Camping with Butane in Winter: making your own blend of winter mix
Ever tried to use your stove in the cold only to find that it just won't work, even although shaking the canister tells you there is plenty of fuel left? Then, when you check it a home to see what the matter is, it works perfectly. You are using butane, and you are not using an inverted canister stove. Butane you ask? Why not use common propane instead? The problem with using pure propane is that it has a boiling point of -43 °F (-42 °C), which means that it has a high vapor pressure at common ambient temperatures, and therefore requires a heavy steel canister to safely contain it (like the heavy 1-pound propane canisters used for Coleman stoves and lanterns). So canisters of pure propane are too heavy for backpacking. Butane is easy to contain because it has a boiling point of 31 °F (-1 °C), but it doesn't vaporize well when the temperature drops below freezing. Thus, pure butane has major limitations for cool-weather backpacking.
The solution is to use a blended fuel consisting of butane/propane, and an inverted canister stove. The thinner canisters can handle up to about 30% propane, with the remainder being n-butane as found in canisters sold in the Asian Markets (boiling point -1 °C). The propane/ butane mix vaporizes well at lower temperatures and provides enough vapor pressure for adequate stove performance at colder temperatures. Basically the propane in blended fuels drives the system. With its low boiling point, it provides plenty of vapor pressure at normal ambient temperatures; the other gases are carried along and burned with the propane. In an upright stove the propane burns off first, causing performance to drop (lower gas pressure and heat output) for the remaining butane in the canister.
(From interview Roger Caffin)
Inverted canister stoves are just remote canister stoves, but they include a preheat tube similar to that found on white gas stoves (see our stove section for an example). Not all remote canister stoves have the preheat tube. The preheat tube allows you to 'liquid feed' and start with a dead-cold canister and cook happily down to about -25 C. That is a huge advantage. The use of a liquid feed out of an inverted canister means the remaining fuel in the canister does not plummet in temperature due to evaporation as fuel is used.
The only thing you have to do is to start the stove at a low power for maybe 10 - 20 seconds - but you can start the stove with the pot already on it. In many cases you can start with the canister upright and then invert it after that time.
One really major advantage of remote canister stoves is that the operation inside the canister is quite different. With an upright canister the energy used to vaporise the fuel come initially from the liquid gas inside the canister. As a result the liquid gas cools down, possibly to the point where it no longer evaporates enough to drive the stove.
This can be dangerous in the cold. Even if it continues to work, the evaporation will be preferentially extracting the propane and leaving the butane. It is quite common for users to complain that their canister is 2/3 full but nothing is coming out of it. Butane boils at -0.5 C: if the propane has been used up and the butane is sitting at -5 C, you have a dead canister.
But when you invert the canister the evaporation of the liquid happens in the preheat tube at the stove, using energy from the flame. The canister does not cool down. The pressure used to
drive the stove comes from the static vapour pressure of the fuel in the canister - a pressure which stays constant as the static vapour pressure stays as constant as the temperature.
The other really major advantage of the inverted canister stove is that the fuel extracted from the canister is the original liquid butane/propane mix. This means that the percentage of propane left in the canister stays constant, all the way to empty. You don't end up with a canister 2/3 full of non-boiling butane. In effect, the propane provides the driving pressure which is given by the pump in a white gas stove.
Your own winter mix 70% n-butane / 30% propane canister will give off fuel down to -25 C. making it marginally better than a commercial 80% iso-butane / 20% propane canister. Canisters with less propane are not so good, and should be avoided. (They are aimed more at the family camping market.) But what matters here is the temperature of the fuel in the canister, not the ambient temperature. If you can warm the canister up beforehand then you can use it to considerably lower temperatures.
The next thing to consider is how you run the stove. If you put the canister out by itself sitting on the snow it is going to drop down to ambient fairly quickly, and that could kill the stove. On the other hand, if you insulate the canister from the snow and let it pick up a bit of radiant heat from the stove - through a gap in the windshield for instance, then you can keep the contents warm enough. Obviously you do NOT let the canister get too hot for safety reasons, but as long as you can put your hand on it (40C or less) you are safe. (We use a neoprene cozy and hand warmer to assist).
If you are going to be travelling at -30 C for some time you will inevitably be carrying more gear than a summer walker. You may well be using a polk or sled to carry some of this gear, and that allows you to carry a bit more weight. At the same time, finding water is going to be more difficult, so you may need to melt a lot of snow. Doing so can literally double your fuel consumption. Under these cold conditions it may be worth while considering the use of small LPG containers such as those made by Coleman. These containers hold a larger weight of fuel, and the LPG or propane will work down close to -40 C - without being warmed.
Anyone contemplating travelling below -20 C should be careful to test their stoves and other gear fairly thoroughly close to home. Grease and O-rings may need to be changed for these temperatures. Standard O-rings like those that come on our adapters can go hard and may leak below -20 C., so be sure to give them a dab of silicon grease. Viton O-rings are good between -26 C and +200 C, Nitrile O-rings are good between -40 C and +105 C, and PU O-rings are good between -50 C and +105 C. It's a pity that Viton cannot go lower in temperature; the +105 C upper limit for Nitrile and PU is really a bit low for safe use near the stove. (But these materials are OK when used on the remote canister connection.) More esoteric rubber are available - at a price.
If I make my own mix, what about clogging?
One pervasive myth about canister stoves is that the jet can clog from using other manufacturer's fuels. Snow Peak "fuels" this myth with their statement: "Fuel canisters manufactured by other companies may contain a mixture of fuel that has larger particles. These particles clog up the GigaPower stove and lantern." This is a pretty vague statement, and is pure hooey if they mean that larger fuel molecules will clog the jet. All canister stoves are jetted for C3 and C4 hydrocarbons to attain a desired BTU rating under a set of average conditions. The differences among stoves are not large enough to require a special fuel. The high pressure (up to75 psi) in the canisters keeps the jet clean. Clogs from the fuel itself are rare. What causes jet clogging is dirty connectors on the stove and fuel canisters. Keeping these connectors clean is good preventive maintenance to avoid stove failure in the backcountry and a trip back to the dealer. It is a good idea to retain the little plastic cap (if one is included with the canister) to keep the valve clean. Make it a habit to blow out the fittings of both the stove and canister before attaching the canister.