Re: Gasifier fundamental question

[AJH <andrew.heggie@dtn.ntl.com>]

On Mon, 15 Apr 2002 13:56:22 -0500, "Paul S. Anderson"
<psanders@ilstu.edu> wrote:

>
>>and At 10:24 PM 4/13/02 +0100, AJH wrote in reply:
>>It is also a function of the earlier statement that offgas from an idd
>>stove is realtively constant, [[**MARK by Paul**]] it is not true when a 
>>toplit stove is
>>allowed to turn into an updraught stove. I think there is some
>>confusion between top lit and idd.
>
>I can agree that there is confusion.  Andrew, can you please explain your 
>statements above that come after the [MARK] and help me understand the 
>differences.

Simply that many fires can be toplit, once the fire is established
(secondary burning) it can be fed and treated as "normal". The  idd is
a special case of toplighting with primary air control. I believe you
published pictures of a toplit (idd) unit with a flame which was
orange with deep purple feathery edges. This showed a diffuse flame in
which the secondary air supply could never provide enough air at the
gases interface for complete combustion. With idd the primary air is
restricted so that pyrolysis products remain constant, combustion
takes place as a diffuse flame.

If you allow the pyrolysis front to rapidly move down the stack of
fuel and then start burning in an updraught fashion you are able to
have the benefits of a clean toplit start with the familiarity of a
traditional fire, which Crispin may be happy with. It will however
always be a slower start up, I think, as the toplit fire has only
radiation and conduction to feedback heat to the fuel stack, the
updraught fire has convection from combustion products in addition.

AJH



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