Kirk Harris has been investigating TLUDs for decades and, as far as I know, his natural draft TLUD burning pellets achieved the lowest natural draft recorded score for PM2.5: 0.7mg/minute at high power (Lawrence Berkeley National Laboratory). This video shows Kirk in China at Shengzhou Stove Manufacturer where Mr. Shen built a copy of his stove to start the process of possibly manufacturing it.
The fascinating aspect in the video is how fast the flame is swirling, keeping the flame below the level of the pot and increasing dwell time.
Adding a fan shaped static mixer between the hole in the concentrator ring and the bottom of the pot has become commonplace in various TLUDS since Kirk invented the technique. We recently added a fan shaped static mixer in a natural draft TLUD to get rid of creosote. The tars were burned up in the hot, swirling flame.
Keeping the flame below the cold surface of the pot is always helpful and can be achieved with the Jet-Flame and in both natural draft and forced draft TLUDs.
To last long enough for commercial/carbon success, the combustion chamber has to be made with cast refractory ceramic. Making the static mixer and combustion chamber from cast refractory ceramic dramatically increases longevity. The Oorja stove in our lab has lasted for about 20 years!
I imagine Dr. Tom Reed smiling in heaven as the stove community moves closer to optimization with:
- clean burning pellets
- a well-engineered TLUD
- a refractory ceramic combustion chamber