[Stoves] Mewar Angithi: An In Situ Modification of the TSH as a Solution to the Problem

Crispin Pemberton-Pigott crispinpigott at outlook.com
Sun Dec 13 19:14:58 MST 2015

Dear Francesco


This device was discussed earlier this year (late last year?) on this list.
Perhaps you did not see those messages. 


In terms of function, it is very similar to the grate added to the
traditional Keren Stove from Java which is produced in the millions each
year by artisans.


The Keren was improved significantly, particularly in terms of fuel
efficiency, by adding a sloped grate under the fire and admitting air at the
back instead of all coming from the front. Another change was increasing the
height of the cylindrical portion of the body above the fuel entrance which
had the effect of lowering the fuel door height. Another modification was
reducing the pot rest height from 25 to 7mm in order to cap t he total gas
flow rate past the pot. This is the poor man's alternative to controlling
air entry.


Here is the original:


And here is the Keren Super



And here is the Keren Super 2 which is in an insulated metal bucket:



The other air entry holes (which were random, really) are all removed, with
air entering only with the fuel and under the rear of the grate.


The grate bar gap is important. It should be 4 to 5 mm (only) and the bars
should be 12mm round or reinforcing bars. It is cheaper to use a smaller
diameter but there is a difference in performance in that the air flow
through the grate is spread over a larger area and the effectiveness at
burning the charcoal is reduced.


The stoves look almost exactly the same at a glance, but the performance is
very different. The energy efficiency (fuel consumed energy to pot energy)
for the traditional layout is about 16-17%.  The Keren Super is 27-28%. The
main contributor is the taller top and lower pot rests.  The CO is reduced
by the grate and air supply.


The fuel saving is pretty large (1-old %/new %)*100% = 40% for such a simple
set of changes.


Anything that produces the same result will work, including the metal grate
inserted under the fire.


Here is a cast iron version of the Keren Super grate.



Note that the legs on the left are taller than the right. The left side goes
at the back and the short ones at the front. The casting pattern has all the
legs the same length. The two sides are identical and the legs shortened
afterwards. It is in two parts so it can fit through the hole.


Care should be taken with the shape of the top of the stove so the different
pot profiles all sit in such a way that the gap is 7mm. The gap is related
to the circumference and the firepower. It does not scale linearly. If you
change the pot and fire size a lot, check each gap 1mm at a time until you
fine that it is optimised. If the gas flow rate is too low, smoke will
emerge from the fuel door. It should almost do that. 


The Indian Chula can be improved by applying theses three adaptions: check
the pot rest height, increase the cylinder height (reducing the door height
as much as you an depending on the fuel that must get into it), add a grate
with air enter at the back (to push the fire towards the centre, not against
the back wall).


The orientation of the grate bars should be front to back, not left to
right. This allows the air entry to do a better job of pushing the fire and
when fuel it fed in, it is more likely to push the ash through the grate and
the charcoal to the back where the rear air will burn it cleanly.


Have fun!



Has anyone seen this addition to a traditional stone heart?  It is has been
developed in collaboration with the University of Iowa.


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