[Stoves] stoves and credits again

[Crispin Pemberton-Pigott]

Dear Neil and All

>> That is OK, in terms of an opinion, but it is not what people are 
>> doing and I expect the main reason is fuel efficiency.

>It always surprises me that no one ever mentions that the char burning stage may be almost perfect for simmering something after bringing it to the boil.  

Well, cooks certainly know this, and plan for it by fueling appropriately so it burns down at just the right time. What is this a surprise? It is not, or shouldn't be.  Read Cecil Cook's descriptions of the manner in which Indonesians cooks prepare breakfast like a conductor managing an orchestra. Different fuels for different stages of cooking, different fuels for holding a very low fire for hours, different fuels for re-flaming and brightening a fire.

>If I utilise fairly fine woodchip I can obtain a vigorous enough burn, but then refuelling is useless if confined to the very end of pyrolysis as there is too much inert char above, and a smoky mess results. 

When building a stove that was able to transition from a char producing to a char burning stage, I found that it is necessary to intervene (add air) earlier than the end of the pyrolysis stage for the reason you mention. I therefore made a transition position for the level to sit between these two stages until the char burning was well established. 

>I appreciate Paul's point about burning char in a TLUD subjecting the firebox to higher temperatures shortening its life...

There are a couple of approaches: If you place the char in the centre like a cylindrical slug of fuel surrounded by new fuel, it can burn with a lower chamber wall temperature, but I doubt it is worth it. It is better to use incoming air as a cooling agent to chill the outside of metal and maintain an inner surface temperature below its destructive limit.

>IMO the 'excess' primary air NDTLUDs make the TLUD extremely versatile as discussed above, because of the very generous primary air, in a way that the very restricted primary air stoves like the Reed stoves cannot be and as mostly discussed here. 

Interesting observation. I agree. Stoves should be able to transition from mode more to the other because , often, that is the way to get the most energy out of the fuel while producing nearly no PM. 

Stick burning is one approach, but requires fuel-metering, a tedious task. Controlling air is a better solution.

Regards
Crispin