Alcohol energy content / stove system efficiencies – methanol / ethanol / mixes

Harald,

Great minds must think alike because I was just dwelling on this very subject. In point of fact, guess what my chemistry students' end-of-year project will be (I'm a high school chemistry teacher)? [By the way, I can't think of a better job than being a chemistry teacher–you get the school year to test this stuff in your lab, and then the whole summer to use it on the trail.] Designing and testing their own alcohol stove (or stove that burns some other fuel source–I have access to a stockroom of chemicals at my disposal), and determining its efficiency (in terms of kJ of energy released per gram of fuel burned). I found that kJ / gram fuel is more useful than kJ / mL fuel because some fuels have different densities. And don't start me on fluid ounces–I still don't understand for the life of me why we still use this silly English system! I can never remember how many cups are in a pint, pints in a quart, etc., but it's always easy to remember that 1 mL = 10^-3 L, etc.

This is a good review of our unit on thermochemistry. You probably already know this, but energies of reactions (for the combustion of the fuel in question) should be calculated using the equation:

Q = m x c x T (where Q is the heat energy in Joules, m is the mass in grams, c is the specific heat of water = 4.184, and T is the change in temperature). By determining the temperature change for the given mass of water that is being boiled, we can calculate the heat released by the fuel. This is much more useful than saying 15 mL of ethanol boils 2 cups of water, etc., etc., because that discussion doesn't include the initial and final temperature of the water. If one wants to talk about the efficiency of certain fuels, the most useful unit is kJ / mol. By knowing the appropriate chemical equation, you could probably look up this number in a table somewhere and given the # moles, you could determine the theoretical heat yield. But since not all that energy is transferred into the water, it's also useful to talk about the actual yield, or percent yield. Or just grams of fuel consumed / kJ heat energy transferred into the water. This is where the efficiency of stove designs comes in.

By the way, where/how did you order 98% ethanol?

There is a somewhat similar discussion going on in another forum.
A point that is often overlooked is that stoves will (generally) perform better with the fuel used when making/testing said stove.
In other words if building your stove you use SLX, by the time you finished tweaking that stove it will perform best with SLX.
That is why , for example, Tinny (Minibulldesign) recommends Methanol (Yellow Heet) with his stoves.
Not because Methanol burns better , hotter , whatever but simply because that is what HE uses making his stoves.

AT FLAT CAT GEAR, we do all of our testing using S-L-X. We have also done limited testing on other fuels. With our stoves, we notice that denatured alcohol with high ethanol content tends to burn with yellow tip. Additionally, it can leave soot on the pot and tends to smell "worse" than other fuels. Adding a small amount of water to these high ethanol fuels tends to slow down the burn rate, allow the flames to burn blue and reduces the odor. I cannot say what these fuels do for other manufactures as I can only speak for the stoves that we make and validate. Best regards – Jon

http://www.flatcatgear.com/page2.php

You could have just asked.

Did you include the water content? It makes a difference. Waters latent heat is very high, so is the heat capacity. Not only doesnt it burn, but it consumes more heat to heat it up and vaporize it.

Unfortunately, heat of combustion doesnt tell the whole story. Ethanol, really doesnt light that well or burn as well by itself, as it does with 25-50% MeOH mixed with it.

I use either straight SLX, or usually spike my SLX with some ethanol to make it about 75% ethanol. It burns a bit hotter, but still lights good. Honestly, not big enough difference to worry about, but since I have a bottle of everclear in my cabinet, what else would I do with it?

Is there any easy way to tell whether Sunnyside is pre 2012 or not? I have a can but I can't remember when I bought it and I'd like to figure out it's composition.

David Poston, thanks for the formulas. All these joules, kjoules, and, the dreaded moles, and the insane mix of units makes this a particular weird challenge to figure out. Most of the figures/data I found don’t even agree with each other, down to simple things like, are there 1054 or 1055 joules in a btu? I link to all my sources there, one good one was an agriculture site that listed all the relevant I assume real world energy densities and conversion formulas for the major fuels. I suspect those numbers are fairly accurate because they probably reflect non theoretical reality, though that could be wrong.

I think I’ll add another appendix with the raw formulas you list, since that ag site also has the joules/liter data, that’s what I ended up using to do my conversions since they seemed easiest to work with, but what I’ve been trying to get is the actual quantity required to heat 2 cups at different starting water temps. One thing I’ve already learned is that if air temp is warmer than water temp, then take water from water sources and let it sit for an hour or whatever is needed to let it warm up, it’s worth it re fuel consumption, particularly on cold days with very cold water.

http://www.goestores.com/storename/highfuelsn/ViewDept-81051.aspx is where I ordered the ethanol, I suggest holding off though, I ordered some and should get it whenever ups ground gets around to dropping it off, probably within a week or ten days. I’ll post on it if it works well, if it sucks, well, $30 isn’t too bad to try to find a source for basically pure ethanol at a fraction of the price of everclear, and legal to buy. I assume it’s denatured with something or other, probably methanol, but not very much. Oops, I looked it up, E98 is 98% ethanol and 2% gas. Oh well, my mistake, I should have realized it has gas in it as the other percent. I wonder how it will burn?

I’ll use those to check, but the problem lies in the fact that we generally use something to measure the fuel, not a scale, so I wanted ml, then worked around that to calculate the outcomes.

I believe I’m closer than I was at this point to having a sense of how the different fuels act.

I also tend to tentatively agree that the fuel used to design the stove tends during the testing/dev process to shape the efficiency.

sgt rock was nice enough also to give me some pointers via email and his results/data as best as he remembers them, he hasn’t been doing this stuff since 2005, since he basically already ‘won’ and doesn’t need to do more testing or dev work, preferring, wisely, to go backpacking instead. He used slx as far as he remembers. Unfortunately I believe the formulation of the denatured alcohols changes batch to batch so it’s very hard to say for certain what it is although I assume you can carefully weigh amounts large enough to get serious accuracy and that should actually help in figuring out what the percentages are. The efficiencies that sgt rock is getting are mind boggling compared to the standard quantities used if correct and properly measured. He stressed the design of the stand/heat shield over the stove itself however.

Jon, I’ll give the kleanstrip dilution with water a try, but since I’m actually going for minimum volume for a trip more than most clean burning, I don’t care about a bit of soot. That washes off pretty easily in streams/sand. I have to disagree re the smell of these however, slx to me is distinctly toxic and I try to avoid burning it inside at all. Kleanstrip smells much cleaner, like ethanol would be expected to smell. Which is exactly what you’d expect burning ethanol vs methanol/ethanol.

Following a nudge from sgt rock, I have correct the 2 cup water weight, it weighs 1.04375 pounds, so I’ve adjusted the 100% number for ethanol/methanol.

I did some retesting just to validate the raw data and realized right away that despite the yellow flame, kleanstrip green has a LOT more energy per ml than slx, by a significant factor, significant enough to make me suspect that slx may be closer to 25% ethanol than 50%. I may make a cone just to see about the heat trapping, but what sgt rock notes about the various points of generating efficiency, he got the results he got without any fancy tricks, just a lot of patient studying of flame heights and screen diameter/height. So for seriously UL cooking, I believe focusing on maximizing ethanol stove setup/efficiency is the low hanging fruit, with a 30% boost in energy compared by weight to methanol, that starts to add up over a week to 14 days.

I primarily want to get real data about energy densities, weights, etc, put up one place where I can reference it, and anyone else who wants. I’m listing in appendixes in my alcohol fuel energy densities article everything related to fuel consumption, altitude, etc as well, and updating it as I get new information that seems pertinent.

This being science at heart, plus engineering, a result one person gets should be achievable by another person using the same setup and fuel, if it’s not, there’s something wrong in the methodologies.

I was looking up data on Sunnyside DA and I noticed a difference in the ethanol/methanol mix. I called up the manufacture and they told me of the change in 2012. I don't know how to tell the difference other than looking up a lot number and calling the manufacture. BTW, Sunnyside had three differnt types of DA (934,836 & 834). Look above the bar code tag for the type

You can bring high % ethanol and dilute it on the trail – no weight penalty. Odor is a subjective matter. My wife can smell S-L-X and I barely notice it. I can smell the Sunnyside and Everclear 150 burning. My 2 cents – Jon

it's worth a try, re water mix, I'll give the blend a whirl, the yellow flames do indicate incomplete combustion so that's not energy that's used fully in any case.

For anyone interested, Sunnyside got back to me and said that the higher methanol formula of their denatured alcohol can be identified because the front of the label will have a skull and crossbones on it. According to them, the prior formula with the higher ethenol content did not have that on the label.

I tested a 10% water mix in kleanstrip green, and all it did was lower the flame height and intensity substantially, you'd have to drop the pot stand about 1/2" so the flames would contact the pot bottom.

Also probably I imagine you'd need to also redo the heat screen diameter and maybe ventilation hole sizes as well, but then you'd be stuck with a setup that only works well for that one fuel type/mixture.

What's interesting about the yellow flame of ethanols is that it points very obviously (to me anyway) to a potential area of fairly substantial increase in fuel / stove performance, the yellow coming from inadequate oxygen flow to the flame, just like you'd see with white gas lit without a stove vaporizing it.

I believe we are not far from making a true on/off switch alcohol stove, it can be a fraction of the weight of white gas stoves because the pressures and flammability are so low, but it would also pass all park regulations for fire season. If I had a machine shop and a garage I'd start on this.

I would bet that what is required is a flame spreader to ignite a vaporized jet of fuel, thus creating the proper oxygen mix. The pressures required would be quite low.

"I tested a 10% water mix in kleanstrip green, and all it did was lower the flame height and intensity substantially"

Did you see a change in efficiency?

no, not particularly, but as noted, the flames were so much lower that I'd have to actually make a new pot stand that was lower to fully check it.

As it was, the efficiency was about the same as non diluted as far as i could tell, it just burned slower. That's about what I'd guess, since the fuel has to vaporize water out of itself while burning slower, any efficiency boost is probably lost in that process.

I just got the e98 racing ethanol which sadly I forgot to check before buying, it contains 2-5% gasoline, but I'll give it a try outside to see how it is anyway, since I have it now. Hopefully it won't blow up a penny stove, we'll see.

If that doesn't work I'll just give it away to a hot rodder, they use it for racing.

Doesn't that mean that a 5% dilution may be fine for your stove setup?

no idea, I think it just means that if you put water in ethanol it will slow the burn, and drop the efficiency, but also a bit gain the efficiency because less goes non combusted in the process.

If I were to guess, and it's just a guess, I'd guess that the two balance out no matter what percentage you use, we all know that 75% aka 151 proof barely burns, for example, so it's just a question of how much work the fuel has to do to boil off the water in it while burning, chemistry formulas would show the loss perfectly but I don't know them.

I actually did more tests with mixing it with slx, but didn't come up with anything conclusive.

I believe, as I noted, that the actual problem with ethanol is that it's not getting enough oxygen into it, the mix is just too rich in these stove setups, unless kleanstrip green is actually using isopropynol or whatever its' called, instead of methanol to denature, or that the ketones make it yellow, I don't know what's in the stuff so it's hard to guess, and neither does anyone else who hasn't sent a sample to a real lab.

If the stove is yellow and sooty, it's lack of oxygen.

If the stove is yellow and not sooty, it could be an additive , like sodium, to make it easier see a flame.

it's yellow and slightly sooty, non fully combusted matter.

just like if you put out a plate of gasoline in a sense only not as extreme.

an UL svea123 type stove made out of very light stuff would probably do the trick, but it would be hard to engineer.

Since the fuel container only needs to hold 2oz max, it's not a huge device if it could be figured out.

I may play around with a heat spreader and see if that changes anything, the penny stoves already put out jets of fuel so they don't need much modification to add somewhere a heat spreader, maybe attached to the pot stand, not sure.

I believe though I'm not certain that the ion stove/stand may get a boost from the flat panels of the stand, which may act as a heat spreader type thing above the flames, getting better combustion that way, not sure though. i made an ion stand out of aluminum sheeting and that didn't do much different, but his are titanium plates, who knows.

"…if you put water in ethanol it will slow the burn, and drop the efficiency, but also a bit gain the efficiency because less goes non combusted in the process."

I have tried Everclear 190 proof in the Caldera Cone with its burner. Blue flame. Slightly longer to boil than with Ace brand denatured alcohol, but EC burns much longer.

Now, about added water: Yes, it takes heat energy to vaporize it, but that energy is returned to some extent when the water vapor hits the relatively cool pot of water. Anyway, it seems suboptimal to have to add water to fuel. When possible, use appropriate fuel.