The Alcohol Stove “Efficiency Percentage” Test Thread

[Galen Benson]

Ben I'm using the spreadsheet as it was setup which may or may not include that adjustment. But when I enter numbers posted by others I match their results so hopefully everything is correct. If not let us know so we can correct it. Thanks.
Total weight of the pot, cone clone, pad, & stove is 6.04 oz

[Richard Cullip]

Galen – did you adjust the heating value to match your fuel? Canister gas, typically a mixture of propane and butane, has almost twice the heating value as the fuel used in alcohol stoves. If you did not adjust for the higher heating value of the canister fuel, your efficiency calculations will off target.

[Galen Benson]

No I did not Richard but the efficiency numbers are just for comparison of the windscreens effect. I don't intend to use this for actual efficiency

Ben here's a prior picture of my setup

[Delmar O’Donnell]

Richard notes above that Klean-Strip Green has more ethanol in it. So I found it at the local HD and bought some. Same testing setup I've used before: 1/4 in standoff screen, MSR Titan pot, 1700 alt, 500 water, 15 fuel, 209 boil temp goal, baro 29.9, ambient 78. I used the StarLyte Simmer for these tests.

Initial water temp; time to boil; time to flameout; efficiency:
Test 1: 79, 9:43, 12:20, 65.0% (first boil of day)
Test 2: 78.5, 9:09, 11:42, 65.7%

Average efficiency about 65+%, a personal best. Maybe that Klean-Strip Green really does eke out a few more Joules. Worth paying twice as much? Doubt it.

I'm starting to have questions. 1) Seems my first boil of the day is consistently a little LESS efficient than the others. Elsewhere I read about how stoves and setups are more efficient when cool, and less efficient when warm. My data shows the opposite; the setup being warmed up, makes for a little more efficiency. 2) Just how much of an efficiency advantage does a frustum give? Granted it certainly excels for wind resistance, and possibly stability, although I couldn't ask for much more stability than the two-skewer windscreen setup I'm using. I'm using a straight, short 3" screen – no frustum, no polishing (yet), no hat. I guess I'll find out when I get around to making a frustum. Would that kick me up into the Galen range, achieving as high as 80%?

Comment:

> "The water temps start out higher which effects the efficiency."

Shouldn't. The water start temp would affect time-to-boil, but the calculations adjust for initial water temp, and the efficiency calc *is not supposed to be* affected by the initial water temp. (Provided the formulas are correct.)

[Ben H.]

"…Seems my first boil of the day is consistently a little LESS efficient than the others. Elsewhere I read about how stoves and setups are more efficient when cool, and less efficient when warm. My data shows the opposite; the setup being warmed up, makes for a little more efficiency…."

Are you running your tests on cement? My first thought is you are warming up the ground with your first test (which takes energy) and it remains warm for subsequent tests. Feel the ground before each test to see if there is a difference.

[Jerry Adams]

"The water temps start out higher which effects the efficiency."

Shouldn't."

As the water warms up, it warms up the outside of the pot which radiates more heat

When the water starts getting hot, it will start evaporating significantly. Even with a lid, there will be more heat loss. Some of the vapor gets out even with a lid. Some of the vapor condenses on the underside of the lid. That will warm up the lid. Then it will conduct and radiate more heat.

But, these may be insignificant.

[Ben H.]

"…Decided to adapt the spreadsheet to use with a canister stove. You guys will know if this is even anywhere near correct…."

Check out my latest spreadsheet I posted (should be a couple threads down). Change the "Fuel Energy" field from 25 kJ/g to 46 kJ/g. That should be pretty accurate for iso-butane/propane mixture in your canister stove.

[James Marco]

"Interesting. I didn’t know that 10 minutes to boil had been discovered to be near optimum."
Hardly a discovery. I went through about four 4-packs of heat about 8-10 years ago or so. My best heating efficiencies were about 15 minutes boil time, then it started dropping off again. A standard 10-12 stove got around 5 minutes for comparison. I used several varients of a Mercury stove or a cone stove. Optimum is the balance between efficiency, enviornment, usability and speed.

"> …he could have reduced the heat out put by about 20% and increased his burn time to about 12 minutes.

I’m not following…as it was, Galen’s burn time was 14:15. If he reduced heat output by 20%, his burn time might have been around 12 minutes? I would have thought reducing heat would make for a longer burn time."
I should have written boil time instead of burn time:
…he could have reduced the heat out put by about 20% and increased his boil time to about 12 minutes.

"Agreed, but isn’t there a tipping point where low heat can become INefficient, even if the setup is still capable of bringing to a boil? Where the cool environment almost but not quite overwhelms the warm stove? I thought that’s where you were going with the 10-min optimum idea, that a longer boil than 10 min might mean a less efficient boil?"
Yes. That was my point. Once you start hitting 80% efficiency, there is not a lot else to be done. Some heat *has* to be wasted to maintain enough heat differential to be pushing in the towards-boiling direction. Insulating the top and sides will help, but you have to exhaust waste products. This also exhausts heat from the pot. So, 20% is a resonable number because it leaves some heat for enviornmental conditions.

If you optimize much further, then you loose the general usage. It will work only if the water temp is 60F say. Drop it to 34F, and you start loosing too much heat and want a stronger stove. If you are near a lake and grab some 85F water, the stove will burn to fast. You really don't want to be bothered with all the varients, you just want a good stove when you are camping. Alcohol always burns so close to the same, no matter what stove you are using, that it doesn't really matter. (Well, as long as it has enough oxygen and doesn't overheat the alcohol.)

I believe that the weight of the alcohol, ie, the density, will only increase the fuel efficiency, if you don't already calculate it.

[James Marco]

David, sure.

[David Gardner]

James, thanks for the picture. Maybe I'm going blind, but I can't seem to see any "dimples."

Also, the pot at the bottom of the picture is very interesting. I looks like the exhaust gases are supposed flow up in the middle, as well as up the outside?

[Delmar O’Donnell]

Embossed rings = "dimples"

Folks, don't miss Ben H's new-and-improved spreadsheet for calculating efficiency, here; although at this point it gives much more optimistic numbers than the SS in current use [EDIT since corrected, see discussion in that thread]:

Ben's Improved Stove Efficiency Calculator/Spreadsheet

Also, a single-boil test of an Imusa mug, same parameters as above, using K-S "Green,"

79F, 8:25, 10:16, 62.4%. So it looks (on a single test) that the smaller Imusa mug may be a skootch less efficient than the wider Titan.

[Dan Yeruski]

Something to keep in mind when testing. High Relative Humidity will definitely increase the time to achieve a boil.

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