FW: FW: [Stoves] RE: Charcoal Stoves - measuring CO

[Dean Still]

Dear Crispin,

In response to your question about calculation of CO emissions....

We are using an emission collection hood connected to a PC which displays in
real-time and records the emissions of CO, CO2 and PM each second.  All
three phases of the Shell/UCB 2003 Water Boiling Test is run under the hood,
bringing the stove to boil from a cold start, again from a hot start, and
then a simmer of 45 minutes.  Data from the WBT and hood measurements is
combined automatically in software written in excel by Tami Bond.  This
software combines the ppm emissions with the flow rate through the hood to
determine mass flow rate and thus the mass of pollutant emitted during each
phase of the test.  We also calculate emission factors and CO/CO2 ratio from
the mass totals of CO, CO2 and fuel burned for each test phase.  CO and PM
"to cook" is the average of cold and hot start mass emission added to
simmer.  We have developed benchmarks for CO and PM emissions based on tests
of over 40 stoves in this manner.  Also we are developing a portable
emissions hood which is of equal quality as our lab hood but at a fraction
of the cost and complication.  We hope it will be available by the end of
the year for about $3000 to people trying to learn about fire and build
better stoves. 

And about charcoal burning in general....

I've also been learning some interesting things about charcoal while testing
two stoves from Africa this past week...  we wondered whether closing the
draft door of a charcoal stove during simmering to lower the power did
increase CO... it turns out not.  Both the CO/CO2 ratio (between 8% and 15%)
and emission factors were actually slightly less during simmering,
suggesting the fuel is burning just as cleanly if not better.  Also, Heat
transfer to the pot was increased when the pot was sitting direcly on the
coals with a grate below compared to sitting 1-2 cm above the coals.  We
believe this is due to the addition of conduction to the radiation transfer.
Emissions did not increase when the pot was directly on the coals.  I also
ran a test with a wire mesh under the coals rather than a grate with only
15% open area, and this did not improve heat transfer or emissions.  So, my
preliminary conclusion is that limiting the air to charcoal does not
adversely effect performance of heat transfer or emissions in these
traditional types of charcoal stoves.  But now Dean went and made a charcoal
rocket stove which operates completely differently and amazingly clean!
Hopefully we'll have time to write up a report of all this soon. 

Best wishes,
Nordica MacCarty
AT Engineer, Aprovecho Advanced Studies in Appropriate Technology Lab 

 



Dear Dean

I am interested in how you calculate the CO produced during a 'cook'.

First, is it from starting the fire to the end of the test, or is the fire
established when the cooking starts?

Then, is it a number based on the total carbon burned combined with sample
CO/CO2 ratios taken on a regular basis?

I have some measurements from testing an alcohol gel stove today and I would

like to work out the CO produced during a boiling test.  On high power the 
CO level was very consistent, and dropped to a consistent level when turned
down.

For example, if the CO produced on 'high' was a consistent 4% of CO2 and the

fuel burned was 60 gm, is the CO produced simply 4% of 60?  If I work on a 1


minute interval and calculate the CO for each mass of fuel burned in that
period is the CO a sum of those results?

I am not sure if you have a computer connected to the test appartus that
integrates the samples on a continuous basis or if it is calculated 
separately.  I would like to be able to make meaningful comparisons with
your tests.

Many thanks
Crispin