Alex Chernov

Advantage of reverse burn [down drafting fires] is theoretically getting cleaner and complete combustion since it is as close as it gets to pure gasification and burning products of pyrolysis without getting to complications of gasifying units.

There are products in North American and European markets that gasify fuel first, burning products of pyrolysis after in manual or automated mode. Wood, pellets, corn, etc (doesn't really matter what) all get loaded bulk and are consumed as needed. In all these units, combustion air is supplied into the burn zone, not to the fuel itself. Heated fuel is allowed to go through stages of pyrolysis in hot and oxygen-free environment, and released combustible gases (and later charcoal) are burned in the burn zone.

During WWII there were plenty of trucks in Russia that ran on cordwood utilizing a small gazification unit on board. [Gasoginias in Brazil too.] It is the same principle.

One simplified example of "downdrafting firebox with vertical fuel placement" is a rocket stove.

Alex

***************
So, could this be why getting rid of a grate improves combustion? Maybe the wood is heated without as much oxygen in partial pyrolysis. Note Alex's comment that combustion air should be added over the fire in the burn zone, not to the fuel itself. Maybe it would be even better if the wood were placed below the hearth and got even less oxygen.

By the way Rocket Stoves utilize vertical fuel placement but only the heating Rocket Stoves like cobb heaters have a downdraft firebox. Not the cooking Rocket Stoves.

Jim Buckley