[Stoves] Heat to sustain TLUD process

[Crispin Pemberton-Pigott]

Dear Paul

I can't change the stove to fit the nomenclature so you will have to develop 
words to describe what happens.  Incidentally this is not an 'improved 
Vesto' it is the original one.  A simplified version is what is on the 
market.  It can't choke t he primary air sufficiently to be a gasifier.

>Please verify that you are igniting at the bottom as in the standard
>Vesto, not

It can be lit either way.  As noted by others, small pieces drop in and 
light the bottom eventually.  It is cleaner to stary with a top light, but 
slower.  I prefer to bottom light a small amount and add fuel when it is 
hot - about 1 minute or 2 later.

>I believe that all of MY TLUDs
>are close coupled with the temperature of the gases as high as I can keep 
>them
>in a TLUD.  Do you have something different as "close coupled"?

There is reall no separation.  You can drop in fuel that is higher than the 
secondary air.  It get roasted below and burned above.  We advise not to do 
that but people don't always do what you suggest.  Whatever you do it 
continues working.  It can be optimised by puttng in fuel cut 150mm long or 
so.

>With bottom lighting, you have the full height (440 mm) to act as a
>chimney to create natural draft.

There is a 40mm air gap under the bottom of the fuel.

>What aspects are you wanting to optimize?

The Vesto stove has a Tsotso Stove (David Hancock) hidden inside it.  The 
air gaps and hole sizes can no doubt be improved to make it more variable or 
to work even better with a wide range of fuels.  It will burn a lot of 
things quite well if you don't over-feed it.

>Do you (or can you) also restrict the in-flow of secondary air so that the
>fullness of the draft is pulling on the primary air during the char-burning
>stage?

When we first went to market I had a separate secondary air controller but 
Rina King had trouble getting people to adjust it correctly so we left it 
out for that reason and to reduce the cost.  It cost $4 to make so it was a 
serious consideration.  I still have the tools for forming it.  There were 
then two levers sticking out and one could perfect the balance between 
primary and secondary air but it is more of a party trick than anything 
else.  You would have to watch it and adjust it from time to time during a 
major burn.  It works well without it and wastes a bit of heat.

>> I am not sure of the total CO emissions from the whole 'cook'. The 
>> charcoal
>> burning phase has much high CO than the gasifying stage, which has nearly
>> none.

>Please watch your terminology.  The charcoal burning is the 
>"char-gasifying"
>stage.  And what you called "the gasifying stage" is actually the 
>"pyrolysis
>stage."  The "purists of gasification" would refer to the charcoal burning 
>(or
>char-gasification) as simply "gasification" and they do not usually refer 
>to
>the pyrolysis as gasification.

Actually it is not fitting well into the descriptions you make.  At the 
bottom, in the middle and at the top, early and later in the burn, all are 
taking place, and often several things at once.  There is char-gasifying 
going on where the 8mm jets hit the (partly burnt) wood.  The wood above it 
is pyrolising.  I though I made that clear already.

It is not the same as any of the stages you describe in the TLUD because it 
is a BLUD with focussed air.  It is very different from the fan or natural 
draft that supplies air to the whole part of the fuel.  Air is predetermined 
by the 3 x 8mm holes 30m from the bottom of a sealed combustion chamber. 
That is the burn rate I want for cooking.  It is that air, drawn by 400mm of 
draft, that gasifies and char-gasifies and burns the volatiles at the 
bottom.

Later a completely different set of circumstances prevails.

I though I posted a video of a Vesto proving the concept made like this on 
the group.  No? I have one looking straight down as it changes back and 
forth between the two burning modes.  Fortunately it can be run in 'semi' 
mode partway between the bottom lit fire and the gasifier so as the 
volatiles come to an end, or just before, additional air can be added, but 
not too much.

I will send it to Tom for posting.  It starts off in gasifier mode, then 
swtiches to straight combustion, then goes back to gasifier mode and settles 
into a shimmering flat bed of flame.  It has a very low flame height 
characteristic of good secondary injection.  If you know my stoves really 
well, you can see tht it was an early grate with too many holes near the 
top.  That upper section is now a plain tube to give the lower holes a 
little more pressure boost.  This also reduced the cost as the holes are 
about 1 cent each to punch.

Regards
Crispin