- Apr 27, 2014 at 3:05 pm #2096931
>>I don't know of any way to obtain the absolute barometric pressure of my locale
> Get your own barometer.
I thought we'd established that a home barometer doesn't have the range to do absolute barometric pressure. Maybe this "station pressure" calc makes it moot.
Oh: And Thanks Ben!Apr 27, 2014 at 3:18 pm #2096932
Bob GrossBPL Member
@b-g-2-2Locale: Silicon Valley
"I thought we'd established that a home barometer doesn't have the range to do absolute barometric pressure."
No, not at all. It depends purely on how or where it is calibrated.
–B.G.–Apr 27, 2014 at 3:56 pm #2096950
The link from Greg seems to be reporting all relative pressures for me., as does the Weatherbug site. Denver should be around 25 inches on a normal day, so when they're reporting around 30 inches, I know it's not absolute that they're reporting.
The conversion calculator Galen linked to, can take the relative pressure and convert it to absolute, which we could then use instead of a compensated elevation, but that's the very thing we're trying to compile into a single process with spreadsheet formulas. I'm using the Antoine equation to do this. Probably not the best, but at the time, there was no input from anyone on this matter, so I winged (wung?) it. It's close enough when used in this manner, that I believe any discrepancies are below one tenth of one degree for boil temps, which would effect the efficiency rating even less than that.
I think maybe the newer electronic consumer level barometers would be able to do this, but I have no idea what they cost, or how viable it would be for the average tester, I can't speak to that. But yes, a normal home barometer with a dial has a range of around 28-31, so there is no way to get absolute pressures with them. You guys can do what you want with advancing this project, but as I've repeatedly stated, MY goal is to keep it simple enough that "someone's mother" could perform these tests without any specialty gear. Since relative barometric readings are what's commonly reported to the general public, that's what I'll be using. The only thing I might change is the formulas for converting them, when/if something better arises.
Sometimes it's the "pro", military-grade model that gets stripped down for easier mass consumer use, sometimes it's the simple everyday product that gets beefed up for more "professional" and industrial use. This project is currently following the latter IMO.Apr 27, 2014 at 4:15 pm #2096952
Greg MihalikBPL Member
"The link from Greg seems to be reporting all relative pressures…"
You are right. My bad…
The table reports that Denver International Airport Altimeter pressure 29.48
Now if That data could be found for the rest of the country….Apr 27, 2014 at 6:10 pm #2096988
It occurs, that we may end up with a finely calibrated spreadsheet that is way, way more accurate than the people using it.
People (self included!) are still going to mis-read thermometers, mis-interpret boil times, mis-measure water amounts, start or stop the stopwatch early or late, exaggerate results, etc.
I don't put much stock in one person's test results vs. another person's test results. Too many variables to control. ("between subjects")
I DO put stock in a single person repeating his/her tests, comparing past with current results. ("within subjects")
And for the latter, a less-than-perfect calculation is more than sufficient.
So while I irrationally long for the perfect calculation, my rational self realizes it's not necessary.Apr 27, 2014 at 6:26 pm #2096995
Bob GrossBPL Member
@b-g-2-2Locale: Silicon Valley
You know, my car has a computer display that shows me the instantaneous fuel efficiency for the engine. Too bad you can't graft one of those onto an alcohol stove. It might need to be calibrated for something different than miles per gallon.
–B.G.–Apr 27, 2014 at 6:27 pm #2096998
Delmar – I agree. Two of the biggest sources of variation, as I see it, are time to boil and fuel type.
Not much discussion, nor reporting of, fuel type as folks are posting efficiency results. Treating all alcohols as the same (25 kJoules/g) has a bigger impact on the efficiency calculation than fine tuning boiling temperature based on local air pressure.
There is some potential for fluctuation around something as simple as time to boil. Can you accurately measure temperature as the water begins to boil without affecting efficiency in some way? Do you take the lid off to stick a thermometer in or to watch for bubbles? What is a boil anyway? How many bubbles, how big should they be?????
It's been a fun discussion and I've learned lots but I'm not much of an experimenter. I get bored too easily to run multiple tightly controlled trials.Apr 27, 2014 at 7:00 pm #2097008
The two setups I've been testing are both blessed with ports (one a spout, the other a hole in the lid) through which I can insert a probe-type cooking thermometer. I just put the probe in the water for the duration of the boil, and when it hits what the SS says is the boil temperature for my altitude, I mark down the time. No, I don't look at bubbles or steam, I just watch the thermometer for that magical "209" to appear.
But without a thermomenter? A boil would be open to subjective interpretation.
But I have had a twinge of doubt about the probe's placement. I read one poster, awhile back, who opined the probe must be mid-pot and not touching any part of the pot itself.
To your point, I'm doubtless introducing error variance, unintentionally.
And how confident am I that my thermometer is well-calibrated? K-mart sells test-quality thermometers, right?
Plenty of slop in the system. Which is why I come back to repeated tests by an individual, using the same or similar setup, trumping competitive tests between two testers.
Agree about energy in fuel…I have no idea. I did one short test that indicated K-S Green > K-S SLX, and I believe it was you who predicted this.Apr 27, 2014 at 7:33 pm #2097021
Since most of the fuels that we use are a mixed blend, without any real information as to precisely what mix they're blending (not to mention production run variance), it was my hope that we could first get the environmental variables under control, then we could begin testing different fuels, once an even platform was developed.
I'd still like to see humidity incorporated, but once again, I'm clueless and quite frankly, am ready to spend more time OUTdoors, than in! :)Apr 28, 2014 at 6:20 am #2097118
Galen BensonBPL Member
Having cancer and just getting out of a 2 week stay post op hospital stay I have a different perspective on things. I enjoy threads like these where people are trying to get the best setup. I've come to the conclusion there needs to be a satisfaction quotient added to all test numbers, weight numbers, etc to say is this REALLY adding to my hiking enjoyment. Or is it something I do just to keep me from being bored with the world when I'm not hiking. Be sure you don't strain gnats and swallow camels ie miss the point of all of this which is to have the best experience in the wild we love. By the way I really am enjoying this thread! Thanks again.
"and quite frankly, am ready to spend more time OUTdoors, than in! :)"Apr 28, 2014 at 6:49 am #2097124
Ken LarsonBPL Member
@kenlarsonLocale: Western Michigan
"Life is known only by those who have found a way to be comfortable with change and the unknown. Given the nature of life, there may be no security, but only adventure."Apr 28, 2014 at 10:25 am #2097188
Dan YeruskiBPL Member
I have spent too much time over the years testing stoves :-)
I have used over 10 gallons of Sunnyside denatured alcohol in my testing career (Oh My!!!) I used 1/2 ounce at a time.
So I know for a surety that high humidity has a drastic effect on time to boil. Most of my testing has been in my garage. On rainy days my testing continued due to the addiction;) But, there came a time when I stopped testing during humid days when I was convinced it prevented a favorite, well tested stove, from boiling 2 cups of water with 1/2 ounce of fuel. I proved to myself over a period of time that humid days were buggers for testing by doing the experiment of boiling water with that same favorite, well tested stove.
My advice is don't test on humid days. You don't have to have humidity as part of your spread sheets. That will only complicate matters. Yousa guys have it complicated way too much the way it is :-)))
As long as you have fun at high tech testing is all that matters :-)Apr 28, 2014 at 3:14 pm #2097290
If there is a function that adjusts boil time by humidity, you can bet Glenn will find it!
And Dan, you should be pleased with the testing…the Starlyte stoves do very well!Apr 28, 2014 at 4:58 pm #2097319
I enjoy building spreadsheets. In fact, before I retired a couple of years ago, it was part of my job responsibilities. I have created a Stove Efficiency spreadsheet to add to the mix.
It has a simple pull-down selection for fuel type. It currently handles Esbit, various alcohol mixtures (use the BPL mixture to get the 25kJoules/g fuel we've been referencing around here). The fuel units change from grams (Esbit and Canister fuels) to ml for alcohol fuels automatically depending on which fuel is chosen.
There's input cells for both Elevation and Barometric (Relative) Pressure. These cells are used to calculate absolute air pressure which feeds into the Boiling Temperature calculation. If you are lucky enough to have a measurement of absolute air pressure just enter that and set the elevation to 0. If you just want to use elevation and don't want to bother with adjusting boiling temperature for air pressure, just leave the barometric pressure at it's default value of 29.921.
Entering time values in min:sec are a bit tricky in Excel. For this spreadsheet, just enter the mins:sec with a .0 at the end (e.g. if your time is 8 mins and 30 secs, enter the time as 8:30.0) For some unknown reason the .0 helps Excel accept the entry as min:sec rather than hours:min. I don't know why. Perhaps it's just an undocumented feature of excel.
Here's the Google Drive link for those who want to take a peak
Here's a screen shot.
If you don't need, or even want, another Stove Efficiency spreadsheet, just pretend you never read this post.Apr 28, 2014 at 5:27 pm #2097333
Ok, if that doesn't meet the criteria for an "advanced" model, I'm not sure what does lol Nice work Richard!
I'll have to dig into the formulas on a regular computer for that one I think.
I think the snag with humidity, is that it doesn't really effect the boiling process, or the temp to boil parameter, or interact with the water much in any way at all. Well, maybe a little in the atmospheric vapor absorption rate, that might baffle down the heat-up process, but can't imagine that would be much.
I think humidity has a direct effect on the combustion process, and directly effects the flame performance of the stove. So in order to have any hope of finding a way to factor in humidity, it would have to be some variable relating to BTU output.
I could be totally wrong on this, but that's how it plays out in my mind, at least for now.
On a side note, I broke down and bought a side opener for my Fosters cans. A more trim top, modified lid, and no bail handle, gets me down to 103 grams complete. Replaced original post over on my thread with new/improved completed setup pic.Apr 28, 2014 at 9:39 pm #2097431
> I enjoy building spreadsheets….
And she is a beaut. Thanks for this! Downloaded!
So, Richard, what is the "BPL" alcohol mixture, then? Somewhere around 75/25? Does such a mixture actually exist, or was it a middling option to cover several different possible mixes?
Don't I recollect a previous post of yours stating that K-S SLX was more like 50/50, and K-S Green was more like 90/10?Apr 28, 2014 at 10:00 pm #2097437
Delmar – Yes the K-S SLX I know is a 50/50 mix and the K-S Green is a 90/10 blend.
The BPL mix doesn't exist in stores. I just added that to get the same heating value (25 kJoules/g) that Ben used in his original spreadsheet. It worked out to a 74/26 mix (Ethanol/Methanol) with the Heating Values I found for Ethanol and Methanol.
My spreadsheet actually works with the BTU values (BTU/g or BTU/ml) rather than in kJoules/g. I like working in BTUs since they work well when measuring temperature in Fahrenheit since it avoids having to convert to Celsius.
edited to add – I'm glad that it downloaded for you. I had never used Google drive until tonight. It's nice to get confirmation that I uploaded it okay and had the settings correct so you could download it. I hope you enjoy it.Apr 29, 2014 at 10:48 am #2097609
I just sent you an email asking you to send me your spreadsheet. You disregard that as I just downloaded it. Very nice looking spreadsheet. Just to confirm, the data you looked up is the lower heating value?
Also, thanks for putting in an entry that matches my WAG that everybody still seems to be using.
I've incorporated the barometric pressure and elevation entries. I've also expanded the larger pull down menus to four entries. I've decided to keep it simple (KISS) and utilize a lookup table (like Richard did) for the fuel entries instead of having the user enter all the properties (with that option still available for advanced entry). It will take me a bit to make the changes. I will let you know when they are done.
In the meantime, I have some questions on the fuels people are using. I've hear 90/10 and 50/50 as the ethanol/methanol ratios. Can anybody confirm that? Also, I am guessing these alcohols have around 5% water; does anybody know the real number?
With cannisters, does anybody know if there is a consistent ratio of iso-butane to propane that manufacturers use?Apr 29, 2014 at 11:24 am #2097620
I used the Lower Heating Value numbers when I could find them. Not sure about the Esbit value as all I could find was the ~13,300 BTU/lb values and it wasn't clear whether it was the Lower or Higher value or if that even applies to a solid fuel like Esbit.
The MSDS docs for Denatured Alcohols are a bit vague about the exact components. As an example, Klean Strip Green Denatured Alcohol sold at Home Depot states:
Methyl isobutyl ketone <10%
Ethyl acetate <5%
No mention of water in there.
Likewise, the MSDS for Klean Strip Denatured Alcohol (aka SLX)
Methyl isobutyl ketone 1-4%
again, no mention of water but the MSDS just lists the hazardous components.Apr 29, 2014 at 1:50 pm #2097650
Gary DunckelBPL Member
I remember reading that when methanol (methyl alcohol) is mixed with ethanol, the methanol displaces the usual 5% of water, which is then easily removed. Perhaps a chemical engineer or chemist can confirm this (or refute it).
Regarding canister fuel, the various companies have different gas proportions. The following is a list of several brands:
Jetboil 25% propane: 75% iso-butane
MSR 20% propane: 80% iso-butane
Snow Peak 15% propane: 85% iso-butane
Optimus 25% propane: 0% iso-butane: 75% n-butane
While Jetboil appears to be the best fuel, they charge the same price ($5) but they give you 10% less fuel (100 grams vs. the others' 110 grams). The problem is that their mixture results in a higher internal gas pressure. It appears that all the above companies use the same canister, except maybe for MSR. So perhaps Jetboil must reduce the amount of the gasses to stay in the safe zone. Since n-butane has a much lower partial pressure than iso-butane, Optimus can get away with a 25% propane proportion. Actually, Optimus sells their 110 gram canisters for just $4 here in Boulder, so it is certainly the most economical. But they don't work worth diddly at temps below freezing, since n-butane doesn't vaporize when it is that cold.
I know, I know–too much information on canisters in an alcohol stove thread.Apr 29, 2014 at 1:59 pm #2097653
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
Ok, it's an alky thread, I know.
> With cannisters, does anybody know if there is a consistent ratio of iso-butane to
> propane that manufacturers use?
The limit is really the pressure inside the canister. That is set by DoT rules. AND, I had better add, the actual (real) propane/butane ratios are about as accurate as some of the labels on alcohols. Like, not very!
CheersApr 29, 2014 at 3:48 pm #2097676
ok, I've updated the spreadsheet based on feedback.
here is the new link (also updated on the original post:
The larger fields have four options so hopefully the scroll bars will be usable on macs (let me know). After strenuous discussion, Glenn convinced me that weathermen specify barometric pressure at sea level no matter what elevation they are reporting it for. You now need to specify elevation and barometric pressure. If you are measuring absolute pressure (or real pressure!!!) just specify an elevation of zero then the spreadsheet won't perform a correction.
Following the lead of Richard, I've abandoned making the user input all of the fuel data. I created a little database (copied Richard's) in the new "fuel" tab. You can modify those entries to your hearts content. I also made a fuel calculator if you got something I didn't specify. Thanks for the fuel info. It looks like the various formulations in cannisters results in a change of less than 0.1 kJ/g. You can play around with the calculator to see for yourself.
Again, I am loving the feedback. Let me know if what you think or suggest changes you think might improve the spreadsheet.Apr 29, 2014 at 5:49 pm #2097714
Much improved for the Mac, thanks. All options selectable.
I see two input fields that are locked (pressure and fuel) but no biggie, can unlock them ourselves through the Protect menu.
What's up with row 10?
Like the Fuel selection, very slick. I find the difference in efficiency unbelievable: with some hypothetical data the efficiency number changes 7% between SLX (erm, you call it LSX) to Green? In testing I noticed a 2% difference. If my testing is representative (big IF–two trials only) people's measured efficiency will go DOWN with Green, compared to SLX.
Playing with the SS, I get a DIV/0 error when I specify Iso-butane/Prop or Butane. Or Propane. Or ethanol.
Many thanks Ben, the revisions are much appreciated. This is turning into a very nice product.
What do we call this one, Ben's Improved V2?Apr 29, 2014 at 7:34 pm #2097747
James MarcoBPL Member
@jamesdmarcoLocale: Finger Lakes
"I remember reading that when methanol (methyl alcohol) is mixed with ethanol, the methanol displaces the usual 5% of water, which is then easily removed. Perhaps a chemical engineer or chemist can confirm this (or refute it)."
No, you cannot completly remove the water by conventional distilation. Some fraction always remains. Methanol does not displace the water. It is the OH radical that makes alcohol soluable in water. Methanol has one. Moonsiners often discard the first 10% of a brew because of the higher percentage of methanol but it still contains methanol, ethanol and water (and a few other toxins) in it. Miltiple distilations are required to get the fraction of water below ~4-5%(depending on the temps and draw off points.)
Some petrochemical processes can produce alcohols with no water as a byproduct of various reactions. This is usually used as industrial fuels, or in other processes, since, it is illegal to sell this stuff for human consumption. (There are slight fractions of toxic chemicals in it usually.) I believe this is where a lot of SLX comes from. But, this is variable. They probably just buy it wherever it is cheapest. Again, it is denatured alcohol and not intended for human consumption.Apr 29, 2014 at 10:18 pm #2097789
"Playing with the SS, I get a DIV/0 error when I specify Iso-butane/Prop or Butane. Or Propane. Or ethanol…" -Delmar
I think this is because the amt of fuel is specified in ml. There is no density entered for the gases so you get the error. Now if you start measuring the volume of your canister gas let me know how. Hmmm… you mention ethanol… that shouldn't have a problem…. I'll look into it. Thanks for the other catches too… V.3 coming out soon!
James: What I get from your post is that in general there probably isn't very much water in these alcohol's, but like every other chemical in there it is variable. We might get a batch with up to 5% but usually less. Is that an accurate paraphrasing?
How about Yellow Heat? Since it is added to gas tanks to absorb water, I would guess there isn't very much in the stuff to begin with.
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