[Stoves] Lowering emissions

[Crispin Pemberton-Pigott]

Dear Tami

I agree with you on the proviso that if the difference is important, it will 
be species dependent.  It is now overly complicated.

I have not noticed a problem regarding length v.s. diameter, but now that 
you mention it, I have been using at lease partially homogenous fuel, in 
terms of length, let's say 75 to 200mm clustering around 125mm.

As the length is vaguely constant, the variations in diameter are the main 
variable.  Heat production is then defined by the burning surface area.  The 
heat lost to the interior of the wood moderates the fire.  Where the volume 
is really small and the surface area of any given mass of wood (say, 1/2 a 
kg) there is significant gassing, compared with wood with 1/4 of the surface 
area.

I am intrigued enough to say I will check to see of the 'burn in rate' at 
the ends is different from the burn in rate at the sides.  I will bet 
softwoods have more variation that hardwoods, and that lowveld acacias with 
salts in the wood (which makes them self-extinguishing and therefore glowing 
coals type fires) has nearly no difference.

Thanks
Crispin

----- Original Message ----- 
From: "Tami Bond" <yark at uiuc.edu>
To: "Crispin Pemberton-Pigott" <crispin at newdawn.sz>; "Discussion of biomass 
cooking stoves" <stoves at listserv.repp.org>
Sent: Wednesday, January 03, 2007 8:19 AM
Subject: Re: [Stoves] Lowering emissions


Crispin,

I'd also suggest that the smallest cross-grain dimension and along-grain
dimensions would be more important than surface area to volume. This
might dictate the rate at which heat transfers in, and volatile matter
transfers out.

cheers
Tami