Friday, March 25, 2016

What Time Is It? - Time for Terminology - TLUD

TLUD is an acronym for "Top Lit Up Draft".  Still confused?  That is OK, you are not alone, you are in the majority.

Fire seeking fuel and oxygen is the simple physics of a TLUD, more on that later.

Wildfire VS Controlled Burn

In a wildfire, flames travel with the wind, as fire spreads everywhere it can find the right mix of heat, fuel, and oxygen.  Some areas in the burn zone may be completely skipped as the fire rages past.

In a controlled burn, the fire is lit across the face of the downwind side.  Instead of the wind quickly blowing the fire out as some would think, the fire slowly marches into the wind as it seeks and finds fuel and oxygen.  Usually this gives a much more complete burn of an area than an uncontrolled wildfire.

A camp fire lit underneath that spreads to the top is an uncontrolled burn.  Lighting a camp fire in the middle on top is more difficult, but better controls combustion rate, and maximizes open air charcoal production.

Dog Simple TLUD

Thank you Adam Bacon for pointing out the fallacy of assuming that anyone can figure out what a TLUD is in even a one hour talk.  The "simple physics" happen to be totally counter-intuitive to what was learned through experience.  Fires are lit on the bottom so the flame grows to the top.  That is just the way it works.  People do not quickly unlearn what has been intuitively established by repetition and experience.

All you have to know about this bicycle, is that steering is reversed, so whatever you would normally do to steer, do the opposite.  Simple? Not as simple as it sounds..

It only took me personally one full week with some of the leading biomass energy and small cook stove experts in the world to get a handle on this, so if you don't "get it" from this post, don't feel bad.  But please start experimenting.

Adam's contribution to understanding, what he calls a "dog simple TLUD" is a single wall flue pipe filled with brush, on top of a pile of brush.

Adam Bacon's Dog Simple TLUD

The holes in the side of the tube are for illustration only.  In practice this is a solid tube.

A fire is started on the top of the pile in the tube.  The hot air rising begins pulling air up through the tube.  The atmosphere above the flame in the tube has no oxygen because all oxygen has been consumed.  A flame roars out the top as the hot flammable gas finds oxygen above the upper rim.

The primary fire seeks DOWNWARD, toward more fuel and oxygen, even as the secondary fire roars on top where the hot gas (smoke) finds a fresh supply of oxygen.

This is the essence of solid fuel "gasification".  By adding ever more physical parts (more complexity) engine grade fuel can be made from wood.  Understanding and experimenting with the basics is critical to success with more complex and advanced designs.

Nobody has it all figured out until we are all driving on natures finest instead of fossil fuels.  If you would like to join in a shared educational experience please send email to

Few will have the greatness to bend history, but each of us can work to change a small portion of the events, and then the total — all of these acts — will be written in the history of this generation. - RFK
Durable Biochar Producing TLUD Campstove on Instructables..

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