I've begun experimenting with alcohol stove designs.
I always used a trangia in the past and loved it, but it "disappeared" during the course of a divorce (even though the ex doesn't bushwalk!). Rather than go out and buy a new one, I'm looking at options that might be lighter.
My main design goals are:
- Work well even when cold
- No need to prime
- Simple to use
I made a "supercat" first as something simple, and something to benchmark other attempts against. It worked well, efficiency was ok on the test bench (about 16ml to boil 500ml of water starting at 15°C) and when the pot was in place it burnt with a fairly clean blue flame.
The aspect I don't like are:
- Has to run for a while to build up heat, otherwise when a cold pot of water is placed on the flame dies down to almost nothing.
- It is very wind sensitive.
- It is very sensitive to ground temperature
If the pot is held over the flame while warmng up you save some of the heat and fuel that would be wasted, but this adds to it being a bit fiddly. And when it's cold and breezy, you have to hold it there a long time or it will die down, then stay burning very low (one test it even went out after a couple of minutes).
Obviously a windscreen will help with wind sensitivity, but a design that was a bit less sensitive to begin with would be better. And insulating it from the ground would solve the cold issue... but again, it's more items to carry and more fiddling.
I've turned my efforts to the Capillary Hoop Stove variants designed by Tetkoba. So far I've achieved designs that work better than the Supercat, but not as good as they could be from what I read online. The main references I've looked at (other than Tetkoba's youtube videos, and some google translations of some of his blog) are the (extremely long!) Alcohol Stove thread on Appalachian Trail Cafe and some posts on WhiteBlaze, mainly contributed top by user BirdBrain.
While I can hold it on my hand for a minute or two, it does end up very hot whereas Tetkoba and others indicate it shouldn't get this hot (one of the supposed advantages).
My boil times are similar to Tetkoba's but not as quick as BirdBrain on the ATC forum gets (around 3:30 IIRC) and my fuel useage is marginally higher than BB, even though I'm using metho (95% ethanol) rather than methanol and theoretically I should use a little less.
My flame is blue at the base, but when no pot is present it is quite orange at the top indicating incomplete combustion. When a pot is in place and is low enough, it is mainly blue and there is very minimal sooting. However with the pot low it forms a bronzy-coloured film on the bottom of the pot in the centre of the flame, which again indicates products of incomplete combustion (although better than soot). Tetkoba's videos show a blue flame even without a pot in place.
I was wondering if anyone else has played with this design?
My thoughts are that a lot of what I am seeing comes down to the fuel. Tetkoba doesn't state what he uses but BirdBrain uses Methanol (Heet) and even goes so far as to state not to use 95% ethanol, which our methylated spirits is down here.
Ethanol has a higher energy content as theoretically should use slightly less fuel if it burns efficiently and completely. But this obviously also requires more oxygen, and a design optimised for maximum efficiency with methanol may require adaption for ethanol.
Also, ethanol boils at 78°C as opposed to Methanol at 64°. This means the hoop at the top necessarily needs to get 14° hotter, which will translate to a warmer base as well. The metho in the bowl at the bottom of mine is not getting hot enough to boil, so that is a good sign and my hotter temp may just be because of the fuel.
The pro's I've seen with my design over the supercat so far are:
- The flame pattern and pressure from the jets in the top hoop make it more stable in a breeze.
- Efficiency was slightly improved
- No issues with the pot killing the flame (although you need a separate pot stand)
- Consistent flame throughout the burn time until only a few seconds before it goes out.
- Much better cold tolerance. As it is only the fuel traveling up the walls to the hoop that needs to be vaporised, the bowl being cold doesn't matter. I put alcohol in one of my stoves, placed the stove in a tray of water, and put it in the freezer until the water froze the stove in place. It still lit within a couple of seconds from a match, and bloomed in the same time as usual when warm, albeit with smaller jet flames initially.
I'm playing with a few design modifications. BirdBrain stated his opinion that 95% ethanol would need a bigger top hoop and a smaller aperture in the top of the stove, ideas I have not pursued yet.
Has anyone else played with this design? Specifically, using ethanol/metho rather than methanol? If so, I'd be keen to hear your thoughts and experiences.