[Stoves] Blown charcoal is the base of maintained good wood-burning

[ajheggie at gmail.com]

[Default] On Sun, 13 Jul 2014 01:09:31 +0200,"Boll, Martin Dr."
<boll.bn at t-online.de> wrote:

>-but first I give the additional result of my very simple tests told some days ago: A piezo-spark does not light some very-light-cotton cloud, containing (spark-incended) motor-fuel.
>It needs the "very fitting fuel-air-ratio".

Martin I shall try this with a piezo spark  but due to the
contrariness of chance all my lighters are full, normally when I need
one it is empty. I find the good old flint ones give a better spark.

As you say most gases and vapours have a small range over which the
premixed fuel and air will ignite, I suppose this is something to do
with the chances of a fuel and oxygen molecule being close enough and
the spark having enough energy to dissociate the molecules, or part of
them. hydrogen and acetylene have a very wide ratio over which they
will ignite and methane is particularly narrow a range.

A diffuse flame is a bit different as there will be an area at the
interface of gas and air where the conditions will be right as the two
gases diffuse into each other. I think this is why Bunsen burners are
lit with the air holes closed.


>
> The low self-ignition temperature of charcoal, is simple to maintain. ( 300°C ; but charcoal-gasification is not below 400-600°C, * P.S. ) Charcoal burns properly (during some time) just beside some fresh air,  ( one cannot blow it out under most conditions )
> The high self-ignition temperature of woodsmoke is higher, (otherwise the smoke would not exist, but self-ignite) ( start about 400°C sure above 550°C, * P.S. )
>My own can-burn-observations are, that a dark red color does not fit to reignite smoke, so I guess, that, to be safe, the temperature must be above the charcoal-gasification temperature, which is, compared by the rates of wikipedia above the self-incending temperature of wood-gas. 
>- Out of that I followed: The C in gas-form is burning and maintains, or re-ignites the woodgas-flame. -I guess, It is at least the 730°C, bright red, slightly orange ( in terms of Tom's given scale)

We see this when we blow on a smouldering fire, the char changes from
a dull red to a brighter red and eventually its temperature gets above
the auto ignition point of one of the components of the offgas which
then propagates a flame. If the calorific value of the offgas is too
diluted by steam or carbon dioxide a flame never develops.
>
>I smile about myself, because it took years for me to get that "really" aware; -So much aware, that I came, for me,  to the simplest and most rational conclusion, that there is no stable burn below the self-ignition-temperature of all burning "stuff". 

I see where you are coming from but I think you miss the phenomenon of
"flame holding", if the flame can stay attached to something then it
remains stable without the containment getting particularly warm as
most of the heat from the flame is convected upwards.

What I found interesting in the tincanium vortex burners I played with
is as things got hot the flame lifted off and would be suspended in
the centre of the vortex as a purple flame. I took this to be because
the hot central are was above the auto ignition point of the woodgas
and if I could maintain 800+ degrees C then there would be no visible
smoke.
AJH