[Stoves] Fwd: Re: Improving cooking with charcoal

[Harris, Kirk]

Andrew,

Thank you for this response!  It is very helpful for me.

Yes, we would need more experience with the stones to get a better feel 
for how it works.  As is, my response to Dr. Larson's statement is 
hypothesis, which hopefully will be corrected if needed.

I also recall another question Dr. Larson raised with me some time ago, 
wondering why the migratory pyrolytic front produces so much CO.  
Reduction of CO2 into CO could add some understanding to this.  There is 
a lot of hot charcoal available to do this.  The mpf may be producing 
CO2, which is reduced to CO by the hot charcoal.  You appear to have 
helped answer this question for me as well.

Kirk H.


On 11/13/2019 1:57 PM, ajheggie at gmail.com wrote:
>
> On Mon, 11 Nov 2019 at 17:36, Harris, Kirk <gkharris316 at comcast.net 
> <mailto:gkharris316 at comcast.net>> wrote:
>
>     Also, the char which falls to the ground between the rocks will
>     produce CO, which has air to burn just below and directly inside
>     the charcoal fuel stack, helping to keep it very hot.  There may
>     be other advantageous chemical reactions which have to do with
>     reduction, or the interaction of water vapor, which I know very
>     little about.  Perhaps some or you, like maybe Crispin, could help
>     with this question.
>
>
> Crispin must be busy; I'm loathe to comment on Kevin's work with 
> stones without seeing a cook actually cooking an everyday meal with 
> charcoal. My experience with cooking with charcoal is on barbecues and 
> I'm not very competent at it.
>
> When I look at char burning in my wood burning, space heating, stove 
> once all the volatiles have flamed off and I am just left with a bed 
> of char I note that when the bed is thin it glows red and there is no 
> discernible flame, if the bed is thick it still glows red but a blue 
> flame dances on the top.  This fits well with the perceived wisdom 
> that oxygen molecules dissociate on contact with hot char and combine 
> to give out a lot of heat and carbon dioxide, no flame is involved. My 
> thoughts are below and I welcome comments either way.
>
> Spread thinly the char will radiate heat and the exhaust gases of CO2 
> and N2 give rise  to convected heat.
>
> As the bed gets thicker less heat can escape and the particles of char 
> mutually radiate thus less heat is lost to the outside and the bed 
> becomes hotter and in the absence of oxygen the endothermic reduction 
> of CO2  to CO occurs, this cools the bed but the CO given off can then 
> ignite into the blue CO flame once it contacts secondary air above the 
> bed.
>
> The late Dr. Tom Reed suggested that if the char bed were twenty char 
> particles thick mostly all the char would be converted to CO.
>
> So we have conditions in a thin bed where the temperatures are low and 
> little CO is produced and in a thick bed contained  in a combustion 
> chamber where predominantly CO is produced. The reduction of CO2 to CO 
> largely occurs when temperatures are above 800C
>
> Most of the time with charcoal stoves we have a mixture of conditions 
> between these two extremes.
>
> I'm not sure how the stones might modify conditions to push the 
> balance either way. If the char is distributed around the stones then 
> they will interfere with mutual radiation and possibly lower the 
> temperature leading to less CO, if they act as a grate, forming a 
> plenum under the fire then more air will be directed under the fire.
>
> I can see that there will be a condition where the balance of 
> Nitrogen, CO2 and CO is such that the CO will not ignite even when it 
> meets air as it will be too dilute in the nitrogen  and carbon dioxide 
> mixture. Apart from being potentially dangerous this represents a lost 
> of heat from the stove.
>
> Andrew
>
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