[Stoves] Re Alexis Belonio article

[AJH]

On Thu, 5 Apr 2007 08:35:31 -0400, Crispin Pemberton-Pigott wrote:

>Dear Andrew
>
>Would you be willing to bet 5 pence that the heat in the steam (heat to boil 
>and latent heat of vaporisation) is sufficient to tip the scale the other 
>way?

You'll need to rephrase the question for me to understand it. From my
experiments, and this may be down to poor implementation, adding a
steam jet (in that case to entrain combustion air with 2 different
types of eductors, Tom Miles posted some photos in 2002) seemed to
interfere with the combustion of wood. I may just have introduced too
much steam AND/OR there were still water droplets in the jet. With
every gramme of steam robbing 3KJ from the fire it can be very
significant.
>
>>...it more likely the endothermy of the vapourisation
>>of this small amount of moisture in the primary
>>combustion zone was just enough to reduce
>>temperatures in this zone to below the temperature that pyrolysis
>>offgas products may crack...
>
>Perhaps this is still small potatoes compared with the gain provided by the 
>extra draft and the better mixing.

Probably a small amount of energy but a significant change in
pollutants.
>
>In the video the flame sounds like a paraffin pressure stove, and for the 
>same reason I feel: small shock waves from the flame passing through 
>episodes of air-fuel and air as they mix in free space.  The main beneficial 
>effect is to shorten the flame which immediately increases the temperature. 

I can see a number of benefits in shortening the flame but cannot see
how it affects the flame temperature without some other outside
influence, the adiabatic flame temperature is largely fixed by the cv
in the fuel gas and the massflow through the flame. Good mixing can
increase the flame temperature by cutting the need for excess air. A
shorter flame also has less propensity to lose heat, through
radiation.

AJH