[Stoves] Philips Stove. Was Re: Jatropha press cake as a fuel

[Paul van der Sluis]

Dear Paul A.,

The TEG generator is mounted below the fire as can be seen  in:

http://money.cnn.com/popups/2006/fortune/better_living/5.html


To prevent overheating it is insulated to such an extent, that the hottest 
fire a user can make, just does not fry the TEG.


For explaning  your question on my  "top feed stove":

Discussion in this group have focussed on 2 types (and I quote from you)"

***********
One is the classical T-LUD method of "fill the fuel chamber, ignite at 
the top,
let it pyrolyze, then either empty out the char or let it continue to 
consume
the char."
*******
or 

*******
The other is what has been discussed here at the "trickle feed" (or 
trickle
fuel) method in which the fuel is continually added (at 20 to 40 second
intervals?) in small amounts dropped in over the top of the stove.  The 
trickle
of fuel could be from the very beginning or done after the pyrolysis stage 
has
been mainly completed.
******

I regard my stove as a hybrid. The preferred way of using the Philips 
stove is to start with small pieces of wood. To get the fire started and 
to make the stove hot.
That should take about 5 minutes. 
One could now trickle feed the stove, but that is very unconvenient for 
the user. That is why I prefer to put relatively large pieces of wood into 
the stove. Something
like 5 cm thick, 8 cm long pieces of branches. One piece at a time, but 
once burning a second and eventually a third piece can be added. This will 
last for 10 -  15 minutes at high power (high fan speed) or up to 30 
minutes continuous at low power (low fan speed). Gives the user freedom to 
cook or walk away. 
Larger pieces cannot be done because in that case the combustion chamber 
(fire) can cool down so much that the secondary flame (the flame burning 
the woodgas) can extinguish temporarily, resulting in large amounts of 
smoke. The stove should have enough thermal mass to be able to do this.
The large pieces now burn in the classical T-LUD method, but not from top 
to down but from outside to the inside of a woodpiece. The pieces pyrolyze 
from the ouside to the inside and become char that is eventually consumed. 
A new piece of wood should be added before all char is gone. When you 
interrupt the combustion and cut a piece of wood into two, the 
outside-to-inside pyrolysis can clearly be seen.
In this way you get the advantages of the clean burn from the classical 
T-LUD, combined with the advantage of continuous cooking of the trikcle 
feed. The disadvantage is that the cooking vessel should be removed to 
accomodate these large woodpieces 2 - 4 times per hour.  If that is 
unwanted, almost identical results can be obtained after splitting the 
branches length wise into two pieces, so they fit into the gap between the 
cooking vessel and the stove (which is 3 cm).
This size of the wood also has an influence on the thermal power. If I 
need really high power (preparing meat), I  feed small pieces in a faily 
high speed into the stove with the fan at high speed. If I need lower 
power I use only 1 large piece, with low fan speed. If I need really low 
power (for simmering) I use char which I saved from the previous cooking 
run and the fan at low speed. A full fill with left over char and the fan 
at low speed lasts for more than 1 hourt of unattended simmering.

It really pays in terms of cooking convenience to put a bit of effort into 
wood cutting. When I use the stove (and I cook on this stove for 2 years 
now for a family of 5) I have a box of wood pieces ready and I pick large/ 
or small pieces as I need it at that particular moment. After all cooking 
runs I throw the remaining char into an air tight metal vessel for later 
use.




*****
Concerning the thermal efficiency of about 40%, please describe the 
arrangement
of the pot (size, with skirt?, stainless steel?, with lid on?, etc) as it 
was
used on the stove when the testing was done.
******

The 40% efficiency is measured without skirt, lid on and a 30 cm flat 
bottom stainless steel cooking vessel holding 4l of water. With a skirt I 
can get efficiencies up to 80%, but who wants to use a skirt??

Regards,


Dr. P. van der Sluis 
Philips Research Laboratories Eindhoven