[Stoves] Adding fuel to TLUD ..... was Re: A review of chronological development in cookstove assessment methods: Challenges and way forward

[Paul Anderson]

Ron,     see below.

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype: paultlud      Phone: +1-309-452-7072
Website:  www.drtlud.com

On 11/27/2015 12:10 PM, Ronal W. Larson wrote:
> 4.  Here is an idea that I wonder if you (anyone) has tried. (I haven’t)
> a.  Start a TLUD in the normal way -  maximum primary air may be best 
>  (since mostly we want high power only at the beginning).
> b.  As soon as the pyrolysis front is clearly well established - then 
> add a “thin” layer of the same (?) combustibles on the top.
> c.  There should be no ignition at the bottom of the new layer, as 
> there is no oxygen there.   But new pyrolysis should occur - so 
> increased power.   The top of the new added layer could ignite, if 
> there is plenty of secondary air there.
> The down side of this is that you probably need to control the 
> secondary air so that you don’t have too much latterm  Most os us 
> never do this.  But there could be some inherent control of the 
> secondary (that secondary follows primary naturally)..
>
This has been done many many times.   It is a way to extend the duration 
of the TLUD operation.   You are correct that causes an increase in the 
pyrolytic gas creation but does not increase secondary air (except 
through increase of draft from more burning gases).   It is a good way 
to put soot on the bottom of the pot. Note that this is anoxic pyrolysis 
via the heat, with no small flames (glowing pyrolysis) present as is 
found in the MPF (migratory pyrolytic front).

Actually two conditions are possible.
1.  As you describe, while the MPF is also functional and descending.
2.  After the MPF reaches the bottom (and stops because it transitions 
into char-burning at the bottom).  This is how people make their unit 
become "continuous" (at least until it chokes up with too much char or 
ash).   But it requires the very frequent attention to the feeding of 
the fuel, thereby losing one of the desired aspects of TLUD batch 
operation (consistent flame without needing to add more fuel during the 
batch time of the MPF).

Therefore, what you describe certainly has been and is frequently done.  
Actually, I did that in the testing in 2005 that won the Cat Pee award 
at Aprovecho.   Then I did not understand it fully. Trickle feeding of 
fuel into TLUD stoves does work, has pros and cons, and is likely to be 
done by some individuals with or without their understanding of why or 
how it works and its limitations.

Paul
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