[Stoves] Charcoal Stoves

[Dean Still]

Dear STOVES,

We have been experimenting with charcoal burning for the last week or so
trying to improve a charcoal burning stove from Mauritania. Saturday I cut
off the bottom of a Rocket stove and plastered shut the fuel entrance in the
side. This created an insulated vertical cylinder 33 cm tall. I installed a
grate in the bottom. 600 grams of charcoal were placed on the grate and lit.

Photos and test results have been sent to Tom to post.

>From the start of the burn there were flames above the fire. After about 15
minutes the cylinder above the fire was at 650C and full of flame. At this
point almost all of the CO was being consumed.

A Jiko type charcoal stove took 29 minutes to boil 5 liters of water. The
Rocket charcoal stove without a skirt boiled the water in 22 minutes.

Emissions made to boil the 5 liters and simmer the water for 45 minutes
using the Jiko type was: CO=74 grams  PM=85 micrograms. Charcoal used was
675 grams.

The Rocket charcoal stove made: CO=12 grams  PM=81 micrograms. Charcoal used
was 604 grams.

In My Opinion:

In our previous tests with a Jiko type stove improving heat transfer by
radiation and conduction helped to decrease fuel use and emissions. 

The Rocket charcoal stove creates a zone of heat and flame above the burning
charcoal that reduces CO. Heat transfer to the pot is mostly by convection.
The tall insulated Rocket 'chimney' above the fire creates velocity that
increases heat transfer to the pot by thinning the boundary layer of still
air under the pot. 

We like to see wood burning stoves use less than 15,000KJ to boil 5 liters
and simmer it for 45 minutes in the International Testing Pot. The Jiko type
charcoal stove uses 26,089KJ. The Rocket charcoal stove uses 23,983KJ.
Velocity may be high in this stove, due to the 33cm high insulated chimney,
but the Delta T seems to be lower compared to a wood burning Rocket (around
950C) so more energy is required. On the other hand, we will try to use a
skirt and adjust the spaces under the pot which could improve heat
transfer...

Proposed benchmarks of performance for wood burning stoves were introduced
at UCB and ETHOS this year. They are: (Boil and Simmer for 45 minutes 5
liters)

Fuel to Cook	g	850
Energy to Cook	kJ	15,000
CO to Cook	g	20
PM to Cook	mg	1500

The Rocket charcoal stove met all the wood burning benchmarks except Energy
to Cook. 2/3rds of the energy in wood is lost when making it into charcoal.
And in the two charcoal stoves it took a lot more energy from the burning
charcoal to boil and then simmer water. Burning wood remains a much more
energy efficient method for cooking. Reducing CO by creating a hot zone of
flame above the charcoal is a simple way to make it a bit safer, when used.

Best,

Dean