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  1. #1

    Default Fuel Canister efficiency

    Do fuel canisters generally (ie under the same conditions re: water temp, wind, air temp etc) become less efficient as they become less full?

    Additionally, if my stove takes 6 minutes to boil 2 cups water the first time I use a canister and uses 7g of fuel, is it reasonable to expect that it may take longer to boil 2 cups water but should take the same amount of fuel when the canister is near empty? Or would it take more fuel and thus more time to boil that last 2 cups?

    Here's some of my thoughts:

    the amount of energy to heat 40 degree water to 212 degrees, all other factors being equal, should remain the same. X grams of fuel will produce Y BTU's on a stove and thus raise the temperature to boiling using the same amount of fuel. However, does the fuel actually "escape the canister faster" and thus burns faster delivering more BTUs over a shorter period of time when the canister is full?
    https://tinyurl.com/MyFDresults

    A vigorous five-mile walk will do more good for an unhappy but otherwise healthy adult than all the medicine and psychology in the world. ~Paul Dudley White

  2. #2
    Registered User colorado_rob's Avatar
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    Probably slightly less efficient, but a second order effect. The power (flame intensity at full) definitely goes down as the canister drains down over many boils, so it will take longer for an equivalent boil, but it is using less fuel during that longer time (lower power means les fuel used per time). The loss in efficiency is because your pot is losing heat during the boil, and the less time it takes to boil the less heat will be lost during this boil, if you follow. Some canister stoves are probably less efficient at high power because the flame leaks around the pot bottom. Jet boil pots, or other pots with a heat exchanger, contain this side-flame-leakage and are most efficient at high power.

  3. #3

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    Quote Originally Posted by colorado_rob View Post
    Probably slightly less efficient, but a second order effect. The power (flame intensity at full) definitely goes down as the canister drains down over many boils, so it will take longer for an equivalent boil, but it is using less fuel during that longer time (lower power means les fuel used per time). The loss in efficiency is because your pot is losing heat during the boil, and the less time it takes to boil the less heat will be lost during this boil, if you follow. Some canister stoves are probably less efficient at high power because the flame leaks around the pot bottom. Jet boil pots, or other pots with a heat exchanger, contain this side-flame-leakage and are most efficient at high power.
    Yes I understand what you said. I have accounted for the fact that times may vary depending on how high the flame is as my pot is narrow and tall. Thank you.
    https://tinyurl.com/MyFDresults

    A vigorous five-mile walk will do more good for an unhappy but otherwise healthy adult than all the medicine and psychology in the world. ~Paul Dudley White

  4. #4

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    I wasn't see much difference in fuel usage but definitely differences in time so that pretty well confirms what you were saying as well. Thanks Rob
    https://tinyurl.com/MyFDresults

    A vigorous five-mile walk will do more good for an unhappy but otherwise healthy adult than all the medicine and psychology in the world. ~Paul Dudley White

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    It's well known that for regular pots (without heat exchangers), heating at full power is less efficient (more grams of fuel needed to boil) than boiling at a lower power. But as pointed out above, at very low rates, heat loss to the environment becomes more significant and efficiency goes down, although I'm not sure I've ever seen that quantified. I would expect that for reasonable boil times, that effect would be minimal. So if you are running at full power you should see an increase in efficiency as the canister drains and power output diminishes. But 6 minute boils would seem to be a rather leisurely heating rate (alcohol stove times). In that case, while there probably probably would be a change of efficiency, I don't know that we have enough information to predict if it would go up or down. However, I would expect any efficiency difference to be insignificant. BTW, there are stoves (Soto Micro Regulator, e.g.) that have a built in pressure regulator that are designed to keep burn rates relatively constant for the life of the canister. I have not used one of these so I can't speak to how effective they are.

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    Maybe.

    If you have blended fuel, you disproportionately lose the more volatile species first. Which leaves you with weaker burning cannister at same temperature due to lower vapor pressure.

    If you are smart enough to adjust flame as cannister depletes, you will probably never notice at warm ambient temps. Near freezing you may practically cease to work, so yeah..it might have an effect

    At low cannister level the vaporization rate cools the small remaining mass more as well, slowing heat output significantly.


    Now the truth...only something like around 1/2 of energy goes into water...rest is lost...so you can affect some things marginally, via heat exchangers and insulation and windbreak design.

    Say you take 7 g fuel to heat 16 oz water 40-212F. Roughly 172 btu. The 7 g fuel had closer to 300 btu for heat of combustion. Much is lost by heating excess air, which lowers your flame temp too.

    My little cannister will basically boil 2 cups rt water on 5.8 g fuel using tight windscreen around pot bottom, and 7-8 min heating time. Only slightly more than the 4.25 g a jetboil does with its heat exchanger and insulated pot. Just much slower. Im 56% efficient. The jetboil is 77%. Normal cannister run high rate without windscreen is more like 38% in my experience (8.5g). But a pot that is wider with more bottom area, may be more efficient than my small one on high.
    Last edited by MuddyWaters; 03-28-2017 at 13:49.

  7. #7

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    I don't know but across different stoves, fuels, and times of year, I have been able to average 10gr of fuel per/ 16oz boil. that's a safe side estimate to account for worst case scenario but I haven't run out yet using that formula...

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    Registered User BuckeyeBill's Avatar
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    As your canister uses fuel, the pressure that it exits at decreases. Temperature also effects the pressure, the colder it gets the lower the pressure. This can be overcome by using a stove that permits the canister to be inverted so that the stove is burn a liquefied gas instead of vapor. This is one reason I switched from a pocket rocket to a WhisperLite Universal. It ways a lot more, but it can burn butane/propane, white gas, gasoline or kerosene. You can tell how much is left in your canister by floating it in a pan of water. Start with a new/full canister and make a mark at the water line as you continue to use the canister keep doing this and eventually you will know where to put your full, half empty or half full, and empty marks on new canister. Hope this helps you out.
    Blackheart

  9. #9

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    Quote Originally Posted by MuddyWaters View Post
    Maybe.

    If you have blended fuel, you disproportionately lose the more volatile species first. Which leaves you with weaker burning cannister at same temperature due to lower vapor pressure.

    If you are smart enough to adjust flame as cannister depletes, you will probably never notice at warm ambient temps. Near freezing you may practically cease to work, so yeah..it might have an effect

    At low cannister level the vaporization rate cools the small remaining mass more as well, slowing heat output significantly.


    Now the truth...only something like around 1/2 of energy goes into water...rest is lost...so you can affect some things marginally, via heat exchangers and insulation and windbreak design.

    Say you take 7 g fuel to heat 16 oz water 40-212F. Roughly 172 btu. The 7 g fuel had closer to 300 btu for heat of combustion. Much is lost by heating excess air, which lowers your flame temp too.

    My little cannister will basically boil 2 cups rt water on 5.8 g fuel using tight windscreen around pot bottom, and 7-8 min heating time. Only slightly more than the 4.25 g a jetboil does with its heat exchanger and insulated pot. Just much slower. Im 56% efficient. The jetboil is 77%. Normal cannister run high rate without windscreen is more like 38% in my experience (8.5g). But a pot that is wider with more bottom area, may be more efficient than my small one on high.
    what's your setup? what stove/windscreen/heat exchanger?
    https://tinyurl.com/MyFDresults

    A vigorous five-mile walk will do more good for an unhappy but otherwise healthy adult than all the medicine and psychology in the world. ~Paul Dudley White

  10. #10

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    Quote Originally Posted by Secondmouse View Post
    I don't know but across different stoves, fuels, and times of year, I have been able to average 10gr of fuel per/ 16oz boil. that's a safe side estimate to account for worst case scenario but I haven't run out yet using that formula...
    I have tested 2 stoves and 2 pots. Returned the new stove and pot as I didn't like the pot and the stove wasn't any more efficient in time or fuel used to boil my water. SO I have a snowpeak 900(?) and a BRS-3000T that actually outperformed the snowpeak giga stove and halulite(?) minimalist pot.

    But I'm trying to improve my boil times and fuel efficiency. generally takes 7-9g fuel per boil depending on conditions. Trying to make my own reflector/windscreen to improve it. I had one "cludged up" that took only 5g fuel to boil. Haven't repeated that though. I need to check my pictures and see if I can figure out what I actually did LOL.
    https://tinyurl.com/MyFDresults

    A vigorous five-mile walk will do more good for an unhappy but otherwise healthy adult than all the medicine and psychology in the world. ~Paul Dudley White

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    https://www.whiteblaze.net/forum/att...7&d=1417908689
    Quote Originally Posted by PennyPincher View Post
    what's your setup? what stove/windscreen/heat exchanger?

  12. #12
    Registered User egilbe's Avatar
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    I use my Caldera cone on a 1.4 liter Snow Peak titanium pot, with a BRS3000. I was using less than an ounce a day to boil approx 8 cups of water. Those are really rough estimates. On a 9 day trip, used about 7.8 ounces of fuel. Water was at air temp, or a bit cooler. Not the lightest set up, but it is fuel efficient.

  13. #13

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    Quote Originally Posted by PennyPincher View Post
    I have tested 2 stoves and 2 pots. Returned the new stove and pot as I didn't like the pot and the stove wasn't any more efficient in time or fuel used to boil my water. SO I have a snowpeak 900(?) and a BRS-3000T that actually outperformed the snowpeak giga stove and halulite(?) minimalist pot.

    But I'm trying to improve my boil times and fuel efficiency. generally takes 7-9g fuel per boil depending on conditions. Trying to make my own reflector/windscreen to improve it. I had one "cludged up" that took only 5g fuel to boil. Haven't repeated that though. I need to check my pictures and see if I can figure out what I actually did LOL.
    yes I agree, 7-9 gr/16oz boil is more accurate but 10gr is a safety factor that takes into account temperature and wind losses, and the probability that I might want an extra cup of coffee or cocoa, or to loan someone who ran out, or even possibly that I spill my pot and have to start over.

    in theory it works great, but I always recognize that and mentally adjust - sort of like setting your clock a few minutes fast so you won't be late. I still haven't run out of fuel using this method though. just divide your canister by 10 and that's the number of full 2 cup boils. and for me, coffee is a full 2 cups...

    the BRS3000t is surprisingly very efficient but not good in even a moderate wind. placing it in a depression or behind a natural windbreak is important for this little stove.

    be careful your windscreen doesn't trap or reflect heat into the canister. it would be bad if it overheated...

  14. #14

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    Quote Originally Posted by PennyPincher View Post
    I have tested 2 stoves and 2 pots. Returned the new stove and pot as I didn't like the pot and the stove wasn't any more efficient in time or fuel used to boil my water. SO I have a snowpeak 900(?) and a BRS-3000T that actually outperformed the snowpeak giga stove and halulite(?) minimalist pot.

    But I'm trying to improve my boil times and fuel efficiency. generally takes 7-9g fuel per boil depending on conditions. Trying to make my own reflector/windscreen to improve it. I had one "cludged up" that took only 5g fuel to boil. Haven't repeated that though. I need to check my pictures and see if I can figure out what I actually did LOL.
    yes I agree, 7-9 gr/16oz boil is more accurate but 10gr is a safety factor that takes into account temperature and wind losses, and the probability that I might want an extra cup of coffee or cocoa, or to loan someone who ran out, or even possibly that I spill my pot and have to start over.

    in theory it works great, but I always recognize that and mentally adjust - sort of like setting your clock a few minutes fast so you won't be late. I still haven't run out of fuel using this method though. just divide your canister by 10 and that's the number of full 2 cup boils. and for me, coffee is a full 2 cups...

    the BRS3000t is surprisingly very efficient but not good in even a moderate wind. placing it in a depression or behind a natural windbreak is important for this little stove.

    be careful your windscreen doesn't trap or reflect heat into the canister. it would be bad if it overheated...

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    I've observed that wind can have a major impact (at least on mine anyway.) Normally I can boil enough water for my dinner in 2-3 minutes but I was out a few weeks ago in pre-storm weather and it took 20 minutes to do the same job. I used more than 1/2 a can of gas for one meal. I went home and made a wind screen after that trip

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    Registered User colorado_rob's Avatar
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    Quote Originally Posted by PennyPincher View Post
    I have tested 2 stoves and 2 pots. Returned the new stove and pot as I didn't like the pot and the stove wasn't any more efficient in time or fuel used to boil my water. SO I have a snowpeak 900(?) and a BRS-3000T that actually outperformed the snowpeak giga stove and halulite(?) minimalist pot.

    But I'm trying to improve my boil times and fuel efficiency. generally takes 7-9g fuel per boil depending on conditions. Trying to make my own reflector/windscreen to improve it. I had one "cludged up" that took only 5g fuel to boil. Haven't repeated that though. I need to check my pictures and see if I can figure out what I actually did LOL.
    I did extensive testing years ago, and yeah, 5 grams for 2 cups is about right for an average for a decent stove. I can get as low as ~4 grams on my jetboil in perfect conditions, my pocket rocket was closer to 6, sometimes 7 (this is all with a half+ filled canister, ~50 degree water, brought just to a boil then shut off). The jetboil doesn't seem to be bothered at all by wind, obviously (to me) because the heat exchanger encloses and protects the flame.

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    Quote Originally Posted by egilbe View Post
    I use my Caldera cone on a 1.4 liter Snow Peak titanium pot, with a BRS3000. I was using less than an ounce a day to boil approx 8 cups of water. Those are really rough estimates. On a 9 day trip, used about 7.8 ounces of fuel. Water was at air temp, or a bit cooler. Not the lightest set up, but it is fuel efficient.
    Interesting, does the pot rest on the cone's top edge? Any issues with the canister being exposed to high temperatures/

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    Registered User egilbe's Avatar
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    Quote Originally Posted by Hosh View Post
    Interesting, does the pot rest on the cone's top edge? Any issues with the canister being exposed to high temperatures/
    Pot rests on the cones top edge. Bottom of the cone is even with the top of the canister. Put the heat low and it takes about 10 minutes to boil 4 cups of water.

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    You should consider looking at stoves with fuel regulators if you're interested in fuel efficiency. The MSR Reactor, as well as the MSR windburner use a regulator and run at very low pressure. The upside is that you get consistent performance even out of the last dregs of fuel the canister. Even in very cold weather. If the fuel can vaporize at all, then the stove will work well. Add to this the fact that the Reactor and Windburner are impervious to wind (boil water FAST in gale force winds where you'd be hard pressed to get other stoves to boil at all) and the fastest stoves on the market and it's a killer combination.

  20. #20

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    Quote Originally Posted by colorado_rob View Post
    I did extensive testing years ago, and yeah, 5 grams for 2 cups is about right for an average for a decent stove. I can get as low as ~4 grams on my jetboil in perfect conditions, my pocket rocket was closer to 6, sometimes 7 (this is all with a half+ filled canister, ~50 degree water, brought just to a boil then shut off). The jetboil doesn't seem to be bothered at all by wind, obviously (to me) because the heat exchanger encloses and protects the flame.
    is that a rolling boil, or when a string of bubbles starts to leave the bottom, or just when the pot start to make noise?

    I'd check those times again. not saying you didn't, but that's not consistent with most people's results who wait for a full rolling boil. Jetboil and other heat-exchanger stoves excepted...

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