which backpacking stove to use

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longri
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Re: which backpacking stove to use

Post by longri » Fri May 17, 2013 8:20 am

The amount of water you heat can affect efficiency. In a cold and windy environment time means heat loss, so the faster you can heat something up the lower the loss and heating a large amount of water is less efficient. Of course you're doing this indoors, presumably. And with a 4 qt. pot you have a larger diameter bottom to catch the flames which favors efficiency.

I think the numbers are confusing because there is a lower and higher value for the heat of combustion. The higher heating value (HHV) is the energy released when the fuel is burned. The lower heating value (LHV) takes into account that some of this energy is used to vaporize the water that is produced during combustion. So the HHV is the energy available to heat your pot only if you first recondense the water vapor combustion product. In practice you can't do this so it's lost energy and the LHV more accurately represents what you have to work with.

The higher heating value (HHV) is about about 50 kJ/g for propane and 49 kJ/g for isobutane. The LHV for propane is about 46 kJ/g and for 45 kg/g for isobutane. For white gas (naphtha) the HHV and LHV are about 48 kJ/g and 45 kJ/g. For whatever reason, I think the HHV for propane/butane usually gets quoted whereas it's the LHV for white gas that gets mentioned.

Assuming I haven't botched this analysis (I'm not a chemist) this would mean that the fuels are very similar in how much energy per gram they provide.

For comparison, ethanol and methanol, which many people burn in stoves, have LHVs and HHVs of about 27 and 30 kJ/g (ethanol) and 20 and 23 kJ/g (methanol). I wouldn't want to go Alaska for a month with a Trangia or a pepsi can stove either!








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markskor
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Re: which backpacking stove to use

Post by markskor » Fri May 17, 2013 9:40 am

longri wrote:Assuming I haven't botched this analysis (I'm not a chemist) this would mean that the fuels are very similar in how much energy per gram they provide.
Have seen all sorts of numbers thrown out, comparing white gas to canister mixes - and this LHV figure, if accurate (and however computed?) seems to confirm that both types compare, about equal energy per gram. Nice work - (if not a chemist, sounds like you stayed at a Holiday Inn...).

Interesting that those here who carry / carried an older MSR XG or similar (Svea 123, Optimus?), always knew that they worked well. Heck, mine wouldn’t die…still love that XG.
If it wasn’t for the tendency to occasionally flare up big time, or the time my whisperlite went chronic flame-thrower (left it Tuolumne - atop a bear locker…gone 10 min later…sucker), or the time the Sigg bottle spilled down inside of my pack…or the white gas stink on gear…or the weight. Gonna miss that comforting jet-like roar too and all the fiddling needed to get it to simmer…yeah right.

My steadfast love for that stove probably kept me from going canister much earlier – just plain stubborn, after all this was the stove of mountaineers.

As a solo, then carried one of those Hank Robert canisters – small and light – weird design and many a hiking buddy looked down on this (received the ol’ stink eye) as a viable stove back then. Design improvement was needed for longer trips but once canister indoctrinated…just easier… Now carry a remote canister.
Mountainman who swims with trout

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Scouter9
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Re: which backpacking stove to use

Post by Scouter9 » Fri May 17, 2013 11:10 am

Ha ha ha!!! I kept (happily) using my XGK for years, for very similar reasons. It worked, it worked pretty darn well and "it's what mountaineers use". :nod: That collection of Nat Geo's featuring the Himalayas was prominent on my bookshelf for a long, long time...

As I mentioned way up above, it was the realization that my whole kit would weigh less than the XGK's stovehead that pushed me into trying these new-fangled cansister stoves and to discover they aren't all Bluet clones. Sprinkle in a dash of Chinese titanium and it's a sure thing the XGK will remain relegated to display, demonstration and "actual" snow-camping/backpacking.

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longri
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Re: which backpacking stove to use

Post by longri » Fri May 17, 2013 2:53 pm

Holiday Inn? Sorry, that one went past me. I just looked the numbers up on the internet. But I have a copy of Perry, Chemical Eng. Handbook, and it says:

isobutane (gas) -> H20 (liq) and CO2 (gas) is 21,242 Btu/lb = 49.4 kJ/g
isobutane (gas) -> H2O (gas) and (CO2 (Gas) is 19,614 Btu/lb = 45.6 kJ/g
isobutane (liq) -> H2O (liq) and CO2 (gas) is 21,096 Btu/lb = 49.1 kJ/g
isobutane (liq) -> H2O (gas) and CO2 (gas) is 19,468 Btu/lb = 45.3 kJ/g

There was no entry in the table for naphtha but all of the hydrocarbons in the table from n-butane (4 carbons) down to n-Eicosane (26 carbons) were within a few percent. So it seems unlikely that naphtha would be 15% less.

The first two numbers above correspond to the HHV and LHV if the fuel is already vaporized. If you need to use energy from the combustion to vaporize the fuel before it is burned (like you do in the winter with a canister stove) then the bottom number is more applicable. With a white gas stove you are always using heat from the combustion to vaporize the fuel, so there is a very small penalty for that. In the summer, canister fuel will vaporize due to heat from the environment.

So why is Paul's liquid stove less efficient? Any ideas?

(edit to fix typo)
Last edited by longri on Fri May 17, 2013 2:57 pm, edited 1 time in total.

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longri
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Re: which backpacking stove to use

Post by longri » Fri May 17, 2013 2:56 pm

The reason I switched to using canister stoves about 15 years ago was because my XGK failed me a number of times in the field. I got tired of trying to repair it over and over and finally just said the hell with it. Then I discovered that canister stoves had all of these nice advantages I hadn't fully appreciated previously. I virtually never use a white gas stove anymore.

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Re: which backpacking stove to use

Post by dsundrwd » Sat Jun 01, 2013 6:51 pm

My Kovea Spider arrived today. Sooner than expected. Originally I was told between June 4th & June 20th. It is definitely smaller & more compact than the MSR Dragonfly I've used since '98. Just holding them in each hand I can't say that it is too much lighter but it is much smaller. I fired it up & it seems to work as a previous poster said. It appears to be a very well built stove. Now if SHig gets his float tubes into production I may be able to cut down some real weight.

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