[Stoves] Studies of pressure variations in a TLUD

[Julien Winter]

Hi Kirk;

I have been running an experiment on burners, including concentrator rings
and nozzles.  I compare gasification rates as I turn down the TLUD by
reducing the number of small holes that primary air to flows through.

I have changed the aperture of the concentrators and nozzles from very
small to almost as large as the TLUD reactor.

With the small apertures, I get an interesting phenomenon; pulsing in the
gas flame, whereby it oscillates 5 to 10 cm in height at a frequencies of
about 1 to 4 hz (cycles per second).   The faster the gasification rate, or
flame size, the higher the frequency.

My first hunch was that the oscillations were a result of pressure buildup
below the burner.   However, when created an open space below one of the
nozzles, the oscillations continued.  I now suspect that the oscillations
are caused by an increase in buoyancy by an expanding flame above the
throat of the concentrator or nozzle.  However, when a larger flame
develops, it can't be sustained by the gas flow through the throat of the
burner, because the throat is choking the flow; so the flame size contracts.

If I am right, then the constriction at the throat of these burners is
limiting the size of the gas flame that can develop above it.

As the diameter of the throat or concentrator rings increase from 25% to
86% of the diameter of the TLUD reactor (7 inches), the gasification rate
increases.  Oscillations were seen in concentrator rings and nozzles with a
diameter <50% of the TLUD reactor diameter.  (Perhaps oscillations were
also occurring in burners with a diameter >50%, but they were not apparent
to the human eye and ear.)

These oscillations were not a good thing, because at the peak flame-size,
they could be a puff of sooty smoke.

I will be presenting data on the turndown curves in a couple of weeks time,
when I have completed the experiment.  At that time, what I am doing will
become clearer.

The burner you presented last week is very interesting, because you limit
the flame size, hence buoyancy, by the amount of air that enters the burner
at various levels.  Thus, you are able to add air in stages as gasification
rate and flame size increases.  In other words, you limit flame size by air
supply rather than (or as well as?) by choking through a narrow aperture.

Cheers,
Julien.



-- 
Julien Winter
Cobourg, ON, CANADA
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