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: fiber down draft firing schedule

updated tue 16 apr 02


iandol on sun 14 apr 02

Dear Don Hunt,

Just one or two points.

I use the term "Stall" to mean that the temperature refuses to rise. If =
your car "Stalled" would you be going faster?

If temperature falls as you increase gas flow then efficient combustion =
is not happening in the kiln chamber. There may be no reduction taking =
place if the gas is not decomposing which it has to do before it can =
oxidise and release the energy. The flames are just the hot gas burning =
when it meets air.

No flame at the lower spy hole suggests you are sucking air in at that =

Closing the damper restricts secondary air intake. Secondary air is =
necessary for burning if temperature is to rise. Pushing more gas into =
the kiln with this setting will waste the gas.

I reduce my little down draught kiln in the following way.

1 Close the shutters on the burners until the flames have a large white =
bush indicating incomplete combustion.=20

2 Open lower spy hole. If the damper is fully open there is be no flame =
and a candle flame held at the opening will show air flowing into the =

3 Close the damper until there is a slight flame issuing from the spy =
hole. I like this to be transparent with a violet blue hue. If it is =
white, get more air flow by pulling the damper a fraction of an inch. If =
the flame disappears increase your gas flow. There should be little or =
no flame from a high stack.

With this setting the temperature on my kiln continues to rise. If =
flames issue from my very low stack I open the damper then check to =
ensure there is a flame at the spy. This is the only way I can control =
secondary air.

If I want to accelerate the rise in temperature I open the shutters on =
the burners to admit more primary air. This curtails the degree of =
reduction but I could compensate by increasing gas flow.

Gas flow is increased on the hour, every hour. The rate of temperature =
rise declines from about 100 Celsius/hour up to 900C down to about 20 =
C/hr when cone 8 falls at an indicated 1040 C. (do not worry about this =
apparent anomaly. I live with it!!).

One question. Are you using an oxyprobe? One more question. What was =
your question? A final question, are you happy with the results you are =

Did you say "Kiln Head" I prefer "Pyromaniac"

Best regards,

Ivor Lewis. Redhill, South Australia.