Norm and All,
1. The amount of primary air is quite small in comparison with the needed secondary air. I see no justifiable reason to try to pre-heat the primary air, even for those last 30 seconds of operation (instead work on keeping sufficient air reaching the hot coals all the way to the end.)
2. Air that enters at 20 deg C will essentially cool the flame by the amount of energy needed to make that 79% Nitrogen of that volume of air become as hot as the rest of the flaming gases. Therefore, if the secondary air could enter at 200 C or higher, there would be some benefit of heat available for cooking. This becomes important in blast furnaces. The importance in cookstoves can be debated, based on the expense of preheating the secondary air and whether the heat for the secondary air was (or was not) taken from the heat that would have otherwise reached the stove.
I learn much of this from the great Indian gasification expert, Dr. Prof. Mukunda of IISc Bangalore, when he taught us about TLUD stoves at a week-long workshop in about 2007 in China. Dean Still was there also, and Alexis Belonio, and maybe 10 others.
Paul
Doc / Dr TLUD / Paul S. Anderson, PhD
Exec. Dir. of Juntos Energy Solutions NFP
Email: psanders@ilstu.edu<mailto:psanders@ilstu.edu> Skype: paultlud
Phone: Office: 309-452-7072 Mobile: 309-531-4434
Website: www.drtlud.com<www.drtlud.com>
Julian;
All I have is the 90% porosity silicon carbide tiles. When I built a holder and adapted them to a natural draft TLUD, they simply did not work as hoped and I stopped tinkering with them. Perhaps one of you has a good idea on how to use them. You are correct that the gas flame ignited over the top of the fuel bed and did not lift off into the burner. If I tried to force the issue by igniting the flame above the tile burner, I only got a typical diffusion flame. That was when I dropped the whole idea.
Yesterday Ron Larson and I were talking my version 19 of our ND-TLUD and how well it performs. I still haven’t taken a video to show all of you in a side-by-side comparison with version 16 which most of you have seen. Anyway, I developed version 20 that preheated both the primary and the secondary air in a ND-TLUD. I assumed preheating both the primary and secondary air would create a higher operating temperatures in a 7 gal. TLUD. Ron told me that he remembered that preheating primary air generally didn’t work. It seems to me it should and could possibly result in lower emissions. I had never heard of any work preheating the primary air in a TLUD. Does anyone know of this work or who performed it?
Norm