Blue_Tractor_Man Posted By Blue_Tractor_Man, Dec 23, 2012 at 9:03 PM

  1. Blue_Tractor_Man

    Dec 26, 2009
    West Tennessee
    I've been using a VC Defiant non-cat for the last two seasons. It will backpuff of whoof every once in a while. When I say backpuff or whoof what I mean is that the stove will be running right along and then without warning it will puff a little bit of smoke out of the top-loading door. Kind of like it is blowing a little smoke ring. It never seems to backpuff when it is running good and hot with several splits in the firebox, or when there are mainly just coals in the firebox. It only seems to do it when I am trying to damp it down for the night with fresh wood in the firebox. It never does it when the air lever is open and there is no shortage of air.

    I have spent a good amount of time observing the fire when the stove has been damped down for the night. What seems to be happening is that the fire gets slightly starved for air and the flames will die down. 5-10 seconds later the gasses in the stove will burst into flames. This process happens over and over if the primary air is cut back. It never happens when the primary air is open. When the primary air is cut back you can observe the flames burning away from the wood surface. The vast majority of the time the small explosion never lifts the top door. Every once in a while the explosion will be powerful enough to lift the top door maybe 1/16 of an inch and a little bit of smoke will puff out. Every blue moon the explosion will be strong enough to lift the lid enough that you can hear a little thud as the lid drops back down.

    It seems to me (as a non-scientist) that the wood is emitting some sort of flammable gas that will only ignite when it has exactly the right amount of oxygen. In my occupation I work with the natural gas industry and I have been told that natural gas (methane) will only ignite when the oxygen level is just right. Too much oxygen-no ignition, too little oxygen-no ignition. I read on another post today that as wood is heated it releases methane or methanol. That seems consistent with what I have observed. The wood is definately oozing something out that is exploding (or better stated bursting into flame).

    The reason this presents a problem is that I would like to load my firebox at night and shut the air intake down to starve the firebox of air and let the secondaries take over the burning. The wood seems to be cooking and forcing these flammable gasses out so that they will be ignited. The process seems to be erratic rather than orderly.

    I suppose this same process happens in all stoves with restricted air supply. I wonder if it only presents a problem on my top-load stove because the force of the explosion has just enough power to lift the lid up slightly and the smoke puffs out.

    Questions: Is my theory correct about the wood emitting some sort of flammable substance that bursts into flame when conditions are just right? Is this common with any stove with a restricted air supply? Has anyone learned any tricks to reduce this phenomenon such as tightly stacking the splits, charring the wood when it is first put in? If there were a little more weight on the top door would it still be able to puff out?

    Any thoughts or guesses would be appreciated.
  2. Blue_Tractor_Man

    Dec 26, 2009
    West Tennessee
    Please ignore this post and check "VC Defiant backpuffing problem"

    Mr. Moderator please delete. Thanks!
  3. HotCoals

    Minister of Fire

    Oct 27, 2010
    Do you get your secondaries to fire off before you close things down?
  4. evilgriff

    Burning Hunk

    Oct 14, 2007
    Northern New Jersey
    My old VC Intrepid II Cat stove would do the same thing with a full load when throttled back. Less than a full load no problem. Never solved that issue. I just never packed it fully anymore.

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