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Thread: FUEL EFFICIENCY TO WEIGHT

  1. #1
    I have just spent a cold wet week with a top seated gas stove with no preheat and it DID NOT , boil 25L plus of water off a 240ml 220g net/370g gross cartridge , probably it would have boiled 10l if I had been careful . Had a multifuel and from a 500ml 350g net/450g gross white gas fuel bottle that is about the same size as the cannister , in the same conditions I achieved 14 litres of water , again probably more if I had been careful. So its a little more efficient than a heavy , cannister seated efficient cannister stove, two extra boils over all, or 80 grammes the extra weight of the multifuel. (BY BOILS I MEAN SINGLE USES INCLUDING SUSTAINED SIMMERING, AND LITRES I MEAN LITRE-ISH PANS FULL!OR USES) wondered if anyone else had the same sort of efficiency results to weight or any better performance .


    p.s. I know pocket rocket equivalents are crap and useless !

  2. #2
    Super Moderator captain paranoia's Avatar
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    > it DID NOT , boil 25L plus of water off a 240ml 220g net/370g gross cartridge , probably it would have boiled 10l if I had been careful

    I am hardly surprised, and not sure where you got the 25l figure from.

    My experience is that it needs about 8g of gas to boil 500ml of water, using a simple pan. So, your 220g of gas would boil 0.5*220/8 litres of water, or about 14l.

    If we look at the energy content of 220g of, let's say, propane, we'll find that it's 52.5kJ/g, giving us 11550kJ, or 11.55MJ.

    Now let's look at how much energy we need to boil water. Starting at 10C, and raising to 100C, we need 4.2J/gK, so, for a litre, that's 4.2*1000*(100-10)J = 378kJ.

    So, at 100% efficiency, we'd expect to be able to boil 30.55l.

    That means that you're expecting your stove to be 25/30.55 efficient, i.e. 82%. Which is asking a lot. My experience of 8g per 500ml gives about 45%.

    You've not stated how you used the stove; far too many users follow the 'speed is good' philosophy so beloved of gear testers (they have no choice as it's the only measure they can easily make), and whack the thing up to 11, which means that most of the heat is wasted up the side of the pan. A much more efficient approach is to use a moderate flame, and take a bit longer.

    Liquid fuels generally have a similar energy density to the gases, so there's not much to choose between them from that PoV.

  3. #3
    Super Moderator captain paranoia's Avatar
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    > One thing that CP hasnt mentioned is loss of heat energy to ambient - as the pot and water got hotter, losses to ambient increase

    Indeed, and another good reason to use a reflective windshield; it does more than shield the wind.

    Tom Beasley on backpackinglight.com has done some interesting experiements with fuel use vs stove setting/boil time, which show that you can crank the stove down really quite low without having too great an effect on fuel use (aka efficiency).

    The other thing I neglected was that I simply brought the water from ambient to 100C. Strictly, this isn't boiling, but it's perfectly good enough for for our purposes.

  4. #4
    Widdler
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    CP= Thats some pretty complex maths, your not Johnny Balls are you?

    PC= I cant back this up by figures, but from experiance with my jetboil I know that as the presure inside the can decreases, the boil time increases, and while the blurb claims 12L per 100g of gas @sea level, I allow 8L, just to give me that extra margin.

  5. #5
    3.5min boil time 1.5 hour burn time ?!?!?!

    Did i just insult the queen ?

    Any way the stove i used did not have a pre heater and was a cannister mount so no inversion ability/ lots of loss of ppressure.

    Has anyone used the primus eta pack light . Supposed to double efficiency . (getting on for 25 boils ........... ha , ha ha ha ha !)

  6. #6
    Mini Goon Lemming's Avatar
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    Background reading.

    Using a multifuel stove (with different jets for the different fuels), I average 9g for a 500ml boil with gas and 11-12 for petrol and kerosene.

  7. #7
    large 21 cm pan with lid

    wind shield.

    Wet

    Soaking rain that killed tukesbury

    7 degrees in the evening and on the morn

    howling gail

    jet boil is crap no canister inversion ( does it pre heat ?)

    elevation 300 m above sea level

    humidity 100%

    and apparently 10l is bad ? I'd like to try it at about 25 degrees centigrade during a dry still summer day with no humidity, maybe a hotel on the costa blanca!

  8. #8
    thats what i mean GOF, i carry a half litre thermos 24 hour flask (350g) because you use alot more fuel doing two 500ml boils than just one 1000ml boil.

    Good flask , still at boiling point after a nights sleep. Worth the weight , hah hah.

  9. #9
    Widdler
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    The ETA is good, cant say about efficentcy, but its comparable to the jetboil in terms of performance.* The ability to turn the can upside down might improve performance/efficentcy but not by much.*

    Have you tried putting the cannister into a shallow pot of hand warm water, or insulating it from the ground with a silicon pot stand(Available from poundland)? or warming it inside a jacket before you use it?

    Also I've had my jetboil for 3 years, and although its starting to get a little rough around the edges it's still a nice little stove that never let me down. Yes I've had damp trips where I've been miserable but I've never had to go without a warm brew soley because of the jetboil.

  10. #10
    i've never used a pre heating inverter , but at half canister volume whenever i've used gas stoves (twenty years man and boy young man) the lack of pressure bites .

    Primus eta pack light is the remote style And they reccon double the efficiency. I realy might ditch the omni fuel

  11. #11
    by the way, i bought a pocket stove ti 58g wood burner, so i hope to use that the majority of the time.

  12. #12

    Syd ;

    it doesnt take long at the conditions listed above to take a toll

    lemmy;

    18g/L from multifuel is very good, which stove as i have a suspicion that the omni is not that good in efficiency.

  13. #13
    Widdler
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    If it bothers you that much why not switch to a more reliable fuel sauce? there is/was a thread similar to this on the bushcraft UK forum, one of the contributers compiled a comparative list of the gas stoves and their performance/fuel efficency, and the different efficentcys of other fuels.

    Anyway, the upshot was that dependent on conditions gas is the best choice for weight/power, but for prolonged trecks you'd probably be better with liquid fuels over gas.

  14. #14
    Mini Goon Lemming's Avatar
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    9g/500ml was with gas and an Omnifuel........

    Regarding the ETA, it is the heat exchanger on the pot and a good windshield that makes the difference - the stove part is the same as the Express Spider.

    But when you compare the additional weight of the pot to the fuel savings it becomes less attractive for anything other than long trips without any resupply.

  15. #15
    is that honest syd???

    Youve got 20 litres from a 220g/370g gross cannister using a jetboil ? What sort of weather etc. Even including the cannister thats about 5 boils extra over the multi fuels 15 for 450g . Or like 66%

    66% is alot

    you see syd most of that info is just schpiel, with no field test, its what i started this thread for , not lots of figures. I would buy a eta pack lite for 100, but i just spent 150 on a omni fuel , i'll do some fair weather testing this summer. Its not that it bothers me but 66% with all the convenience of gas and 2lbs lighter with three fuel cannisters sounds very worth while !

  16. #16
    air pressure 950 milli bars by the way.

  17. #17
    Widdler
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    I agree its worth while, its the reason that I opted for the jetboil in the 1st place.

    I normally use 100g cannisters, but yes I have had 10 liters from one can. Although, like I say I normally allow for 8. I'm Normally in the peak district 2-3 times a week, rain or shine, and its done me upto 636m(pouring rain with biting wind on the top of kinder) and down to -5 deg without any problems.

    Normally I'm at more modest alt but still no problems.

  18. #18
    but thats only 4 to 6 litres, about the same as my Epigas gas stove (now called Coleman) . Swear to god they reccon 80% efficiency , double mine ,

    have thought of buying a heat exchange pot , primus 1.7l only 350g, if theyre that efficient.

    Have also thought of the rose head efficiency of gas stoves, omnifuel still seems crap too . Might buy a primus spider and connect it to the omnifuels pump.

  19. #19
    thing is with gas is it takes more packaging,

    220g of gas plus 150 for the cartridge @ 10l= 37g/l

    multifuel 350g for 0.5l of white spirit plus 100 for the bottle @ 15l = 30g/l but add in 150 for the extra weight of the stove = 40g/l , and thats without the problems of liquid fuel (FOR ALL ONLOOKERS FIGURES FROM BAD CONDITIONS NOT YOUR KITCHEN)

    SYD they do a 1l jetboil cup , try a flask with it. Very convenient too !

  20. #20
    ‹bermensch Montgomery Wick's Avatar
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    Wet

    Soaking rain that killed tukesbury

    7 degrees in the evening and on the morn

    howling gail


    I'd like to meet her, she sounds like my kind of girl

    jet boil is crap no canister inversion ( does it pre heat ?)

    elevation 300 m above sea level


    i bought a pocket stove ti 58g wood burner, so i hope to use that the majority of the time.


    Do you think a wood burner's going to cope better with those conditions? In terms of efficiency, what benefit do you think inverting a cannister in those conditions would have achieved?

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