[Stoves] Stove comparison coming

[Crispin Pemberton-Pigott]

Dear Alex

Sorry for the delay answering.

>Your familiar categories all reflect how pyrolysis and gasification proceed
in relation to the air supply.

I hope so.

>They don't say a lot about the continuing combustion reaction downstream. 

Well, generally speaking the flames are contained in some way, with a pipe
becoming more common as we learn.

>That has a lot to do with unburned hydrocarbon particulate and soot.

Agreed. I am becoming more convinced that temperature has more to do with it
than perfectly balanced air supply. I am seeing some unexpected things. One
is a very low PM level from a TLUD stove with 0.5% excess air.

>Are there categories of burners that can suffice as a suffix to the fuel
dynamic categories, to give a more complete picture?

That is really worth a decent, long think. I am not sure. What I can add for
the moment is that when the power level is high, just about everything works
well and burns clean. The challenge is to get lower power levels burning
cleanly in the same physical space (too big) during the times when the fuel
is not yet fully devolatilised. After coking (charring) it is hard to make
PM.

>How easy is it for the untooled or unschooled user to spoil the result by
getting the secondary air wrong?

It appears to be easy to get CO but hard to get PM if a) the temperature is
high and b) the fuel is mostly carbon. This is important for the gasifier
guys who have been saying all along that the reason the stoves are PM-clean
is because they are not burning the char. My experiences are showing that it
is hard to get PM when burning char alone if it is hot. The implication is
that all the char making stoves could continue to produce lots of PM-clean
heat if they were made to do so.

Interesting, eh? Burn cleanly the volatiles then burn even more cleanly the
carbon. Perfect for biomass stoves. To put a number on it, stoves with
nearly no non-carbon in the fuel pile are consistently produces only a few
microgrammes of PM over a period of several hours. It is in the non-carbon
gasification phase that the PM is produced (potentially). As you know, the
essence of the biomass gasifier stove claim is that it is the gasification
process that creates a clean burning gas, by leaving the PM producing carbon
behind. It is not supported by observations that include real-time
monitoring of the PM (i.e. watching when it is produced and when not).

The above is conditioned on there being a stove that burns well. Anything
can be made to smoke if operated badly I suppose. I am thinking of the dozen
or so stoves we have tested now that clearly have consistently low PM during
the high carbon fuel burning phase. It is not evident that having perfect
excess air is related to this. Many of them have poor air control and high
EA is much more related to high CO than it is to high PM, AFTER the fuel is
coked/charred.

I am suspicious that high BC emissions do not arise from fixed carbon.

Regards
Crispin in freezing Waterloo