David,

I now have a modular, natural draft, TLUD heat engine. Shown at right in full operation: no smoke, no flames out the top. I value feedback and suggestions.

All photos taken in Peacham, VT. There is only ONE place on earth with the name "Peacham"—a good name for this heat engine. So, I call the 1-gallon fuel chamber model the Peacham 6-4-3 Natural Draft TLUD.

1. 8 components; 5 store bought
2. Fully assembled, set on 3 angle irons, stands 29.5 inches tall
3. Burns 75 minutes on 3 liters of wood pellets in 1-gallon can
4. Near-Zero Soot [NZS]—essentially keeps all combustion in combustion chamber
5. Very good turbulence pattern in the combustion chamber
6. Delivers 1,500 degrees at exit (1,400 degrees one hour into pyrolysis); heat probe turns red hot in exhaust stream at exit
7. Process ends with zero smoke [new test: If biochar smokes when flames go out, there is residual 'junk']
8. Biochar is very clean
9. Scales from soup can size up to 1-quart & 1-gallon paint cans
10. Each module can be made of ceramics; some have two parts.

As for NZS: There's just a trace of soot around the tip of the exit tube—less than 1/2 inch. Key appears to be that long yellow flames don't escape the system, as they generate fine black carbon particles (soot) that are quite visible and a health hazard.

This new approach to secondary air ensures very good turbulence in the chamber. It also yields—early and late in the process—deep blue flames with hot red outlines around the edges. They remind me of peacock feathers. They must be seen to be believed. Blue flames don't photograph well, and are best seen operating unit in the dark.

If the Blue Flames lasted the entire time, I would call it The Blue Flame Special. I also have a soup can unit, and a 1-quart can unit that are similar, with the same combustion chamber design.

Turns out, it's also important to tune or blend the fuel for the system, or the system for the fuel. Working with excellent wood pellets from VT Wood Pellet Co. is like working with rocket fuel. I now blend it with various amounts of old grass pellets from some years ago. Works better.

At right: view into about 1,500 degrees exiting the combustion chamber. Note the turbulence and multiple layers of flames.

Cheers, Jock Gill
Connect & Ignite
Peacham, VT
802-503-1258