I thought exactly the same as you, but as you can see from the graph, it shows something different, that’s something I don’t understand again.
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If you have a small nozzle with high velocity
or a large nozzle with low velocity.
The higher velocity, will go deeper into the middle of the combustion zone, and will stir up the fire, knocking ashes off and giving more surface area. Giving the effect of a stirred up, larger fire with more surface area. Kind of like the difference a flame and a swirl burner.
The object for pyrolysis is to get it hot enough to release gases and adding as little oxygen as possible.
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They didn’t have different sized nozzles, the diameter of the nozzle head is 265mm.(10,43")
The difference is in the narrowing, the one that gives the best gas and the least resistance is 87mm,(3,424") the other one which is 124mm (4,88") gives worse gas and higher resistance.
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This could be very hard to calculate, a bigger restriction may let more char down in reduction zone,(not because of the bigger area, more of the lower temperature in the restriction) which leads to reduction zone becomes constipated.
This is very difficult calculations, which almost only can be tested out.
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If I look at the middle graph, it shows that the gas temperature after the unit is lower with less restriction, which it should be if the gas has a higher calorific value.
Could it be, as you say, Göran, that the less restriction creates higher gas speed so that the charcoal in the reduction cone is cleaner?
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