[Stoves] Re Alexis Belonio article

[Crispin Pemberton-Pigott]

Dear Andrew

Last first:

> A shorter flame also has less propensity to lose heat, through
>radiation.

That is what I have noted on the FSP stove experiemnts.  As I was able to 
get the mixing better and better over the course of a year, the flame 
shortened and got hotter, the CO dropped and I was able to get the excess 
air down to 100%.  In general I expect Alexis can get the same things, but 
he will have a materials problem right away because it is going to melt 
everything.

Then:

>[steam] seemed to interfere with the combustion of
>wood. I may just have introduced too much steam
>AND/OR there were still water droplets in the jet. With
>every gramme of steam robbing 3KJ from the fire it can be very
>significant.

I want to look carefully at the possibility that some of this heat can be 
recycled.  I had a long talk about this today with Mike Spendlove from 
Engineers Without Borders from Waterloo University.  There is at least the 
possibility that heat picked up on the inside of the steam boiler, that is 
with a coiled superheating tube, could usefully be returned to the fire 
provided the overall effect was not to a) increase the volume of the gases 
to the point that heat is lost past the pot from high velocity, and b) the 
heat transfer ability of hot steam (being twice that of air) more than 
compensated for the heat lost creating the steam.

We agreed it was likely the latent heat of evaporation would be lost for 
sure and that is a big tax on the system.  It may be that the main effect is 
to raise the power output from any given stove at the cost of lower 
efficiency at higher power.  Smaller stove, bigger power....possibly 
interesting...

We agreed that there was at least the possibility that having very dry fuel 
mixed with a controlled amount of steam could produce a lower emission level 
in a relatively choked fire, perhaps the EA at 25%, which means that one 
could reduce the excess air significantly while still maintaining the clean 
burn.  This seems the most promising possibility, to me.

The heat transfer enhancement might offer some gain to offset the ...shall I 
call them 'steam losses'?  If the overall effect is to capture heat going 
through the stove body and run it back into the fire, then the combustion 
temperature is raised which in general lowers CO and hopefully PM 2.5's.  My 
inclination is to greatly limit the steam quantity admitted, superheat it to 
a temperature above that of the exiting gases with an internal coil, and 
them limit the excess air until the emissions rise to the acceptable limit. 
Such a stove might be surprisingly small for its power output.

Regards
Crispin