[Stoves] Ecocina testing report responses

[Dean Still]

Hi STOVERS,

 

Dean is forwarding this response from Nordica MacCarty, lab manager at
Aprovecho.

 


Dear all,

Thanks to everyone for the positive response and great questions about the
Ecocina testing report.  I always enjoy reporting on a stove test series.
This report was similar to the ones we do regularly for folks who are
interested in having their stoves evaluated.  Usually we will also recommend
and implement a change to the design, and then retest the stove to see the
effects of these changes. 

As for the questions we've had so far, I'll answer everyone in one email:

Crispin:
Yes, the system used for testing is the Portable Emissions Measurement
System (PEMS) that we have developed and displayed at ETHOS.  The intent of
the system is to serve as a simple and inexpensive emissions testing system
to be available to all who are interested in having emissions testing
capability for the lab and field.  The hood collects all of the smoke from
the stove, plus some extra room air.  The air flow through the hood is
measured, and the concentrations in that flow are measured as well.  The
volumetric flow rates are multiplied with the volumetric concentrations to
allow calculation of the mass of each pollutant leaving the stove.  Dilution
ratio does not need to be known because both the flow rate and concentration
of the diluted gases are known.  

While it would be interesting to know the excess air, that would require
direct measurement of the undiluted oxygen concentration as it leaves the
stove.  Because this sample is unmixed (unless you have a chimney stove),
you can not simply place a probe somewhere in the direct stove exhaust and
have a good measure of the average.  This is why we use the collection hood
for our CO, CO2, and PM measurements: the sample is well mixed and
represents the total emissions leaving the stove.  Unfortunately the oxygen
concentration in this measurement would go to ambient quickly and most
oxygen sensors do not have sufficient resolution for this measurement, so we
do not know the excess air entering the stove.  However, we have found that
knowing the output of pollutants can be more informative in terms of design
than knowing the exact input of excess air.

The spreadsheet and protocol we use is based on the UCB 2003 test updated to
clarify pot size and several other issues in 2007.  This can be found on our
website, http://www.aprovecho.org/web-content/publications/pub2.htm.  We
have incorporated this in-house to provide automatic emissions data import
and processing.  The spreadsheets have not been updated for the most recent
discussions currently revolving around the methods group, because none of
these issues have been closed yet.  As you will recall, the moisture content
calculation was only substantially effected by the most radical outliers of
fuel type and moisture.  The effect will be less than 1% under our
conditions.  So, no, the equations have not been updated *YET* but the
effects of the changes on this type of test series will be quite minimal.  

Chris Adam:
Thanks for your question about a skirt.  Generally the "rule of thumb" we
have found in our many tests of skirts is that a skirt with equal
cross-sectional area gap provides a reduction of 1/3 the fuel and emissions
as opposed to a stove used without a skirt.   

Data from about 20 of the stove tests is provided in our publication
"Comparing Cooking Stoves."  Unfortunately, the EPA/PCIA has been promising
to publish this "any day now" for more than a year.  We are told that it
will be released for print and online publication soon!  Other stove test
data may be proprietary to the organizations requesting the stove testing.
I do plan on publishing a journal article in the next few months detailing
the fuel use and emissions results of over 40 stove tests, though.  This
data is broken down into many stoves within 7 stove-type categories: the
laboratory three-stone fire, stoves without combustion chamber, rocket
stoves, gasifier stoves, fan stoves, charcoal stoves, and liquid fuel
stoves. 

Jean-Francois.
Yes, we certainly do calculate CO/CO2 ratio for stoves.  Personally I find
the CO/CO2 ratios quite interesting.  "Comparing Cooking Stoves" has a
chapter on the CO/CO2 ratios of the stoves tested there.  I have found
CO/CO2 ratio depends primarily on the type of combustion.  Higher combustion
efficiency is indicated by a lower CO/CO2 ratio.    For example, fan stoves
can have a ratio below 2%, while charcoal can be as high as 30%.  We see
most rocket stoves can be between 1.5% and about 7% or so.  The Ecocina at
high power averaged at 1.9%, while at low power it was 3.6%.  We can also
automatically calculate emission factors and conduct a carbon balance as a
check.  I frequently leave these out of reports because most reports are
intended for a less technically-minded audience and we try to keep to the
basic need-to-know information.  

As for variation, our minimum requirement in our Quality Assurance Plan is
25% or less among 3 tests.  Usually our variation is much lower than this.
Some tests run this week were less than 5% variation on all measures.  

Thanks everyone,
Nordica
-- 
Mrs. Nordica MacCarty
Laboratory Manager, Mechanical Engineer
Aprovecho Research Center
www.aprovecho.org
541-767-0287 Oregon, USA