how cold can you use a liquid feed canister stove?

Jim is probably right about the effect of altitude: I suspect he has been checking the Pressure/Temperature charts.

But I keep saying that what matters is not the ambient temperature but the temperature of the canister. If the canister travels in your pack next to your water bottle – which does not freeze due to body warmth, then the canister is going to be quite 'warm'. If you keep your canister warm overnight in your SB/quilt, then it will still be 'warm' in the morning.

In short, what matters is not what the ambient temperature is, but rather how smart you are at handling the conditions.

Cheers

In short, what matters is not what the ambient temperature is, but rather how smart you are at handling the conditions.

Very well put — and very much in line with ultralight philosophy.

I’ve actually been proposing a four step, pragmatic approach on my blog. In summary:
1. Choose good fuel (isobutane not n-butane).
2. Start with a warm canister.
3. Keep the canister warm.
4. Heat the canister if needed.

HJ
Adventures in Stoving
Hikin Jim’s Blog

OK
but where do I go wrong ?
Assume:
100% n-butane with boiling point of ± -0,5°C at sea level.
air pressure at 3000 feet (if you got 1013 mbar at sea level): 906 mbar
So to get enough pressure in the canister at that altitude, you have to start from that 906 mbar (+ add some extra pressure to get the stove working) which 100% reaches at -3,4°C (?).

Now, then taking the MSR Isopro-blend at 2000m where the air-pressure would then be ±795 mbar. You get that for that blend at ± -29°C if my calculations are wright. But are they ?

BTW, a simple explanation of what is boiling would be a handy addition to the article on canisters and cold, I think. I always learned that that is the point where the internal pressure of the liquid is equal to the air pressure. Just an idea.

I’m running out the door, so I only have time for a short answer right now. Part of the issue is that not only does one have to be above the boiling point of the fuel for the fuel to vaporize, but one has to be quite a bit above for there to be sufficient pressure to run the stove.

But it’s not just the boiling point. Being, say 10C above the boiling point in 5C ambient temperatures will not give you the same pressure as being 10C above the much lower due to elevation boiling point at -5C ambient. The pressure is not just a function of the boiling point.

Is that helpful?

HJ
Adventures in Stoving
Hikin Jim’s Blog

Perhaps.
Here's what I understand:
at every altitude, a stove needs a certain pressure to work. That pressure depends on the altide thus P = f(A).
Now part of that pressure comes from the vapor pressure of the fuel, but for the stove to work, there's an added pressure needed. At that altitude, that added pressure can't vary and because the fuel pressure can in function of the temperature, you would get something like this: at altitude X the pressute needed Pn = Padded (= constant) + Pfuel (= variable in f(T)).
Am I on the wright track ?

Woubeir, consider modifying you last equation and adding a new one:

1)Pn = Padded (= constant) + Patmos(= variable in altitude).

2) Pcanister = f(Temp_canister, fuel composition). Internal pressure is a function of both fuel temperature and composition.

Also note for upright canister use with a mixture of fuels:
fuel comp = f(%total fuel remaking). As the fuel is burned the most volatile fuel approaches 0% of total and the mixtures' boiling point approaches that of the least volatile fuel.

When 1 > 2 youre stove won't work (internal pressure too low)

When 1 < 2 the stove works fine.

James,

That’s pretty good. The pressure you need (Pn) is the atmospheric pressure plus some additional pressure, a constant, over and above atmospheric pressure.

The pressure in the canister (Pcan) is a function of fuel composition and temperature and PCan needs to be >= Pn in order for your stove to run well.

Now, that’s all very well and fine, but how does that work in practice in the field? Well, if you open your valve fully and your flame is weak, then obviously Pcan is too low. How do you boost Pcan? You heat the canister.

Therefore my four step approach:
1. Select good fuel.
2. Start with a warm canister.
3. Keep the canister warm.
4. Heat the canister if needed.

There is knowledge to be employed at each of the steps. Hence my article: Gas Stoves: How Cold Can I Go? The title is a bit rhetorical in that you can go as cold as you want so long as you can perform step four such that Pcan >= Pn.

Now, what is that constant amount of pressure that is over and above atmospheric pressure that we need to run a stove reasonably well? In practice, somewhere between 5 psig and 10 psig, seems to work fairly well, in other words somewhere in between 5 and 10 psi above atmospheric pressure. I’m working on a blog post on this very subject.

HJ
Adventures in Stoving
Hikin Jim’s Blog

In the old, old days of butane canister stoves, we had never even heard of butane blend, so the cold weather performance was particularly bad. A hanging stove inside a tent leaves the bottom of the canister wide open, so that was the target for a candle flame. The most junior person of the tent group would have to sleep in the center, so they got elected to hold the candle. That also means that anything wet that slopped out of the cook pot landed on their sleeping bag. However, you can hold a candle flame burning right onto the canister bottom for quite a few seconds before anything explodes. We wouldn't let the metal get anywhere close to "hot." But just raising the bottom surface to 80*F in a spot may get the butane contents well into the operational range. Avoid the seams for that extra heat.

–B.G.–

Bob, YEP…..we were risk takers back then were we not!

"1)Pn = Padded (= constant) + Patmos(= variable in altitude).

2) Pcanister = f(Temp_canister, fuel composition). Internal pressure is a function of both fuel temperature and composition.

…

When 1 > 2 youre stove won't work (internal pressure too low)

When 1 < 2 the stove works fine."

"Now, what is that constant amount of pressure that is over and above atmospheric pressure that we need to run a stove reasonably well? In practice, somewhere between 5 psig and 10 psig, seems to work fairly well, in other words somewhere in between 5 and 10 psi above atmospheric pressure. I'm working on a blog post on this very subject."

Looking forward to that blogpost. En explain what Padded is en why it's necessary and why Pn can't be simply equal to Patmos ?

explain what Padded is en why it’s necessary and why Pn can’t be simply equal to Patmos ?

If the pressure inside the canister = the pressure outside the canister, then there won’t be any flow. The pressure has to be higher in one or the other for there to be flow. The gas will flow from the higher pressure to the lower pressure.

Try this at home: Take a deflated balloon. Now there’s a little bit of air in even a deflated balloon, but is there any flow? No. Now inflate the balloon. The elastic walls of the balloon press in on the air inside the inflated balloon, creating what we call pressure. What we really mean of course is relative pressure, that is that there is relatively more pressure inside the balloon than outside. If we poke a hole in the wall of the balloon, air will rush out until… until the pressures are equal. Once the pressures are equal, flow will stop.

Likewise with a canister of gas, gas will rush out if you open the valve if there is relatively more pressure inside the canister than outside.

Notice that I often quote pressures in terms if psig not just psi. Psig means gauge pressure, not absolute. Gauge pressure is the pressure relative to the surrounding atmosphere. If I have a reading of 25 psig, that means that there is 25 more pounds per square inch of pressure relative to the surrounding atmosphere. Air pressure at sea level is I believe about 14.7 psi. A reading of 25 psig means that my total pressure is 39.7 psi (25 + 14.7 = 39.7).

If a canister has 39.7 total pressure (usually called absolute pressure or psia) and the atmosphere has only 14.7 psia, then there will be flow from the high pressure (39.7 psia) to the low pressure (14.7 psia).

The “pad” in this case would be 25 — the difference in psia between the canister pressure and the atmospheric pressure. At 25 psig, your stove will perform well indeed. Your stove will continue to perform reasonably well at 10 psi above atmospheric (10 psig). At 5 psig, your stove’s performance will have fallen off noticeably. Below 5 psig, your stove’s performance will be very weak.

It is typically the difference in pressure that we measure with a gauge. Example: A tire on a bicycle. It is the difference that causes air to flow out of a bicycle tire when we get a puncture. Therefore on a canister of gas, there must be a difference between the inside of the canister and the atmospheric pressure outside. If they were equal, there would be no flow.

HJ
Adventures in Stoving
Hikin Jim’s Blog

After I posted, I read your blogpost 'Gas Stoves: How Cold Can I Go?' and I had something like 'of course' and 'why didn't I think of that ?'. So simple. :-)

Oh, OK, good. Always happy to hear that I actually enlightened rather than obscured. Sometimes I wonder. :)

HJ
Adventures in Stoving
Hikin Jim’s Blog

Please don't wonder. Your first post on this thread is going in the scrapbook for future reference along with many of Roger's. Thanks.

@Jim
is that 10 psig more or less of a recommended upper-limit and why ?
I can think of few reasons but those are also rather easily taken care off.

The pressure in the canister has to be greater than atmospheric in order to force enough gas through the stove jet to produce a reasonable size of flame. I reckon you need about 0.5 Bar (7 psig) as a minimum (as an aside, thats what you get when the gas mixture is 10C above its boiling point). When the pressure is less than that the flame is tiny. If the pressure is greater then that then thats when you use the needle valve to control the flow.

Stuart,
just my idea and if the pressure is so high that e.g. it blows out the flame with which I want to lit the stove, then I just use the valve to lower the pressure till I can. But I thought there was perhaps another reason ?

If the canister pressure is high, use the needle valve to reduce the gas flow so that the stove can be lit.

"I thought there was perhaps another reason" – for what?

Well,
because HJ said something about between 5 and 10 Psig. And in bed I thought: why 10 and why not higher ? Did I forget something ?

Woubeir,

My saying “something between 5 and 10 psig” was intended to describe the lowest canister pressure where your stove would work well. This is based on some experiments an acquaintance of mine did. I’m working on a post on that subject, but it will have to wait until after Christmas.

I don’t know what the upper limit is although I do know that canisters, per EN417 standards, must be able to withstand the internal pressure that occurs when the canister temperature is 50°C (122°F). Needless to say, you won’t be needing to heat your canister at 50°C! Roger Caffin did an experiment to see where a canister would burst. As I recall, it burst at 100°C (212°F), however, I would not ever want to let a canister get hotter than 50°C. There are no guarantees above 50°C. And there’s no reason to want the canister hotter than 50°C. Your canister pressure at 50°C, so long as there is still liquefied gas present inside the canister, will be very high. In fact you probably wouldn’t want to open the valve fully.

HJ
Adventures in Stoving
Hikin Jim’s Blog

I reckon you need about 0.5 Bar (7 psig) as a minimum (as an aside, thats what you get when the gas mixture is 10C above its boiling point). When the pressure is less than that the flame is tiny. If the pressure is greater then that then thats when you use the needle valve to control the flow.

I like that number (~0.5 Bar). Canister pressure of 500 mBar sounds a lot more like an estimate. 7 psig sounds like some exact figure which it is not intended to be.

Canister pressure of about 500 mBar should be sufficient to run a canister stove well. Below 500 mBar you will most likely experience a noticeable fall off in performance (i.e. a weak flame). Above 500 mBar, you’ll have increasingly good pressure, pressure that you will want to control via the valve on your stove.

HJ

Adventures in Stoving
Hikin Jim’s Blog

aaaahhhh, that makes sense.

"Roger Caffin did an experiment to see where a canister would burst. As I recall, it burst at 100°C (212°F)"

I am surprised it was that low. I am use to seeing 3x the max working pressure. Definitely need to me very careful when warming a canister!

Well, if I remember well, the advise was to let a canister never becoming so hot that you couldn't touch it anymore with your hands without burning them.

122 F/50 C is not so hot you can't touch it – just "warm" or "hot"

another thing is where you touch it. If the top of the canister that is facing the burner, but there's not fuel there, it will get warmer. Even warmer than 122 F. I think this is okay. You have to touch the canister below where the level of fuel is, or towards the bottom.