Dear Crispin,The pellets are 6mm dia. 1-2.5 cm long. The hole is 5cm in diameter. I tried a few chips to block the hole. It usually took more than one to stop it, and put out the fire. There isn't much evidence of the fire mving up into the hopper. The attached picture shows the position of grate in relation to the hopper. It is adjustable. A mount of glowing charred pellets form in the bottom half of the tube (6.2 cm ID pipe) out in front of the grate. This seems to be self limiting, at least over the five hours it ran today.
I ran it with a second hopper tube such that the air flowed outside the inner 14cm diameter hopper (with lid) and inside the outer15.5cm diameter hopper. The air has to pas through pellets in the cone portion only.
Shutting off the grate air does reduce the burn rate by as much as half, but that is a guess and I am unsure if it works for hours.
but wood pellets are cheating... next, a complete redesign for chips... courting failure.... Alex On 18/01/2012 3:39 AM, Crispin Pemberton-Pigott wrote:
Dear AlexHey that is a good idea. The fire-under-hopper (FUH) is the approach taken in the GTZ 7 stoves and I worried about the fact that the fire would spread into the hopper if it bridged (which it did). But the main issue for a more fire resistant set of parts was the loss of power when that happened. The layout is not exactly the same so I will consider it. The rest of the number look OK. Having a predictable fuel is an important part though. What was the length/diameter of the fuel? What is the L:D ratio? What is the hole diameter? What is the L:Hole diameter ratio?I'll bet there is a good chance the fire will choke and smoke then recover if the bridge collapses.Retained heat to keep the chimney working will be important if it does. Thanks Crispin
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