[Stoves] Accidental TLUD technique discovery

[Paul Anderson]

Dear Neil,

Very nice description of what you accomplished / learned.  Very useful 
information.

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

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.

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.

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.

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.

OR

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

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.

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?

RESULTS:

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

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).

As I said, I like what has been discussed.  Pardon me if I have 
misunderstood something.   Looking forward to your next message or 
comments by others.

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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