HJ, you have mail.
On topic of sorts. Just thinking if you had too much fuel capacity in your stove and you filled that up, would that slow down the stoves ability to reach high heat output? I've noticed on my old brassy stoves, that when I prime them, it takes a few minutes for the flames to really get going as the fuel needs to vaporize in the priming pan to burn. Could a larger alky stove be used for slower cooking or best to just rig a simmer cap/ring on the normal sized stove? Your thoughts, just throwing something out here.
Duane

Hi, Duane,

At least with what I've tried, adding more fuel hasn't appreciably slowed the stove down throughout the burn. Adding more fuel might cause the stove to take longer to warm up, but it doesn't really cause more efficient burning in my experience.

A stove with more physical mass will likewise take longer to warm up but won't necessarily burn more efficiently overall.

I'd say the best way to get an efficient burn is to use a burner that is efficient by design.

Now the whole simmer ring idea is very intriguing to me. In my experimenting, I've come across some designs with very low flames, generally a tall stove. It occurs to me that I could cut the top off a tall stove and press fit it over the top of a shorter stove whenever I need a low flame. You'd basically have two settings: High without the "over cap" and low with the "over cap." This isn't a particularly elegant solution, but it is simple and would work.

A more elegant solution is one where you can truly vary the flame not just have a high and a low setting. This is more where my interest lies. With something like a 12-10 stove, with ventilation ports in the side wall, you could construct a "ring" cut from the wall of an aluminum can that would slide over the 12-10 stove's outer wall. The "ring" would have holes cut in it that align with the ports in the 12-10 stove. If you aligned the holes exactly, the 12-10 stove would function normally. If you rotated the "ring" slightly, you would partially block the 12-10's ports, causing a smaller flame.

I've talked to guys online who have done something along these lines, and I've seen some photos of DIY rigs, but I've not tried it (yet) myself.

A DIY stove of the sort shown in my blog doesn't have ports that you can use to vary the flame.

The first solution I mention above (an "over cap" instead of a "ring") might be youre only option with something as simple as the stove on my blog.

HJ
Adventures in Stoving

The idea behind this blog post was to list out some design elements of decent DIY alcohol stove (within a certain scope, e.g made from aluminum beverage cans).

With any project, it's important start with the desired result in mind, so maybe you'll want to take a look at the appendix: Standards for DIY Alcohol Stoves. These are a set of "standards" by which you can benchmark a stove and say, "yep, it's a good stove." or "nope, still needs a little work."

You may need to tweak my "standards" to fit your particular style and needs, but at least you've got a starting point all in one place in a fairly concise form. I wish when I started looking at alcohol stoves in 2007 that I had had a clear idea of what constituted a good stove.

I hope that these "standards" will at least be food for thought and discussion.

HJ
Adventures in Stoving

Edited by hikin_jim on 12/15/2011 21:02:51 MST.

James Marco wrote: > Basic stove design really isn't a matter of stoves. It is a matter of *systems*. Small stoves that seem to not burn that well can burn quite well with proper mods to other pieces of the system.

James Marco wrote: > 1/2oz seems to be about average for the best of the alcohol stoves in the real world, ie out of a lab or kitchen. While it is generally possible to carry over some results, not all will work in the field, or, are simply too fiddly to bother with.

James Marco wrote: > There is NO relationship between opening size and height ... so the 45* angle you describe (1:1) ratio is not fixed except with a certain type/material/size (parameters) of the burner. [emphasis added]

James Marco wrote: > There are basically 5 types of stoves.
1) A plain "Altoid" burner: with or without fiberglass insulation (or pearlite)
2) A ducted port or "chimney" stove: like a Brasslite or 12-10
3) A semi-presurized stove, like many of yours, relies on liquid weight to vaporize fuel to pump the burner.
4) A pressurized stove: with fully enclosed fuel vaporization to pump the burner
5) A wicked stove: which allows full control of fuel vapourization while burning.

Jim,

Feel free to use whatever you can glean out of my poor writings. I cannot keep them organized. Besides, making and building alky stoves is an old subject. Rand at TD sent me a picture from the Civil War for one a couple years back. It was an older design then that seemed to be fairly effective, though likely heavy made out of brass. Since it was in production at that time, I assume it was based on earlier designs.

Anyway, some other important considerations:
1) Oxygen (or air)
2) Heated Fuel vapour
3) Mixing of the two
4) Some kindling flame, preferably *after* mixing
5) A control of some sort

Plenty of heated fuel and air. Initially, a small reaction, then larger flames as the fuel air warms. BOTH need to react. BOTH need to be heated. Not just the fuel. Whatever fuel you use, a primer, it might be a self primer, is needed. The fuel and air need to be brought to kindling temp before they can react, but some sort of additional spark is required to start the reaction. Some controll of the reaction is needed to prevent runaway reactions (self limiting is the usual methode for small camp stoves like you pictured.)

I was focusing on mixing the fuel/oxygen for efficient burning. Some observations: Swirling seems to add a lot to mixing, and tends to focus heat to the bottom of a pan. The later disipation leads to wide pots, up to a point, being much more efficient than tall pots, but even these can benefit from a smaller, more focused flame. Using a press pin, rather than a drill, it should be possible to angle the jets. In a dynamic flow, this will create a swirl, helping to focus heat, and create a greater degree of mixing turbulence. Adding air inlets into the combustion chamber seems to help by increasing the burn time available to the fuel. Probably not possible on the stove you picture. For some slight modifications to the stove you pictured, turbulence in a semi-pressurized stove design can help, too. I would submit, that the jets should be alternated between the inner and outer part of the stove, allowing more turbulence to the inner, open priming/combustion chamber, and more oxygen to the outer jets. This should have the effect of delaying the burn slightly for the inner, open fuel by reducing available oxygen. And, heating the fuel vapour so it will burn more quickly when it IS mixed with the oxygen. Again, using a push pin, angle the jets upward A slight diameter decrease would also help by reducing the ammount of oxygen available to the inner combustion chamber. The control is important because the initial heat output(for the first minute or so) is different from a stable system. This means that initially a slow burning stove may overheat and become a fast burning fireball(two extremes.) So moderating the maximum heat helps maximize the efficiency and prevents the high secondary heat outputs, and comensurate loss of efficiency, common with small stoves. This is really difficult with the stove you pictured, however. I believe the modifications I suggest will help some. Again, expect no more than 5-10%, though. But, it should also solve the ethanol/soot problem. Higher reaction temps will usually mean cleaner burning, provided the reaction gets enough oxygen. Just a thought...

Hi, James,

Thanks for your thoughts. Your ideas for causing greater mixing (angled jets, varied placement) sound good.

The principles listed in the blog post make for a fairly efficient stove as they now are. I can boil 500ml of 7C water with 15ml of fuel. The trick now is to see if I can get a bit cleaner burning design.

HJ
Adventures in Stoving

HJ,
Yeah, same thing actually. Clean burning is usually efficient. Just some thoughts, anyway.

Well, that's what's been bugging me. I'm getting good results in terms of efficiency, but I'm getting soot.

My efficiency numbers: 500ml of 7C/45F water boiled with 15ml green denatured alcohol at 1260ft/385m elevation. Those are good results.

I hardly think this is an issue unique to the stove I'm using. Trangia in their instructions suggests adding water to eliminate soot, so clearly it's a common problem with alcohol stoves. I'm just frustrated that there isn't a good way (that I've yet found) to have a sootless burn on high ethanol content alcohol blends.

HJ
Adventures in Stoving

I wonder if the you could increase oxygen access to the "ring of flame" around the "open well" by using a non-circular aperture; increasing its circumference for the same well area:

eg an elipse / plus sign / several smaller holes etc (getting harder to fill).

Roger Caffin used a plus sign wick (with no centre in plus) in a candle wax burner for this reason (BPL article).

-------
http://www.backpackinglight.com/cgi-bin/backpackinglight/candle_stoves.html
But the person who did all the work was Mark Hurd. I just helped him write the article.

Cheers
Roger Caffin

Edited by rcaffin on 12/22/2011 14:03:49 MST.

< Also, per #2 above, if a stove requires priming, it's not the stove for me. Priming is by definition inefficient.>

I agree, stoves that require priming are inefficient.

.

Yeah, the numbers look good. The soot says you could do better. Water slows evaporation of fuel, so, that is an easy fix. It also cools the flame, so you don't gain anything. Nor do you loose anything because it burns longer. Playing with reagent grade ethanol made me aware of that. It really made no difference in overall efficiency with a properly tuned stove.

Soot means too little air, or, too much fuel in the fuel/air mix. Its burning too rich. This means incomplete combustion. This means loss of efficiency.

If you must tune for high content ethanol:
Smaller jet holes? Less fuel in the mix, ergo, more oxygen available.
Smaller center hole? Less vapour escaping, ergo more oxygen available.
Distributed jets? More air availibility to each jet...
Greater turbulence? Better mixing, ergo, more heat available and higher efficiency.

Like tuning a kero stove to WG. Or WG stove to Propane. You need to change the jet diameter a bit. Changing between the approximate 1/4 greater heat density of ethanol from methanol is really no different. Fettling a old Optimus to run on vodka is a good example of what you are doing and my thought train.

James Marco wrote: > Yeah, same thing actually. Clean burning is usually efficient. Just some thoughts, anyway.

Alan Bradley wrote: > I wonder if the you could increase oxygen access to the "ring of flame" around the "open well" by using a non-circular aperture; increasing its circumference for the same well area:

eg an elipse / plus sign / several smaller holes etc (getting harder to fill).

Roger Caffin used a plus sign wick (with no centre in plus) in a candle wax burner for this reason (BPL article).

James Marco wrote: > Soot means too little air, or, too much fuel in the fuel/air mix. Its burning too rich. This means incomplete combustion. This means loss of efficiency.

James Marco wrote: > If you must tune for high content ethanol:
Smaller jet holes? Less fuel in the mix, ergo, more oxygen available.
Smaller center hole? Less vapour escaping, ergo more oxygen available.
Distributed jets? More air availibility to each jet...
Greater turbulence? Better mixing, ergo, more heat available and higher efficiency.

James Marco wrote: > Like tuning a kero stove to WG. Or WG stove to Propane. You need to change the jet diameter a bit. Changing between the approximate 1/4 greater heat density of ethanol from methanol is really no different. Fettling a old Optimus to run on vodka is a good example of what you are doing and my thought train.

Edited by hikin_jim on 12/18/2011 22:52:22 MST.

Addendum to the above:
I've been hesitant to do it so far because of cost and availability, but I'd like to compare Everclear 190 proof to Green denatured alcohol. Part of me wonders if the soot issue will be reduced if there are no denaturing additives. Sounds like the topic of a future blog post. :)

HJ
Adventures in Stoving

HJ,
Yupper, especially if they are using Octane or the like as a denaturing agent. The heavy molecules are little sticks...they require time to replace CO2 and Water with ionized O...you end up with soot when it doesn't happen fast enough. 2-3% will start causing soot, as I remember...again, lost data...

Interesting. Well, if I get a chance, I'll do some testing with Everclear this weekend.

HJ
Adventures in Stoving

Just for fun, I thought I'd post a photo of one of the pots I used for this past weekend's stove testing. Now, in all fairness, this was after probably 20 to 25 tests, and no I didn't clean the pot off between tests. Still working on the soot issue in other words.



HJ
Adventures in Stoving

Wow, that is bloody TERRIBLE. Hmmm....I don't remember an issue between reagent grade ethanol and SLX...they both burned fairly clean. I am only somewhere around 1000' in elevation, though.

I think it's pretty clear you are running too rich, based on the pic. Somewhere along the line, you are not getting enough oxygen into the fuel/air mix.

That *does* look like my pot after burning WG a few times in the mercury stove.

Jim,

Are you sure you weren't testing a wood burning stove with that pot in the picture? ;-)

Party On,

Newton