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Sunday, February 10, 2013

Advantages (?) of Regulator Valved Stoves, Part II

In my first post on the subject, I linked to a video produced by Soto Outdoors showing their Microregulator Stove (OD-1R) in a "burn off" against a non-regulator stove.  The video seems to imply that there is some advantage to having a regulator valved stove in cold weather over a conventional needle valved stove.

There's just one problem here:  It doesn't make sense from the standpoint of physics and chemistry.  I mean, the relative pressure in a canister is a function of the fuel inside, the pressure outside, and the temperature.  Compressed gases, such as those in the canister of a backpacking stove, follow certain rules of physics and chemistry.  Changing the valve type won't cause that pressure to change.  I've talked to engineers, chemists, and physicists.  No one seems to think that a regulator valve will be of any benefit in cold conditions. 

So, I thought I'd try a cold test of my own to see what I might find out.  I define cold here, in the context of an upright canister stove, as a fuel temperature (not necessarily air temperature) less than ten Fahrenheit degrees (about 5 Celsius degrees) above the boiling point of the fuel.

Now, in Soto's test, we don't really know how cold the water is, we don't know what's in those fuel canisters, etc.  In other words, we really don't know much about the test conditions.  So, before I go on, let me lay out my test conditions.  Hopefully this section isn't too boring.  :)

Testing Conditions
  • Elevation:  Approximately 6,000'/1825m.
  • Temperature:  31F/-0.5C as measured on a digital probe type cook's thermometer.  No calibration was employed on the thermometer.
  • Conditions:  Light wind.  No precipitation.
  • Fuel used:  100% n-butane.  No isobutane or propane was used.
  • Air pressure:  Unmeasured.
  • Canister temperature at initiation of test:  Unmeasured but assumed to be ambient.  The canisters were left out for a considerable time while I did various things at the location I stopped at, including setting up the test. 
Important Chemistry and Stove Facts
  • Boiling point of n-butane at sea level:  31F/-0.5C
  • Boiling point of n-butane at 6,000'/1800m:  About 19F/-7C
  • Normally, the temperature of a compressed gas fuel needs to be about 10F (or 5C) degrees above the boiling point of that fuel in order for a canister stove to have decent operating pressure.
  • Releasing gas out of the canister causes the canister's internal temperature to drop.  In other words, an upright canister stove's fuel gets colder as the stove operates.
Conduct of Test

I started both stoves, the Monatauk Gnat first, then the Soto Microregulator.  Once both stoves were lit, I opened both valves to their maximum open position and let them burn.  Both stoves were on top of a Ridgerest closed cell foam pad. 

I let the video run for a combined total of about 20 minutes.  The "short" video clip below is from the last three or so minutes of that approximately 20 minute period.  The "long" video posted in the appendix was started before the burn began and extends for about 17 minutes.



Discussion
I started the test at a temperature of 31F/-0.5C, about 12 degrees Fahrenheit above the boiling point of the fuel.  The flame's sizes show that there was reasonably good pressure at the start of the test.

The Microregulator had a much larger initial flame than the Gnat.  Obviously, it would have been a better test to have two nearly identical stoves, one with a conventional needle valve and the other with a regulator valve, but I had no way to get two such stoves.  However, even without closely matched stoves, one can assess whether or not a stove's flame has been significantly impacted by the temperature. 

Errata:  In the video you may hear me say something to the effect that the ambient temperature is equal to the boiling point of the fuel.  While that would have been true at sea level, the video was shot at ~6000'/1825m elevation, therefore the ambient temperature was actually about twelve degrees above the boiling point of the fuel.

In the video, I said something about the canisters being perhaps above the ambient temperature because they had been in my pack.  On further reflection, I realized that I had taken the canisters out well before the test was started.  The canisters were resting on a snow free metal surface that had been in the open all day.  The canisters were undoubtedly at ambient temperature at the start of the test.

Observation
At the end of the test period, both stoves had similarly sized, very small flames.  The Soto Microregulator offered no discernible advantage in cold conditions, as I define cold (see above definition).

Concluding Remarks
No criticism of the Soto Microregulator stove is intended here.  It is one of the nicest built upright canister stoves that I have.  It is craftsmanship at its finest.  Again, my only point here is that I could not establish that there was any advantage to a regulator valved stove in cold conditions as I define cold, above.

I'm not sure what Soto was trying to show in their video.  Soto is based in Japan.  There may be some language barrier here.  People here in the US have taken Soto's video to mean that the Soto Microregulator has an advantage in cold weather.  I could discern no such advantage in cold conditions (as I define cold) nor is there anything in the chemistry or physics of either the stove or the fuel that would suggest such an advantage.

I would be very open to hearing from Soto a response to this blog post.  In particular, I would love for them to describe in detail a set of conditions under which a regulator valve stove might have an advantage over a needle valved stove, an advantage that I might be able to corroborate through testing.

I thank you for joining me on another Adventure in Stoving,

HJ


Appendix

In Soto's test, they let the stoves burn for about five minutes.  In the "long" video, below, you might want to watch the first six minutes.  I start the stoves about a minute into the video, therefore six minutes into the video is about five minutes of burn time.  I think you'll see that at five minutes into the burn, both stoves have significantly reduced flame sizes as compared to their respective flame sizes at the start of the test. 


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