Penny alcohol stove vs. chris' stove

[sierraDoug]

So I went out for three days in the Sierras here in CA and tried out the two stoves I made. The first is the Penny Alcohol Stove...
http://www.csun.edu/~mjurey/penny.html
I quickly found out the importance of a decent stand and windscreen. In my haste before the trip I bent a coat hanger into a pot stand and grabbed my MSR windscreen. The stand drooped so low it almost smothered the flame and the screen was way too tall for such a squat little stove. So, being the ever-prepared ex-Scout, I improvised. I held the pot's bail handle with my hand. Not recommended as a long term practice, but it got the noodles cooked.

Since the Penny Stove doesn't hold a lot of alcohol and I was messing around with no stand, I switched to my second stove. This was as designed by (our) chris...
"In terms of design, I would suggest the following, as it works and is easy to build. Buy a twelve pack of something like Old Style beer. Drink the 12 beers, saving one of the cans. Use a kitchen knife to puncture the can about 3 inches from the bottom. Then, use a pair of scissors and the puncture to cut the bottom of the can off. You want something like a 2 inch tall cup. You are now done with your alcohol stove."

I poured several oz. of juice into this advanced stove and boiled so long the noodles were limp. Did have one question though. Chris, if you're listening (or anyone else), how do you avoid yellow flames and soot on the pot?

[tlbj6142]

how do you avoid yellow flames and soot on the pot?That sounds like you might be using the wrong fuel? Or that the pot was too high above the flame.

BTW, I assume you still needed a windscreen with the "Chris Stove"? How about a pot stand?

[sierraDoug]

I used denatured alcohol from a paint store. With Chris' stove I was still holding the pot by hand, so the distance above the stove was variable. Does the height affect the sootiness?

[tlbj6142]

I've just noticed that the very tip of the flame looks a bit sooty. But you'd have to be holding your pot 3"+ above the flame to get that affect.

[chris]

I used denatured alcohol from a paint store. With Chris' stove I was still holding the pot by hand, so the distance above the stove was variable. Does the height affect the sootiness?

The sootiness suggests that the alcohol you were using was cut with something else, or perhaps had a good amount of isopropyl alcohol in it. My chemistry is too weak to tell you the difference between ethyl and isopropyl, but I think iso has an extra carbon atom on it and so burns hotter (?) and sootier (?).

Height won't affect sootiness, but it will affect boil time. Using a pot stand, I found that if the stand is too low, the boil time is way down. Too high, and the same thing happens (though less burn time due to more oxygen getting at the fuel).

Incidently, an easy way to make a pot stand is to take a can of beans (eat them, of course, first), and use a heavy pair of snips (heavy kitchen shears might work) to cut away at the can to get a stand. Cut out large air holes.

Also, I've found that bringing the water to a boil and then adding the noodles works better than bringing the water up to a boil with the noodles in it. Cook time seems about the same, but the texture is much better.

[sierraDoug]

So, is the pot stand supposed to to be one inch above the top of the stove with your type of stove? Thanks for the help.

[chris]

Anywhere from an inch to two inches, with 1.5 inches being about right. SGT. Rock wrote up something about the ideal height, but I usually don't measure.

[sierraDoug]

Anywhere from an inch to two inches, with 1.5 inches being about right. SGT. Rock wrote up something about the ideal height, but I usually don't measure.
Thanks, I'll try it out and see what works best.

Happy Trails.

[Lanthar Mandragoran]

The sootiness suggests that the alcohol you were using was cut with something else, or perhaps had a good amount of isopropyl alcohol in it. My chemistry is too weak to tell you the difference between ethyl and isopropyl, but I think iso has an extra carbon atom on it and so burns hotter (?) and sootier (?).
Yup, Ethly has two carbon atoms... isopropyl has three, though what makes is "iso" is that the OH (hydroxide ion) is bonded to the center carbon rather than the end.

The extra carbon atom causes it to have more stored chemical energy and burn at a higher temperature, but more importantly (for sooting reason) causes it to require (50%) more oxygen in order to burn completely. This is the primary reason that iso soots up. the temp doesn't get hot enough and not enough oxygen is supplied to the flame in order to get complete combustion. For iso to work properly (aka burn completely), you'd have to increase the height of the pot over the flames (more time for the oxygen to react with the flame) and punch bigger air holes (more o2 available to the flames). I have some ideas on how to accoplish this, but I need to get time to test my theories...

[Dances with Mice]

Yup, Ethly has two carbon atoms... isopropyl has three, though what makes is "iso" is that the OH (hydroxide ion) is bonded to the center carbon rather than the end.

The extra carbon atom causes it to have more stored chemical energy and burn at a higher temperature, but more importantly (for sooting reason) causes it to require (50%) more oxygen in order to burn completely. This is the primary reason that iso soots up. the temp doesn't get hot enough and not enough oxygen is supplied to the flame in order to get complete combustion. For iso to work properly (aka burn completely), you'd have to increase the height of the pot over the flames (more time for the oxygen to react with the flame) and punch bigger air holes (more o2 available to the flames). I have some ideas on how to accoplish this, but I need to get time to test my theories...Trouble is ya just can't fool mother nature and she keeps real close score in this game. Doing the math for a complete burn:
2 CH3OH + 3 O2 --> 2 CO2 + 4 H2O + energy
2 C2H5OH + 6 O2 --> 4 CO2 + 6 H20 + energy
2 C3H7OH + 9 O2 --> 6 CO2 + 8 H20 + energy

Which is pretty much what you said. But it looks like getting iso to burn clean is going to take more oxygen than a scooch more room under the pot or a bigger hole punch can provide.

[sierraDoug]

I used denatured alcohol from a paint store. Doesn't say the percentages, but lists the ingredients as "ethyl alcohol, methyl alcohol". Probably the soot was from cooking too close or too far away from the stove, and maybe from cooking for so long (over ten minutes).

Thanks for the help.