[Stoves] Accidental TLUD technique discovery

Sun Nov 13 16:49:07 CST 2016

TonyV

Re lighting the Prime:

Everyone having any difficulty at all should try using a lighting cone and all those problems will disappear in a hot glow.

Lighting damp fuel goes much better with a lighting cone.

SNV has been testing them in the field for more than a year ‎in Laos and report dramatic improvement in lighting times, smoke reduction and a little fuel saving. They are rolling out nationally as a universal tool that provides consistent benefits. People with one use it just over an average of twice a day.

Ignition problem?
Lighting cone.

Sizes and details vary. SNV has the best handle.

Regards
Crispin

Tony & Neil:

Of course for all stoves, fuel species, moisture content, and type is going to have a significant impact on combustion outcomes.  You maybe missing the big picture though, and consider opting for a larger insulated TLUD or Rocket Stove with robust combustion chambers.  Choose a stove designed for home use cooking application.  The simple Chinese gasifier you mention, or our improved SilverFire Scout TLUD is an uninsulated trekking stove, it was not designed to be an everyday home use TLUD.  It is uninsulated intentionally, for quick cooling on the trail, for on the move cooking applications.  It was never intended for base camp or home cooking.  We also tested the larger Prime unit last year and felt it had the combustion short comings that you discuss.

Our larger home units (natural draft & fan units) incorporate more robust combustion chambers that are insulated.  They are more forgiving, with less than desirable fuel.  However, fuel is obviously the most important denominator for most efficient outcomes (crappy wet fuel makes for crappy outcomes).  One of our oldest customers and best intuitive cooks we have met (4 course meals on our stoves), simply plans ahead.  During the dry season she places garden clippings (grape vine clippings, garden debris, & twigs in a small bundles tied off with jute string) in a locking lid rubber trash can.  These prepared biomass fuel bundles are then inserted in stove at each meal time.  She has 2 large cans with a couple hundred bundles always on the ready.

There are a lot of insulated stoves out there designed for home use that we would speculate would provide you with better outcomes, however attention, to fuel and preplanning may also improve your outcomes.  Good cooking!

Regards,

Todd Albi, SilverFire Stoves & Cookware
www.silverfire.us<http://www.silverfire.us>

On Sun, Nov 13, 2016 at 6:42 AM, Tony Vovers <vovers1 at gmail.com<mailto:vovers1 at gmail.com>> wrote:
Neil - I have found similar effect with a Prime Cookstove from Indonesia. A lot of the local found Biomass is not dry and storage is not easy in the tropics. I think these high efficiency TLUD might need a better wood drying feature even something that could be put on top at the end of cooking to get the next batch ready.
The Prime seems to have "primary" holes both below and along the sides of the burn chamber. This makes it a little more tolerant to the effects you observed.
the stove consistently burns for 50-70 minutes on 1-1.3kg of Biomass. It's a bit finicky to start but lovely to use and simple to cleanout.

With wetter biomass adding extra small stuff on top keeps it burning in a different "mode" but too much will cause too much ash.
I am wondering if a "tool" like a blow tube could be used to kickstart it and clear some of the ash.
Glad to see that others are looking at performance in suboptimal conditions.

I would be very interested to get feedback on how to get these stoves to light quickly and reliably without creating too much ash, this part seems to be the toughest so far as the tinder material ash then affects the initial performance making it a tough "sell" to some users.

TonyV

Tony Vovers
+1 281 7381000<tel:%2B1%20281%207381000> (VOIP)
+62 (813) 3888 9062<tel:%2B62%20%28813%29%203888%209062> (HP)

On Sun, Nov 13, 2016 at 9:54 PM, <neiltm at uwclub.net<mailto: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/<http://www.telegraph.co.uk/technology/2016/10/12/man-spends-11-hours-trying-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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