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Thursday, December 22, 2011

Priming Alcohol Stoves

"Priming" is a good technique to know about for alcohol stove users.

What is Priming?
Priming is a sort of a heat before the heat.  Basically, when you "prime" an alcohol stove, you heat the stove so that the stove will be at normal operating temperature and function properly.

Take a look at this stove.  This is a closed jet (pressurized) type alcohol stove.
A closed jet type alcohol stove.
Notice that flames are coming out of the "jets" around the rim of the stove.  Pressure inside the stove causes vaporized alcohol to stream out of the jets .  What pressurizes the stove internally?  Heat.  If you heat alcohol, it vaporizes, and that vapor pressurizes the stove.  In order for this stove to work properly, the alcohol has to be hot enough to vaporize.  How do you get the alcohol hot?  You prime the stove.

Generally the most effective way to heat the alcohol inside a stove is to light a fire underneath it.  Here's another closed jet stove.  Notice the small pan I've placed underneath the stove.  Do you see the blue flames coming out of the pan under the stove?  I'm priming the stove.
An alcohol stove being primed.  Note blue flames coming from the priming pan.
To prime the stove, I place alcohol in the priming pan.  I light the alcohol in the priming pan on fire.  I let the alcohol burn a bit, and then as the stove heats, vaporized alcohol starts coming out of the jets.  Sometimes, the alcohol coming out of the jets will ignite without further intervention.  Sometimes you have to light the alcohol coming out of the jets.

Now, with some stoves, you pretty much always have to prime them to get them to work.  The two stoves in the above photos are like that.  They really don't work until they get hot enough to vaporize the alcohol, and they really don't get hot enough to vaporize the alcohol unless you prime them.

Other stoves don't normally need priming.  Take a look at the three stoves in the photo below.  These stoves are open jet (semi-pressurized) stoves.  They will generally light right up if you light them in their center opening.
Some open jet type alcohol stoves.   This type of stove generally doesn't need priming.
Cold Weather Considerations
Now, notice that I said that open jet type alcohol stoves generally don't need priming.  When it gets cold, you may need to prime a stove that doesn't normally need priming.  Now, if you've got a little pan that your burner will fit into, then that in my opinion is optimal.  I use the lid from a tin of tea that you saw in the priming photo above.  If your stove has a cap, like a Trangia burner, then you can set the stove on the cap (remove the "O" ring first!) and use that to prime.  In my experience, using an object smaller in diameter than the burner does not work very well.  It's better to use a pan that your burner will fit into.
Left:  A Trangia burner set on top of its own lid (with the "O" ring removed!), ready for priming.  Right:  A small pan that the burner will fit into.  The small pan is a much better option for priming.
Preference Considerations
I generally prefer open jet type burners over closed jet type burners.  That's my preference.  It's not like a stove that requires priming is automatically a bad stove.  I just find that it's harder to put fuel into a closed jet burner, and to me priming is a bit of a hassle.  I haven't found that stoves that require priming are better than stoves that don't, so why go to the hassle of priming?  An open jet burner is easy fuel and easy to fire.  You just dump fuel into the wide opening and strike a match or flick your Bic.  Works for me, and that in general is my preference.  If a really great stove came along that required priming, I'd be interested in it, but somebody would have to call it to my attention. Stoves that require priming aren't an area I'm actively looking into.

Efficiency Considerations
Generally, priming is inefficient.  You're using fuel to heat the stove rather than to heat your dinner.  With a stove that requires no priming, 100% of the heat produced can go into the cooking.  Generally.  Now, of course the bottom line of efficiency is how much fuel does it take to accomplish a given cooking task, e.g. boiling two cups/500ml of water.
For example:
Stove "A" requires priming but can boil two cups of water with 0.5 fl. oz/15ml of alcohol.
Stove "B" does not require priming but takes 0.75 fl. oz/22ml to boil the same two cups of water.
Since stove "A" can accomplish the same task with less fuel, stove "A" is clearly more efficient than stove "B," priming or no priming.  The amount of cooking you can do with a given amount of fuel is the bottom line of efficiency. 

Still, as a practical matter, I have found that stoves that require priming are typically less efficient than stoves that do not require priming.  Absent more precise data, I would choose a stove that does not require priming if I were looking for an efficient stove.

HJ

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4 comments:

  1. With my Trail Designs 12-10 Alcohol stove I find priming works best; mainly because of my inept skills with a Light My Fire Firesteel. That said I can easily boil 300 ml of water in an ambient temperature around 20C with 15 ml of fuel when using the priming pan.

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  2. The best technique is the one that works. :)

    HJ

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  3. I have found that in cold weather, or even cold water, when you put the pan on the stove, it acts as a "cold" sink, and a stove that was burning vigorously, will significantly slow down, until the pot of water starts to warm up.

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    1. That makes sense. Alcohol stoves burn the vapor produced by the alcohol (not the liquid). If the alcohol is hot (particularly if it's boiling), a lot of vapor is produced, and a stove will burn hotly. If anything cools down the "system," then the stove will not burn as hotly.

      Likewise, running a stove on a cold rock can slow a stove down.

      HJ

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