I've been waiting for a couple of months to do some patio tests of a canister cozy concept that I've come up with. So we finally are 'enjoying' our first sub-zero *F temperatures of the season here in Boulder. Time to do some testing. I'm posting about it in this thread, because it seems to be somewhat relevant to the theme.
But first, I'd like to report on something that I learned last week, before this cold wave hit. I am using a Snow Peak Giga stove with an integrated wind screen and reflector. A detailed description of this setup can be seen in this 2 year-old thread:
The aim of this test was to compare the boil times and fuel consumption of 2 cups of 50* tap water with different levels of flame intensity in high wind conditions. It was a very windy day (gusts of up to 45 mph), with ambient temperatures of 50* F. I did 2 tests at each level of flame intensity, and averaged the results, which were as follows:
Flame intensity, Boil time, Oz. of fuel consumed
Very low, 6:00 minutes, .25 ounce
Medium, 4:45, .25
Medium-high, 4:00, .20
High, 3:40, .20
What is curious to me is that this stove was actually a little bit more fuel-efficient when I opened the valve more fully, which goes against conventional wisdom. The bonus is that the water also boils faster.
OK, enough of this. Let's get to the cold weather tests. I came up with an idea that I thought might help when using a canister stove in very cold conditions. I made a canister cozy from Reflectix and duct tape. In the following photo you can see the components. I cut the compass off an REI zipper pull to give me a cheap thermometer, which I secured to the bottom of a fuel canister with duct tape. This is there to allow me to monitor the approximate temperature of the canister, to be sure that it doesn't overheat. There is also a 1/8" piece of Lawson's Evo pad, and a slightly larger diameter piece of titanium foil. These act as a stable non-conductive base for the canister. What is not included in the photo is a single chemical toe warmer, which is the key to this whole setup.
The next photo shows the canister inserted into the cozy, and sitting on the insulating base:
This final photo shows the stove and windscreen attached to the canister, ready for testing.
Yesterday morning the air was +10* F, it was lightly snowing, and there was no wind at all. I had placed everything on the patio table the night before, to let things get as cold as possible. I took the cold pot inside and put 2 cups of 50* F tap water in it and stepped outside to see if I could fire up the stove. For this first test I did not use a toe warmer, so everything was +10* F. I was somewhat surprised that the stove actually lit, after holding a Bic to it for about 5 seconds. There must have still been a little propane in the mix (Snow Peak canister fuel = 15-20% propane, 80-85% isobutane?). I had to open the valve fully to maintain a flame. The boil took 7:30 minutes, and it consumed .20 oz. of fuel.
For the second test, I placed a toe warmer under the canister, and fairly well sealed the bottom of the cozy against the Evo pad underneath.I didn't want to completely seal it, as the toe warmer needs a bit of air to feed its chemical reaction. I let the warmer do its stuff for 15 minutes before I fired up the stove. Just before I lit the stove, the little thermometer showed 45* F--it warmed things up nicely. By this time the morning sun was shining on the black duct tape of the cozy, so that might have helped to warm things up. The air was still only +10* F though. This time the stove fired right up. I only had the valve open about half way, which is all I needed for a robust and steady flame. The water boiled in 5:00 minutes, and again, used just .20 oz. of fuel. After the boil, the canister thermometer read 35* F. I assume that the canister had cooled itself slightly. The cozy and toe warmer combination seemed to do what I'd hoped.
Alrighty then, now comes the Phase II trial. At 5:30 AM this morning, the ambient temperature on the patio table was a bracing -9* F! Not a hint of a breeze, not snowing, just friggin' cold. All the stuff was left out on the table overnight, as before. Now I could find out what the real deal was. I put on my WM Flight pants, my warmest parka, my beloved BR beanie, and the BR down mittens Doug sold me, grabbed a mug of joe, and went to it.
The stove wouldn't even give a hint of lighting without the toe warmer setup. So I placed one, and went back into the house for 15 minutes. The toe warmer raised the canister temperature to +10* F, and the stove did light after a few seconds with the Bic. I had to turn the valve completely open to keep things lit. The flame was pretty weak, but it kept burning, slowly. I finally got a boil at the 23:00 minute mark. The boil consumed .25 oz. of fuel.
I think I learned what I wanted to know. The toe warmer concept does does seem to sort of work, at least until the temperatures go really low (its performance decreases as the temperatures drop). My results with the toe warmer setup at +10* F were about the same as the windy 50* F day test I first reported on, but at -9* F it sucked. Maybe a hand warmer with its higher heat output would work better. But I'm thinking that only something like an inverted canister or a copper wire feedback thingy will achieve decent results at 0* F or below. White gas, anyone?
These results confirm for me Ryan's observation that one uses about the same amount of fuel for a boil at any temperature. I also feel certain that very cold conditions will sap heat from the system, prolonging the time to boil. I'd love to have one of you physics types to tell us about partial pressures and how fast each type of gas gets used up. Would a canister composed of 25% propane-75% butane (eg, Optimus brand) function well at zero degrees until the propane is depleted? Actually, I might have learned something about this. Read on, I haven't told you everything yet.
I also tested my new 1.0 liter Reactor under the same conditions (I first tested the Snow Peak/cozy, and while it was cooling down I did the Reactor). For the Reactor, I used a new Optimus 25%-75% canister, no cozy, no insulating base, and no toe warmer. The results:
On the +10* F morning, The reactor fire up right away, it took 5:30 minute to boil, and it consumed .25 oz. of fuel. A slowish boil, twice as long as usual, but still OK.
But this morning, at -9* F, it was a far different story. It took 20 seconds with the Bic, and then it barely heated up. Never a bright orange glow, but just a bluish dancing flame. I placed the pot to capture what heat I could, and then after 4 minutes the blue flame went out. The higher propane content didn't do much at all, so I'm thinking that the Optimus blend is a dud for cold conditions. Maybe next time I'll try the MSR blend--it's likely the best-of-breed.
Thanks for indulging me, folks. Now I'll read what I've posted and correct my spelling errors before BG whaps me.