Hollow Center Jet Burner Alcohol Stoves?

No, but I found this instructable:

http://www.instructables.com/id/Self-pressurizing-chimney-type-alcohol-stove/step9/Ninth-Step-Firing-It-Up/

Looks neat. I have some of the materials already. I might try this.

I have always loved Tetkoba's designs. They were my inspiration for a center-draft alcohol stove I made several years ago, which is still my primary backpacking stove:

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=72582

The center-draft design, which I attribute to Tetkoba, is more efficient and more wind-resistant than some other kinds of alcohol stoves, in my experience. But I've found that my design, at least, is finicky and less stable than more conventional alcohol stoves.

When I was making prototypes I learned that very small differences in the size of the jet holes result in a stove that burns weakly or else flames up and becomes a hazard. I learned a similar lesson about different fuel mixtures. Since the flames are surrounded by the fuel reservoir, anything that slightly changes the heat output has a much bigger effect on the boiling rate of the fuel than for a more conventional top jet alcohol stove (like a penny stove), which is designed so the flames are directed away from the fuel. The result, at least for my design, is a sensitive and somewhat unstable stove. I don't know if Tetkoba's center-draft designs have the same problem.

What do you mean by less stable? Less consistent output or it's liable to explode?

One thing i noted about Tetkoba's stove compared to your design is that your center-draft is much larger. Have you experimented with restricting airflow to the center draft? It also looks like the burner holes are slightly lower down and closer to the fuel than the bottle design.

What are your reasons for using a mixture of fuel? I mostly carry grain alcohol with me for fuel, do you expect that would perform as well or worse?

Just wanted to post this guys video as well. Same design with TWO AND A HALF MINUTE boil of 400ml. Burn time of just over 5 minutes for one oz of fuel! Eat your heart out Jetboil.

https://www.youtube.com/watch?v=W0RosfKZ-sg

https://www.youtube.com/watch?v=uXKEcs_Tnww 3 minute boil, 6.5 minute burn time

https://www.youtube.com/watch?v=oMQofa-WDZw 2:50 minute boil, 5.5 minute burn time with blueprints

I've heard that a faster boil comes at the cost of fuel efficiency, but with this design it seems like you get the best of both worlds.

Along with those boil times, you want to add the time for pre-heating.

–B.G.–

Steve, I haven't tried restricting the airflow through the center. I'll consider trying that. I settled on the fuel mixture I'm using just by experimenting with my current stove until I found a mixture that had the best performance.

When I say my stove is a bit unstable I mean it tends to fluctuate a lot in its heat output. It flares up for 10-20 seconds, then simmers down and burns weakly for a few seconds, then produces a medium sized flame for a little while, then fluctuates again. It still manages to be very efficient, and it fares better in gusty winds than any other alcohol stove I've had, but it usually doesn't hold a nice consistent flame for very long. It never flares up enough to be alarming, and it never goes out, just tends to fluctuate.

Based on numerous prior threads, the de facto performance standard for alcohol stoves seems to be about 15 ml of fuel to boil 2 cups/500 ml of 60-70F water. Boil times for this standard vary widely, from about 6:30 min. to 11 min. or longer. Good efficiency is in the 50-60% range. Very good efficiency is in the 60-70% range. Excellent efficiency is over 70%. I thought I would see how these CHA stoves compare.

For true "boil times" I include priming time, and use the time from ignition to boil.

Where enough information is given, I have calculated efficiency using the formula from the "The Alcohol Stove Efficiency Percentage Test Thread" (http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=89347)

A couple things to note. All of the chimney stoves need to be primed, which takes time and fuel. Other than Colin's, most of the stoves look pretty heavy and complicated to fabricate.

The video in the OP (https://www.youtube.com/watch?v=LA97x9o0_2Q) uses 35 ml of fuel for the stove and priming, but does not show the starting water temperature or total burn time. Ignition to full flame = 30-40 seconds + 3:30 min to boil = 4:00 to 4:10 min to boil 400 ml. 35 ml to boil 400 ml is not efficient, unless the water started at a very low temperature.

The second video (http://www.instructables.com/id/Self-pressurizing-chimney-type-alcohol-stove/step9/Ninth-Step-Firing-It-Up) uses 20-25 ml of fuel plus "a few more ml" for priming. It does not give any information on priming time, water volume, boil time, total burn time.

Colin's thread for his CHA stove (http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=72582) does give all the necessary information. "In three boil tests this stove brought to a boil two cups [473 ml] of about 57F tap water in an average of 6:33 min. and burned for an average of 7:51 min. using 15 ml of a 50/50 blend of methanol and ethanol." It uses some additional fuel for priming. For comparison purposes, I will assume 5 ml for priming (Colin, please correct me if I am wrong), which I will assume for all of the stoves. It is not clear if time to boil started at ignition and includes priming time, but I will assume that it does (again, please correct me if I'm wrong). Efficiency = 52%. 6:33 min. to boil two cups of water is good for an alcohol system. 15 grams for the stove, stand and primer pad is very good.

The Silver Chimney (https://www.youtube.com/watch?v=W0RosfKZ-sg) by Silvio Leonard uses 25 ml of fuel + 5 ml to prime. Time from ignition to start of timer = 1:06 min + 2:30 boil time = 3:36 min. Total burn time = 1:06 priming + 5:11 to flame out = 6:17 min. 400 ml of 16.4 C (61.5 F) water. Efficiency = 41.4%.

The Silver Chimney version 2 by Silvio Leonard (https://www.youtube.com/watch?v=uXKEcs_Tnww) uses 20 ml of fuel + 5 ml to prime. 400 ml of 21.4 C (70.5 F) water. Ignition to timer start = 56 sec + 3 min. boil time = 3:56 min. Total burn = 56 sec prime + 6:30 timer off at flame out = 7:26 min. Efficiency = 42.8%

The Combo Chimney Stove by Silvio Leonard (https://www.youtube.com/watch?v=xBH-craDVUg) uses 25 ml of fuel + 5 ml to prime. 400 ml of water, but temperature unknown. Ignition to timer on 43 sec + 3:15 boil time = 3:58 min. Total burn time = 43 sec prime + 5:40 min. to timer off at flame out = 6:23 min. Efficiency unknown, but 30 ml to boil 400 ml is not very efficient (again, unless the water was cold).

The RED capillary hoop chimney video (https://www.youtube.com/watch?v=oMQofa-WDZw) also by Silvio Leonard uses 25 ml of fuel + some more to prime. Again assume 5 ml to prime. 2 cups of water (473 ml) at 16.7 C (62.1 F). Ignition to timer start = 1:22 min + 2:50 min. boil time = 4:12 min. Total burn = 1:22 min. prime + 5:25 min. to timer off = 6:47 min. Efficiency = 45.2%

So, while these stoves are fast, they are not particularly efficient. The general experience is demonstrated again: a faster alcohol stove is less efficient than a slower one. The holy grail continues to elude us. Perhaps someday a system with a protected heat exchanger like an MSR Windboiler, or some other innovation, will get us closer.

It still comes down to a preference for speed vs. a willingness to carry more weight of fuel. Assume you're having a 2-cup hot breakfast and a 2-cup hot dinner every day on the trail. Efficient stove uses a total of 30 ml per day. Fast stove uses 60 ml. For a 9-day Sat-Sun trip, that's 270 ml vs. 540 ml. Alcohol weighs approx. 0.8 gm/ml, so it's the difference between 216 gm vs. 432 gm (7.7 oz vs. 15.4 oz). For a 30-day trip, the total difference would be about 26 oz.

Wow awesome work with the maths David. This is really interesting stuff to think about. For me personally, I probably wouldn't go 6+ without wanting to re-up on food and fuel but ~7.5 ounces certainly isnt anything to sneeze at.

Colin You might try taping some aluminum foil around to your stove-stand ring to limit airflow and pushing holes through to increase airflow.

I found a couple tetkoba designs that are similar to Colin's design and gott similar boil times.
This one is more practical to DIY. 30 seconds to prime with a 4 min boil.
https://www.youtube.com/watch?v=rVPAcbBwsbY
And this one is more developed but harder to make. Prime + Boil time of under 5 mins total.
https://www.youtube.com/watch?v=8Dy75aO_2z4

it seems like with these open-center designs, the right mixture of air and fuel is required to get these super-hot super-fast burns.

In another tetkoba design with adjustable air-intake, it appears that limiting the airflow increases boil times. Low (high airflow) gives boil times of 6:20, while High (low airflow) gives boil times of 4.5 minutes