[Stoves] Accidental TLUD technique discovery

neiltm at uwclub.net neiltm at uwclub.net
Mon Nov 14 06:11:05 CST 2016


On 13 Nov 2016 at 14:45, Paul Anderson wrote:

> Dear Neil,
> 
> Very nice description of what you accomplished / learned.  Very useful 
> information.
> 

Thank you.

> Question:   "riddling" is a UK word for "shaking"?
> 

Yes, if 'shaking' is American English for agitating the grate to release 
ash and fines to maintain air flow?

> What you have described refers to when the fuel is sufficiently damp to 
> hinder proper / expected TLUD performance with a descending Migratory 
> Pyrolytic Front (MPF)that does not sustain the processes (plural).  But 
> not so wet that there can be no MPF pyrolysis.  There is some 
> mini-burning of some of the created gases so that the pyrolysis can 
> continue at the MPF.
> 

Yes, that seems a good description.

> But the pyrolytic gases that move above the MPF are either:
> A.  too cold to be combustible with the secondary air later, or
> B.  too insufficient (quantity) to sustain the secondary combustion, or
> C.  have too much water vapor (therefore are "diluted" to sustain the 
> secondary combustion, or
> D.  combination of the above, or something else.
> 

All three I would guess.

> Whatever the case, things are not working.
> 
> So, you are showing that a small, frequently tended, additional zone of 
> combustion (another fire that I will call the "middle fire" because it 
> is between the MPF and the secondary combustion) can be made perched on 
> top of the charcoal that was created by the MPF that continues to move 
> downward.
> 

Yes.  Although this all started from the outset and the way all TLUDs are 
started with some sort of starter fire on top of the main charge, if only 
the top layer of the main fuelling soaked in alcohol.

> That small additional "middle fire" could be with several variations.  
> Please tell us about your experiences and observations regarding the 
> following (You might do some intentional further experiments to confirm 
> or deny the following):
> 
> The middle fire must get SOME oxygen from somewhere to be sustained.   
> The O2 either has come up through the fuel-MPF-charcoal (which is quite 
> possible because it is blowing past the MPF where the pyrolysis is so 
> weak because of the damp fuel.)
> 
> OR
> 
> The O2 is coming downward from above, circulating in and keeping things 
> hot enough for pyrolysis to occur.
> 

It will be both.  With the fuel charge built up to just below the level 
of the secondary air holes, when it is lit it is very obvious, 
particularly with the Reed fan stoves, especially at the point of 
starting the fan and observing the flame disturbance that the secondary 
air is probably enough directed air regardless of the primary air from 
below.  I guess that with keeping the pyrolising mass at that level 
through refuelling, this remain true.  With this morning's burn it seemed 
that the main pyrolysis front was contiguous with the pyrolysis of the 
added fuel, that they were not discernably separate layers, there being 
no body of non combusting char between them, and the level of fuelling 
gradually lowered with the pyrolysis of the main charge.  I hope that 
made sense?  It is perhaps worth remembering that the height of the 
secondary air holes is a mere 5 inches from the ground.  Only through a 
batch burning of very fine chip does the MPF noticeably lower beneath a 
combustion chamber largely remaining full of non combusting char.

> OR
> 
> Your stove might be one with some side holes in the wall of the fuel 
> chamber.
> 

It isn't.

> Whatever the case, there are a couple of options:   (What did you observe?)
> 
> A.  The middle fire is actually more of pyrolysis (and a shortage of O2) 
> so there is more "smoke" (pyrolytic gases) created and they rise 
> together with whatever is from the MPF to come into contact with the 
> secondary air, giving some cooking fire as is normally associated with a 
> TLUD with dry fuel.
> 
> OR
> 
> B.  The middle fire is actually a "diffusion fire" with pyrolysis and 
> burning of gases AND even some char-gasification, resulting in a rather 
> traditional fire perched on top of the charcoal in the TLUD.
> 

I think it is more B than A, except that as explained above I think it is 
probably misleading to think in terms of two separated combustion 
processes. That might be possible to achieve in this stove though.  
Firstly the main charge would have to be very fine such that it retained 
a significant body of non combusted char above the MPF, which it 
invariably does with fines.  Under these conditions as can be imagined, 
placing fresh wood on top of the char where the MPF is at the bottom of 
the stove with a mass of non combusting char above it, results only in 
the slow build up of uncombusted smoke, but I would expect it to be 
possible to separately ignite such a top layer of fuel, certainly if near 
the secondary air holes.  I've not conducted this specific experiment, so 
cannot say if fresh wood at a mid chamber level would find sufficient O2. 
I imagine separately lighting such a mid layer might be too problematic 
because of restricted access and hot gasses extinguishing the ignition 
flame as has always happened when I have tried to sustain a match below 
the level of the secondary holes. A small braiser's LPG torch however 
will ignite such a layer. 

Bearing in mind the squatness of the stove, the mid fire experiment would 
be more meaningful with a taller fuel chamber I think, otherwise the 
separation of layers is likely to be too uncertain in so few inches. I 
feel clear that when large lumps of wood are burned as the entire fuel 
charge, the vigorous unrestricted primary air flow ensures that even 
where there is char above the MPF when it has reached the bottom, the 
entire body of char is consuming very rapidly, and producing a nice blue 
flame from the top of the char.  The large amount of primary air present 
from the outset of the firing I feel ensures a continuous close 
connection between the MPF, and the fuel igniting immediately above it.  
With completely dry medium sized wood as a TLUD this stove is a 10 minute 
towering inferno.  By introducing larger fuel size, damper and denser 
material such as my hoard of mice opened plum stones, the burn time can 
be extended easily to 20 minutes or as much as 30, which is a lot easier 
to cook with of course.

> To test the difference between A and B, what is needed is that the 
> middle fire is down lower into the metal fuel chamber (cylinder), not up 
> near the top.   So, does the same advantage occur if the cylinder is 
> sufficiently taller?
> 

I would need to modify one of my taller tincan stoves to replace the 
bottom of the fuel chamber with a wire or expanded metal grate, so can't 
answer that Q very quickly,  but have been intending to revisit these.

> RESULTS:
> 
> 1.  If A above, that final combustion might have low emissions of CO and 
> PM such as with normal TLUD usage.
> 

I think I see what you are getting at, but what I'm having difficulty 
with is envisaging achieving this without a separate ignition at a half 
way stage of a batch burn.  It might be a possible if tricky experiment, 
but rather impractical otherwise surely?  But perhaps I have 
misunderstood?  Achieving this 'dual front' stage naturally from start 
up, the mid fire would presumably either have to produce its own MPF 
(more statically than migrating), or not consume the body of char left 
unburnt by the initial MPF, at least at as fast a rate as the descent of 
the initial MPF?  Can a batch loaded TLUD be made to split into two 
'fires' by top fuelling before the batch has consumed?  I don't know the 
answer to that, but I feel as sure as I can be that is not what is 
happening in my stove.

> 2.  But if B above, the emissions would probably be more similar to a 
> regular "contained" fire (not an open fire like 3-stone type).
> 

Yes, I think so.  This stove is sold with no instructions or mention of 
being used as a TLUD, so most will simply light a small fire in the 
bottom of it and continuously feed it.  It does work well that way, and 
placing a lit pine cone in the bottom and another 2 or 3 and/or some 
twigs on top is an almost instant fire needing no preparation.  But it 
does tend to burn with less smoke as a TLUD, and is my preferred way to 
start it. Sustaining it indefinitely beyond the batch loading is where it 
gets most interesting.

> As I said, I like what has been discussed.  Pardon me if I have 
> misunderstood something. 

I don't think so, except perhaps where you conjecture a fire 'perched on 
top of the charcoal'.  Probably not achievable in these stoves at least.

> Looking forward to your next message or 
> comments by others.
> 

Thanks for your thought provoking response.  I hope this reply clarifies 
more than confuses!

Here is a question though?  What happens if building a conventional open 
fire, not straight onto the ground, but on top of a base of wet or damp 
wood instead? The base wood would eventually dry out and be consumed, but 
surely to the advantage of the main fire above it which might be the more 
stable for such a base?  I think this is essentially what I achieved in 
miniature, and enclosed of course.

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 11/13/2016 7:54 AM, neiltm at uwclub.net wrote:
> > There have been days of rain here in the SE of England, and my outdoor
> > wood, consisting at the moment mainly of Hazel coppiced two or three
> > years ago for runner bean poles, but now too weak and snappy to be
> > re-used, but ideal easy fuel for the (ebay/amazon) Chinese wood gas camp
> > stoves, has been getting progressively wetter as the softening (rotten)
> > fibres cease to be able to repell water as well as more freshly or
> > quickly dried or seasoned wood.
> >
> > So this morning, despite having loaded the stove yesterday for this
> > morning's breakfast, and kept the stove indoors, the wood simply hadn't
> > dried out well enough to sustain the pyrolitic front once the top
> > ignition layer of well dried fuel had been exhausted.  This is an old
> > learned lesson, that there is no use, beyond a subtle difference at least
> > in stratifying a TLUD in the hope that it will be going well enough by
> > the time it reaches a lower layer to cope with meeting wet wood.  There
> > is an extent to which you can get away with it, but it's too easy to
> > miscalculate, although it does have the potential if you can manage it
> > for a strong boiling flame to turn itself into a simmer flame at the
> > point where you want that.
> >
> > Rather than tip the whole smoky mess out into a tin and put the lid on
> > it, I hoped that it might not be too far off and might sustain if I just
> > put more dry tinder and candle wax gratings on top, as is often the case
> > with a failed start.  Three times I did this.  It did not want to burn
> > that damp wood.  Still I didn't bail out, but instead contented myself
> > with feeding the top with thin dry wood, and cooked on that, continuing
> > refuelling as I went, just as you would if continuing the burn of a TLUD
> > batch AFTER it had all pyrolised because you still want a fire.  In other
> > words this morning I worked this in reverse, refuelling from the outset
> > as slowly, the batch burned right down by the end of the cooking.
> >
> > It was immediately apparent that this way round had several advantages
> > over the more expected batch burn, then refuel to extend.
> >
> > The fire was a much steadier middling heat level throughout the cook,
> > which was better suited to what I was cooking.
> >
> > The fire was easier to sustain for the length of time and amount of the
> > cooking, needing less rather than more tending as the batch burned down.
> >
> > The problem of sustaining a fire in these stoves after the batch has
> > burned are twofold:
> >
> > Firstly ash builds up and chokes the primary air requiring riddling,
> > (there are no lower on the side primary air holes).  Secondly, unless the
> > lumps of wood are large, so much small char builds up with only the base
> > ignited, that no amount of riddling will permit refuelling without smoke.
> >   If the fuel is large, the char is burning vigorously with its own blue
> > flame, but this results in the refuelled fire losing its base eventually.
> >   Refuelling works great for a while, but then unless refuelling is
> > sustained at quite a high rate, the base of the fire simply disappears,
> > leaving insufficient embers to ignite new fuel.  However, even with these
> > vigorous stoves maxing out on primary air, not even trying to design for
> > a soot free fire, it is possible to add too much fuel and start to make
> > smoke, something that the cleaner burning 1:6 air ratio stoves suffer
> > from to a much greater extent.  In general though it is the greater
> > forgiveness of lack of fine tuning and fuel fussiness that is the
> > strength of these stoves, and why IMO they are so much better in camping
> > situations, where adaptability to whatever fuel is available is key.
> >
> > But my persistence this morning resulted in discovering a different way
> > of using these stoves that worked well, once I adapted to continuing the
> > refuelling from the outset, and which I can easily adapt to doing by not
> > initially filling the stove right to the top.
> >
> > There is a clear advantage, in camping type situations at least, but
> > possibly elsewhere such as refugee camps maybe where there might be a
> > problem of sufficient dry wood, to know that there is a good way of
> > utilising a batch loading of wetter wood, by lighting and refuelling a
> > conventional fire on top of it with dry wood until it will sustain the
> > rest of the batch, or perhaps with decreasing feeding of dry wood
> > depending on how wet the wood is, or strength of flame wanted.
> >
> > There is also an advantage in gaining greater heat control, and the
> > primary air supply will remain more constant with reloading at the start
> > of the burn rather than at the end.  The wet wood batch sitting
> > underneath the dryer wood fire acts as a buffer, a stabiliser of the
> > small fire on top in a way that simply lighting a small fire straight
> > onto the grate does not.  This must be because there is a stable, but
> > slow pyrolytic front constantly at the base of it.
> >
> > I'm not advocating this as a generalised preferred way of using TLUD's,
> > merely sharing, for me at least, a newly discovered versatility that
> > definitely has worthwhile application in some circumstances, but in
> > general does perhaps show that some TLUD designs that have or can permit
> > less restricted primary air can be highly versatile and adaptable stoves,
> > capable of utilising in the same physical stove a very wide variety and
> > condition of fuel, and being controllable through fuel
> > modification/selection rather than, or in addition to stove damping.
> >
> > I can't help but conjecture that where an end user has spent their
> > lifetime daily tending a three stone fire, they will have such a wealth
> > of experience with fire and fuels that they can bring to maximise the
> > potential in a TLUD, that if that TLUD permits greater versatility
> > through permitting at least a maximum possible of primary air, then this
> > surely might be one key to continued adoption of a stove, that it permits
> > wide adaptation and uses the lifetime empirically gained knowledge of how
> > to use fire that the user brings to it.  If on the other hand it's design
> > is too specialised, and cannot adapt, its future will be the more
> > dependent on the supply of a consistent and affordable fuel that it works
> > well with.
> >
> > I'm guessing that when Paal Wendelbo used to say 'start with the fuel and
> > build the stove around that', what he was mostly doing was adjusting the
> > size/proportions of his Peko Pe stove and primary/secondary air ratios to
> > most suit the fuel he found?  Good principle where the fuel and cooking
> > needs are more of a constant, but the Chinese camp stoves, as with the
> > similar Bush Buddy stoves and derivatives (like the Solo range) with wire
> > grates, maximising the primary air, encourages an endless learning curve
> > that teaches the user how to get just what they want from them.  It
> > teaches you no less about biomass, different woods, their condition and
> > preparation, and fire making, than an open fire does.
> >
> > There is real satisfaction in that, just as I've just been reading about
> > traditional hay making with a hand scythe delivers, despite back breaking
> > labour, a profound happiness and contentment.  Another unquantifiable
> > dimension to contend with, LOL.
> >
> > Maybe that sort of unsuspected intangible is why Bangladesh once came top
> > of an early 'world happiness survey' in the 90s, despite great poverty
> > and loss of life in natural disasters.  I can easily afford to cook
> > breakfast on natural gas in our centrally heated kitchen, but something
> > that gives me a satisfaction I find hard to resist, drives me out even on
> > frosty mornings, to cook it on a simple wood stove instead.
> >
> > But here is what we are intended to aspire to in the affluent west:
> >
> > http://www.telegraph.co.uk/technology/2016/10/12/man-spends-11-hours-tryin
> > g-to-make-cup-of-tea-with-wi-fi-kettle/
> >
> > Tears rolling down cheeks!  A candidate for the Darwin awards perhaps?
> >
> > I don't think so.  I'll stick with my eccentricity!
> >
> > Neil Taylor
> >
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