JetBoil pot vs Normal pot using an alcohol stove

You might want to run another test when you use a wide diameter pot. You might find close to the same performance without the extra weight of the flux bottom. I found the evernew .9 and 1.3 pots used approx 20% less fuel than a narrower/taller MSR pot, and were even more efficient that some of the narrow pots like a snowpeak trek.

–mark

Hi Mark,

You are correct in that there is a relationship between flame size, pot diameter and efficiency. Small burner/large diameter pot is more efficient than large burner small pot. I have done some test on this problem with canister stoves but beyond a certain pot diameter there was not much of a gain, I will do some soon with alcohol stoves.

But that was not the aim of these tests it was to see what the effect of the flux ring was with the side burner cat can stove that is why I tried using two pots of similar size.

There are many stove/pot tests that I want to do but time and money slow me down.

Tony

“You might want to run another test when you use a wide diameter pot. You might find close to the same performance without the extra weight of the flux bottom. I found the evernew .9 and 1.3 pots used approx 20% less fuel than a narrower/taller MSR pot, and were even more efficient that some of the narrow pots like a snowpeak trek.”

In reply to Marks comment about pot size and fuel efficiency I decided to do some more tests. I tested three standard non flux ring pots diameter 137.5 mm, 157 mm, and 204 mm, to see if a larger pot could be as efficient as the JetBoil 1.5l flux ring pot. The test technique is the same as the JB vs std pot tests.

Below is s graph of my results; I currently do not have a 250mm pot so I extrapolated the results.

Caution these results are for a particular cat can side burner stove that I made, diameter 61mm, as the stove is a side burner stove that is also the pot stand and the flame is much larger than 61mm. Other alcohol stoves could and will give different results.

The graph shows that for this stove a pot of about 230mmm-240mm would be as efficient as the 1.5l JB pot. The reader can decide if a 225mm (9”) – 250mm (10”) pot is a better option than the 1.5l JB pot.

I have started to test smaller pots e.g. the Heinekin pot and small billy to compare with the results above. Further work will also be done to determine if there is an optimal stove/pot size relationship.

Tony

Tony,

This is really great stuff!

It is really nice to have numbers to put to the general experience that the bigger the diameter of the pot the more efficient a given stove becomes. That is: less heat is lost up the side of the pot. and one of the reasons that a Caldera Cone system works so well.

The JetBoil flux ring offers a lot more surface area (like a larger diameter pot), but it also interferes with the flow of heat across the bottom of the pot and up the sides. I wonder if one could clamp a ring of sheet metal to the bottom of a regular pot so that it hung down below the pot a few cm. It wouldn't be a flux ring exactly, but it would offer an increase surface area and would interfere with the flow of heat up the side of the pot. Might work? Just thinking out loud.

Anyway, nice work, Tony, as always. I look forward to your smaller pot experiments.

Cheers,
-Mark

I just made a 4 1/2oz Kelly Kettle today (see MYOG forum)and measured it's performance. I was constrained by the size of the Kelly Kettle (1 Pint 456g of water) and the burner (a tealight candle pot which held 11g of UK issue purple methanol).

It raised the tap water from 12C to 88C giving the same g/C ratio of 0.156 as your jetboil pot/can stove setup.

I don't know if this is a valid comparison, as I didn't get the water up to boiling point before the tealight ran dry, but I'll post back when my nion alcohol stove has arrived with another test result.

Hi Mark,

“That is: less heat is lost up the side of the pot. and one of the reasons that a Caldera Cone system works so well.”

I have not tested a Caldera Cone yet, although I have done some temperature testing of heat flow up the side of a pot in a cone type situation, I was using a canister stove and it is more complicated that I originally thought. I might get a Caldera Cone as a friend is going over to the US soon.

“The JetBoil flux ring offers a lot more surface area (like a larger diameter pot), but it also interferes with the flow of heat across the bottom of the pot and up the sides. I wonder if one could clamp a ring of sheet metal to the bottom of a regular pot so that it hung down below the pot a few cm. It wouldn't be a flux ring exactly, but it would offer an increase surface area and would interfere with the flow of heat up the side of the pot. Might work? Just thinking out loud.”

On the flux ring slowing down the hot gasses under the pot I think this is where a lot of the heat transfer gain is rather than the extra surface area. I would like to test a MSR Backlight pot as it has a grooved bottom to see what difference that makes.

Clamping a ring around a pot so it hangs down a few mm or a few cm’s might be worth a try, thanks for the idea.

That is some of my thinking aloud too.

Tony

Thanks Rog Tallbloke for your test results they are interesting, you are probably getting those figures because your pot/stove ratio is fairly large, I have had similar 0.156 g/C ratio figures with some of my smaller alcohol stoves, I have just gone through my lab book this seems to be a fairly standard figure for denatured alcohol fuel stoves except for the Cat Can side burner.

I do not know of Purple methanol I would like to see a data sheet on it if you can point me to one.

Tony

Hi Tony,
I'm not using a pot, I'm using a 3" diameter aluminium drinks bottle with a 1" chimney welded up the middle. Have a look at the photos in the thread I started on the Make Your Own Gear forum: 4 1/2oz Kelly Kettle.

The stove is basic to say the least, it's just the aluminium cup from a tealight candle and weighs 1g. The flame ran slightly yellow and I hope the Nion alcohol stove on it's way to me from the states will improve the efficiency quite a bit. The nion's jets are orientated inwards from the edge, so should keep the heat where I want it to go.

Purple meths is what we get in the UK. It's alcohol with something obnoxious added to it to discourage folks from drinking it. Not sure of the spec, but probably pretty similar to other denatured alcohols available round the world.

Very impressed with your test rig by the way. :-)

I believe 'purple methanol' just refers to denatured or 'methylated spirits'. The purple colour (and bad smell) are added to keep smart folks from drinking the stuff. As for the specs, it no doubt varies with region, but in my tests comparing lab grade methanol to our local purple meths, the purple meths actually burns better (more efficient). In fact, when I was having trouble getting my White Box stove to burn hot and blue, an ozzie suggested I water it down with 10% water to tame the flame. This actually worked and increased the meths efficiancy while reducing yellow smoking flames!

I have long noticed better fuel efficiency when using larger pots. Takes less time to boil 2 cups in a 2 liter pot than it does in a 750 heine can, for instance. This is interesting stuff guys. Thanks.

Hi Rog,

“I'm not using a pot, I'm using a 3" diameter aluminium drinks bottle with a 1" chimney welded up the middle. Have a look at the photos in the thread I started on the Make Your Own Gear forum: 4 1/2oz Kelly Kettle.”

Sorry I did not look at your MYOG posting close enough, I know the Kelly Kettle, I have not tested them yet, I might look at making one myself.

“Purple meths is what we get in the UK. It's alcohol with something obnoxious added to it to discourage folks from drinking it. Not sure of the spec, but probably pretty similar to other denatured alcohols available round the world.”

Denatured alcohol varies a bit in Australia it tends to be 95% ethanol with water or methanol making up most of the rest. In the US it is from 50% ethanol up with lots of different mixtures but mainly methanol making up the rest, I will check out UK denatured.

“Very impressed with your test rig by the way. :-)”

Thanks, I am a technician in a research lab and accurate temperature measurement is one of my areas of expertise, I have put a lot of time an money into getting set up at home, it is nice to be able to do accurate testing.

Tony

Hi Alison,

“but in my tests comparing lab grade methanol to our local purple meths, the purple meths actually burns better (more efficient). In fact, when I was having trouble getting my White Box stove to burn hot and blue, an ozzie suggested I water it down with 10% water to tame the flame. This actually worked and increased the meths efficiancy while reducing yellow smoking flames!”

Thanks for the information I have tested Denatured/water but not Methanol /water

Mixing water with metylated spirits is common here in Australia, some say that it improves efficiency and some do it because it keeps the pot clean.

I am in the process of doing some comprehensive testing on different alcohols and mixes including alcohol water mixes, which I am hoping to get an article published. I have to do some more test to fill in some gaps, the weather is too hot at the moment and soon I am off for a trout fishing/walking trip in the North Island NZ I expect that it will be a few more weeks before I will have it finished.

Tony

I bought the 1.5 L. JetBoil pot (not the stove) and found it to boil faster than my old 1.5 L. pot. Both have the same diameter. The Jet Boil was tested WITH the cozy in place. Suppose now I'll go back & test the JetBoil "naked" and see what I get. I'm sure the JetBoil will still beat my old 1.5 L. pot.

Eric

Tony, you're going to so much effort and being so thorough with this. I'd be happy to send a sample of the uk stuff but I'm not sure how the international post feels about fuels being sent. There again, alcohol goes by post in many forms, for drinking and in perfumes etc. Let me know if you want some.

Hi Eric,

Thanks for the information on your JB pot, I have not yet done tests on the effectiveness of the JB cosy, I left it off in these tests because I wanted to test the improvement in efficiency of the flux ring only.

I am guessing that the cosy would have a major efficiency gain in very cold temperatures, Further tests that I plan will show what effect it has.

Tony

Hi Rog,

Thanks for the offer of sending me some Purple Meths but I don't think that the Australian Customs would let it through. I have looked it up on the net and it appears that it has 90% ethanol with various other additives.

There is some good info about Methylated Spirits on this site http://answers.yahoo.com/question/index?qid=20060904072927AAtJxTP

Tony

Here are some more tests comparing different pot sizes on a cat can side burner alcohol stove.

6 pots where used in the tests, 84 mm (heiny), 106.3 mm, 123.5 mm, 137.5 mm, 157 mm, and 204 mm diameter. The stove diameter is 61 mm but being a side burner the flame projects out to have contact with the bottom of larger pots to about 75 mm to 110 mm in diameter which gives an approximate annulus area of 5000 mm^2, this flame contact area is different with smaller pots as the flame was shared by the bottom and the sides, pot/stove ratio is a difficult area to define and in the results I have used the stove diameter in the pot/stove ratio.

Test conditions: 600m (2000ft) elevation, ambient around 20C. Fuel used was standard Australian Methylated Spirits (denatured alcohol) 95% ethanol content. 0.5 liters of tap water was heated from ambient (about 20C) to 95C then g/1 C/0.5l was calculated the result was then standardized by multiplying by 80 to get g/80C/0.5l, which are used in the final results. NOTE: I recorded up to a 5% difference in the amount of fuel used for some pot /stove combinations for these tests, this appears to be a normal amount of variation for stove tests and is why these results are slightly different than some previous results.

RESULTS:

Pot dia mm ,fuel used g, pot/stove dia ratio, % of fuel/ compared to 204 pot
84, 21.48, 1.38, 146%
106.3, 19.38, 1.74, 134%
123.5, 18.25, 2.02, 126%
137.5, 17.37, 2.25, 120%
157, 16.23, 2.57, 112%
204, 14.48, 3.34, 100%

Sorry I am unable to lay the table out properly on the site, if any one can help with this I would be greatfull.

NOTE: these results are for this particular cat can stove (pictured below) other stoves will give different results.

CONCLUSION To me there is a clear relationship between pot sizes and flame sizes and efficiency, the greater the pot flame ratio the more efficient the pot/stove system will be.

Future work: I am hoping to do the same tests with a smaller side pressure stove and with some top burner stoves to see if I can find a critical pot/stove ratio.

Tony

Pot diameter vs fuel used

performance curve: temperature rise vs time

Stove used in tests

Smallest pot used, notice the flames up the sides

The stove above doesn't look like the "Sgt Rock" cat can stove. Is there directions somewhere on how it's made ?

Thanks.

Hi John,

I used the "Simplified Zen Alcohol Sideburner Stove" (http://zenstoves.net/Stoves.htm) design as the basis for my Cat can stove, I machined out the hole on my lathe and pushed in a sleeve from a deodorant can, that is why it looks different.

This stove is reasonably fast boiling but is not very efficient.

I am new to myog alcohol stoves and I am currently trying to understand them.

Tony

>
I am new to myog alcohol stoves and I am currently trying to understand them.

Hi Tony, the height above the stove of the pot is crucial.

As a simple standard comparator, try using an open cup burner such as a tealight candle cup.Using one of these in my MYOG kelly kettle, I boiled 454g (1 US pint) of water with 14g fuel after playing around with the height of the burner in the combustion chamber. This was with 10C tapwater in 16C ambient tmperature room at an elevation of around 300ft.

My MkII kettle should do a lot better, I'll post results soon.

My latest kelly kettle design gives the following results:

10C cold water 15C ambient 300 ft altitude.

0.5 litres boiled in 8 minutes 45 seconds using 12 grams of alcohol, giving a temp/fuel ratio of 0.133g/C at an efficiency of 72%. The unit weighs 82g including the burner.