[Stoves] Rocket stove fuel channel

[Crispin Pemberton-Pigott]

Dear Friends

I have been working with some simulations of heat and gas flow through a Rocket Stove-like structure and have a couple of suggestions.

They relate to three of the downsides of the classic rocket layout, namely the absence of a grate, the tendency of the flames to run up the back wall and when a chimney is fitted, the tendency of the chimney to pull the hottest gases to one side (the back) where heat is already concentrated. This leaves the front of the pot relatively cold.

Recently I have measured stack temperatures as high as 680 C at the exit from the stove body (which was a Muvero sunken pot large stove).

I am sending two videos separately because of the size. The first shows a typical channel layout but with three changes from the classic pattern. 1) There is a primary air supply under the fire chamber provided through 25 holes. 2) There is a perforated diffuser plate under the pot distributing the hot gases pretty evenly across the bottom surface. 3) The pot is modified on the outside to prevent direct access to the chimney so the gases are forced to go round the pot body.

Apart from these modifications the hot gas flow into the fire chamber is standard as the other changes only affect what happens after that.

In the second video the last brick crossing the top of the fuel channel is cut away at 45 degrees. Note the difference between the two routes taken by the hot gas when in a state of thermal equilibrium.

I will prefer that some of the primary air enters from the back but it happens that the setup we have for building them is complex enough without adding a second grate with different dimensions. That flow could in theory put the flames in the centre, front-to-back.

There is an ash clean out channel passing from the box under the grate but it is not shown. At the end of it is a primary air entrance hole.

What you see is the hot gas flowing, with none of the stove shown. What you see as "shape" is actually the volume within the stove body.

It is very easy to add this 45 degree cut and it definitely improves the gas flow keeping it largely off the back wall.

The efficiency of this stove, considering high and low power, is just about 60%. For efficiency, PM and CO it is ISO Tier 5 when burning 14% moisture eucalyptus grandis.

Best regards
Crispin
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