[Stoves] DIY camping TLUD with walnut shell fuel

[kgharris]

Mangolazi,

This is a much improved flame.  The solid round disk helped move the gas out 
to the air, eliminating the central column of gas, and giving better mixing. 
The slits are giving you even more mixing.  The active mixing is giving you 
more heat, buoyancy (draft), and thus a cleaner flame than the former 
diffusion flame, (https://en.wikipedia.org/wiki/Diffusion_flame).  I think 
you are on a good path.

The holes are not pilot holes, they are the secondary air entrance.  Pilot 
holes are small and few in number, making small flames, like a pilot light 
on a gas water heater.  The purpose of pilot flames is to keep the main 
flame going, re-igniting it as needed.  For your stove, pilot holes would be 
small holes just below the current large secondary holes.  On turn-down they 
would keep the flame alive down to a lower power level.

Thank You for sharing your work, please continue,

Kirk H.

----- Original Message ----- 
From: "Mangolazi" <mangolazi at yahoo.com>
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>
Sent: Thursday, June 16, 2016 4:39 AM
Subject: Re: [Stoves] DIY camping TLUD with walnut shell fuel


You're right about the fuel type and density affecting flame height more 
than primary air. I put a metal disk on the grate to block 2/3 of the 
primary air, added a fan-shaped obstructor just below the pilot holes and I 
still got a tall flame towards the end of the burn. Total burn time went up 
to 15 minutes from 12 minutes, probably because of less primary air.

There was no smoke and the flame was a rolling turbulent mass with lots of 
blue - a sign of good air/fuel mixing?

On June 15, 2016 8:24:10 PM GMT+08:00, neiltm at uwclub.net wrote:
>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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