[Stoves] Correcting a misconception that approaches myth status

Tue Dec 16 10:21:09 CST 2014

Dear Paul

I think this is an important modification of the fuel feed story that is
worth noting.

>>I fed in some wood vertically and it worked just fine. I continued to do
so and it continued to run long after it should have gone out. Thus I proved
to myself (and Paul) that TLUD's can be refuelled but not too much at a
time. OK, that was valuable and contradicted received wisdom. 

>What Crispin did then in 2002 was what BP-Oorja, Biolite and Philips and
others did years later.   They were all trickle feeding additional fuel into
the TLUD well above the pyrolytic zone.   

This is not what I did. It is possible to make a gasifier that does not have
an MPF. Feeding such a device that has vertically stacked fuel bed is quite
possible. I realise this is not the same thing, but we should not be
diverted into thinking there is only one way to make a gasifier. The fuel is
tucked in alongside the other (charcoaling) fuel and it works quite well. It
was not anything like an attempt to put fuel on top of a packed bed, if you
get my drift.

>And when the MPF reached the bottom, and with new fuel placed on top of the
char (not into the hot zone), the unit switched over to operating with
Bottom Burning (BB) as a rather normal UpDraft gasifier.   

Well, be careful here. It depends on how the fuel is patterned. If it is not
in a packed bed, it can gasify if the air is sufficiently under control.
Remember that gases can be produced with no air at all (in a retort) so the
switch from an MPF to a gasifier is not necessarily to a bottom-lit updraft
config.

As I have written in "Micro-gasification Terminology: An Instructional
Summary of MG", available at my website.   See:
http://www.drtlud.com/wp-content/uploads/2013/11/micro-gasification-terminol
ogy-14nov2013.pdf  

Therefore, there are actually two types of TLUD (device name) gasifiers, one
being TLUD-MPF and the other being TLUD-BB. 

Well, I don't agree that it is a TLUD if it is burning at the bottom. It has
ceased to be top lit if the combustion is taking place at the bottom. I
suspect the misdirection is caused by a desire to force the combustion into
a pre-defined set of modes. The modes should instead describe the
combustion.

The two types are quite distinctive in operation, and deserve separate
recognition and study. The common usage of the "TLUD" name today means more
than the TL of "Top-Lit" can signify. ...... snip ...  In essence, TLUD is a
name for the small updraft gasifier processes/stoves and is not a
description of what process (MPF or BB) is actually happening. 

Just as I said. It certainly is supposed to be a description of what is
happening. What would be the point of calling something a crossdraft burner
if it was not burning crossdraft? And vise versa.

However, we expect that in common usage, the TLUD name will designate
TLUD-MPF, unless the UD-BB mode is specified.

>However, many people continue to ignore the transition from MPF to BB.   

This is still a limitation on the 'definitions according to Paul' instead of
describing what is taking place. There is an assumption in the statement
that we are burning chipped fuel. That limited view cannot be allowed to
overtake and limit all the possible configurations. Paul, I think as someone
very interested in classification you should address this and come up with a
more complete lexicon.

I repeat:   

However, we expect that in common usage, the TLUD name will designate
TLUD-MPF, unless the UD-BB mode is specified.

Paul, that is currently your opinion and it is incomplete and inadequate. We
can't accept something that arbitrary. 

First, there are at least 4 variations, not 2: TLUD with MPF, MPF converting
to BLUD, retort, and retort with at least some air. All make combustible
gas. What was happening on the porch was the last of the 4.

Now what?

Crispin

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