[Stoves] Igniting TLUD stoves (off shoot from Re: Very small stoves and reheating food)

[Paul Anderson]

Dear Frank and Stovers,

I changed the subject line so that this conversation about igniting 
TLUDs does not mix with the small stoves discussion that I hope will happen.

Igniting a TLUD stove can be accomplished in several ways, but the 
bottom line is that a "sufficient" (not yet quantified) layer of hot 
charcoal is across the entire top layer of the TLUD fuel so that the 
pyrolysis front can progress downward.

At the first moments of ignition, the oxygen for the combustion of the 
ignition material comes from the immediately surrounding air.   I am 
sure that as the initial combustion sends flames upward, the initial air 
(which serves both the primary and secondary combustion) is pulled in 
from the sides of the top of the TLUD.  But soon it is also being drawn 
from below, that is, upward through the pile of fuel.

It follows that there needs to be sufficient ignition materials to 
establish the up draft and also create the initial layer of hot charcoal 
on the top.

Let's say that there are three scenario:   Too little ignition material; 
the right amount; and too much.

1.  Too little is quickly observed with self-extinquishing of the 
ignition material, or maybe some fire in only one sector of the surface 
of the pile of fuel.

2.  Too much has two variations:

a.  The excess starter material could actually being burning like the 
main fuel.   And since in general the starter is more costly (in money 
or preparation time or scarcity) , excess starter is wasteful.  So in 
general we do not want to overload with starter material, but if it is 
plentiful, be sure to use a sufficient amount.

b.  The excess starter material could have an undesirable 
characteristic.   For example, this occurs when the starter material is 
fuel pieces that have been "enhanced" with a small amount of more 
volatile material such as kerosene, alcohol, wax, or if it is natural 
biomass such as "fat wood" (resin-rich wood) or birch bark.  The correct 
amount of starter is great, but excess will result in too many volatiles 
so that the secondary air is insufficient, resulting in a taller sooty 
flame until the extra volatiles are gone.   Therefore, do not overdo the 
amount of these "enhanced" starters.   (and that also represents waste 
of the more valuable starter material).

3.  The correct amount of starter is the "Goldilocks' just right" 
situation.   And there are several observations, and I hope that others 
will add even more.

First a NOTE:   From the Boy Scouts.   Fires are made with tinder, 
kindling, and main fuel.   Tinder (such as wood shavings) can be ignited 
with a match.   Kindling (small twigs, etc) would need too many matches, 
so it is ignited by the burning tinder.   And the main fuel (sticks, 
pellets, wood chips, etc) is ignited by the burning kindling.    Tinder 
in general cannot ignite the main fuel unless you used quite a bit of 
this thin and dry biomass.

A.   In Uganda, the common way that I have observed is for the user to 
first fill the TLUD with the main fuel, and then in the top 2 to 4 cm of 
the fuel chamber to make a small "teepee" of thin tinder and then some 
kindling above the tinder.   This would generally have a diameter and 
height of about half the diameter of the fuel chamber.   This little 
material is ignited and carefully tended, for perhaps 1 to 4 minutes, 
without any concentrator lid being used.   It is a very clean burn.  
When it is clearly burning well, the starter fire is spread with a stick 
or rod to cover the top layer of the main fuel.  There is not rush, but 
the concentrator lid is soon put into place with an appropriate riser to 
enhance the updraft.

(Personally, I lack the patience and skill to do that type of ignition, 
but my Ugandan associates do it all the time, with great ease.  Their 
success negates any criticism that extremely poor people cannot afford 
or have access to even a small amount of kerosene to start the TLUD 
cookstoves.)

B.  The other way is to use some "enhanced starter material" that serves 
the function of the tinder and kindling.  In the past (in the early days 
of TLUD stoves as recently as 2006), the critics of TLUDs at stove 
testing events smiled only slightly when they referred to the use of 
enhanced starter material as "cheating." Thankfully such comments seem 
to have disappeared.   But it is appropriate to note whenever they are 
used.   And also note that if too much starter materials are used, they 
can give off excessive emissions at the beginning that unfavorably 
obscure the otherwise extremely low emissions of TLUD stoves.

C.  Starter materials are commonly liquids or wax-type substances that 
catch fire easily when the match is struck.  Those can be either

(1) added onto the main fuel shortly before ignition.  This is not the 
best way because drips can run down the sides of the fuel or fuel 
chamber.   or

(2) can be added to (coated or soaked into) some kindling-type biomass 
that is then placed on top of the pile of fuel.  How much to use is 
learned by experience because each starter material has different 
characteristics.  NOTE:   If you are tending to the ignition stage for a 
minute or two, you can watch for the three scenarios of too much, too 
little and just right.

Too much will be obvious, but be aware that the initial high and sooty 
flame might not be leaving behind sufficient charcoal over the whole 
upper surface of the column of fuel.   And it is unwise to attempt to 
remove ignited starter material.

Too little can be overcome IF you have some additional starter material 
prepared to add carefully.   This is NOT a time to be spraying volatile 
liquids into a burning area.  Better to have some pre-soaked pieces of 
fuel that can be dropped in as needed.

Goldilocks' Just Right is by far the best scenario.   And it does take a 
little practice.  But when it goes well, you will know it and you will 
replicate that situation easily the next time.

4.  About starter materials:   There is a wide range.   Here are a few:

a.  Liquids:
Kerosene
Charcoal lighter:    very good, if available
Lamp oil
Diesel fuel (not great)
Alcohol  (91% or higher):  VERY clean burning, but is quite volatile, 
can go "poof", and can be burning but not visible especially in sunlight.
Turpentine

NOTE:   Gasoline is NOT acceptable.   Simply too volatile.

b.  Solids:
Candle wax
Fat-wood
Commercially prepared fire starters (sold in hardware stores).

c.  Preparation of appropriate fire starters:

Whatever fire starter you prepare needs to be saved in an appropriate 
seal-able container.   I like to use clear-plastic jars such as those 
for peanut butter or mayonnaise.  (Glass can break, so I do not use 
glass.)  It is generally convenient to prepare the fire starter in the 
container that will store it. The amount in a standard peanut butter 
size jar (about 500 ml.) should be sufficient for starting 5 to 10 fires.

With moderate care, select pieces of fuel that are kindling size 
appropriate for your size of TLUD and place them into the jar. Add as 
SMALL amount of the liquid, close the lid and shake so that the liquid 
comes into contact with most of the pieces.   The liquid will be 
absorbed, so there should be no liquid visible in the container.

The intention is to NOT saturate the fuel pieces.   Very little of the 
liquid is needed to get the kindling pieces ignited.

Note:   Pellets are highly densified and do NOT absorb much of the 
liquid (or they would start to break up).  The liquid on them will 
vaporize quickly and will generally not ignite the pellets.   It is far 
better to have some wood chips with starter fluid to ignite the layer of 
pellets below.   Note that pellets can be difficult to ignite initially, 
but once they are pyrolyzing, they are a fantastic fuel in TLUD cookstoves.

5.  Another trick (logical but often forgotten):   When the fire started 
is ignited, most of the heat goes upward.   Therefore having "some" 
(undefined quantity) of regular kindling-type fuel spread thinly ABOVE 
the enhanced starter material greatly assists to create the needed layer 
of charcoal.   This is especially important if the main fuel below is 
pellets.

Summary:   Provided that the main fuel is dry and ready for pyrolysis, 
and provided the stove user has some minimal experience with TLUDs with 
that fuel and an appropriate fire starter, the ignition should be quite 
easy and virtually without smoke.

Further comments are welcome from everyone.  We will try to get them 
incorporated into some useful document to post at www.drtlud.com and at 
other sites.

Paul

Paul S. Anderson, PhD  aka "Dr TLUD"
Email:  psanders at ilstu.edu   Skype: paultlud  Phone: +1-309-452-7072
Website:  www.drtlud.com

On 10/20/2012 1:15 AM, Frank Shields wrote:
> Dear Paul,
>
> I am interested in knowing what is the common method used to ignite the fuel
> in your small stoves? I'm thinking steps to making igniting the fuel easier
> is perhaps the next limiting factor to making these stoves more useable-
> agree?
>
> Thanks
>
> Frank
> .
>
>
> -----Original Message-----
> From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
> Paul Anderson
> Sent: Friday, October 19, 2012 10:38 PM
> To: Discussion of biomass cooking stoves; Hugh McLaughlin; James S. Schoner;
> Noeli Anderson; Steve Sewell; John M Bare; Doc Anderson
> Subject: [Stoves] Very small stoves and reheating food
>