Here is series of tests with a perlite-concrete afterburner. Flue gas was measured with Testo meter. Here a test from February. There is a simple “box for coal” on the right and a round afterburner on the left. No specific mixer. Natural draft.
The connector (red hot) has holes for secondary air, no regulation. When there was too much primary air, smoke appeared (and the CO level was around a few thousands). At moderate power, there was no smoke and the content of carbon monoxide was quite small and stable.
And the last attempts below. The same afterburner was connected to a better stove with better air regulation and with heated secondary air (double walls of the hearth). The stove box is at the bottom and above is the afterburner in a tin housing. Fuel tank on the side (coal). Inclined grate, the constructor is not quite satisfied with it yet.
The afterburner is in a metal casing, a construction is similar to Peter van den Berg’s batch box stoves with the difference that the exhaust is not very chilled, and the main source of the draft is a traditional chimney.
A lot of heat escapes through the glass, but it’s an experiment and it’s important to see what’s going on. That’s how the hot afterburner looked like during test, a flame inside the red part.
Below are two movies. Observation is hindered by ash sticking to the glass. The second video shows that the flames sometimes leave the afterburner, what generates pollution.
After adjusting the situation on the grate and setting correct proportion of air, the flame was within the red part of the afterburner, and the measurement results were very good.
When reducing the excess of air, the flame gradually began to flow out of the hot part of the afterburner and contaminants appeared.
The fuel flow on the grate is not perfect yet, and sometimes the coal was suspended and burnt out. This resulted in excess oxygen, cooling of the flame and, as a result, formation of impurities. The smoke was not visible, but the meter showed a higher level of CO. Low temperature of the afterburner may also result in leaving unburned residues.
The “0 ppm” result should be taken with caution due to measurement error of the meter. Nevertheless, we are at very low CO levels. Soot and hydrocarbon concentrations should also be very low.
ps. A question was asked in the comments for a more detailed description of the fuel feed. It slides off the container from the side to the sloped grate inside the stove. If we would like to consider it as “manual load”, it is not the best yet.
ps.2 I do not have a movie showing the inside of the afterburner at 0 ppm CO readings. The following video comes from another test, more related to the grate. One can see flame parts that escape from the afterburner and cause the CO level to rise to several ppm. By the experimenter’s relationship situation in the afterburner at the “0” readings looked similar, the afterburner was red to about half, the only difference was that the entire flame ended nicely in this lower part. There was a necessity of pushing coal on the grate, but otherwise it was a stable state.