MYOG – A Winter Canister Stove using your Summer Upright Stove and the Brunton Stove Stand

Hi Steve

> As in wrapping the canister with sleeping pad material and covering the "bowl" with the water in it with a piece of silnylon or something?

Anything like that. A 'cozy' covering the top and sides and made from bubble wrap would probably do. Just stop that evaporation!

I gave Sue some luke-warm water one morning in the snow so she could wash our plastic breakfast bowls out. She rinsed them clean, put them down wet and went looking for our mini-teatowel to dry them. By the time she had found it, the water left in the bowls had frozen! All she had to do was tap the plastic bowls so the ice fell out, and they were dry. Thus evaporation heat loss!

Another way of handling the problem is to leave the windshield around the stove open for a few inches and to position the canister near the opening in the windshield, so it gets a bit of the hot air and radiation from the stove. Needless to say, with this trick you MUST sit there and monitor the temperature of the canister. Luke warm is what you want; hot is absolutely NOT.

How much hot water, replaced how often? Depends very much on the conditions (and any evaporation loss). The key thing to remember here is that there are huge differences between using an upright and an inverted canister, thus:
* With an upright the gas is boiling inside the canister and the energy for this comes from the canister – so it chills down fast. You have to keep pumping in more energy or the canister will chill too far to boil.
* With an inverted canister there is almost no evaporation at all inside the canister: it happens at the stove using heat from the flame. So the canister does not chill down quickly. Get it warm and it will stay warm, barring external heat loss.

Cheers

Inverted Canister Stove – 01/04/2006

Inverted Canister Stove

Hi Brad

Replied on other thread. Yes, quite different fuel delivery systems.
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=16401&disable_pagination=1

You are right about the confusing use of 'boiling' and 'evaporation'. I use 'boiling' to mean that lots of vapour is coming off, as in an upright stove or water boiling in a pot. With an inverted canister there is a high internal pressure from the gases, but the vapour at the top of the canister does not escape. I used 'evaporation' for the process of creating the pressure: it is similar to pumping a WG fuel tank.

Cheers

I put everything together, and am having a few problems. I am using an MSR PocketRocket, but that shouldn't matter. My block parts and fin were made of brass, the screw was steel. The blocks were made it out of one piece of brass and drilled the holes before cutting it in half. The rod I put inside the brass tube was about 1.8 or 1.9 mm. There is a slight gap between the blocks (more so on the top). I was using Snow Peak canisters, and all of my testing was done in temps in the mid to low 20s (F). I did however, throw the canisters in the freezer to cool them and better simulate winter conditions before the testing began. Each test lasted about 10 minutes.

I cannot get the gas to vaporize properly. When the canister is upside down, I get a continuous fireball, even on very low power. Even after the stove heats up and the upright fin appears to be warm, but it does not appear to be vaporizing the gas.

To try to correct this, I added some thermal compound between the blocks and between the fin and one of the blocks in an effort to increase heat transfer. This did not work, and the stove never settled down.

Also, I can settle the flame be leaning the canister slightly while upside down. I am using mostly-empty canisters. However, as soon as I tip the canister fully upside-down, the stove fireballs again.

As I see it, I can cut a new blocks and hope for a better fit and/or make the fin out of copper to increase heat transfer. I also think I should add a thicker rod inside the brass tube to decrease gas flow.

Any suggestions?

Hi Matt

> When the canister is upside down, I get a continuous fireball, even on very low power.
> Even after the stove heats up and the upright fin appears to be warm, but it does not appear to be vaporizing the gas.
> My block parts and fin were made of brass

I have had this problem myself too. I found that the brass strip I had installed was simply not conductive enough. I swapped over to a copper strip (lying on the bench …) and the arrangement worked fine.
Have a look at this page
http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html
You will see that the thermal conductivities of relevant metals are:
Brass 109 W/(m.K)
Aluminium 255
Copper 400

Brass is only 1/4 as conductive as copper. So while using brass for the solid block is OK, you have to use copper for the fin. You could try thick aluminium if you like (1/16" maybe) but there is always the risk of melting it.
You could also try a hard Al alloy for the block if you have some.

> I also think I should add a thicker rod inside the brass tube to decrease gas flow.
Secondary imho.

Cheers
Roger

tbeasley wrote:

>Ti is an amazing material that solves many problems; weight, strength, corrosiveness, durability, heat weakening. But poor heat conductivity makes it a poor choice for a cooking pot. Thin aluminum pots easily outperform Ti pots when you weigh in the extra time and fuel consumed

I thought the same before I did some tests, I could not make Al pots perform better than my Ti pot, this was true with alcohol and canister gas. Below is a graph of my results and the points are boiling time for different flame settings. SS even performed better than Al.

Tony

Pot Efficiencr graph

If the graph came through, the small study shows that if you want minimum fuel consumption, use of a four minute boil or so is much more important than the choice of pot material — at least between Stainless Steel, Aluminum and Titanium.

This conclusion probably doesn't encompass the inclusion of heat exchanger devices attached between the burner flame and the pot. It makes sense that heat exchangers would increase the efficiency, and someone (JetBoil)has probably done tests to demonstrate this.

If you're in the sleeping bag with the canister it would keep it warm and maintain fuel pressure. I don't know how much the vapor would cool in its path through the long hose, however. I also don't konw how much fuel you'd lose in a long hose, between uses.

In an unoccupied sleeping bag the effect would eventually be the opposite, as the bag would insulate it while it naturally cooled and it would freeze up. You'd be better off stuffing it into your jacket.

> I don't know how much the vapor would cool in its path through the long hose, however.
Actually, the temperature of the hose does not matter at all. As long as there is pressure in the canister to drive the gas out of the jet, that is enough.

> I also don't konw how much fuel you'd lose in a long hose, between uses.
Yeah, a problem in principle, but most hoses are actually filled up with something to reduce the volume down to a reasonable level. Think of the heavy SS cable in the big fuel lines of some MSR white gas stoves. The effect is there, but it is not quite that great.

Cheers

I LOVE IT!

May I ask for permission to use this photo (somewhere, with acknowledgement), PLEASE!

Now to the question of why this works. Several steps.

The MSR red canister contains iso-butane, which has a boiling point of (roughly) -11 C, and propane, with a boiling point of about -42 C. This canister will work to about -24 C in liquid feed mode.

In the photo the stove is chugging along happily while the canister is embedded in ICE! I am going to guess that you froze the lot in an ice-cream tub in the freezer? So what temperature is the ice at in the photo? My guess is that it might be somewhere between 0 C and -4 C, what with the warmth of the sun etc. Note: this is well above the boiling point of iso-butane!

Finally, let's look at what the block of ice is doing. It is in GOOD thermal contact with the canister. The fuel inside is boiling away and would be cooling down, except that the huge mass of ice is busy pumping energy into the canister. I would guess that the stove is burning both propane and iso-butane (but I am not sure at what ratio).

This is (one reason) why MSR puts iso-butane rather than n-butane in this canister: it will function at temperatures slightly below freezing, and for many walkers that is as cold as they get. The downside is that the canisters are dearer than commodity 70% n-butane ones. Well, you pay your money and take your choice.

Cheers

Over-arching question – how will using the stove stand affect stove efficiency i.e. how will it affect the amount of fuel used per pint of water boiled/snow melted?

Testing of the PocketRocket, and other can stoves, was done by BPL in this thread: http://www.backpackinglight.com/cgi-bin/backpackinglight/lightweight_canister_stoves_test_report.html. Note that the gas cans and the stove were cooled to 10F before testing. The curious thing about this is that the PR was run at max flame, but fuel consumption decreased because the stove was running at a slower pace. "Under cold conditions (column 4), fuel consumption decreased because the stoves burned more slowly (equivalent to a moderate flame), even though they were set at full throttle." (under Table 2). Given that, is it advisable to run the stove at full throttle? If so, at what temps?

Second: If isobutane has a boiling point of 10F, do I need to turn the canister upside when temps are above 10F? In testing in approximately 30 degree weather, the flame increased dramatically when I turned the canister right-side up.

Third: Also, how does temperature and canister position affect which fuel (isobutane or propane) is burned?

Thanks as always.

> fuel consumption decreased because the stove was running at a slower pace
Absolutely. Running a stove flat out wastes a whole lot of heat up the side of the pot. Running it at about half power is far more efficient and heats the water almost as fast. I never run my stoves flat out, under any conditions (except for lab stove testing!).

Here's what I don't get. On the testing, a PR in cold conditions at full flame used less gas to bring 1 qt of water to a boil than a PR in optimal conditions at moderate flame did. Can you explain?

I assume I would save even more fuel if I operated the stove in cold conditions at a moderate flame.

I'm going to go test things out tonight in about 10F and report back.

i took a pocket rocket apart and found that the threads in the bottom of the mixing tube are the same as the threads on the brunton stove stand. i took the jet out of the PR valve and mounted it in the brunton base, and mounted the PR directly on the base. a spacer was required to get the proper hieght. then i got rid of the brunton legs and built a new set out of aluminum. it turned out to be a nice little stove.

Daren….