Efficiency of Methylated Spirits/Water mixtures

[Tony]

Efficiency of Methylated Spirits/Water mixtures as fuel for Bushwalking Stoves

Introduction

Trangia alcohol stoves are very popular here in Australia, according to a recent survey on aus.bushwalking newsgroup users, 27% of bushwalkers are using Trangia stoves(1).

Methylated Spirits is the main alcohol fuel of choice, it is of a very high quality, with a standard of 95-96% ethanol content, but it can leave a residue or sometimes soot on the bottom of cooking pots, adding water to Methylated Spirits is common practice to try and reduce the amount of soot. Trangia instructions suggest ‘To avoid sooting, dilute the fuel with 10% or max. 15% water’ but Trangia do not mention if adding water has any affect on fuel efficiency.

The aim of this study is to investigate if adding water to Methylated Spirits has an effect on the efficiency of Methylated Spirits as a Bushwalking stove fuel?

TESTING

Methylated Spirits/Water mixes from 100% methylated Spirits to 75% methylated Spirits 25%water content by volume where tested in 5% increments, I did try higher water content but I found that the higher water mixes went out very easily and took more time to boil than was practical for field use.

I have access to some very accurate density measuring equipment, repeatability 1E-6 g/cm2 at 20ºC +-0.001ºC, which I used to determine the densities of the Methylated/Water mixes both before the tests and after the tests.

To keep this report short and to the point, I have left out some of the boring technical details, these details will be published if full detail on my soon to be live web site or if someone wants some more detail I can send it to them.

Equipment and testing method

Stove used: Trangia No 27-1, 23-hole burner.

The heating tests where done using some specially built temperature measuring equipment and the data logged on a computer using a program written in Labview, with a National Instruments USB-6008 A-D device. A standard 0.5 liters of water was used in the tests at tap temperature water which was usually around 17ºC, the weight of fuel was measured at start and when the water temperature reached 95ºC the stove was extinguished and the fuel re-measured, the fuel measurement was then recalculated to normalize the results to g fuel used/80ºC. After the stove was extinguished the remaining fuel was weighed and a sample of the remaining fuel mixes was taken
for density measurements. These tests where repeated three times for each fuel mixture and the results where averaged.

The tests were done in my garage elevation 600m, ambient temperature of between 20ºC-25ºC


Testing equipment


Test results charts


Graph 2 Comparing pre-boil densities to post-boil densities

Does the alcohol burning off by itself leaving mostly water

To test this I took a sample of the remaining fuel after the burner was extinguished and then re-measured the density using the density meter. As can be seen from graph below the alcohol/water ratio is very close to being maintained, there was a little more alcohol burned than water evaporated but basically there is very little change in density from pre- to post test density. Why? I am not sure; this will need some more investigating.




Heating rate

As can be seen from the heating rate the more water added the slower the heating rate.


Fuel used to heat 500 ml of water 80ºC (blue line) and Methylated Spirit content in that fuel (pink line).

In the results graph above the blue line, which shows the test results of the total Methylated Spirits/Water mix used to raise the water 80ºC per %, mix. The pink line is the calculated amount of Methylated Spirits used per % mix. Note that the Methylated Spirits results line closely follows the 12.0 grams line which is the 100% Methylated Spirits result.

Conclusion

The aim of this study that was to investigate “if adding water to Methylated Spirits has an effect on the efficiency of Methylated Spirits as a Bushwalking stove fuel?” The answer that I concluded from the tests results is adding up to 25% water concentration by volume to Methylated Spirits does not reduce the efficiency; there is some evidence that in some concentrations 5%-10% it may slightly enhance the efficiency. As to why at the moment I am unsure but I am looking into it.

Is adding Water to Methylated Spirits worth doing, In my opinion NO, the maximum measured improvement to fuel saved is 6% at 10% water added, to get the concentrations right you would need some reasonably accurate measuring equipment and this extra weight and effort would negate some of the advantage. Tests have shown that a blackened pot surface helps to improve heat absorption (2)(3) (Black body radiator effect).




References

(1) http://adunk.ozehosting.com/trangia.html
(2) http://www.bioenergylists.org/stovesdoc ... Berick.pdf
(3) http://www.aprovecho.org/web-content/pu ... s/pub2.htm

[Robbo]

Quite exhaustive, Tony.

Thanks for taking the time and effort to do it, and share your findings with us.

Tony Robinson

[Son of a Beach]

Yes, I second that. It's some fairly impressive effort you've put into this, Tony. Thanks for sharing your results here!

(Even having just converted my Trangia to gas, it's still very interesting to see ).

[frank_in_oz]

Wow,
Many thanks for this Tony. Great to see pure science applied to something as "simple" as this.

Not being a Trangia user, my understanding was that adding the water had the goal of reducing blackening of the pot. Did you observe any significant differences depending on the % water added?

Great post, now after getting blisters on my heels on a 6 nighter (with broken in boots) how about some research on blister prevention............

[Nuts]

A fraction too much friction Frank?

Tony, wow, you win!
I guess you could repeat the tests at different temperatures (down to 0*)?
Also, the sooty pot would in fact heat quicker? Making straight metho more efficient?

I tried a MSR reactor stove last week, didn't last the week in real conditions, the jet must have blocked and couldn't undo the brass fittings in the field.... Also the thing slows to a crawl as soon as the temp drops!

[Franco]

Hi Tony
That makes sense with the Trangia (over 50% of campers cooking inside the hut at Bluff (Vic) last w/e had them !) but I would still like to find out "scientifically" what happens when using a pressurised stove like the White Box and a relatively narrow pot . As you know I get a narrower flame adding water and that seems to make it more efficient.

Nuts
Reactor
Roger Caffin has reviewed the stove for BPL (http://www.backpackinglight.com/cgi-bin ... art_1.html, you need a subscription) but this is his brief conclusion :
It is a somewhat dangerous stove for carbon monoxide emission. It can't simmer, and it is not designed for use at or below freezing -
Franco

[Tony]

Thanks Tony, Nik and Frank,

I am a Technician in a Geophysical Fluid Dynamic research lab, temperature measurement is one of my specialties as is density measurement, viscosity measurement and flow visualization, I also design and make scientific equipment and help run experiments. Stove designing, making and testing is my hobby.

I have not used my Trangia for over 15 years when Bushwalking but I enjoy playing around with alcohol stoves, I like to understand what is going on. From this I have design one of the most efficient and lightest alcohol stoves around.

This article was written for Trangia users in Australia and is only small part of a series of articles on Alcohols for bushwalking stoves, which I am going to post on some US based forums. There are some advantages to adding water to alcohols which I am researching, I will post the results later.

Not being a Trangia user, my understanding was that adding the water had the goal of reducing blackening of the pot. Did you observe any significant differences depending on the % water added?

I have not yet tested if adding water to metho does keep the soot from depositing on pots, I plan to do some tests soon (will post results when I do), in this series of tests I did not notice the pot going black as it was already very black from many hundreds of tests and I prefer black bottom pots and shiny sides for better efficiency.

how about some research on blister prevention

I have not got the time to do the stove research that I want to do.

Tony

[Nuts]

Hi Tony

Reactor
Roger Caffin has reviewed the stove for BPL (http://www.backpackinglight.com/cgi-bin ... art_1.html, you need a subscription) but this is his brief conclusion :
It is a somewhat dangerous stove for carbon monoxide emission. It can't simmer, and it is not designed for use at or below freezing -
Franco

That would be an interesting article, We use cannister stoves a lot and I have been searching for something more efficient in the cold. We use the MSR windpro and warm the canisters within a large heat shield with the stove. The reactor was very good...till the temp dropped and the jet blocked...

[Tony]

Hi Nuts,

I guess you could repeat the tests at different temperatures (down to 0*)?
Also, the sooty pot would in fact heat quicker? Making straight metho more efficient?

That would be nice to be able to tests stove in different ambient temperatures and I have looked into it, I would love to be able to test at 0ºC and -20ºC it is not that simple or cheap to do. Cold mornings and days are not simple either as the temperature can change over the hours needed to run the tests

You are right about sooty pots being more efficient.

I tried a MSR reactor stove last week, didn't last the week in real conditions, the jet must have blocked and couldn't undo the brass fittings in the field.... Also the thing slows to a crawl as soon as the temp drops!

Very interesting, thanks for that info, Roger Caffin would be very interested in this information as Franco has mentioned he has reviewed the reactor, after his first review they delayed its release by a year or so as the CO levels where very high.

Tony

[Tony]

Hi Franco,

Hi Tony
That makes sense with the Trangia (over 50% of campers cooking inside the hut at Bluff (Vic) last w/e had them !) but I would still like to find out "scientifically" what happens when using a pressurised stove like the White Box and a relatively narrow pot . As you know I get a narrower flame adding water and that seems to make it more efficient.

I am going to test the White box stove with water mix soon as I think that a water metho mix would help. The reason why I chose the Trangia stove was because it is tuned for optimum efficiency, my test shave shown that the WB flame to strong for this to happen, adding say 10% water should improve the efficiency, I will post results soon.

Here is a graph of the trangia fuel usage to boil 1 liter of water, the first point is without the simmer ring and the others are with simmer ring at different closures, note that in all cases no matter how long it took it uses basically the same amount of fuel, which tells me that the Trangia has been tuned for optimum efficiency



Tony

[Whos_asking99]

Wow Tony, good post, very detailed...even if I did get a headache from trying to decipher the numbers

[Franco]

Hi Tony
Thank you for that. I have gone the Caldera Cone way because I only boil water but the White Box stove results should apply to other similar designs like the very easy to make Supercat ( ?) . The various stoves I tried of that design (including a couple from Mini Bull) all had a too wide and mostly red flame .
Franco
http://jwbasecamp.com/Articles/SuperCat/index.html

Trangia :anywhere,anytime,every time.

[Tony]

Hi Whos_asking99 ,

Wow Tony, good post, very detailed...even if I did get a headache from trying to decipher the numbers

Thanks for your comments , sorry about your headache, It has taken me much longer to understand and writeup the results than doing the actual tests, I tried to keep it fairly simple, the full writeup looks like being another 4-5 pages.

Tony

[Tony]

Hi Franco,

Hi Tony
Thank you for that. I have gone the Caldera Cone way because I only boil water but the White Box stove results should apply to other similar designs like the very easy to make Supercat ( ?) . The various stoves I tried of that design (including a couple from Mini Bull) all had a too wide and mostly red flame .
Franco
http://jwbasecamp.com/Articles/SuperCat/index.html

Trangia :anywhere,anytime,every time.

I have started testing my Caldera Cone stove and the initial tests show that with no wind it is no more efficient that a well designed normal windsreen but with wind it looks like it might have an advantage, but more on that later. My volcano stove works very well with the CC.

I have looked at Jims supercat stove, he has a good article on keeping things dry.

http://jwbasecamp.com/Articles/DryGear/index.html

Tony

[rcaffin]

That would be an interesting article, We use cannister stoves a lot and I have been searching for something more efficient in the cold. We use the MSR windpro and warm the canisters within a large heat shield with the stove. The reactor was very good...till the temp dropped and the jet blocked...

Yep, they sure do. There's some info here http://www.bushwalking.org.au/FAQ/FAQ_Mixtures.htm about what happens in the cold. The bottom line is that you need to change to a stove with a remote and inverted canister supply. They work just fine in the snow. The gold standard for snow use is the Coleman Xtreme, but sadly this is off the market. The FAQ does mention some other stoves. There are some extensive articles at Backpacking Light about this too.

cheers

[Irate Shane]

Interesting topic.

It appears the simple process of combustion is not understood and thus the methodology applied is wrong.

Burning alcohol - or most other fuels is a process of mixing the fuel vapor with the oxygen. The reason why soot forms on the base of pots - is because of incomplete combustion - pure and simple.

The two reasons why this occurrs is because burning is a process, from the beginning of the premixing and or flame construction.

In essence fuel vapor only has a limited mixture range with oxygen - where it will burn; too much fuel or too little fuel and it won't burn.

At the exact (more or less) ratio that enables all the fuel to burn completely there has to be an oxygen rich flame.

Experience dictates that a slightly furl rich mixture provides a more stable, easier to light and practical flame.

As the flame (assuming a premix or not) starts to burn - there is the initial premixing with the air and the light blue flame, progressing through to a solid blue flame and, as the amount of free oxygen decreases in the mix relative to the increasingly hotter core of unburnt, partially burnt and burning fuel vapor the flame progressively becomes yellow.

It's the construction of the flame - that dictates how much unburnt fuel there is at the end of that combustion cycle, and how close the food container is to the flame or more exactly - where the container has been stuck into the combustion process.

If you want a soot free flame, you need to increase the premixing of the flame, and increase the vigor of the actual flame it self - this means moving away from a nice clean candle type of flame, to a bushy swirling blow torch type of flame; and to increase the distance of the cooking container from the flame or combustion process.

I shall fudge a bit here as I am busy and have other things to do rather then chemical research and refreshment on the subject.

Typical fuel grade (denatured) alcohol on a hydrocarbon basis - not a chemistry evaluation - at best it has about 95% hydrocarbons (alcohol and things to make it taste awful) and it also has about 5% of chemically combined water - which is different to added water.

Given that ethyl alcohol has a boiling point of about 82*C, water will evaporate quite quickly with the alcohol at a proportional ratio (this gets complex) to the alcohol.

The "steaming" of the fuel gas will expand the flame as water vapor (without nit picking on temperatures and detail) as one cc of water has about a 1000 x expansion ratio - thus giving the flame a higher volume and area to mix with oxygen.

BUT the water takes HEAT to evaporate, and it also cools the flame. Providing the flame is burn in an efficient heat exchanger, the net transfer of heat into the cooking product, high water content should make no essential difference, but cooking in the open and hopefully still air, will decrease the amount of heat that transfers into the food, through increased radiation and convection.

The best way to increase the efficiency of the alcohol cooker is to increase the premix ratio to feed more oxygen into the flame - while keeping it below the combustible ratio threshold, and to increase the flames turbulence and contact area.

Adding water in a vapor form to an externalised combustion process with alcohol or some other fuels - is has definite advantages in industrial process's with specific outcomes.

For instance adding steam to an oil combustor (injection / sprayer) in a confined space (limits and controls oxygen) sprays the fuel, preheats it, reduces the amount of free oxygen in the mixture and it cools the flame temperature right down.

It's the industrialised way to make carbon (soot) for inks, pigments, carbon fiber and other process's.

The adding of water (steam / water vapor) to alcohol for cooking - will produce some "cleaning up" of a flame but it does not go any significant way towards solving the problem of less than desirable flame construction - as a dynamic process.

Basically most "carbonacious" alcohol burners are identical to a Bunsen burner with the premix hole closed up a bit too much.

Fix that by altering the air to fuel ratio - and depending upon the stove design - for the pressurised stoves by opening up the premix a wee bit, or closing it down a bit thus reducing flame size for the evaporative types - or reducing the surface are of the alcohol to reduce the mixture strength; and raise the distance of the cooking pot from the flames a little - problem solved.

[rcaffin]

It appears the simple process of combustion is not understood and thus the methodology applied is wrong.

An interesting conclusion in itself. Perhaps you would care to state your academic qualifications for this claim?
For the record, mine are BSc, MSc, PhD and 35+ years experience as a research scientist. Tony's are given above.

> Burning alcohol - or most other fuels is a process of mixing the fuel vapor with the oxygen.
> The reason why soot forms on the base of pots - is because of incomplete combustion - pure and simple.
Well, obviously. Did anyone say otherwise?

The rest of it is quite well-known basic combustion chemistry, which both Tony and I are are quite familiar with.

> Typical fuel grade ... has about 5% of chemically combined water - which is different to added water.
Fascinating. You can provide academic references to support this claim of 'chemically combined'?
And what form does this 'chemically combined water' take, at the molecular level? It may revolutionise physical chemistry.

> Fix that by altering the air to fuel ratio - and depending upon the stove design - for the pressurised stoves by
> opening up the premix a wee bit, or closing it down a bit thus reducing flame size for the evaporative types
Ah - just how do you do this with the basic Pepsi-can stove, pray tell?
The method would of course be of very great interest to the (tens of) thousands of users who so far have not managed to do this yet.

Cheers

[eddie the eagle]

Thanks for the posting Tony.

The other side of the equation, irate_shane, and maybe giving you a possible answer/line of enquiry, Tony.

Heat transfer from a flame occurs by conduction, convection and radiation.

The trangia has good conduction (transfer of heat from one thing to another - the aluminium's not bad at it and, as well,) there's not a lot of gap between the sides of the Trangia and the pot, allowing for a fair degree of heat transfer. To improve the heat transfer here, increase the residence time (increase turbulence.)

Convection, the flow of heat from the burner to the pot occurs well - there's good updraft in a Trangia.

Radiation is where the water comes in. If you can burn the alcohol flame in reducing conditions, you make soot. The soot produces a far higher amount of radiation than the plain gas flame, resulting in more rapid heat release from the flame. The soot then subsequently burns out later to get the full heat release.

If you don't burn out the soot, then you lose that heat effectiveness.

The optimal (gas/clear vapour) flame makes soot, then burns it out later to use the full calorific value of the fuel. Obtains extra 'free' heating capacity from having (highly) radiant soot.

As you said, water plays around with flame temp at the expense of higher heat consumption (interestingly, not shown in your results - experimental error? loss of calorific value due to unburnt fuel/soot/higher carbon monoxide emission?) Above 800°C, Carbon Monoxide is the preferred oxide, below 800°C, Carbon Dioxide is the stoichiometric oxide. CO then re-burns to achieve full combustion. 2CO = CO2 plus C (soot); C -> CO2 via a two-stage oxidation. If you can keep the flame below 800°C, then CO2 forms preferentially and less sooting occurs. Ellingham diagrams will show this - the optimal temp was 800°C, give or take 30 degrees from memory, last time I worked with burners was last century.

Cheers,

eddie
(a former metallurgist and process engineer who used to play with 10-25tph coal burners daily to optimise them, but hasn't had to dredge this stuff up in a fair few years.)

edit: I started writing this reply before Roger Caffin wrote his, but fell asleep - looks as though he covered the other basics.

edit II: Just noticed your density measurements, which I'm not disputing, as "the facts is the facts." Just a query, however, as something doesn't gel in a sleepy, dozy frame of mind. If pure metho has a density of 808g/L, and pure water at 20°C has a density of 996(?)g/L, wouldn't a 20% (v/v) mixture of water in metho give a density of 846g/L? I've been wrong before and I'll be wrong again, just an observation that didn't make sense on a first take. [edit III - hydrogen bonding occuring between the metho and the water, decreasing volume? just a wild guess and a probably wrong.]

[rcaffin]

Just noticed your density measurements, which I'm not disputing, as "the facts is the facts." Just a query, however, as something doesn't gel in a sleepy, dozy frame of mind. If pure metho has a density of 808g/L, and pure water at 20°C has a density of 996(?)g/L, wouldn't a 20% (v/v) mixture of water in metho give a density of 846g/L? I've been wrong before and I'll be wrong again, just an observation that didn't make sense on a first take.
[edit III - hydrogen bonding occuring between the metho and the water, decreasing volume? just a wild guess and a probably wrong.]

Actually, your edit III is quite right. There is a polar interaction at the molecular level which means the simple weighted-average result is not quite correct. Tony may give more details.

Cheers

[Tony]

Hi Eddie,

edit II: Just noticed your density measurements, which I'm not disputing, as "the facts is the facts." Just a query, however, as something doesn't gel in a sleepy, dozy frame of mind. If pure metho has a density of 808g/L, and pure water at 20°C has a density of 996(?)g/L, wouldn't a 20% (v/v) mixture of water in metho give a density of 846g/L? I've been wrong before and I'll be wrong again, just an observation that didn't make sense on a first take. [edit III - hydrogen bonding occuring between the metho and the water, decreasing volume? just a wild guess and a probably wrong.]

I think his may help, it also confused me early on.

The answer has to do with the different sizes of the water and ethanol molecules. Ethanol molecules are smaller than water molecules, so when the two liquids are mixed together the ethanol falls between the spaces left by the water. It's similar to what happens when you mix a liter of sand and a liter of rocks. You get less than two liters total volume because the sand fell between the rocks, right? Think of miscibility as 'mixability' and it's easy to remember. Fluid volumes (liquids and gases) aren't necessarily additive. Intermolecular forces (hydrogen bonding, London dispersion forces, dipole-dipole forces) also play their part in miscibility, but that's another story. http://chemistry.about.com/od/lectureno ... bility.htm and it is not linear.

As you said, water plays around with flame temp at the expense of higher heat consumption (interestingly, not shown in your results - experimental error? loss of calorific value due to unburnt fuel/soot/higher carbon monoxide emission?)

It maybe experimental error but the test where done under controlled conditions to get repeatability and the results where consistent, this could be an explanation "Adding water to the alcohol will reduce the size of the flames. The reduced flame size means that far less of the flame goes up the side of the pot to be wasted. Instead, the smaller flame manages to get more of its heat into the pot, although the heating time may be slightly longer." a full writ-up by me and Roger Caffin of the tests can be obtained at http://www.backpackinglight.com/cgi-bin ... t_two.html and http://www.backpackinglight.com/cgi-bin ... t_one.html you do have to be a member to read full articles

The trangia has good conduction (transfer of heat from one thing to another - the aluminium's not bad at it and, as well,) there's not a lot of gap between the sides of the Trangia and the pot, allowing for a fair degree of heat transfer. To improve the heat transfer here, increase the residence time (increase turbulence.)

I have done some work on heat transfer to and from the sides of pots you maybe interested in reading my results viewtopic.php?f=15&t=2794

Tony

[Orion]

Ethanol molecules are smaller than water molecules, so when the two liquids are mixed together the ethanol falls between the spaces left by the water. It's similar to what happens when you mix a liter of sand and a liter of rocks. You get less than two liters total volume because the sand fell between the rocks, right?

The other way around. Ethanol molecules are larger than water molecules.

...there is some evidence that in some concentrations 5%-10% it may slightly enhance the efficiency

Did you do an error analysis? Just taking the standard deviations suggests that you do not have the data to make this claim.


Did you ever get around to posting the full details?

What temperature(s) were the fuels at when you measured their densities?

[Tony]

Hi Orion,

Thank you for your questions and I do appreciate any input that you can give.

The other way around. Ethanol molecules are larger than water molecules.

Yes you are correct, this error was in the stated source, thank you for pointing that out.

Did you do an error analysis? Just taking the standard deviations suggests that you do not have the data to make this claim.

No I did not do any error analysis, I did repeat the tests for water Methylated Spirits several times and did similar tests with Methanol and IPA. They all showed similar trends that up to 10% water showed no decrease in efficiency and may actually improve efficiency slightly. A possible explanation is in my previous post. My expertise is in measurement, I am certainly not a chemical or combustion engineer, if you can help with an explanation I would love any information you can put forward.

Did you ever get around to posting the full details?

Yes but not on this forum, as mentioned in a previous post the full written up results co-authored with Roger Caffin are on BPL who now owns the copyright. The original posting above was some of my early research into the water/alcohol mixes and was done with the Australian bushwalkers in mind.

What temperature(s) were the fuels at when you measured their densities?

All density measurements where done at 20C, + or - 0.01C

Tony

[Orion]

I did repeat the tests for water Methylated Spirits several times and did similar tests with Methanol and IPA. They all showed similar trends that up to 10% water showed no decrease in efficiency and may actually improve efficiency slightly.

So there are more data than you showed above? Perhaps that provides better statistics.

A possible explanation is in my previous post.

It seems reasonable that a lower flame would improve the efficiency. It's a shame that the two variables are confounded in your experiment. But if that hypothesis has merit then why wouldn't the effect also be present in higher water concentrations?

...as mentioned in a previous post the full written up results co-authored with Roger Caffin are on BPL who now owns the copyright.

Darn! I'm very curious to see it but I'm too cheap to pop for the $25 membership. I'd rather spend that on unmethylated spirits!

I'm wondering a few other things though. How did you determine the water percentage? Did you measure it volumetrically and then determine the density, or was it the other way around. Your chart implies the latter but I don't understand how you could do this calculation without first determining the composition of the unadulterated fuel.

I'm also curious about the actual fuel volumes used, what you started with and what percentage was burned in a given test since that bears on the change in alcohol concentration.


I'd love to ask you a bunch more questions but maybe I should just go have a beer instead.

Cheers!

[Bill P]

Thanks Tony,

I've used my Trangia since 1981 and my pots and kettle bear a nice matt black patina. I went walking with a bloke lake week using his newish Trangia (cos mine looked a bit sus) and he insisted on diluting the fuel in the burner pot with water. (hang on mate, its below zero outside, 1000m above sea level and you're watering down the fuel?) I'd never heard of this before and found it counterintuitive.

I thought his burner pot was harder to ignite from cold, taking several matches to light. Perhaps that's due to the lowered overall volatility of the fuel mix?

Also, do you have any hypothesis or thoughts on how much fuel is lost to evaporation when one extinguishes a hot burner? I've often wondered after what time interval is it better to let the burner run vs extinguish & relight, while swapping pots etc.

Bill P

[Tony]

Hi Orion,

Again thank you for your comments.

It seems reasonable that a lower flame would improve the efficiency. It's a shame that the two variables are confounded in your experiment. But if that hypothesis has merit then why wouldn't the effect also be present in higher water concentrations?

A good point and I do not know the answer, as a friend of mine once said "the more you know the more you realize that you do not know".

Darn! I'm very curious to see it but I'm too cheap to pop for the $25 membership. I'd rather spend that on unmethylated spirits!

A good idea.

I'm wondering a few other things though. How did you determine the water percentage? Did you measure it volumetrically and then determine the density, or was it the other way around. Your chart implies the latter but I don't understand how you could do this calculation without first determining the composition of the unadulterated fuel.

I'm also curious about the actual fuel volumes used, what you started with and what percentage was burned in a given test since that bears on the change in alcohol concentration.

I made the mixes by weight, I find this is easier and more accurate than by volume. I mixed a range of mixes by weight and then measured density on a Anton Paar DMA 5000 density meter, I then made a chart of the results, as mentioned before the results are not as expected and the line was not linear.
I used 50 g of fuel to test. As can be seen in the results, with metho the tests used 12-17g of fuel, after the tests I weighed the remaining fuel then I took a sample for further analysis on the density meter, once I determined the density I then went back to the chart and determined the ratio of water alcohol remaining in the fuel.

I know the results would have been different if I had of started with a different volume of fuel but I had to decide on a start volume. After each test I emptied the burner cleaned it out let it dry and used new fuel. I hope this helps and as suggested I would love input in improving my testing techniques.

I'd love to ask you a bunch more questions but maybe I should just go have a beer instead.

Now there is a research project that I would love to do "what is the best beer for backpacking" maybe we can write a paper together on this one day, another project is "comparing US beers to Australian beers"

Tony

[Tony]

Hi Bill,

Thanks Tony,

I've used my Trangia since 1981 and my pots and kettle bear a nice matt black patina. I went walking with a bloke lake week using his newish Trangia (cos mine looked a bit sus) and he insisted on diluting the fuel in the burner pot with water. (hang on mate, its below zero outside, 1000m above sea level and you're watering down the fuel?) I'd never heard of this before and found it counterintuitive.

I thought his burner pot was harder to ignite from cold, taking several matches to light. Perhaps that's due to the lowered overall volatility of the fuel mix?

Also, do you have any hypothesis or thoughts on how much fuel is lost to evaporation when one extinguishes a hot burner? I've often wondered after what time interval is it better to let the burner run vs extinguish & relight, while swapping pots etc.

Bill P

I have not measured how much fuel evaporates after the flame has been extinguished, I am usually trying to stop this happening but it might be worth doing one day, it will depend oon the thermal mass of the burner and how much fuel is left.

On another note I have noticed that if a trangia burner is continually topped up the remaining fuel can be contaminated with a higher proportion of water, this is because Metho has 5% water in it and very small amount does not burn off and long tern the water % builds up, it is a good idea to empty the burner every now and then and refill with new fuel..

Tony

[Orion]

Hi Tony,

I made the mixes by weight, I find this is easier and more accurate than by volume. I mixed a range of mixes by weight and then measured density on a Anton Paar DMA 5000 density meter, I then made a chart of the results, as mentioned before the results are not as expected and the line was not linear.
I used 50 g of fuel to test. As can be seen in the results, with metho the tests used 12-17g of fuel, after the tests I weighed the remaining fuel then I took a sample for further analysis on the density meter, once I determined the density I then went back to the chart and determined the ratio of water alcohol remaining in the fuel.

I think I get it now, more or less. You produced a chart that relates the water-fuel mass composition to the mixture density, correct?

Since the density changed negligably during each test you had the luxury of treating the mass composition as a constant. So the mass of fuel used was simply (grams of mixture used) X (% fuel by weight), the latter you obtained via the density measurement and your chart. It's not obvious to me why you didn't just weigh the components before the test to get the % by weight.

My main confusion is over how you determined the % by volume. In your table you use the "% water measured from graph..." to calculate the mass of fuel used. So this has to be % by weight. But then you refer to % by volume in your description and in the first graph. What am I missing here?

Now there is a research project that I would love to do "what is the best beer for backpacking" maybe we can write a paper together on this one day, another project is "comparing US beers to Australian beers"

Yes, a subject I could really throw myself into. It would require MANY repeated experimental trials.

Cheers!