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The Alcohol Stove “Efficiency Percentage” Test Thread
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Rog Tallbloke
(tallbloke) - F

Re: Re: Re: The Alcohol Stove “Efficiency Percentage” Test Thread on 04/01/2014 02:27:08 MDT Print View

Glenn, yes, the flue runs up the middle. The removeable top section vents the exhaust and conducts heat back into the water. That 2 cup design uses a stove design which has flame jets both up the inside flue and the outside of the can. Best time with 9C starting temp was 2mins 45s to rolling boil with around 17g of fuel. Not as efficient as this one cup model, but real fast.clever kettle
This one uses the fosters can as a windshield to prevent conduction loss in wind, and the smaller kettle is inside.

Edited by tallbloke on 04/01/2014 02:34:26 MDT.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Re: Re: Re: The Alcohol Stove “Efficiency Percentage” Test Thread on 04/01/2014 04:45:40 MDT Print View

We did a similar analysis on the old BackPackingLight Yahoo list about 12-13 years ago. I used an old Heinekin Keg/Can for the pot with a rolled aluminum center JB welded in. It turns out that this was fairly efficient (I was getting close to 75% but this was not using your formulas) but wasn't worth the trouble (mostly volume loss.) A heat exchanger on the bottom supplies roughly what the internal chimney supplied, in terms of efficiency increases. A cone on the outside provided about the same wind protection/heat trap. Your set up is a bit smaller but it looks much lighter.

The trouble with an internal chimney is the nature of the design is removing surface area from it as it gets smaller. For small 1 cup boilers this means the internal chimney is about 1/3 to 1/5 the surface area of the exterior. Anyway, after two tries I pretty much gave up with this because: 1) The JB weld leaked after each trial. 2)The efficiency gain was less than I'd hoped for (~15%.)

The 1) above can be ignored. I was thinking this could be resolved with better manufacturing. But, the water was a bit scummy...I was afraid to drink it. Even after 5 tests it still had a bit of scum on it.

2) above involves more thought. 2a) was the surface area as described. 2b) The center chimney was funneling heat at an increased rate. This meant less heat to the outside, or increased baffling to slow the exhaust gas. (Starts looking like a heat exchanger.) This is possible with a reversed cone inside, also. This lets you slow the exhaust gas (heat, if you will) and maintain good efficiency by increasing the surface area as the cone shaped chimney increases in diameter.

Anyway, this pretty much parallels my own experiments. With increases only around 15%, I decided to move to a wider pot with a heat exchanger rather than continue the internal chimney trials. The 15% was about the same as I get with a good HE pot but maintains the internal volume and was a whole lot easier to make. I'm glad to see this, you are doing some great work!

Rog Tallbloke
(tallbloke) - F

Re: Re: Re: Re: Re: The Alcohol Stove “Efficiency Percentage” Test Thread on 04/01/2014 14:55:34 MDT Print View

It took me months to perfect the art of soldering the very thin aluminium. But that's a tale for another thread, I don't want to derail this one.

David Gardner
(GearMaker) - M

Locale: Northern California
Soldering aluminum on 04/04/2014 14:50:04 MDT Print View

Rog, would love to see you start a thread on soldering aluminum!

David Gardner
(GearMaker) - M

Locale: Northern California
Re: The Alcohol Stove “Efficiency Percentage” Test Thread on 04/04/2014 15:33:27 MDT Print View


Thanks for starting this thread. Contemplated making efficiency tests as scientifically as possible, and have the following thoughts to add to your OP:

For the sake of precision, we might want to consider measuring the amount of fuel in grams. With a digital scale that displays to the nearest .01 gram, we can measure to .005 gram accuracy. I'm not sure there is any volumetric measuring device that accurate or as readily available. So we can weigh 11.84 grams of alcohol, but express it as 15.00 ml. (I mistakenly used 12.84 = 15.00 ml in some of my previous tests, skewing the efficiency results.)

Same thing with water. We can weigh 500.0 grams of water, and know that it is 500.0 ml.

Of course 15 ml and 500 ml have more practical application because they can easily be measured in the field vs. taking a scale and measuring 11.84 grams and 500 grams. But when we are in the lab trying to measure efficiency to within .05 percent, it can make a difference.

"Boil" is problematic as to its accuracy, since the temperature at which water boils depends on barometric pressure. "Boil" only equals 212* F/100* C if you're at 1 bar of pressure. At higher altitudes or when when a storm is coming and barometric pressure drops, the water will boil at less than 212*F/100* C and never reach that temperature. Conversely, if you are at sea level but a high pressure weather system moves in, water will not boil until it exceeds 212* F. So rather than elevation, we may want to quantify this factor by stating the barometric pressure at which tests were conducted.

Also, rather than visually observing "boil" (which is somewhat subjective), we may want to consider measuring the actual maximum temperature reached by the water and the time it takes to reach that temperature. I think (but will defer to those with more education and experience in this area) that this will account for any differences in barometric pressure.

Another factor to be considered is the effect of humidity. When I do boil tests with cold water in high humidity, there is a considerable amount of condensation on the outside of the cans, which sucks up a lot of heat before it can get into the can. Not sure how to factor this into efficiency ratings, except by only doing tests with water at a starting temperature high enough, or humidity low enough, to avoid condensation.

My two cents.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: The Alcohol Stove “Efficiency Percentage” Test Thread on 04/04/2014 15:47:30 MDT Print View

rather than talking about "boil", measure temperature of water before and after. Assume that when you say "boil" you mean raise temperature 90 C (or whatever).

As long as there's a lid, and you don't get too close to boiling, it's fairly linear.

Best thing is to, like in Roger's tests, have a hole in lid, stick thermometer through it, make sure thermometer doesn't touch bottom, maybe in center of water in height, halfway between center and edge in the sideways direction.

You can just get a digital cooking thermometer, like for measuring temperature of fluid or meat.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Re: Re: The Alcohol Stove “Efficiency Percentage” Test Thread on 04/04/2014 18:00:04 MDT Print View

Jerry, what you describe here is almost identical to my test stuff.
My starting temp was different only because my water stays between 40F and 50F (4-10C) year round. Berhaps a better test would be to start with 32F/0C water by taking a pitcher of ice water. Simply add a bunch of ice and wait till it stabilizes (about 10 minutes to reach 31F-34F or about plus/minus 1/2 degree C.) Note that there is always a difference between water supplies. Minerals/salts make more difference than a 1/2 degree C.

I avoid the altitude issue by simply heating to 200F or about 93C. Unless you are exceptionally high in a bad storm, this should cover most situations.

Condensation is probably not too important. At first, it will add heat to the system. Later it will take that same heat away as it evaporates. I doubt that himidity has much of an effect either way unless you condense enough for actual drops off the bottom. Even then it would be minor compared with the overall heat to boil two cups. This could be as high as 2-3%.

I used two cups as a measurement. This is 16oz or a pint, or, ~473ml. A more standard measurement would be 500ml.

Being as close as possible, I ran the same boil test 10 times with the exact same setup. I got a devation of about 6-7%. So, I would say that a 10% error in any measuments would be expected. Beyond that would be significant.

Delmar O'Donnell

Locale: Between Jacinto & Gorgonio
Both? on 04/04/2014 20:18:22 MDT Print View

David: First off, I really appreciate your dedication to experiment.

I agree with your points for making the efficiency calculations more accurate: measuring weight of fuel and water in ml; measuring end-of-test heat with thermometer instead of “boil,” (which can be done with Ben’s spreadsheet); factoring in barometric pressure, which is more accurate than elevation; and accounting for the potential effect of humidity. I think adding these parameters are the natural evolution of what’s been started here. I’m all for building more complex, accurate formulas that account for more variables, if we can do it. I don’t have the background to do that, but we do have thermo engineers who frequent BPL.

On the other hand, simpler formulas allow more people to participate. For example, I don’t have an accurate enough scale for ml; my resolution is .02 oz. I don’t have a barometer. And I don’t have a hygrometer. Chances are low I’ll obtain these to do testing. And I don't need them to do comparative testing among my own experiments. This seems to always be the decision that must be made: more accurate but less data with more effort and expense, or less accurate but more data with less effort and expense. In my experience, raising the bar too high means that only a few experts participate, and you get the “academic journal” effect, ie, most people tune out. But lowering the bar too far yields junk data.

Maybe we can cover both ends of the spectrum if testers simply report which of the various spreadsheets they’re using. So far we've got:

- Ben's original sea-level spreadsheet that allows for multiple tests (mostly metric)
- Glenn's single-test sea-level spreadsheet (many measurements modified for English standard)
- Glenn & Delmar's single-test altitude spreadsheet (mostly English standard)

Edited by Bolster on 04/04/2014 20:22:05 MDT.

Glenn S

Locale: Snowhere, MN
Re: Both? on 04/04/2014 21:54:56 MDT Print View

Well I'm still not convinced that altitude has any real bearing, since the lower boil points and the less fuel used to reach them seem to offset each other proportionately. Of course unless I go climb a mountain, I'd never be able to prove it. Barometric pressure might play a larger role, and if I had a barometer, I'd use it, maybe someday, but not today, sorry.

I won't be weighing my alcohol, since I feel a 1% variation is acceptable, and easily attainable with a simple 5 ml oral medicine dropper. I do weigh my water, and I don't think that's expecting too much from anyone on this forum, since owning a scale is practically a prerequisite to being here ;)

I like simple, keeps more people interested. Eyes tend to glaze over if things get too technical and it's just no fun anymore. Which is why I simplified Bens original spreadsheet in the first place, and to eliminate conversion errors like David mentioned. I did the same thing initially, now, no more.

I'm certainly not against more data, but I think the point of diminishing returns has been reached. Piling more data on at this point would change outcomes by what? a couple percent max? Probably not much more than boil to boil variations from crude fuel mixtures anyway.

Delmar originally suggested posting all pertinent data, not just efficiency reading outputs. I agree'd then and I still do. Anyone can then use either the "basic" calculation, or the "advanced" model to reach their desired conclusions. Meanwhile, the individual user can get good relative comparisons using whichever model they feel comfortable with to better improve his/her designs.

To this end, I feel there should be only 2 worksheets, the basic, and the advanced. We have the basic, and it should be left alone. The advanced can always be improved upon for those so inclined to push the envelope further, factoring in barometric pressure, elevation, humidy, etc. Whatever our engineering friends would happen to bestow upon us by way of formulation. The advanced worksheet can continue to grow, while the basic remains the foundation of the project. That's my 2 cents anyway.

I would also like to add that I'm under no delusion that any of us are breaking any new ground here. This has all been done before, ad nauseam. But proper understanding comes from a bit of self discovery, so there's only so many shoulders of giants we can stand on if we want a deeper learning for ourselves. I guess I think of it as a chemistry kit as a kid growing up. Nothing new, just fun to learn. :)

Edited by Glenn64 on 04/04/2014 22:33:49 MDT.

Richard Cullip
(RichardCullip) - M

Locale: San Diego County
The Fuel-to-Boil Formula can be simplified on 04/04/2014 23:00:02 MDT Print View

In a former life I was a spreadsheet geek so I'm a bit bothered by the Fuel-to-Boil formula. It's a bit more complicated than need be. As coded up, the two .789 constants cancel each other out so they are not needed

Original - C8 = The Fuel-to-Boil Formula (ml) =C4*.789*C2/C3/.789

Simplified - C8 = The Fuel-to-Boil Formula (ml) =C4*C2/C3

As I understand it, it's just a simple ratio of Boil Time to Burn Time used to estimate the amount of fuel burned to get the water boiling.

Delmar O'Donnell

Locale: Between Jacinto & Gorgonio
Does efficiency vary by altitude, pressure, humidity? on 04/04/2014 23:37:47 MDT Print View

It's an interesting hypothesis that stove + setup *efficiency* may not actually vary by altitude (or that if it does, it's decimal dust). Boil time will certainly vary, but that's not the same as efficiency. At high altitude, a boil represents less fuel used to reach a lower temperature, compared to low altitude where your reach a higher temperature with more fuel. If that hypothesis holds, then the next questions to follow are: would barometric pressure or humidity affect a stove + setup's *efficiency*? Tempting as it is, let's not conflate time-to-boil with efficiency.

It's testable. As Glenn says, measure efficiency of the same stove+setup at low elevation and high. Easiest to test would be the humidity hypothesis. Do a boil in your (dry) bathroom, and another in your (moist) bathroom with the shower running. I'd guess that high humidity would lower the efficiency, but...who knows? Maybe the flame would shrug off the moisture in the air.

At any rate, each variable (humidity, altitude, pressure, wind) would need to be treated as orthogonal...just because one does or doesn't have an effect, tells us nothing about the other variables (with the exception of altitude/pressure which should be highly correlated).

PS: I like the two-formula solution, basic and advanced, for the time being. But we should test to see if advanced is actually necessary, if it gets a better bead on efficiency or not. Occam's razor, you know.

PPS: Richard: the beauty of peer review. Thanks.

Edited by Bolster on 04/04/2014 23:58:28 MDT.

Glenn S

Locale: Snowhere, MN
Re: The Fuel-to-Boil Formula can be simplified on 04/04/2014 23:43:51 MDT Print View

Ah, there's the redundancy. I knew it was lurking in there somewhere. Delmar eluded to it earlier, but we were still trying to convert the original formula from grams to mm for fuel consumption and comparing spreadsheet readouts from the original.
Thanks Richard.

Heading over to my Fosters thread to make the appropriate changes :)

Edited by Glenn64 on 04/04/2014 23:53:55 MDT.

Glenn S

Locale: Snowhere, MN
Re: Does efficiency vary by altitude, pressure, humidity? on 04/05/2014 07:03:06 MDT Print View

Regarding the altitude calculations within the advanced spreadsheet..

Earlier in this thread, I had mentioned "providing a chart with the corresponding boil temperatures that the end user could then enter" instead of using a formula. After thinking on this some more, I think it's the only viable option because just entering elevation into a spreadsheet does not tell the user at what temp to take a reading for boil time.

I'm at 900 feet elevation, so I plug 900 feet into the spreadsheet, but how am I to know that I should mark my boil time when the water reaches 210 degrees? I can still get my water to 212, and have been doing so, but it's 5-7 seconds after a visible boil and the water is really roiling. If there was a chart that I looked at to gather my boil temp goal for my appropriate elevation, and entered the upper temp limit accordingly, instead of the actual elevation, then I would know where to take my timer reading at and the formula would just calculate off the lower entry.

On an aside, my ratings appear to be taking about a 3/4% penalty by not factoring in my elevation. Not that my efficiency actually got any better, just that the calculations were factored at sea level from the start.

Which makes me rethink the elecation vs efficiency theory I had earlier. I still maintain that it quite possibly is a negating factor, as I mentioned, however... That would only apply when comparing the same system to itself at different elevations. The efficiency of THAT system wouldn't change much. But now if we're to compare say, Davids system at sea level, to my system at 900 feet, then I guess we probably should be factoring elevation to get an apples to apples between the different systems at their operating elevations. Am I making sense? I think my head is starting to hurt lol

Delmar O'Donnell

Locale: Between Jacinto & Gorgonio
BS vs. WS data on 04/05/2014 09:38:05 MDT Print View

Glenn, Just a quick comment on your final paragraph (still thinking about the rest of it):

The name given for the type of research where you compare David's results to Glenn's results is called "Between Subjects" data. The name given to research where David is boiling with a small lid or a big lid is called "Within Subjects" data--in that case, one subject (David) is providing multiple data points to compare with each other. Analyses with WS data are more sensitive (less random error, easier to find effects) and often have built-in controls (David did all his lid boils within an hour of each other, at the same location, so no need to collect altitude, humidity, pressure...). It's when we start comparing our gear to someone else's gear that we have to start worrying about all those other variables that might affect the results. So, yeah, if you are doing your own testing where you compare one variable to another, say, does a black pot beat a brushed pot, then a simple efficiency formula will tell you what you want to know, which is: which one wins.

What we're chasing now is a way that people can compare results with each other. That puts us into "BS" data (no pun intended) and is of greater complexity, since you try to control or account for variables that impact the results. This underscores your previous musing that we can get by with one simple formula (which we already have) and one complex formula (which we're working on). The existing formula is sufficient for WS "which setup is better" analyses; the complex formula will be best for BS "is my setup better than yours" analyses.

It would be easy to say that the WS data is what we really want and the BS data is just a pissing contest of sorts. But comparing results really does motivate us to try harder. If David and Glenn are getting 70% efficiency scores, you think Delmar can sleep on his NeoAir at night, knowing he's only getting 40%? Think of the BS data as driving innovation.

Regards knowing exact temp of boil at a particular elevation, anything wrong with using the chart we've already found?:

The exactitude worries me a bit; not sure our thermometers update quickly enough (or accurately enough) to take advantage of the additional accuracy afforded by the chart.

Edited by Bolster on 04/05/2014 10:31:36 MDT.

Glenn S

Locale: Snowhere, MN
Re: BS vs. WS data on 04/05/2014 14:10:12 MDT Print View

I think that chart is great, a little too great actually. I agree that it's too much info for our purposes. I think some rounding of values would be in order. A quick overview seems to suggest that steps of 500 feet, with occasional steps (every 3500 feet or so) of 750 feet, would make for whole number temp readings that were only rounded from a 2/10 of a degree. Again, this was just a quick readthru.

Of course we could keep your calculation in the formula, and just have another cell that displayed the target temp data based on the user elevation entered, which might be more precise, and only be more complicated behind the scenes. Since we've been able to display our formulas within the forums here, a simple copy/paste method by the user should afford some leeway for spreadsheet elaborations.

Here's what I getso far with that idea:


Edited by Glenn64 on 04/05/2014 15:40:51 MDT.

Delmar O'Donnell

Locale: Between Jacinto & Gorgonio
Like the Target. on 04/05/2014 21:02:30 MDT Print View

I like the display of the target temperature, that would take a lot of "slop" out of the system determining what, exactly, is an adequate boil.

Went back and reviewed my excel functions, and the vlookup command would work well here. The columns are just pasted in from the chart we found online, and I made the formula visible below. (Note I did not take the time to weed out small increments, just pasted the chart in wholesale.) As I understand the vlookup function, if you enter in a unique number not in the table, it'll default to the next lowest number that is in the table.

So, for clarity, you enter your altitude at "Enter Alt Ft" and the "Targ Temp F" is supplied by Excel's lookup function. The range E2:F86 defines the table (I only went to 20K feet), the "2" says return the matching figure from the 2nd column of the range, and TRUE gives permission to round to the next lowest number in the table.


I think at some point it'll be easier for folks to get a copy of your spreadsheet, than to build their own. You know how easy it is to misplace a parenthesis or etc. Particularly, if you put the whole lookup table into your spreadsheet. But, that's your call.

(And I can't help but get the impression that your spreadsheet really wants to be a smartphone app someday.)

Honestly, I think you are on the right track making a simple (but accurate) calculator. The easier you can make it for people to calculate their own testing, the more tests we'll have...a renaissance of stove testing, perhaps.

Edited by Bolster on 04/05/2014 21:10:58 MDT.

rick .
(overheadview) - F

Locale: NYC
simpler efficiency? on 04/05/2014 21:38:43 MDT Print View

A final boil time is helpful, but is that what you're after? Aren't efficiency and time to boil very related but slightly different measurements?

If the temperature rise is linear enough (that's an IF, it has been said it is, but I don't know) would a "time to raise 50celsius" be a simple efficiency test?

You could plot the time per 10c rise, and blow out and weigh the fuel at 50.0c rise. Or plot temp rise every 30 seconds.

It removes starting fuel amount, stove "bloom", start temp, elevation and possibly other variables.

Would recommend 500.0g water as the baseline for any test. Cooking grade grad cyl are several percent variable once you include person-person variation. We all have a scale. Measure, weigh then repeat in a couple of days if you don't believe me.

Also, someone needs to make and share a google docs spreadsheet. And decide on a test protocol. Only then will I spend an afternoon boiling water for no good reason (5 cups of tea?). I have a brasslight to toss it's hat in the ring when the parameters are settled. Curious to see how it stacks up (it is a very heavy alc stove tho, but feels efficient).

Delmar O'Donnell

Locale: Between Jacinto & Gorgonio
Re: simpler efficiency? on 04/05/2014 21:55:23 MDT Print View

> A final boil time is helpful, but is that what you're after?

It's specified as a target, to help you mark an accurate time to enter into the formula. Efficiency (not boil time) is the goal for this exercise.

> Aren't efficiency and time to boil very related but slightly different measurements?

Distant relations at best. Take my SuperCat, for example. Fast boil time, very poor efficiency. Sucks fuel like a '70s muscle car.

> "time to raise 50 celsius" be a simple efficiency test?

That would be a speed test. Granted, that's what some folks are after, and there are times (eg, you're hypothermic) that speed is more important than efficiency. The unstated goal of this exercise, however, is to see how little fuel we can carry and still get our oatmeal cooked each morning. We're trying to eek out every last joule of energy and turn it into heat. Too fast and it's wasteful of fuel. Too slow and the heat is carried off into the environment without completing its assignment.

If you read David's thread where he's testing "aluminum hats," you'll see that, based on boil time, we thought the hats were a bust. But then Ben calculated efficiency, not speed, and it turns out some of the hats increased efficiency. Since efficiency was what David was after, the benefit of his invention was hidden until Ben gave us a way to test. Speed as a proxy led us astray on that one.

Would love to see your brasslight tests, when you get the time.

Edited by Bolster on 04/05/2014 22:12:51 MDT.

Glenn S

Locale: Snowhere, MN
Re: simpler efficiency? on 04/05/2014 22:01:42 MDT Print View

Boil time is just one of the many variables we're trying to factor in. Boil time alone does not equate efficiency, which is how this project came into existance.

Heatup only becomes linear about 30-45 seconds after the stove warms up, after the bloom. At least that's been my observations when I monitor the process. So measuring fuel mid-burn seems haphazard at best.

A google doc sounds interesting. I don't even have a google wallet though, but I'll look into it when I get home. It would be nice to see some more parameters addressed before an actual "release" though. Barometric pressure seems an important one. I'd think if we could nail that one down, I'd be comfortable with a Version 1.0 :)

Edited by Glenn64 on 04/05/2014 22:03:44 MDT.

Delmar O'Donnell

Locale: Between Jacinto & Gorgonio
Baro. on 04/05/2014 22:18:28 MDT Print View

I'll be bummed if your final SS requires barometric pressure, as I own no barometer. But, if it's an important variable, it has to go in. Science Uber Alles!

Looks like 1000 feet changes Hg. by about 1 In. and vice versa?

Edited by Bolster on 04/05/2014 22:25:33 MDT.