[Stoves] DIY camping TLUD with walnut shell fuel

neiltm at uwclub.net neiltm at uwclub.net
Wed Jun 15 07:24:10 CDT 2016


On 15 Jun 2016 at 9:06, Mangolazi wrote:

> I've always wondered what causes that towering inferno to occur. I've had
> this happen a few times with a tiny tin can stove and with a big paint can
> biochar burner. I try to avoid it so my pots don't get damaged. 
> 
> Is it too much primary air? Lots of wood gas from certain fuels? Fast gas
> flow from a tall chimney? 
> 
> Looking at a bunch of papers on TLUDs, it seems there's a trade off
> between temperature and burn time. You can throttle primary air to get a
> long burn time but temperatures may not get high enough to burn cleanly,
> whereas a more complete and hotter burn means the fuel is turned to char
> much faster. 

If you make one of early TLUD pioneer Paal Wendelbo's ww2 Norwegian 
resistance stealth fires in the woods when they met to discuss resistance 
actions and he observed as a teen, this should help answer some of these 
questions.  In other words, build a small stick fire, crossing the sticks 
in meshed layers, and set fire to it from the top.  It should burn down 
through the stack, consuming every stick, and do so relatively 
smokelessly and steadily, even travelling against a side wind I found. I 
found it quite a revelation to do this. If your wood is thin and dry the 
stack will go up quickly, and vice versa and so on.  When you do the same 
thing in an enclosed stove, the biggest difference I suppose is the 
reflection back into the fire of the heat - its concentration, but this 
will surely only amplify the effect you would get with an open fire top 
lit.  Then you can also play with air ratios to better control the fire 
for cleaner emissions, greater heat, longer burn time etc.

Since you can build the type of top lit open fire you want to achieve, so 
can you also do this within a ND TLUD, with greater versatility the more 
open a grate for the primary air.  I don't want to discourage you from 
experimenting with controlling the primary air with the stove, but my 
experience of doing this has been far less rewarding than varying the 
fuel, so I would certainly encourage such experiments, probably without 
modifying your existing stove at all.  Since fuel will always be variable 
anyway, especially if camping, being able to anticipate the burn 
characteristics of fuel, and mix and match and size accordingly is always 
going to be part of the overall picture, and can surely never come down 
to air ratios and stove architecture alone.  This was even more true when 
I was using the well configured Reed Woodgas campstoves, because their 
configuration for cleaner burning was less forgiving of a wider variation 
in fuel dryness etc.

Best wishes,   Neil Taylor (who just successfully controlled a breakfast 
frying flame using a residue of very small but well dried woodchip 
relying on the stack restricting the primary air - then made a smoky mess 
trying to continue the burn at the rather congested char stage.  Should 
have left it alone at that point!)






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