Alcohol Stove Math
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Dan Durston
(dandydan) - M

Locale: Cascadia
Alcohol Stove Math on 08/10/2009 19:36:37 MDT Print View

I'm trying to figure out how much weight I would save by switching from my MSR Pocket Rocket Canister stove to a FeatherFire alcohol stove. I'm trying to decide if it's worth the switch.

If I switch to alcohol I'll initially be buying the FeatherFire because I need the simmering capabilities for hiking with my wife. However, this math easily applies to other alcohol vs. canister stove scenarios since you can just switch the stove weight figures.

Here's what I got so far:

STOVES:

- MSR Pocket Rocket (w/o case) = 87g
- FeatherFire = 51g + 11g windscreen + 3g reflector = 65g

Savings: 22g (0.8 ounces)


FUEL & BOTTLES:

I have a 20 fluid ounce Ginger Ale bottle that I would use for holding ethanol alcohol. This bottle weighs 27g. Based on some research, I believe one fluid ounce of ethanol weighs 23g.

Accordingly, in a scenario where I need 8oz of fuel, then Ginger Ale bottle and ethanol setup would weigh 211g (7.4oz) vs. 365g (12.9oz) for an 8oz fuel canister (230g of fuel plus 135g canister) which is a 154g (5.4oz) savings including the stove weight difference.

This is looking good so far, but there are a few issues:

1) This scenario is quite charitable to the canister stove because it assumes 8oz which is a readily available volume. If I assumed another figure (ie. 11oz) then I would need to carry 2 canisters which would be a lot heavier.

2) One fluid ounce of ethanol does not equal 1 fl oz of canister fuel in terms of energy density. This is where I need help. If canister fuel goes twice as far, then that will cancel out the weight savings. Does anyone know anything about this? Does canister fuel goes 2x as far? 25% further?

Perhaps I can figure this out using the weights of the respective fluid ounces? A fl/oz of ethanol weighs 23g and 8fl/oz of isobutane/propane weighs 227g, which is 28.4g per ounce (data from Brunton fuel canister, MSR is similar). Does this mean that the canister fuel will go 23% further (28.4/23)? So really, energy density is a non-issue and 100g of each fuel will burn just as long only the alcohol will take up more volume? I've been rambling on way too long based on speculation. I need some help please :)

Edited by dandydan on 08/10/2009 19:44:43 MDT.

Lynn Tramper
(retropump) - F

Locale: The Antipodes of La Coruna
Re: Alcohol Stove Math on 08/10/2009 19:52:40 MDT Print View

A fluid ounce of compressed gas is a non-sequitor. It is merely weighs an ounce (28.4 grams). So your confusion comes from mixing apples and oranges (a unit of volume compared to a unit of weight). To make sense of your question, you would be best to weigh your alcohol rather than measure the volume. This way you can make meaningful comparisons between the two stove systems.

This article at Thru-Hiker may help you with your calculations:
http://thru-hiker.com/articles/stoveweight_vs_time_14days.php

As a little extra info, how far your fuel goes also depends on how high/fast you burn it. You can increase fuel efficiency with a canister stove by turning the flame down and waiting a little longer for a boil. Same may apply to the Featherfire. I have also noted improved fuel efficiency when I over-filled an alcohol stove and then recovered the excess fuel, compared to trying to add just the minimum amount of fuel needed to cook my meal. YMMV

Edited by retropump on 08/10/2009 19:57:02 MDT.

Dan Durston
(dandydan) - M

Locale: Cascadia
Fuel Weights on 08/10/2009 23:23:28 MDT Print View

According to an another article on Thru-Hiker.com, the Pocket Rocket averages 0.24oz of canister fuel per pint boiled (based on heating water from 60F to 210F). That corresponds to 6.8g of fuel used.

Conversely, PackaFeather.com claims their FeatherFire stove uses 0.54 fluid ounces of alcohol to boil a pint from 60F to 210F. Since a fluid ounce of ethanol weighs 23g, that means 12.4g of ethanol was used to accomplish the same thing.

Obviously these figures are rough and there are a lot of variables going on but this should provide a general idea....maybe not though. Please speak up if you think these figures are too rough to even provide a general idea.

By extrapolating these results to a full canister, 227g of canister fuel (one 8oz canister) should provide as much heating energy as 413g of alcohol (18 fl oz).

When I add in the weight of the containers (130g canister, 27g pop bottle) that brings the fuel + container weights to 357g vs. 440g. So even though the alcohol stove is 22g lighter, the alcohol setup ends up being 61g heaver overall (444g vs. 505g).

Two things that affect all of this are:
1) It's unclear which type of alcohol Packafeather used in their tests. According to the BPL article on the performance of different alcohols, Methanol uses 40% more fuel (by weight) to accomplish the same thing as ethanol.

2) This whole scenario is based on needing an 8oz fuel canister. If I assumed an amount other than 4oz, 8oz or 16oz then you'd either need to carry two canisters or a partially full canister which would hurt the canister stoves case significantly.

Ashley Brown
(ashleyb) - F
Re: Fuel Weights on 08/10/2009 23:41:05 MDT Print View

Here's a fuel calculator you may find useful.

Dan Durston
(dandydan) - M

Locale: Cascadia
fuel calculator on 08/11/2009 00:54:23 MDT Print View

Wow thanks for the great link Ashley! That link is perfect. It compares a pocket rocket to an alcohol stove...exactly the info I was trying to find. It sounds like my previous post was generally right, but I forgot to consider how the weight would change over the trip. Since almost all of the alcohol stoves' weight is fuel, it drops to very little by the end whereas the canister stove's weight stays high since the canister is such a big portion.

BTW, I found a 3.8g finger toothbrush at Wal-Mart today. It's meant for brushing your dogs teeth but whatever....sure beats the 25g behemoth I've been lugging around.

Edited by dandydan on 08/11/2009 00:55:08 MDT.

Troy Ammons
(tammons) - F
Alcohol Stove Math on 08/11/2009 08:13:05 MDT Print View

If a FeatherFire stove will boil 16oz of H20 with .54oz of fuel, I will eat my hat. That is roughly 1 TBSP of alcohol.

Brad Groves
(4quietwoods) - MLife

Locale: Michigan
Re: Alcohol Stove Math on 08/11/2009 08:36:22 MDT Print View

You might have to eat your hat... my Ti-Tri uses about 1T (15 ml of fuel) under decent conditions. But that's using the cone technology, too... with a FeatherFire on simmer and a good windscreen, maybe...

Troy Ammons
(tammons) - F
Alcohol Stove Math on 08/11/2009 09:27:40 MDT Print View

Well let me see which hat I dont want anymore. Good thing I am hungry. I still want to see it to beleive it. It may get to 210, barely, but no way a rolling boil. Seems like I read 7 minutes too and that does not sound realistic.

I am sure its an idealized test. I have been building and testing all sorts of alcohol stoves for the last year, and I have found its highly dependant on the pot, size, material, shape, IE big bottom, domed can etc.

If they really can boil a pint of h20 with a tbsp of alcohol I am missing something big.

Dan Durston
(dandydan) - M

Locale: Cascadia
fuel economy on 08/11/2009 09:56:39 MDT Print View

it's good to know real world fuel economy may significantly vary from this.

Brad Groves
(4quietwoods) - MLife

Locale: Michigan
Re: Alcohol Stove Math on 08/11/2009 10:31:11 MDT Print View

I've actually boiled--to a rolling boil--a pint with as little as 12ml of 95% ethanol in my Ti-Tri... Repeated tests yield 15ml pretty regularly, but in standardized "testing" conditions, ie 65*F everything.

Troy Ammons
(tammons) - F
Alcohol Stove Math on 08/11/2009 11:25:10 MDT Print View

That sounds like its more reasonable. Thats about 2.25 tbsp.

I had one efficient stove that would heat a cup very close to rolling boil with 1 tbsp of alcohol. It was bubbling, just not rolling. Thats why I can see how they can heat twice the amount of h20 to 210 with the same amount of fuel.

Towards the middle to the end it must have a flame about like a candle.

Brad Groves
(4quietwoods) - MLife

Locale: Michigan
Re: Alcohol Stove Math on 08/11/2009 11:56:36 MDT Print View

Hey Troy-
onlineconversion shows:

15ml = 1.014TBS

12ml = .81TBS

20ml = 1.35TBS

Greg Mihalik
(greg23) - M

Locale: Colorado
Re: Re: Alcohol Stove Math on 08/11/2009 12:18:07 MDT Print View

Troy,
I just got back from 5 nights out, all above 10,500', 50°F air temps in the evenings, water temps around 40° and a windy environment, I boiled 12 cups of water in a Fosters Cone on well under 4 ounces. And I wasn't watching the pot, so there were times when I used more fuel than required, and I was less than careful when filling and recovering.

Now, at home-
2 Cups of 40° water, a 70° air temp, no wind, 7600' elevation, in a 1.3L pot with lid:
Bubbles at 5 minutes, 'rumbling' at 6 minutes, and boiling (197°) at 7:15 --- ~9 grams of Sunnyside Denatured Alcohol were used. [Edit: 2 tests. 8 grams the first time, 10 grams the second time.]

4 Cups of 40° water, a 70° air temp, no wind, 7600' elevation, in a 1.3L pot with lid:
Bubbles at 12 minutes, 'rumbling' at 13 minutes, and boiling (198°) at 16:00 – 21 grams were used.

You Are missing something big: Caldera Cones work. Design, integrate, test, repeat……

(when looking a volume/weight measures remember that alcohol has a density of .79g/cc, so a gram of alcohol is about 1.25 ml. I'm a weight-based guy. Teaspoons are pretty ambiguous.)

Edited by greg23 on 08/11/2009 13:20:54 MDT.

Troy Ammons
(tammons) - F
Opps on 08/11/2009 12:27:13 MDT Print View

So my stoves are 1/3rd more efficient than I thought. I have been using a baby 10ml syinge to fill my stoves and got confused with the numbers. IE 10ml = 1tbsp when its 15ml.

Thanks

Edited by tammons on 08/11/2009 12:28:26 MDT.

Troy Ammons
(tammons) - F
Alcohol Stove Math on 08/11/2009 12:45:13 MDT Print View

Looks like I have to eat my hat now.

No wonder I have gotten so frustrated with trying to improve the efficiency of my stoves.

One of my last rigs, the micro stove will barely boil 1 cup of h20, 65dF at sealevel in about 4:30 - 5 min on 7.5ml of alcohol. Thats in a 12 oz heineken can pot. Rolling boil with 10ml no problem.

Thanks for pointing that out.

Edited by tammons on 08/11/2009 12:46:00 MDT.

Brad Groves
(4quietwoods) - MLife

Locale: Michigan
Re: Alcohol Stove Math on 08/11/2009 15:24:24 MDT Print View

Perhaps you could fashion a hat out of some crepes? Or a bread bowl with a side of chili? ;P

Lynn Tramper
(retropump) - F

Locale: The Antipodes of La Coruna
Re: Re: Alcohol Stove Math on 08/11/2009 15:32:41 MDT Print View

A caldera cone makes a great and stylie hat...you can't eat it but you can sure cook a nice hot fuel-efficient meal with it ;)

Gordon Smith
(swearingen) - MLife

Locale: Portland, Oregon
Caldera Cone Hat on 08/11/2009 19:14:58 MDT Print View

Yeah, that chap Jeremy from the Top Gear show has been sporting a Caldera Cone Hat recently. It seems to be catching on.

G

Rand Lindsly
(randlindsly) - MLife

Locale: Yosemite
Re: Caldera Cone Hat on 08/11/2009 19:20:14 MDT Print View

caldera hat?

Hummm.....I think I see a whole new marketing opportunity here.....

:-)

Edited by randlindsly on 08/11/2009 19:22:02 MDT.

Lynn Tramper
(retropump) - F

Locale: The Antipodes of La Coruna
Re: Re: Caldera Cone Hat on 08/11/2009 19:29:23 MDT Print View

Yeah Rand, I think an anodised titanium 2L fissure would make a great accessory...you can wear it fully assembled as a sun/rain hat, or split it in two and invert it to make to Caldera Crowns ;)

Cone Head

Cone Head

Edited by retropump on 08/11/2009 19:39:31 MDT.