Well, so much is dependent on what you cook, how you cook, at what altitude, in what types of winds, type of stove, wind screen, and so on, I tend to ignore what other charts and graphs say except in extreamly general terms.
I look at basic fuel density. A) heat per weight of fuel B) weight of fuel carried per volume.
B) is easy. These generally run between .7 and point .8 for Alcohol, WG, isobutatane, or propane. I just use .75 and get close enough.
A) is a bit more difficult, but using the info from http://en.wikipedia.org/wiki/Heat_of_combustion
We find that Methyl: 9,800 BTU/lb Ethyl: 12,800 " Butane: 21,700 " Propane: 20,900 " Gasoline: 20,400 "
With the liquid fuels we find that a 3/4oz soda bottle works as a container for about a half pound of fuel. Or, about 1.5oz per pound. We call denatured alky about 10,000 btu to account for the methanol denaturing agent and the water from distilling it. Inexact, since it will vary from batch to batch, but always a bit more than that. The proportion of fuel to weight is 9.375%. We see that we get about 9537.1BTU/lb carried. (??? 9375TU/lb) (EDIT: for math errors)
With gas we need about 3.75oz (about average weight) per 4oz canister... or about 15oz per lb of fuel. We call the fuel 20,000BTU/lb since it is Isobutanae, not butane, and it is mixed with 10% propane...roughly. (It depends on your canister.) The proportion of fuel to weight is 93.75%. We see we get about 10625BTU/lb carried. (??? 9375BTU/lb) (EDIT: for math errors)
In conclusion to your question, there is no difference in fuel weights carried for any duration trip once you add in for the containers. (EDIT: Not quite true. Close enough not to invalidate things. It depends on the canister. My first three sets of numbers all were bit more than 100% done with MSR 4oz canisters that weighed ~4.05oz empty. The last set was done on the fly using 3.75oz from a Primus canister...corrected. My apologies for the error, above.)
An 8oz canister is more efficient at roughly 6.5oz for ~8oz of fuel... One of the "depends" I was mentioning. But adding in for the stoves again changes the figures. As does the "step" functions for canisters.
BTW: Doing the same math for WG: We call WG about 18,500 BTU/lb. (WG is NOT gasoline.) Adding a 1.5oz container gives us about a 9.375% proportion of fuel to weight, as with alcohol. We see about 17632BTU/lb carried. (EDIT: for math errors)
Note that only the stove weight really effects the calculations much. The UL alky stoves and foil windscreens (or Caldera Cone system) are my choice for short trips, ie less than 5 nights. For more than that I use a WG stove. When I first did these numbers several years back, I got a LOT of arguments. But, numbers don't throw BS at me. I gave away my canisters and canister stoves.
(EDIT: Same conclusion, my apologies, I blew my computer as I was trying to work up the numbers. Again, my aplogies till I can get a real one back up.)
Edited by jamesdmarco on 04/24/2011 19:45:13 MDT.
