[Stoves] TLUD pellets stove with a venturi burner. Pictures of a cooking cycle.

[Crispin Pemberton-Pigott]

Dear Roberto

You describe very well two clear 'cases' that can be used for teaching this subject.

When you have more side holes you do indeed get more gasification of the char, as indicated by a flame with more blue colour. Close the holes and the air does not hit the char in the bed so it doesn't create the CO. ‎Less blue and less power.

When you have a low gasification rate the char is not hot enough to ‎keep the char burning so it stops burning (mostly) and the air passing through the holes becomes, instead of primary air to char, secondary air mixed into the gas. If you had an oxygen meter you would find that the instability you have observed is caused directly by high excess air. The flame will go out more and more easily as the bed deepens and the air coming through the vertical walls goes unused in the char bed.

When you close the air from the sides the low power flame stability will improve, as will the late session stability. The char yield will increase, and the total gas energy will drop.

Everything is linked and follows a set of simple rules.

Regards
Crispin

Dear Alex,
Yes, this vertical side holes are there for gasify the top char, and to try
to have a premixing flame. Other objectives is to try to shorten the flames
at higher gasification rates.
But in this experiment, i put a top ring without holes to eliminate the
effect of the vertical holes in the combustion chamber.
The flame colour, with or without the vertical holes, are very similar,
maybe more bluish with the holes.
Without the holes, the flame is a little more stable at low rates.
With the top ring on, maybe there is a little portion of air that surpass
the joint, but i thing is not relevant.
I will make another series of burns with a completly sealed combustion
chamber, and with the vertical holes.

Best regards
Roberto Poehlmann
Valdivia, Chile

"Roberto,

It looks from your pictures that there are some side holes into the fuel
container. These would  gasify some char  and possibly channel some air
through to contribute to partial premixing. Are there any other spots like
seams or joints that could allow a bit of air in prior to the secondary air
holes?
Alex
"
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