uses a stepped can, so the 'vapour chamber' is very narrow, but doesn't suffer the premature pressure loss, as the inner wall comes down almost to the base of the container.

Inner-facing jet rings are good for small diameter pots, as they focus the flame, rather than allowing it to play uselessly up the side of the pan.

Kevin Beeden
(captain_paranoia) - F

Locale: UK
details, details... on 06/21/2011 12:09:05 MDT Print View

What's the bottle, BTW? One of the World Cup Buds, or a smaller bottle?

The long burn sounds potentially useful, and I'm wondering why it burns slowly; maybe just the small number of jets.

re. my comment about the dimple; that can be pressed flat again. I notice you don't seem to have 'fuel ports' (i.e. little cuts in the neck of the bottle to allow liquid fuel into the vapour chamber). This might prevent gas leaks and premature loss of jets.

I can't seem to post photos at the moment, so here's a picture of my inverted conic burner

Techno Tinker
(TechnoTinker) - F

Locale: New Sarum
Just my two-pennyworth ... on 06/21/2011 12:16:25 MDT Print View

Mr Beeden said:

"there's nothing to stop the vapour leaking into the centre of the burner,"

In this case there is - if you look at the photos carefully you'll see that the threaded portion has been sealed off - with a UK copper two pence piece. It's been driven into the threads which have then been peened over. I was in some considerable doubt about doing this - as the jet holes are then the only pressure release - but I have achieved a good overlap between the two parts and there's no evidence of any leaks. The adoption of this "feature" was one of the reasons that my testing moved outside!

An early version had a loose, but chamfered bevel, 2p coin - mediocre performance - and I re-used the bottle for a prototype of this one.

I will leave the way of filling the stove as an exercise for the reader - but it doesn't involve syringes or straws ...

Regards,

TechnoTinker

Techno Tinker
(TechnoTinker) - F

Locale: New Sarum
Re: details, details... on 06/21/2011 12:30:45 MDT Print View

The bottle is a Poundland (UK cheap store where everything costs ... 1 Pound) camping/cycling drink bottle. Hence my name for this burner; the 102stove - 100 pennies for the bottle and a 2p coin for the neck stopper.

The bottles are available in a variety of anodised colors, but I've stuck with the plain ones so I can see what's going on with the joints.

george carr
(hammer-one) - F

Locale: Walking With The Son
Re: details, details... on 06/21/2011 21:35:47 MDT Print View

Kevin, the stove most likely burns slow because unlike a side jet burner which heats the outside of the can, thus increasing temps and causing a harder boil, this stove has a cooling effect on the outer walls due to the cooler air in contact with the outer wall. If there was a way to reflect the heat energy back on the stove it would most likely behave differently. Maybe a wider pot and a tighter windscreen setup. If it reacts the way I think it will, you would have the best of both worlds - a stove that can be regulated to burn hot and fast or cooler and slower.

Edited by hammer-one on 06/21/2011 21:36:56 MDT.

Kevin Beeden
(captain_paranoia) - F

Locale: UK
re: Just my two-pennyworth on 06/22/2011 06:02:15 MDT Print View

> if you look at the photos carefully you'll see that the threaded portion has been sealed off

Aha! I could see there was _something_ at the bottom, but not what it was.

My guess for filling is that the inner part simply clips in and out; that's what I've found when making side burners with this sort of bottle. e.g.



Poundland and the 99p Store are regular haunts for me; always a nice collection of bottles and cans. Trouble is, since I dislike waste, I can rarely bring myself to discard the filthy muck contents in them...

I found the discussion in the OM Q&A thread; it was on the last page...

And here's the OM discussion on the Lynx can stove.

Edited by captain_paranoia on 06/22/2011 06:07:00 MDT.

Kevin Beeden
(captain_paranoia) - F

Locale: UK
'inverted conic' burner on 06/22/2011 06:07:43 MDT Print View

Here's the 'inverted conic' burner:

[edit] no it isn't; BPL doesn't seem to like the format of the URL for HTML 'img' tag insertions...

Edited by captain_paranoia on 06/22/2011 06:10:12 MDT.

Techno Tinker
(TechnoTinker) - F

Locale: New Sarum
back to the work bench ... on 06/23/2011 04:21:31 MDT Print View

Thanks to all for the links to resources elsewhere and for ideas as to where to take this particular combination.

I already have an effective side-burner (made from one of these bottles) that answers my original requirement for a stove - so development of this one is for curiosity only.

However, I can't walk away from George Carrs observation;
"If it reacts the way I think it will, you would have the best of both worlds - a stove that can be regulated to burn hot and fast or cooler and slower." Who could?

So - it looks as though I need to get the possibility for greater pressure, without sacrificing the existing economical and long boil characteristics of the stove as currently enabled.

These bottles are quite thick walled (0.7mm) and there must be quite a lot of energy wasted in raising the temperature of that mass of aluminium. I can reflect heat back to at least part of the stove body by a different potstand design - for trial I'll just mask off some of the holes with tinfoil. I'll also try the tabbed reflector I saw described - but I don't want to reduce heat transfer to the bottom of the water pot.

Something that can be altered to *regulate* the heat output mid-burn - like a sliding collar around the perforated stand needs to be tried. I've tried regulating the side-burner with a castellated collar that shuts off some/or part of the

To save others who might try this some time I found that if all the holes were made to be the larger size then the stove would burn fiercely, and fail to bring my standardised water load to boil before the 25ml fuel was used, if all the holes were the small ones (0.5mm) then I just got fine jets that, whilst burning for nearly 30 minutes, were prone to extinguishing from draughts and failed to get enough heat into the pot to bring to a rolling boil. Hence the two sizes.
I've tried two rows of holes, staggered alignments, different positions in the "cup" all sorts. I suspect the position is dependent on the cross-section of the two walls. Perhaps a shim of thin aluminium introduced during construction into that area would reduce the volume at the top and encourage greater pressure and/or heat transfer back to the fuel.

Filling (with the neck of the flask completely sealed off) is acomplished by pouring the measured amount of fuel into the "cup" part, and then tipping the stove so that the pool of fuel is over two of the larger holes and one of the smaller ones. It then flows freely into the interior with the displaced air leaving from the other holes. You need to leave enough fuel in the neck section to power the initial burn - I've found that just below the neck level is sufficient.

[Edit: I have thought that if I could thread the outside of the stove at the top and create a suitable threaded lid (with a seal) that this would be a useful transportable stove, not needing to be burnt out each time. That having been said, with the internal jets, it is possible to reverse the filling procedure and collect most of the unburnt fuel into the neck section, and then briskly tip into the fuel bottle, with minimal return to the interior of the burner.]

By accident I did make a completely sealed side-burner - the way I press the halves together is fairly robust - and fuel did not pass into the twin-wall section, requiring me to drill weep holes through the threads. Tricky! But it's probably better to ensure sealing with a metal disk. The copper probably soaks up too much heat in the wrong place - but it amused me to use a coin - especially given the heritage of Mark Jurey's "Penny Stoves".

Hours of fun ....

(Distracting me from my top-lit/updraft woodburning stove project which is "getting there")

Edited by TechnoTinker on 06/23/2011 04:34:25 MDT.

Kevin Beeden
(captain_paranoia) - F

Locale: UK
re: thermal mass on 06/23/2011 06:08:03 MDT Print View

> These bottles are quite thick walled (0.7mm) and there must be quite a lot of energy wasted in raising the temperature of that mass of aluminium

Yes, heating the burner does take energy, and marginally reduce the efficiency of the system, but then so does heating the pan...

I've made a spreadsheet to calculate burner efficiencies, and it takes into account the pan and burner temperatures. 55% to 60% (transfer of the lower heating value of the fuel to the water)is fairly easy to achieve.

As for the hole sizes and configurations, you're into 'holy wars' territory there; a subject of wide-ranging, heated (excuse pun) debate...

Edited by captain_paranoia on 06/23/2011 06:08:44 MDT.