[Stoves] Accidental TLUD technique discovery

[neiltm at uwclub.net]

On 15 Nov 2016 at 11:41, Paul Anderson wrote:

> Neil,
> 
> I will bring some of your questions to the top and answer them here, 
> with other comments mixed in:
> 
> 1.  A stove that is short and wide has advantages as a charcoal stove so 
> that the charcoal is spread out and close to the bottom of the pot.  
> However, we are discussion TLUD stoves, and in them the advantage of the 
> height is the longer time of combustion (and with less fire tending.)  
> Unless using the TChar concept (see it at my website), taller TLUD 
> stoves actually are NOT good for charcoal combustion.   The char is at 
> the bottom (near the incoming air) and there is an undesirable layer of 
> char above the hot area, resulting in less heat reaching the pot.   
> Charcoal cooking utilizes radiant heat, and any obstacle (char or 
> otherwise) is not good.

Understood and experienced.

> Neil wrote:
> > There can be at the end of a burn, a quarter full of
> > char, all aflame. And I can't see why this wouldn't be occuring all the
> > way down?
> But it will not be all aflame UNLESS there is O2 reaching that upper 
> amounts of char, which would be a forge down in the bottom and not good 
> for the stove or for cooking.
> 

I can only to try to better explain what I see which is all the remaining 
char engulfed in flame (at the end of the TLUD batch process with 
moderate to large dry wood chunks), or perhaps more precisely an attached 
blue flame which can reach the top of the stove.  Compared with the 
stainless steel Reed XL stove which burnt out at the secondary air holes, 
these ss trekker stoves are holding up really well with no significant 
distortions or any significant carbonisation of the steel.  I suspect we 
are both having some difficulty mentally scaling up and down respectively 
here.

> 2.  you wrote:
> > Are you saying that a mid fire's MPF will not consume char below it, left
> > from the original MPF?
> Yes, it will not consume that char that is below the middle fire.
> 

Thanks.  I guess that will be because its producing its own.

> And note that the middle fire was NOT a TLUD fire so there is no MPF 
> funtioning in the middle fire.   Also remember that WHERE the air enters 
> to sustain the MPF is an influencial factor.
> 

Yes.

> The MPF in a regular TLUD has some flame (combustion of gases) 
> pressent.   But if raw fuel is placed above the hot char but is without 
> spark or flame, then that raw fuel is pyrolyzing in a RETORT-fashion 
> without burning in that area.  Pyrolysis does occur, but it is different 
> from the pyrolysis in TLUDs.
> 

OK, but does that additional gas consume cleanly at the secondary air 
point?

> 3.  Neil wrote:
> > my experience of the smaller ones is that invariably the fire is
> > hottest towards the end of pyrolysis, which conversely may coincide with
> > wanting a more simmer heat.
> The increase in fire is with all the TLUDs (operated normally) at the 
> end of the batch.   What happens is the MPF reaches the bottom and there 
> is no fuel below to take in the DOWNWARD RADIATING heat, so all that 
> heat is available to boost the pyrolysis of the last fuel at the bottom, 
> giving a spike in gases created, and a larger secondary flame.   But 
> that is rather short lived (less than a minute usually), and then the 
> secondary fire cuts back or even dies because much less gases are coming 
> to the top.
> 

That makes sense, thanks.

> Note:   adding dry fuel on top of the charcoal bed at that time can get 
> pyrolytic gases (and water vapor) that are NOT being combusted by the 
> secondary flame IF the secondary flame is no longer there. THAT results 
> is smoke escaping.   

Oh yes! :-(

> Throw in a match or flaming fire brand.  Something 
> needs to restart that secondary combustion.   At the risk of having 
> smoke, some blowing ONTO THE TOP OF THE NEW FUEL might get an ember to 
> glow and ignite the gases.  It can be done, but if done incorrectly, it 
> can get a bunch of smoke, 

Mmm :-(

> and irritated (maybe drunk) husband who then 
> beats his wife because of the smoke.   She needs practice and success, 
> or she will not be doing that "add fuel to the top" stunt more than once.
> 

I've only got the neighbours to worry about fortunately, and no one has 
complained so far, but it is not good when this happens.

> 4.  Neil wrote:
> > I three quarters filled the pot with chunked
> > hazel which has remained outside uncovered and was damp/wet, and I
> > deliberately left the bark on and didn't split it!  I then filled up the
> > rest with 'stove top' dried and split wood.  So unused to doing things
> > this way, and with hindsight not really leaving enough working room for
> > the top fire, the thing reached the damp wood and went out very suddenly
> This is different from what you described of having damp fuel SOMEWHAT 
> FUNCTIONING in TLUD mode, and then puttin the middle fire onto it.  What 
> you describe (above) give NO heat to the damp fuel to help dry it out 
> because all of the heat is going up, and not impacting the lower, damp 
> fuel.
> 

I'll try and be clearer.  It went out because I failed to catch the small 
top fire with fresh wood before it exhausted, that's all.  As long as I 
can sustain the fire on top of the bed of damp wood, the damp bed will 
dry out and entirely consume within the same cooking time where I would 
normally be reviving the stove with fresh dry fuel after the batch 
loading has pyrolised. The need to refuel therefore diminishes as the 
damp batch dries out and its MPF descends. The damp fuel does all consume 
with a slow MPF.

>From my cooking pov the above is preferable since the fire is strongest 
just after start up on the dry wood as everything needs to heat up, and 
the food needs less tending than the fire.  By the time the food needs 
more tending and removing cooked, the fire needs less attention.

> Neil, I do not normally (because of lack of time) do this much 
> explanation for an individual.  However, in this case,
> 1.  you raised interesting new-ish questions about damp fuel
> 2.  you are actually doing the experiments and reporting your results to 
> all of us, and
> 3.  this is a public forum and our Stoves Listserv discussion is 
> preserved for later use.  (I would not do this on a one-to-one private 
> basis.)
> 

I am pleased if this thread has value to others on the list, which is 
where it should be in that case, but I'm still appreciative of your time 
and explanations which I value, thank you.

> However, most postings of emails are not collected as in prepared 
> documents that have titles and can be more easily accessed.  I hope that 
> you (or others?) might take the time to pull this info together into a 
> document.   I know from experience that I will not get to that task.
> 

As a listowner myself for nearly 20 years I know only too well the truth 
of the limitation you mention. Lists are not databases.  I'm not a 
scientist myself, so anything I write will be more intuitive, speculative 
and empirical but it had occurred to me that I probably should try to 
share techniques for these small 'trekking' stoves at some point.  I 
would need to learn a lot more with your type of stove as it sounds as if 
Tony Vovers has with the Prime stove in Indonesia before being able to 
make adequate sense probably, but happy to help with anyone else on this 
subject if wanted.

> Keep the discussion going.
> 

Indeed.  I'll spare you all daily reports!  But when I have something new 
to report.....

Best wishes,   Neil Taylor

> Paul
> 
> 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 11/15/2016 9:57 AM, neiltm at uwclub.net wrote:
> > On 14 Nov 2016 at 12:12, Paul Anderson wrote:
> >
> >> Neil,
> >>
> >> This is a very informative conversation.  I hope a number of Stovers are
> >> reading the messages.
> >>