[Stoves] Space between biomass fuel and cookpot in an open-fire cookstove

[Crispin Pemberton-Pigott]

Dear Kevin

I looked into this when developing the Vesto and there are two answers. One is the correct height (minimum?) Above the fire to get good draft to pull air into the fire at a high enough velocity to get good mixing, and the flame space needed to complete combustion.

For wood, I found the vertical space needed is at least 100 mm, with a preference for 110 mm, and for charcoal 50 mm with  preference for 60 mm.

You drawing shows two parallel rows of bricks. This should be two semi-circles in order to limit drawing in useless air. Cooling the flame with unnecessary excess air is a major cause of PM with wood stoves and CO in charcoal stoves.

Having a fuel hole and an air hole is important, closing everything else if possible. Putting a stone/pebble grate as you have been, is a great help. That allows incoming air to burn the accumulating char, raising the combustion temperature. That of course reduces all emissions from incomplete combustion.

Sheltering a fire on three sides is so-o much better than two parallel walls. So if they have bricks, even mud bricks as are common in the Eastern Cape, the result can be pretty good.

As a general rule, put the air entrance at the back bottom, opposite the fuel entrance, not on the same side as per rocket stove. It will keep the flame centered and away from the walls. That plus >100 mm flame space will give a reasonable result.

Keep up your good work!

Regards
Crispin
From: kmclean56 at gmail.com
Sent: July 22, 2022 9:41 AM
To: stoves at lists.bioenergylists.org
Reply to: stoves at lists.bioenergylists.org
Subject: [Stoves] Space between biomass fuel and cookpot in an open-fire cookstove

What is the minimum distance from the top of the fuel to the bottom of the cookpot?  I've heard that 8 cm is the minimum to get the best combustion.

We are training cooks to use common bricks to elevate two cookpots over one cooking hole.  I want to make sure the cookpots are high enough.

[2 burner drawing.jpg]
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