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Secondary holes in Wild Woodgas Stove: air or woodgas?

Technical Query

Hi, I watched your video on how the stove works. You need to get your facts right before publishing information about stuff you do not understand. That is not how a wood gasifier works. The ring of little holes are not to provide a secondary air inlet! That is where the wood-gas comes out and is burnt. Also you don’t light it that way. You pack it with wood first and light a fire on the top.  DF

Wild Stoves Response

Thanks DF for taking the trouble to write to us about this. I assume the video you are referring to outlines the operation of the Wild Woodgas Stove Budget, as below:
[youtube https://www.youtube.com/watch?v=RdSbJLIXyfk&w=420&h=315]

(NB – the Budget model is still available, but has been superseded by the MKIIt which is lighter-weight and has a more versatile and strong pot support.)

  • With regards the secondary air holes: this woodgas stove is a natural draft IMG_0268TLUD (Top Lit Updraft Gasifier), so in this case the air travels up through the fuel bed, providing primary air to the combustion. Only air travels up between the outer-walls of the combustion chamber to be pre-heated before being drawn into the combustion chamber to meet the woodgas. If you look carefully at the flames emerging from the secondary air holes the burning edge is underneath, whereas if woodgas was coming out of these you might expect the burning face to be on top, where the woodgas met oxygen.
  • With regards the fuel-feed method, as you’ll see in our instructions, we suggest two main ways of feeding these stoves. For dense, consistent fuels (e.g. wood pellets) you are quite right you can batch-feed and top light the stove (hence the ‘Top Lit’ TLUD). However, if using more ‘wild’ fuels like twigs and pine cones, on the one hand these are not always of sufficient density or consistency to sustain top-lighting; and because they burn through quite quickly, a batch-feeding approach would mean inconvenient gaps between fuelling.

In downdraft gasifiers, you do get mixing of air and woodgas within the stove which can then exit as the top holes, but these tend to have different architecture to allow for this.

However – perhaps your experience of this stove is different. Have you managed to get it burning in downdraft mode, with woodgas whipping out of the grate and round and up to the secondary air holes? Please leave a reply below with your experiences – we look forward to hearing.

We are committed to describing our products and the science behind them as accurately as possible!

Further information

Wikipedia Natural Draft TLUD Page

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