Does red hot really mean a hot running stove?

Discussion in 'Stove Forum' started by hikerduane, Feb 15, 2020.

  1. hikerduane

    hikerduane Subscriber

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    I've been questioning this for a few years now, does a red hot burner really mean the stove is running great? Does the flame have to be a perfect blue, some yellow seems to be just as good. So many variables. Oxygen, fuel quality, make up of metal, distances between burner parts, etc. My main experience and observations are my extensive Primus 96 and other makes of lipsticks collection. Blue flame doesn't necessarily mean the burner plate will turn red or turn red quickly, even at times the flame doesn't have to be full out. Also, many take five minutes or so to turn red, the bell may start turning a dull red though. All this is just on my work bench, usually no pot on for a "tea test". Quickest I have seen the burner plate turn red was this winter on one of my recent 96 finds, plate was noticeably red in 20 to 30 seconds.
    Duane
     
  2. geeves

    geeves New Zealand Subscriber

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    Difficult one as it depends on burner design and usage.
    Putting a pot on the stove will reflect some heat back to the burner so the burner will be a little hotter so will go red quicker. Roarers burn inside the burner so the bell should get red but the flame spreader has the fuel being squirted at it which cools it so at high power it is rarely red. Silents should burn outside the burner so should not get that hot although the large Primus 4 burners do seem to glow red in use.
    A blue flame is a sign of perfect combustion. This is where the stove is making minimal carbon monoxide and you are getting most heat per unit of fuel. Yellow is a sign of unburnt carbon in the flame so efficiency should be down and pollutants will be up.
    Sometimes though a yellow flame can be taller which might heat a pot faster if the pot supports are too high
     
  3. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @hikerduane
    Interesting topic Duane.

    First thoughts, I doubted that a contemporary purchaser would have cared and perhaps only as collectors we aspire to blue flames.

    But then, I remembered that Coleman made a big thing in their early advertising of the attractiveness of a blue flame, their ‘Band O’ Blue’ so maybe not.

    Compared to a rich-burning yellow-streaked and smelly flame depositing carbon on pots, a blue flame is surely an indication of correct fuelling.

    Consider this, however. I’ve recently been tinkering with a Russian Prim Compact stove and though there are blue flames aplenty and it doesn’t run rich, the steel of the outer burner cap glows red (a metallurgy thing?), as does the brass of the burner shroud and the pot rest, all of which confer a red colour to the output.

    DF801CD0-A804-416D-80AB-0791D04338D1.jpeg

    B0D7AB40-045D-46CE-8960-773FDEEB1A7A.jpeg


    Regarding your experience with ‘96’s, you’re speaking of a relatively low output and not particularly efficient burner type. The 0.23 millimetre jet orifice (true too of the larger 100-series lipstick burners) has nearly half the outlet area of a 0.32 millimetre jet, with a corresponding impact on the burner power - and its capacity to get metal components in its path to glow red.

    John
     
  4. BradB

    BradB United States Subscriber

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    What size jet would my Aida 100 have?
     
  5. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @BradB
    Lipstick and not a ‘tubular’ burner would be 0.23mm also.

    Point of the 100-series was to give longer burning time on a modest output and relatively large tank’s fuel capacity.
     
  6. Twoberth

    Twoberth United Kingdom Subscriber

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    Good questions Duane. I wish I knew all the answers, but here is my take on the subject.

    A stable blue flame from a stove burner indicates stoichiometric combustion, where the fuel is mixed with just enough air to provide oxygen to burn all the hydrocarbons in fuel. If there are no impurities in the fuel then the only products are carbon dioxide and water.

    In theory, this stoichiometric flame’s temperature is the hottest you can get from mixing that fuel with air. Too little air and all the potential heat is not generated as the fuel is not fully burned, too much air and the heat generated is diluted by the extra (initially cold) air. So theoretically, a stable blue flame is the hottest you can get. However it’s blueness may be masked if there is red hot metal surrounding it.

    Its fairly obvious that when a metal gets hot enough it glows red. The brighter and yellower the reddish glow, the hotter the temperature. What is less obvious is that the same ‘redness’ indicates the same temperature regardless of the metal.

    Whether the metal surrounding any particular flame gets hot enough to glow red depends on how close to the flame it is and the metal properties (heat capacity, conductivity, thickness etc), so a thin burner bell/plate may glow redder than a thicker one, and a stainless steel one may glow redder than a copper one.

    It is possible to have two stoves producing identical flames, but having two different metal burner bells or two different thickness flame plates. One burner may glow bright red, while the other remains dark with a blue flame. However they may both be producing exactly the same amount of heat per second.

    Looks, as you know, can be deceptive.
     
  7. hikerduane

    hikerduane Subscriber

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    Thank you, have wondered why red hot can come via two directions.
    My next test is for those after market lipsticks and what seems to me more thermal feedback than the stock. Just got a different one today with a stove.
    Duane
     
  8. Twoberth

    Twoberth United Kingdom Subscriber

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    Hi Duane,
    My avatar is a photo of a butane roarer flame surrounded by a stainless steel windshield/wok stand. The stand glows red (about 900C) where the flame impinges on it, as stainless steel is a bad conductor of heat. You can touch the outside of the colder spots between the red areas. If the stand were made of brass the heat would be quickly conducted away from the hot spots, and the whole thing would be at a lower temperature and appear dark.

    I have been experimenting with stainless steel lipsticks, and comparing them with brass lipsticks. In theory the stainless lipstick should get much hotter at the top where the vaporisation takes place. In practice they both work fine, but I have never done a comparative tea test.

    Maybe I will now!
     
  9. hikerduane

    hikerduane Subscriber

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    The lipstick burner I got yesterday with a stove was unused, the one without the nipple on top and has a basic nut at the bottom. Good flame color, but fount got pretty warm. I need to try tests with same amount of fuel at same temperature to start, using a thermometer to check before and after temps. Seems the other after market burner I got a couple years ago did the same thing.
    Duane
     
  10. LollyKat

    LollyKat United Kingdom Subscriber

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    My Primus 96 with a 100 flame plate from Stu (loco7stove):

    [​IMG]

    The original plate also glows red. I haven't done a proper scientific test to see which one boils a pan of water faster, or if there is any difference.
     
    Last edited: Feb 16, 2020
  11. hikerduane

    hikerduane Subscriber

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    Very nice. If nothing else, the red is great to see. A BD replacement plate for one of my 100's gets nice and red, material it is made from.
    Duane
     
  12. OMC

    OMC Subscriber

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    I appreciate content-rich comments. This is just a slice from above:
    Whether the metal surrounding any particular flame gets hot enough to glow red depends on how close to the flame it is and the metal properties...

    Duane, You said most of your tests are without a pot on top.
    What the hell man (said the burner inventors).

    While wind protected a very quick test is as follows:
    grab an excellent performer, gets redder quicker, 96.
    Set stove in specific water temp to cool it (as you suggest start the tests at a same known temp).

    No pot on. Time how long it takes for flame spreader to have complete glow. Note flame color if you wish. end
    --------------

    Restart test with efficient aluminum water boiler pot:
    bottom diameter a close match to outer points of the pot supports, and.
    more rounded bottom such as Trangia design.

    Time how long it takes for flame spreader to have complete glow.
    Note flame color if you wish.
    BTW I do not know this result.
    A guess will be heat is "spread" by design, away from center and spread onto larger surface area of bottom of pot. Not sure if plate gets just as red despite this but, by design, flame and heat is "spread " outward away from center.
    ----------------

    Whatever the result, it is the same burner. Optimal burner performance would not be measured in redness, imo, but with heat transfer to the bottom of a pot. The age-old 1 liter boil test. The pot should be a good fit for stove top <-- this is what 1880-2020 burner inventor's strive for.
    What may be debatable but I suggest they want the most robust perfect blue flame with a pot on (less perfect flame w/o a pot could be ok).
    Additionally, I would credit Tony with consistent reminder, no soot on pot bottom is an indicator of good performer (vs flame color).

    As you have pointed out, there are many variables which includes having a pot on and type of pot/pan.

    For comparisons of which burner is producing most heat... the key is which burner transfers the most heat to the bottom of a pot. I am a proponent of apples to apples boil tests.

    BTW, unlike redness, a boil test can "start" w/96 at full roar, place covered pot with 1 liter water atop (water at same start temp), await rolling boil.
    It will not surprise me if burner w/quickest boil time, does not burn perfect blue w/no pot atop. sorry it's long answer, I gotta run
     
    Last edited: Feb 17, 2020
  13. hikerduane

    hikerduane Subscriber

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    Yes, apples to apples. Heat transfer to pot. Same as a race car, snowmobile, you need to get the power to the ground.
    Duane