Butane canisters: Low temperature performance improves with altitude
The aerosol-type butane canister uses a bayonet-type connector (pictured left). This allows rapid and safe connection and disconnection between canister and stove. This simple connector does not suffer from wear from repeated use.
To enable aerosol-type butane canisters to be used with screw thread stoves, lanterns and gas torches, KOVEA created the butance adapter (pictured right).
The KOVEA butane adapter uses its patented "Push And Turn" mechanism to make a secure leak-proof connection. The butane adapter also incorporates a safety valve to ensure that no gas escapes from the canister when the adapter is connected without a stove attached.
Graphic above shows how the vapourisation point of pure butane decreases with altitude according to the Trouton-Hildebrand-Everett rule.
The implication is that it is possible to use cheap aerosol-type butane canisters (around £1.20 for 227g) down to much lower temperatures than is generally recognised.
Butane and propane have virtually the same calorific value which means that in normal usage above freezing they generate the same amount of heating.
Screw thread canisters certainly work better at very low temperatures due to the presence of 15-30% propane in the mix. The boiling point of propane is -42 °C. But given that most backpackers also use screw thread canisters in comfortable conditions (i.e. well above freezing), we think there is scope to save users a lot of money. If the cost of running a stove can be dramatically reduced by switching to cheaper butane, users can do more with their stoves for lower overall running costs, make more and better food, and hopefully have more fun in the process.
Aerosol-type butane canisters are made of much thinner steel than screw thread canisters. This is because they are designed to contain gas at only 2 atmospheres of pressure, rather than 4 atmospheres for screw thread canisters. Because the metal is thinner, it is easier to warm the gas inside the aerosol-type canister.
MercatorGear.com has been experimenting with butane canisters as an alternative to traditional screw thread canisters. The results have surprised us.
Below freezing at sea level
We decised to try out a KOVEA Spider running on pure butane during cold spell at sea level. The air temperature was -2 °C and a strong easterly wind was blowing. A butane canister was kept inside a jacket for around 5 minutes before connecting it to the Spider. The stove lit straight away, and with protection from a windshield took around 5 minutes to boil 500 mls of water in an aluminium kettle.
This was slightly longer than using a screw thread canister because the butane canister cooled quickly from contact with the ground and the cold air.
We improved performance by placing the canister close enough to the stove that it received sufficient warming to counter the cooling effect of the environment.
We also rolled the canister through 180 degrees to allow liquid butane to be fed to the KOVEA Spider. This had an immediate impact on performance and also arrested the cooling effect caused by butane vapourising inside the canister.
Above freezing at medium altitude
At medium altitude 2,600m (8,530ft) in the Swiss alps we found no difference in performance with a KOVEA Spider using a butane canister compared to using a branded screw thread canister.
In this test, air temperature was around +5 °C. The altitude provided an equivalent of an additional 7°C of air temperature. The conditions of altitude and air temperature were similar to a temperature of +12°C at sea level. Under these conditions there is no effective difference between branded screw thread and cheap butane canisters.
Freezer Test: Cold Start from -18oC (0.4oF) at sea level
In a bench test, we left an aerosol-type butane canister in the freezer at -18oC for 6 hours. We took the canister out of the freezer and attached it to a KOVEA Spider (at room temp) using a butane adapter.
After 15 seconds at room temperature the stove could not be lit as there was insufficient vapour pressure in the cold canister. After warming the canister with body heat for a further 90 seconds we could hear the butane inside the canister starting to boil. We then had enough vapour pressure inside the canister to achieve stable ignition.
This analysis supports the work MercatorGear.com is doing to show that the KOVEA Spider & Butane adapter can be run on cheap aerosol-type butane gas canisters in fairly extreme conditions if the canister is warmed before use. Altitude improves performance even further by around 1oC per 1'000ft. At certain altitude/temperature combination the canister should not require warming at all.
(Further details about using screw thread canisters in low temperatures can be seen on Hikin Jim's excellent post, here)