Isobutene “cold” performance

>SOMEWHERE (!) on BPL there's a thread with a really great photo of a canister frozen into a block of ice burning away merrily (Roger may know where, I know he's also seen it)

Try this page on Rogers Bushwalking.org site

http://www.bushwalking.org.au/FAQ/FAQ_Mixtures.htm

It also has the Pressure/Temperature graphs for all of the canister gasses/mixtures.

Tony

Hi Larry

> my performance problems were due to the LONG run times that dropped the temperature
> of the canister too much.
You got it.

> what the minimum pressure requirements are for a full flame on the "average"
> screw on top canister stove?
I am not sure there is such a *defined* thing! But you should be able to get reasonable performance from most stoves at a relatively low pressure – say just a few degrees above the boiling point of -0.5 C.
Mind you, if the canister is sitting at 40 C (the upper practical limit for safety), most stoves can 'overdrive', which can be a bit risky. Not good stuff.

Cheers

> a really great photo of a canister frozen into a block of ice burning away
Two of them actually:

They are from our article on Stove Maintenance. I think there may be other similar pics somewhere as well.

Cheers

Assuming no radiated heat from the flame to the canister, the canister looses heat as it is used. The drop in pressure causes the drop in temperature. The resultant boiling of the "gas" will eventually require heat to be added to the canister to keep the temperature of the "gas" well enough above the boiling point that it can produce enough pressure to force the gas through the jet with enough force to provide the level of flame desired.

Correct. Good summary.

I think my performance problems were due to the LONG run times

I think you've hit the nail on the head there.

You need to add heat. If you try a wind screen, as Roger says, keep checking your canister's temperature with your hand. If the canister feels hot, take corrective action. If it feels really really hot, I hope you're a fast runner. ;)

If you have a remote canister (where the canister is connected to the stove by a hose and not directly screwed into the canister), you can invert the canister if and only if you have a pre-heating tube. Of course you'll need some method of propping the canister so it remains upside down.

> I have struggled to get my stove to work in temps below -20*C (0*F). I bought the Coleman Xtreme last year and still have problems.

From Roger’s website:

A variation on the conventional gas stove treats the liquefied gas as a liquid fuel – like petrol or kero. The gas canister is arranged so the gas pressure from the propane forces the liquid fuel into the stove, where it is heated in a preheat tube and burns normally. This is identical to a petrol or kero stove, except that most of those rely on pumped pressure to drive fuel to the stove. Since propane boils (and pressurises) at -42.1 C, this sort of stove can be run down to below -20 C (the limit is about -26 C). This is colder than most anywhere in Australia. Why can’t it work down to -40 C? This is discussed in the page on Gas Mixtures.

It sounds like temps below -20C are approaching the limits of the design of and type of the stove. The Xtreme’s a good stove, but it too has it’s limits. Try some of the tricks like warming it while you sleep and a pan of water, but even then the Xtreme will have a lower limit. Might be time to try a white gas (Coleman type fuel) stove…

The Coleman Xtreme stove … is regarded by some as the finest winter/snow canister stove on the market – the Gold Standard. (Updated in 2008: the Xtreme is no longer produced… the second hand prices on eBay for the Xtreme are rising …)

The prices are indeed rising. On eBay they sell for about US$45 – 50 dollars. A stove clearly marked as defective recently sold for US$35! I bid US$50.00 for an Xtreme stove on eBay yesterday, and I lost. People clearly know about these stoves.

"But you should be able to get reasonable performance from most stoves at a relatively low pressure – say just a few degrees above the boiling point of -0.5 C."

Thanks Roger, that seems to agree with my observations. I'll bet when I had problems my canister hadn't warmed up much past 40*F (4*C). It doesn't take that much to get down to -0.5*C.

The performance jumped up quickly when placed on a warm rock by the fire.

And thanks everyone. I've got some really good ideas now. And the theory is fun too. :-)

P.S. I'll have to tell my brother to take care of his Coleman Xtreme. ;-)

This is my own page on cold performance for 30/70 propane/n-butane on a normal upright canister stove here
This clearly shows how pressure rapidly drops as the gas is used. As mentioned before, evaporative cooling will reduce the canister temperature further when it is used for longer times. Sometime soon I will get around to working out the numbers for a n-butane/i-butane/propane mix