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Alcohol Stove efficiency
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Greg Mihalik
(greg23) - M

Locale: Colorado
Re: Esbit on 12/29/2010 16:11:50 MST Print View

"I'm skeptical as to the Gram Cracker being "set to the correct height" for all Caldera cones, as the distance from the floor to the pot seems to vary model to model."

For most Caldera Cones the pot support height (beer band or formed rib or pot lip) is optimized for the 12-10 stove. The stove height does not change, the cone height changes. So if the 12-10 works, the Gram Cracker works.

The TD guys thunk it out.

Edited by greg23 on 12/29/2010 16:21:45 MST.

John Roan
(JRoan) - MLife

Locale: Vegas
Re: Re: Esbit on 12/29/2010 16:43:19 MST Print View

Thanks Bob, I haven't tried the air underneath thing yet. Better stop and get some more Esbit to run some more tests!

Greg, I agree, those guys are very smart! I guess I just have to see for myself.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Re: Esbit on 12/29/2010 16:54:59 MST Print View

"I haven't tried the air underneath thing yet."

If you look at it, the titanium X keeps the heated air moving straight up against the pot, and it prevents much side-to-side air movement. Still, I only used the thing with a piece of aluminum foil around the outside for a windscreen.

If you run short on titanium metal, just run out and recycle some old Russian fighter jets. They used titanium skins.

--B.G.--

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Re: Esbit on 12/29/2010 17:50:31 MST Print View

"So if the 12-10 works, the Gram Cracker works."

Greg, the lower heat of the esbit means they should be set a bit higher than the alky stove to acheive the optimal heating distance.

My research on the K-Mart grease pot model, showed they set the height to the lower optimal height of the alky stove. Raising the cone a half inch does nothing to the boil times within a statistical deviation of about 15 seconds. (Same starting temp. But uncontrolled humidity for 20 test runs after a 10 test run base line was established.) The alcohol stove seems to have a larger "sweet" spot.

However, raising the gram cracker by a half inch improved the boil times significantly for 4 runs (I ran out of esbit tabs at that point) after a six run base line was run at the standard heights. Esbit was ALWAYS slower, but, burned about the same weight of fuel once I raised it. The mess, smell and time spent boiling made me drop it from further consideration, though.

At that point I was looking at minimizing boil times with an alcohol stove for a trip I was planning.

Hikin' Jim
(hikin_jim) - MLife

Locale: Orange County, CA, USA
Re: Re: Re: Esbit on 12/30/2010 11:50:48 MST Print View

James Marco wrote: Esbit was ALWAYS slower, but, burned about the same weight of fuel...

The same weight of fuel? Hmm. Not so good. I was of the understanding that Esbit would boil the same amount of water for less fuel. In your testing you found that the weight of fuel was about the same, is that right?

HJ

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Re: Re: Re: Esbit on 12/30/2010 13:07:34 MST Print View

Yeah. For raw fuel we are talking.
After adding in for a fuel bottle it is slightly less weight, overall. But, it is not that big of a differance... hundreths of an oz.
From Heat of Combustion at Wikopedia:
100% Ethanol is 12800BTU per pound
Hexamine is 12900BTU per pound (Trioxane is fairly similar but burns slower)
After computing eutectics at 95% and the weight of a fuel bottle esbit is better, but esbit also does not burn cleanly. It produces soot and by products. It looses efficency at about the same rate, maybe a bit less. The tables assume complete combustion.

Over all, the difference between the two is mostly a matter of choice. The slower heat, set to the perfect height will give slightly better results than alcohol. At
a different air temperture, it might burn more becasue it heats too slowly, allowing heat to radiated away from the water at a faster rate. Anyway, for between 40F and 70F it isn't significantly different...maybe as much as .1oz.

My tests pretty much follow this. I could not isolate the exact distance at which esbit was optimal, not enough tablets. And I suspect that this would vary with the air temp anyway. Like alcohol, there is a sweet spot, but it is much narrower since the amount of heat is much less.

I HAD expected them to be much better. I only looked up the heat of combustion figures after the test runs because I thought I must be doing something wrong. I had assumed that they were around midway between WG and alcohol and was surprised that I could not get them to burn better. I should know better...but, it still surprised me.

Anyway, I dropped them becasue they really don't buy me enough to be worth it.
They are quite wind sensative. I often loose more than I gain. Soo, after 7-8 trips out, I just quit using them. I have several packs of fuel tabs here now, actually.

Hikin' Jim
(hikin_jim) - MLife

Locale: Orange County, CA, USA
Esbit vs. Alcohol Weight on 12/30/2010 14:52:04 MST Print View

Interesting. So the weight advantage of esbit vs. alcohol is essentially negligible. BTW, did you factor the weight of the stoves into the equation? I assume that wouldn't change your calculations much.

If the weight advantage is negligible, then other factors like ease of use seem more pertinent. For me, alcohol is easier to light, cheaper, and burns cleaner. Seems like alcohol is almost the no brainer choice, yes?

HJ

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Esbit vs. Alcohol Weight on 12/30/2010 15:08:58 MST Print View

I use all sorts of stoves (white gas, butane mix, alcohol, Esbit). Mostly the Esbit gets carried along as an emergency fuel, since it is a compact solid and doesn't leak or degrade. I have one titanium Sierra cup, one butane lighter, three cubes of Esbit, and wrap that with aluminum foil, which can be a windscreen. All of that adds up to about three ounces.

If Esbit were a liquid in a bottle, I would have to keep checking on it before every trip, to make sure that nothing had leaked.

--B.G.--

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Esbit vs. Alcohol Weight on 12/30/2010 15:33:34 MST Print View

For raw heat, yes. Like I say, other factors seem to determine peoples choices, though.
If you cannot get ethanol (I cannot get everclear in NY) it looks a bit better. But I had access to lab stuff at Cornell, so, I could do more difinitive testing.
Methanol is not quite as good as ethanol.

As Bob was saying, for emergency use, it makes sense for a few ounces. I don't bother carrying it at all. If you have access to large ammounts of water, chemicaly treated or UV radiated, it doesn't need to be boiled, and can make sense.

If the water is already warm, around 80F or so, it can make sense.

There are a lot of variables that are uncontrolled. By the numbers, it is no better than alcohol and a lot more expensive.