[Stoves] Wendlelbo's : Re Large TLUD --- TLUD Stove history

ajheggie at gmail.com ajheggie at gmail.com
Mon Aug 29 07:30:03 CDT 2011


On Sunday 28 August 2011 14:49:48 Paul S. Anderson wrote:
> (It took me four years 2001 to 2005 to get to that point of having  
> concentrator lids on the TLUDs.

Even the Reed-Larson stove diagrams from 1995ish showed a concentrator, 
essentially to disrupt flow and increase turbulence but it used the 
term "bluff body", this is to induce mixing in the eddies downstream. In 
that case it lead to a circle of flame around the edge of the stove, 
mimicking a flame from a pre mixed gas appliance.


> Those stoves only got that TLUD name   
> in 2005, and were first named "Top-Lit UpDraft" in 2004 in the  
> Anderson-Reed document at the LAMNET conference - found at the Stoves  
> website).  From 1985 to 2005 Reed called the technology IDD, for    
> Inverted DownDraft.)

If one considers the strict interpretation of the terms then the IDD 
gasifier is more correct, it implies air control, Top Lit UpDraught can 
be applied to any fire that is toplit and then develops as an updraught 
fire and indeed in the early days of this list its use was explained by a 
person involved with masonry stoves in US domestic buildings. The reasons 
behind it are simple, if one lights a heap of biomass at the bottom the 
small amount of heat initially allows a low temperature burn of the char 
initially formed, most of the fire smoulders and heats the layers above 
to dry then pyrolise them. As things get hotter a flaming region under 
the fuel develops but the offgas is diluted by combustion products, water 
vapour and is quenched by the fuel it is heating up. The fuel:air mix is 
wrong to allow the flame to propagate. Freshly formed char will ignite at 
low temperatures but gases need a flame or to be above their autoignition 
temperatures to burn. Hence lots of smoke until a flame establishes at 
the top. If the fire is top lit all the combustion products are exposed 
to fresh air and a flame as an ignition source without having to pass 
through a mass of cold fuel wood. The only restraints on air supply are 
the natural air movements.

This differs from the gasifier or pyrolyser concept which inherently 
control the air supply to restrict combustion to that necessary to gasify 
( about 1/6 stoichiometric air for combustion) or pyrolyse ( less still) 
the biomass. Even The initial demo Tom Reed talks of has the shielding of 
the cigarette paper restricting air to that blown from below.

AJH








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