[Stoves] Thickness of flame front

[AJH]

On Sat, 12 Jan 2008 12:52:53 -0600, Paul S. Anderson wrote:

>> so
>> while [the up-coming primary air] cools the particles below the front 
>> it immediately gets hot
>> and expands as the oxygen dissociates and reacts with char and carries
>> heat upwards and away from the reaction zone.
>
>All correct, but I have one question.  Is there also some use of the 
>oxygen for
>combustion of some species of the pyrolysis gases that are being 
>released?  And
>is this different at the bottom, middle, and top of the fuel/char materials in
>the pyrolysis zone?  We are discussing a zone of about 25 mm (one 
>inch). Certainly some of the oxygen moves upward into this zone.  So if 
>in the upper
>half of the pyrolysis zone there is found O2 and pyrolysis gases, will 
>there be
>combustion of some of those gases instead of the O2 combining with the char?

We've disagreed on this in the past, I have given my reasons why I
think it unlikely oxygen would react with offgas in this region and
why reaction with char is more likely but there's never a distinct
line in the combustion questions because it is dependant on the
probability of reagents meeting in the conditions where they can
react.

The two test I can think of are

1) How much oxygen is present in the offgas in the char bed above the
pyrolysis front

2) is a flame present at the pyrolysis front
>
>We know that by blowing in excess primary air, we can have some O2 arriving
>above the pyrolysis zone 

Do we? See above.

>
>If both CO and H2 plus hydrocarbons are present with the O2, what takes 
>the O2?
>
>And is that important or not??

I'm betting it's H2 and the resultant heat could then reduce the CO to
C but I cannot see its relevance to this discussion.

AJH