[Stoves] RE Relationship between High and Low Power CarbonMonoxideand Particulate Matter Emissions in Rocket Stoves

[Dean Still]

Dear Crispin,

Sounds very reasonable to me. I wonder what would happen if we put a damper
above the fire or had an adjustable skirt. Baldwin suggested adjustable
skirts in "Biomass Stoves...".

Best,

Dean

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Crispin
Pemberton-Pigott
Sent: Friday, July 14, 2006 2:39 AM
To: Stoves
Subject: [Stoves] RE Relationship between High and Low Power
CarbonMonoxideand Particulate Matter Emissions in Rocket Stoves

Dear Nordica

I read the charts with interest and offer an alternate or additional
explanation that may explain what might be considered by some to be an
anomaly in the tests.

Your notes say

. CO Emissions are usually lower during boiling but higher during simmering
when there is less flame.
. PM Emissions are higher during boiling when there is more flame but lower
during simmering.

The stoves used have no air control and thus the amount of excess air is
very different when boiling or simmering.  When the power is high there is
both less excess air and more flame.  The flame temperature is high because
the excess air is not chilling it as much as later on.

During simmering there are two factors increasing the CO: first is the bed
of charcoal and small bits of wood that have fallen off the ends of the
sticks which are more or less smoulding under the fuel.  There is a lot of
CO from that bed not present during the boiling.  The second is that there
is a much higher level of excess air passing through the stove, lowering the
flame temperature.

So you have a situation where you are producing much more CO from a
non-flaming source combined with the chilling factor of excess air. The
(fewer, cooler) flames are thus less able to burn the CO.

A proof of this observation would come from insulating still further the
combustion chamber. The effect would be to increase the flame temperature
and raise the CO burn rate slightly.  This is indeed shown in the chart when
boiling though not the CO simmering.

A further proof would be to limit the air flow through the stove by either
placing something over the holes admitting air or placing a tight skirt
around the pot that limited the exgess of gas.  The chart again shows that
there is a reduction in CO when the air flow is limited both for boiling and
simmering.

The inclusion of a Rocket Stove with secondary air is valuable, showing that
producing less gas and burning it better gives a cleaner result, and also
for showing that introducing more excess air chills the fire and increases
emissions relative to using the correct amount.

There are in these two charts many proofs that we need to be looking at
small, hot, air-controlled fires burning in insulated spaces.

Best regards
Crispin
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