William, your listing your fuel consumption by weight made me at first scratch my head, then have a slight eureka moment, then I searched it and found this fine article on the ion stove and fuel consumption. That article covers the joules contained in fuels, the btu's required to boil water (9 ml alcohol at 100% efficiency for 500 ml, didn't mention which type of alcohol though, it matters, but we can easily calculate that using the data provided).
So this reminds me, virtually all online comparisons between gas and alcohol weights over trips are wrong, not all, but most. I weighed my slx fuel and found it weighs 7.6 grams per 10 ml, ie, it has a specific gravity of 0.76. That means 10 oz in a container, by volume, does not weigh 10oz, it weighs 7.6.
For example, in my current models, I get consistent rolling boils at 17.5 ml, which is about 50% efficiency give or take, which is not bad, not as good at the ion's 75%, but not bad. At .76 sg, that's 13.3 grams of fuel, which suddenly is quite different from .6 oz to .75oz fluid volume, or 0.46 oz per boil of 500 ml (I find it's useful when testing to boil the standard amount so that consumption/effiency can be properly compared, too many things change when the volume of water changes, in often unpredictable ways). So all this time I'd been banging my head against the 1/2 oz boil and it turns out I've been past it for quite a while in my testing, due to the specific gravity/fluid volume issue of alcohol.
Another thing that struck me as I reconsidered the fuel weight vs volume, and this is yet another big plus for alcohol stoves, as if they needed more, being ultralight (both the stove and the fuel container), simple, silent, and easy to obtain fuel for anywhere, is that all along I've been just thinking of the volume = the mass, ie, a 10oz bottle of fuel weighs 11 oz, give or take.
then it struck me, gas is never really compared in this way as apples to apples, ie, what is the efficiency of gas in different stoves/setups vs alcohol in different setups, ie, the test has to be at standard temps, 500 ml, then by weight, not volume, of fuel consumption. That article noted that gas stoves were about 30% efficient, but it's an old article, so that may have changed, but I certainly do not recall such matters being frequently discussed here or anywhere else when comparing the fuel stove methods.
It's also worth noting that if you are using one of the super efficient stoves like the ion, which is giving you 75% efficiency, and if the gas stove is for example giving you 30%, then you are roughly equal in terms of btus delivered to the water.
thanks for the mental nudge William, I wouldn't have stopped to consider this until you very correctly listed your fuel by weight, not volume.
So for totally accurate comparisons, you need the following data:
- ambient temperature, which will change the specific gravity
- Temperature of water
- weight of 10 ml of the fuel you are using, in grams, at that ambient temp.
- weight of fuels consumed to bring to a rolling boil 500 ml of water, which I assume is pretty much 212 degrees F at or around sea level, though a thermometer will show it more accurately. this will in turn give the efficiency of the fuel/stove.
- type of wind/heat screen used, if any
- weight of fuel container
- weight of stove
- weight of screen/pot stand, if any
- Use of a real lid, ie, one that is capable of holding in some pressure. This one is almost always ignored, why, I'm not sure, it matters. A lid that can actually hold in some pressure is going to make a difference.
Once you have all these listed explicitly, you can start to make apple to apple comparisons which are actually analytically useful.
For example, here in these forums you will read all the time some post about x gas stove that weighs x or y grams, but not a word about its actual efficiency, which often could totally nullify any weight savings.
Standardized quantity of water, 500ml seems like a good one because it's basically two cups, but not quite, it's a bit more, which means also, sticking to one system, metric is sensible in this context since it's easier to deal with the units.
Then we can actually see what the various options actually compare to, not that anything can beat alcohol due to the factors I listed, but the comparison is more fair then, since almost all gas stove data is always weight of fuel consumed, whereas almost all alcohol stuff online is volume, and totally fails to differentiate between types of stoves or efficiency of stoves, from what I can see, which makes a pretty major difference. It's almost like there's all too frequently a pre-established selection bias in the comparison tests to favor gas...