Solo cooking set.

A few quick comments on efficiency:

1) Efficiency will be higher if you don't heat all the way to a boil. At higher water temperatures more heat is lost to the surroundings, so if you just heated water from 40F to 100F then you'd likely get decently higher efficiency vs heating to 212F.

2) All of my tests were done to a rolling boil which lowers efficiency a bit because some energy goes into changing the state of the water starting at about 95 degrees C. The more repeatable and fair test is probably heating from 40F to 200F.

3) Efficiency is higher when you're boiling larger volumes. All of my tests are with a small volume (pint or 500mL). A larger volume is more efficient for several reasons, including (1) energy going into warming up the stove is proportionally smaller (2) the ratio of volume to surface area of the water is typically better, so less heat is lost to the surroundings, more volume usually means a larger pot which will better capture the heat coming off the stove.

I don't have data for my cone setups, but my old FeatherFire stove was about 43% efficient with 500mL and 51% efficient with 1000mL in otherwise equal setup (methanol, indoors, 65F to a boil).

The problem stopping a test prior to boiling is that you could have significant thermal gradients in the pot. The local temperature you measure may not be indicative of the average water temperature. Boiling mixes the water and will bring the whole system into thermal equilibrium rather quickly.

It would be interesting to measure temperature throughout its heating to see how efficiency changes during the process.

Pulling data off of wikipedia is perfectly fine. That is what I did too. I think you grabbed the higher heating value (HHV) though, which is not really correct. The HHV assumes water in the combustion gas is a liquid. I've never seen that happen. The Lower heating value (LHV) assumes the combustion gas contains vapor water.

Fair enough. I wasn't aware of the difference. Using LHV instead of HHV, Methanol should be 19.9 rather than 22.7, while ethanol should be 28.9 rather than 29.7. Interesting that methanol drops so much more. There's nearly a 50% difference in energy content between these fuels, which should be on the radar of any alcohol stove user.

Here's a good link with lots of heating values for anyones reference:
http://en.wikipedia.org/wiki/Heat_of_combustion

"I conserve maximum fuel once my boil is achieved I quickly snuff the flame out with a thin sheet of silicone oven liner that is in disc form as you can see in the photos. Really helps prevent vaporization of fuel."

I use the same technique, but by quickly wrapping a corner of my foil ground protection cover over the top of the stove after I blow the flame out.

"My needs are different from most. I'm a big guy, eat a lot, laugh a lot and enjoy life ;-)"

Me, too, only at the opposite end of the spectrum. I'm a little guy who doesn't eat a lot and is austere by nature. But I still laugh a lot, mostly at myself, and enjoy
each day of my life, for the precious gift that it is. Comes with age, I guess, for those who don't figure it out earlier. ;0))

"1) Efficiency will be higher if you don't heat all the way to a boil. At higher water temperatures more heat is lost to the surroundings, so if you just heated water from 40F to 100F then you'd likely get decently higher efficiency vs heating to 212F."

+1. Which is why I only heat to ~170. Plenty hot for drinks or soup.

As far as " more heat being lost to surrounding environment" past 100 degrees, I simply dont find that to be true.

With a resonably efficient stove setup ,the temperature rise and fuel usage is pretty linear for the amount of time you run the burn.

I have timed boiks with a thermonmeter in the water. If your theory about heat dissapation to the environment were actually true, then there would be a fast temperature spike in the beginning and then the temp would rise slower as you got to a boil.

If anything, the opposite is true with some stove setups. As the entire stove system come up to temperature it HOLDS heat. Thermal feedback occurs.

Its really a tradeoff at that point. The heat cinserve within the system is at keast as much as any heat radiated.

As always, environmental factors are huge. Thats why windscreens are so important and cooking in a windbreak is god ptstice as well. No stove design made does its best in high winds. The MSR Reactor us the only exception I have seen to that rule.

My own practice us once I start to see bubbles form at the bottom of the pot and vibration and / or steam at the surface, its a good bet I am at 170 degrees+ and time to shut off the stove. In any temps where I would want a hot meal or drink, 100 degrees simply is not hot enough.

The reason I made the XL was so I could boil/heat 4 cups of water at a time.

Dan, I used your regular StarLyte w/pot support quite a bit last year and always brought to a full boil 4 cups of water using a little less than 30ml alcohol (Klean strip). Used the Toaks 1.35L and cut-down MSR windscreen. Always took about 11 min, give or take.

I like my big coffee, more water for Mtn House dinners than stated on the package (and lots more rehydration time), and also I feed my pooch dehydrated dog food, so I need a lot of hot water.

Bob,
You strike as a guy who would spoil his dog with hot food..;)
Good on 'ya for doing that. ;)

if you heat it up to 170 F you won't kill bad things, you need to treat the water

if you heat it up to maybe 190 F, with the lid on, and leave the lid on for a couple minutes, then you don't have to treat the water

to rehydrate food, probably better to heat to boiling and let it sit for 5 minutes

to brew black tea, you're supposed to heat to 195 F or so

a guy who would spoil his dog with hot food..;)

Ha, well as those who have hiked with us can attest, he's definitely loved and pampered, but not spoiled – he's a good boy!

And the dehydrated dog food (Honest Kitchen) is super handy for UL-ing with a dog.

But I agree with Jerry in that I like to get the water pretty hot. I get that far and figure I might as well 'spend' another 5ml to ramp it up and kill some cooties, especially since I don't pre-treat water for coffee and dinner/breakfast. I rarely do any trips more than 3 nights out, so fuel rationing isn't quite as important.

I don't feel this is necessary for drinking water from melted snow… warm seems okay. I just make sure the source snow isn't yellow or brown or pink! ;^)

Bob M., how does your dog take his coffee?

–B.G.–

Jerry this issue has been covered before:

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=26188&disable_pagination=1

Unless your heating raw sewage (?) heating to the pasteurization temperature (150-170F) is sufficient and saves time and fuel.
Read more here:

http://solarcooking.wikia.com/wiki/Water_pasteurization

Sorry for thread drift but I don't like to see fuel or time wasted.