cyccommute 

Methanol: 14,000 kcal/gallon
Ethanol: 19,000 kcal/gallon
Isopropanol: 21,000 kcal/gallon
Isobutane and gasoline: 28,000 kcal/gallon

But...

It gets murky when you actually go to burn alcohols. Methanol, for example, will give off it's entire heat load because methanol doesn't carry water with it during distillation. Ethanol may or may not have water in it depending on the source and the way in which it is distilled. 95% ethanol has a lower heat of combustion than 100% ethanol because you have to put energy into volatilizing water. Drinking alcohol burns but because it has around 70% water, it burns cold.

Isopropanol has a couple of problems. First is that it is difficult to find in low water concentrations. "Rubbing alcohol" can often have a 70% (or higher) water content which greatly reduces its energy content and cools the flame. It will tend to burn with a yellow flame.

However, even when in a pure form, it's volatility is low so it doesn't mix well with air and gives a yellow...i.e. cold...flame. It could benefit from a pressurized method of burning but it's on the edge of being to volatile for a pressurized system and not volatile enough without it. If you had the right jet, you might be able to control it but I don't think anyone makes such a jet for liquid fuel stoves.

nun

Rubbing alcohol is usually 70% isopropanol and 30% water and other stuff. If it was the other way round I'm not sure it would burn at all.

robow

Cycco, Thanks for muddying this up even more for me. So what do you think of the high ethanol content denatured alcohols such as Sunnyside and Klean Strip Green that supposedly come in at about 90-95% ethanol? Do you know if they leave a varnish like residue as to what I read last night in a couple threads over in a backpacking forum? Some claim that the SLX and and other brands contain too much methanol as well as other unhealthy bi-products from the denaturing process? Looking thru the MSDS for these products is quite difficult for someone who hasn't refreshed his organic, physical and bio chem in almost 4 decades.

nun

The Evernew Appalacian set up has something called a "reactor plate" that is between the stove and the pot. It gets heated to red and is supposed to improve the efficiency of the stove. I think this is a load of hooey. I don't see how using energy to heat the flat plate will help in any way. Maybe the heat exchangers on stoves like the Jetboil can capture and deliver heat more efficiently, but I've found the most efficient way to use an alcohol stove is to make sure the flames stay well within the circumference of the pot's base and cook in a sheltered location with a good windshield. KISS often works.

nun

Those will have at least 90% ethanol and methanol, the other 5% or 10% of organic compounds might be responsible for your "varnish".

3speed

Seriously. I'm currently looking into dropping way more money than I should on a multi/liquid fuel stove. They're really expensive, but I didn't like not having a fuel canister for days on my last trip. We couldn't seem to find them anywhere in the towns we were riding through.
Yeah. Shake can, approximate how much is left. You can tell when it's pretty close to empty. If anything, just assume that it'll run out faster than you expect. It may get you a few more meals out of it than you expect, but that gives you a day or two to track down a new canister. If you get the new one and the old one keeps going for a couple days, you're not carrying that much extra weight anyway considering the old one is basically empty. Sometimes finding the new canister, however...

ak08820

One solution I was thinking was to determine weight of the full or empty canisters of different brands/sizes to be used. One can then ask a grocery store clerk to weigh the used one to find out how much is used/left. Luggage weighing scales are about $5 (e.g., 10 40kg Muti Function Blue Hanging Scale Portable Fashion Luggage Lastest | eBay) with 5-10g accuracy and can be used to weigh the canisters. They themselves weigh about 4 oz or so and easy to carry if one chooses to do so. They have a hook so the canister can be weighed by tying a string and creating a loop. A mechanical one would not be as precise but would not need batteries, e.g. Household Portable Spring Scale | eBay
I am using an electronic one as a postage scale and the batteries last forever.

staehpj1

I have another suggestion. You might consider a pop can stove as a backup. If you can't find a canister you probably can find alcohol. The pop can stove and stand weighs less than an ounce and you can probably use the same windscreen and pot as with your canister stove.

I usually just take only the pop can stove, but if taking the canister stove somewhere I might run out of fuel and have trouble finding it I'd carry the pop can stove as a backup. That or just make one if I need it. In a pinch it can be as simple as just a cut off pop can and a stand bent out of heavy wire (coat hanger works well). I prefer something a bit more elaborate, but any port in a storm...

nun

If you want to "weigh" a gas cannier just float it in some water. If you've done some prep and know where the water level comes to on full and empty cans you can estimate the amount of gas left. Or you cold rig up a simple balance with a bit of string and twig and some reference weight, or just carry a spare cannister.

I use an transparent 8 oz squeeze bottle to carry my alcohol and know that 3 squirts (about 1/3rd of a floz) will bring 2 cups of water to around 180 F. You don't need it to boil as you just spend time waiting for the soup or tea to cool enough to drink it. I'll make tea with one cup I water and cook Ramen or couscous with the other using my clothes as a pot cozy.

Ekdog

How about making one of these? You could put some kind of a rack on the top for cooking.

bikenh

Like I said originally, the way to deal with the sooting is to watch the spacing between the top of the stove and the bottom of the pan. That spacing is VERY critical. You have to a 1 inch gap, anything more or less and you will get a yellow flame and get the sooting that goes with the yellow flame. If you control the gap you get very little yellow flame.

ak08820

If you always heat a known quantity of water for each meal, you may come up with the number of times a canister lasts and start looking for a replacement when you near that number.

edthesped

I've been fixating on a wood gasifier lately. Has anyone tried using one?

staehpj1

Yeah, I have toyed with them. I'd be more likely to consider using one for backpacking or bike tours with long periods between restocking. Most of my bike tours allow frequent enough restocking that fuel weight isn't enough that I am willing to put up with the other compromises.

Problems I see with wood gasifier stoves that I have tinkered with:

1. They are a enough heavier than my alcohol stove that there is only a weight savings when I need to go a good ways between fuel resupply.
2. They are messy and get soot all over the pot. They stay sooty and have to be bagged carefully to keep the soot off of everything else.
3. They are kind of a pain to use. It does get easier with practice though.

cyccommute 

Soot is indicative of other problems that spacing isn't going to solve. A yellow, sooty flame like those shown in the video Ekdog linked to indicate incomplete combustion and a cold flame. While the values for the amount of heat per gallon of fuel I gave are valid, they are only valid for complete combustion of the fuel to carbon dioxide and water. A yellow flame indicates that a significant amount of the fuel isn't being combusted so you aren't getting the same amount of heat out of the fuel as you could theoretically. A flame that produces soot indicates an even higher percentage of the fuel, and thus heat, is being wasted.

Moving the pot lower into the flame is even counter-productive. You can move the pot into a zone where the fuel and air are mixing but combustion hasn't begun yet. Depending on the fuel this can even be an area of the flame where the temperature is colder than the surroundings as the fuel evaporates and cools before combusting.

If you are burning wood, a downdraft gasifier has a slight increase in efficiency over just burning wood but wood is a poor fuel for cooking. It's energy density is low and the weight, if you have to carry it, is high. If it is wet it doesn't burn well and it can be hard to obtain in certain parts of the world. In my state of 104,000 square miles, about 35,000 square miles of it have no place to gather wood to start a fire. And my state has a lot more trees than many of the surrounding states.

A gasifier might be fun to tinker with but it's tough to bet liquid fuels for energy density. Even alcohol...which I wouldn't use...does a better job than wood.

nun

Most campsites will have fire pits and I use those when I can to save alcohol. I'll collect some twigs and fallen branches and arrange a few rocks to hold my mug over the fire. The downside is the mess it makes of my mug.....but it's fun.

ak08820

Here is the latest in stove design - named the eFrevo stove. Uses only 1 can. Only drawback is that it will need a pot stand.
https://www.youtube.com/watch?v=zjeyT5wlQms