Hi, James,

The nice thing about the "basics" that I've described (low to moderate flame, use a lid, use a windscreen) is that they can be applied to pretty much everyone's set up. In other words, you don't have to buy any new gear to implement these (well, maybe a windscreen).

I completely agree with you that there are additional factors. A pot that is wider than tall generally is more efficient (unless you're talking about something like a JetBoil or Reactor pot with a heat exchanger).

Even more efficiency is obtained when one creates a set up where exhaust gasses are entrained such that heat transfer is maximized. Controlling the flow of the exhaust gasses is the "secret" to the efficiency of stoves like the Caldera Cone, Trangia, and Reactor. I've seen test results indicating that efficiency suffers less on high flame with such a set up, which would tend to corroborate your results.

HJ
Adventures In Stoving

I ran some tests with the 4 pots I own:
455g of water was raised by 125F (~55-180F)
Stove output adjusted to maintain temperature increase at ~20F/min (so ~6:00 run time)
Lid used for each pot, No windscreen, testing performed inside
3 runs per pot averaged
The above would requires a minimum of ~2.9g of canister fuel.

POT 1: Generic Ti Cup, OD 3.63” 5g fuel burned n=58%
POT 2: Imusa Al mug, OD 4.5” 4.5g fuel burned n=64%
POT 3: Stanco Al pot, OD 5.25” 4.2g fuel burned n=69%
POT 4: Backcountry Ti Pot OD 5.5” 4.1g fuel burned n=71%

POT 4 has 2.3X more surface area (on the bottom) than POT 1 and required ~20% less fuel -- non-trivial. While hardly exhaustive I think this shows, generally, pot selection is non-trivial.

Updated info based on error described below....thanks Stuart!

Edited by jnklein21 on 03/06/2012 19:51:13 MST.

Excellent data James, well constructed experiment

what is n?

So, wider the pot the more efficient, that makes sense

Did you wipe off any condensed water off the canister after each run

Jerry, I did wipe the cansiters before each weighing (per your recommendation elsewhere)...but really didn't notice any condensation (I guess it was warm and dry enough in my house).

Sorry I forgot to define "n"...it is effieciency as defined by:

n = (minumum theoretical fuel required)/(actual fuel required)

How do you calculate minimum fuel required?

I calc it by considering the heat capacity of water and the energy density of fuel.

1. Heat capacity of water:
A material's "specific heat capacity" (or C) tells you how much heat is required to raise one unit mass by one unit temperature. The specific heat capacity of liquid water is ~4.184J/g/defC (this is where the energy unit "calorie" comes from).
That is 1 J will raise the temperature of 1g of water by 1degC.

So to increase the temperature of 455g of water by 125F (~69C, sorry to mix units)...you need ~69 X 455 X 4.184 = 131,000J = 131kJ of energy

2. Energy density of the fuel:
A fuel's "heat of combustion" tells you how much energy is release by buring a unit of that fuel. Typically this value will be given as either Higher Heating Value (HHV) or Lower Heating Value (LHV). LHV assumes that water resulting from combustion is in the vapor state, HHV assumes it is a liquid (for this reason I use LLV).
LHV for butane/protane/isobutane is ~46,000 J/g or 46kJ.
That is 1g of fuel burned will give of ~46kJ of energy

3: Fuel required
I calc minimum fuel required by: min fuel = (Energy required) / (energy density of fuel)...
=[131kJ]/[46(kJ/g)] = ~2.9g.

edited to add...
the above calc assumes that every bit of energy makes it to the water. The pot mass is negligible. All water stays in the liquid state. No combustion vapor condenses on the cookpot. It represents the very best you can do without breaking the law(s).

Edited by jnklein21 on 03/06/2012 11:45:53 MST.

Hi, good experiment James and sound calcs. However if I may be picky... something is amiss with the data for Pot 4. Try graphing efficiency (n) vs diameter and you will see what I mean.

I have measured 57% efficiency for a 130mm dia pot, 7C -> boiling, using a Gnat at a higher output (~1400W), so very similar results (apart from afore mentioned pot 4).

Edited by Scunnered on 03/06/2012 13:49:43 MST.

Thanks James

Surprisingly efficient for best case (76%)

Or if it's slightly different as Stuart observed

Not much more room for improvement

Re: POT 4:

Yeah, I know...it is the reason I ran a third set of burns.....

I'll give it another go tonight just for good measure.

Edited to add.......

Good catch Stuart. I re-ran POT 4 twice: Dropping highest and lowest gives an ave fuel consumption that rounds up to 4.1g. 4 of the results varied by less that .2g. 1 of them was ~.7g (%20) lower!
I am betting I forgot to tare the scale w/ the empty pot when I measured out the water for that run, that would mean I heated about 100g less water (~20% less water).

Each of other three pots' sets varied by less than .2g.

I'll update the post in question.

Edited by jnklein21 on 03/06/2012 19:48:20 MST.

POT 1: Generic Ti Cup, OD 3.63” 5g fuel burned n=58%
POT 2: Imusa Al mug, OD 4.5” 4.5g fuel burned n=64%
POT 3: Stanco Al pot, OD 5.25” 4.2g fuel burned n=69%
POT 4: Backcountry Ti Pot OD 5.5” 3.8g fuel burned n=76%

"I've noticed in particular that it just doesn't pay to carry a smaller, narrower pot even though such a pot is lighter and more compact"

FWIW: The lighest pot in the bunch is actually POT 3, I have yet time find a pot that will hold >2cups lighter than this one (@2.3oz).

From a pot design point of view...for a given volume and thickness the weight of the pot will be minimized by having the pot diameter equal to the pot height. I guess that is why we tend to see relatively narrow pots.
The above optimization assumes pot lid of equal thickness also, ignoring pot lid says weight will be minimized for dia = 2 X height.

lol. Good point. I shouldn't assume that a little mug type pot is necessarily the lightest option.

What is the approximate capacity of each pot?

HJ
Adventures In Stoving

These are ballpark as I'm away from home...

Apprx Volumes/wieghts(no lid) are:

POT 1: .5L / 3oz
POT 2: 1.25L / 3.5oz
POT 3: 1.0L / 2.3oz
POT 4: 1.25L / 4oz

Does anyone actually sell this stove?

you can find the gnat here:

http://www.moontrail.com/monatauk-gnat.php

also you can buy it rebranded by olicamp here:

http://www.amazon.com/Olicamp-Kinetic-Ultra-Titanium-Stove/dp/B007OJKI0M

Edited by jnklein21 on 08/04/2012 21:15:45 MDT.

Thanks a lot! Moontrail seems to even have the neo air xlite small instock, not something easy to find in canada.

I have the gnat, bought it a couple years ago by chance after stumbling upon it during my search for lightweight canister stoves. I found that the stove is really quite fast to boil, but that it isn't quite as efficient in the long term as other stoves, because it is very prone to wind related weaknesses. If you carry a shield, or build a little wind wall you will find the efficiency greatly improved. If you are going for a long thru-hike read this:

http://www.backpackinglight.com/cgi-bin/backpackinglight/2011_sotmr_integrated_canister_stoves_part3.html

and that:

http://www.backpackinglight.com/cgi-bin/backpackinglight/monatauk_gnat_stove_review.html

before deciding.

But I love my gnat. Its my favorite stove of all that I've owned and it works just fine in the cold with the right canister.

"but that it isn't quite as efficient in the long term as other stoves, because it is very prone to wind related weaknesses"

More so than other upright cannister stoves? Neither article mentions this.