Caldera Cones – My Adventures in Improving the ULC system
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"I'm interested in your improved draught through the cone. What is the total area of air holes you have now ?"
The picture below shows the 8 standard sized hole punch holes that I added in addition to the 5 larger ones that were original.
Adding these holes definitely increased air flow and improved the combustion efficiency, since before the boils were both slower (10:07 average) and fuel hungry (17.25g average). With the 8 added holes, boil time average went to 9:45 and fuel economy improved a lot to 15.65g. It's clear that combustion wasn't very efficient in the original setup.
However, it's possible that simply lifting up the pot a bit would have had the same air flow increasing effect as adding the holes. I did some quick pot height tests prior to modifying the cone, and raising the pot up 0.2" gave nearly the same results as adding the extra holes. So you've got two factors to play with here to get the combustion dialed in. The nice thing with not adding extra holes is that it might perform better in windier conditions. I didn't add too many holes though, so I don't think windy day performance will be too bad. I could easily set a rock or two in front of a couple holes on the wind ward side if it was really gusting.
BTW, this silicone band is now down to 2.5g and 1/4 of its original width, but it was a 'thick' wrist band that was about twice as wide as a normal wrist band. Even cut down this skinny, it seems to hold very well. I can pile at least 5 lbs on my pot without the band slipping, and a full 750ml pot would only weigh about 1.5 lbs so there seems to be no danger of that. I'm really happy with it.
I've ordered two normal wrist bands off of eBay ($0.99 shipped each) to experiment more with.
One thing to mention is that if you have a pot with lower handles, that could cause interference with the silicone band. The Evernew ECA278 750ml pot is the ultimate because it's high handles allow you to both use a silicone band and eliminate the handle cut out. Other pots could work with the band too, but you need a pot with removable handles so you can remove them to get the band on.
The most efficient stove we ever made didn't achieve boil until 37 minutes…..and used almost no alcohol to get there. Slow = efficient….almost always….
Good One Rand Good belly laugh on that one.
Here is how I determined rough pot support to pot. Used a pyrex pot. I would view the flame pattern through the water from above.
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</center>Well, interestingly enough, Rand recently sent me a sort of choke device to beta test. Using the choke, I got a boil at about 30 minutes and a run time of about 45 minutes about 3 or 4 weeks ago in Monrovia Canyon using 0.75 fluid ounces of alcohol.
This is totally experimental beta gear, so don't anybody bug Rand for one. I'm just saying that what Rand posted above is for real.
Flame without choke:
Flame with choke:
It does work well. Omelet:
Rand's choke looks like the same concept as the Featherfire choke. Only at a fixed setting (can't tell from the photos).
I've played with a variable choke on a chimney stove before; actually, it happened by accident when making a dual-wall chimney burner for my vaned kelly kettle…
I made the burner using techniques used in the 'Pepsi can burner'; i.e. a fuel cup base into which is inserted another can. Since I wanted to make a chimney burner, I punched holes in the outer can, and then punched mating holes in the inner can before assembling the two. Assembly proved to be tricky, so I ended up opening up the inner holes (since I didn't need a good seal, unlike in a jetted burner). This meant that the inner can was relatively loose, and could be rotated. Thus, the alignment of the two sets of holes could be changed, and, in doing so, the cross-section of the holes could be changed.
I can't remember the results…
I've suggested the same overlapping circles method for air control for wood stoves (to allow experimenting with primary and secondary airflows, and to 'bank' the primary air flow to reduce the heat output).
> Rand's choke looks like the same concept as the Featherfire choke. Only at a fixed setting (can't tell from the photos).
Nope….it's variable….we'll be releasing it soon. Here are some pictures in the mean time:
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