Step 9: The Alcohol Stove
With the boiler now finished, I had the dimensions of the stove. This was where the project would succeed or fail.
I found out that of the two kinds of small alcohol stove designs out there, the sealed ones where a bit safer. But still, if you tipped one over, you could still get alcohol lit all over the place.
And there was also the problem of the amount of fuel need. In all the designs I found you filled up the stove with fuel and used it until it ran out.
I build prototype #1 based on this concept. It was small, it ran for 20 seconds before using up its fuel and almost got me burned.
Now I knew that I needed to get more fuel into the stove, but that meant a bigger stove and that would break constraint 1. This told me that my stove had to be externally fed.
Online research only gave up 1 type of stove that fit the bill (www.minibulldesign.com/) but looking at those beautiful stoves, it was clear that they broke design constraints 2,3 and 6.
I had no option but to design a new kind of tiny, externally fed, intrinsically safe, alcohol stove.
It took me over a month of work, lots and lots of research and tinkering and refining ideas, but finally, lucky prototype number 13…..Waass aaliiiveee !!!
It ran 18 min, 36 seconds on a full charge of alcohol.
I actually had the intention of staging an “accident” where I would tip over the stove full of fuel in a controlled environment.
Luck would have it, that my clumsiness got there first: during a second run of the stove, after about a minute lit, I accidently hit it with my hand and tipped it over. Since I was still using a piece of tape as the security cap and air flow control, all the alcohol got out and spilled over the table and on me. The stove turned off immediately after it tipped so the spilled fuel never got lit.
The design was a success!
The end design is really simple and obvious in the way good designs tend to be. The hard part was getting there.
The stove has three main parts:
1. Fuel tank with flow control
3. Diffuser and heat exchanger.
The stove works on the principle of vaporizing only the amount of fuel to be immediately burned. This gives us two good things: it allows an external fuel source and since only a small amount of vapor is available to the flames, any interruption in fuel supply would automatically turn off the stove (constraint 6).
I made a lot of different types of flow controls (one using the valve out of a lighter) but in the end, a simple unplugged syringe with a bit of tape over the top with 1 pin sized hole in it gave me the one-drop per second that a stove this size needed. It was simple and cheap (even though they don’t sell any at Home Depot, you can get them at any pharmacy). The flow rate is so small, that the fuel tank tap only needs a tiny hole at the top to balance the pressure and keep the flow going. This also is a big win in the safety department, because the hole is in fact so small, that if you tip the fuel tank on its side, no fuel comes out.
If you want (and I can bet someone will) you can very easily scale the stove to a size big enough to use as a camp stove (there’s an idea for a future Instructable).