[Anderson wrote: Crispin and I have long ago come to agreement that energy efficiency is not the same as fuel efficiency.
[RWL: I do not know how to interpret this. Can you or Crispin express this statement in equation terms?
No. When dealing with two different concepts (energy viewed as MJ and fuel viewed as tree or piece of wood) that each have different parameters for being evaluated, writing an equation that reflects only one shared parameter or variabled (in this case it is units of energy) will not carry forward the other important parameters (such as the other uses of pieces of wood or the need — or not need — to protect forests in different environments.) One of those other parameters is the “value of charcoal” which canNOT be ONLY expressed in terms of energy content.
$ value of MJ does NOT equal the $ value of wood (trees) with equivalent number of MJ.
$ value of charcoal does NOT equal the $ value of MJ / 3 (assuming 2/3 of the MJ are being lost when the charcoal is made).
Crispin and I stopped agrueing about this a long time ago. The concepst of fuel and energy are different. And this becomes much more evident when discussing “char-making stoves” where there is a useful by-product (or co-product), and not just buring all the way to ashes.
For eons of time, combustion science has as part of its mission the extraction of as much energy as possible from whatever might be the “fuel” (immediate source of the energy). But it happens that the simple Migratory Pyrolytic Front (MPF) that occures in TLUD stoves makes charcoal in a batch mode, mainly without consuming much of the created. Regular fires are consuming the charcoal during the standard burning processes.
Energy in Wood fuel = the Energy in the Pyrolytic Gases + the Energy in Created charcoal.
I like the comment from Frank earlier today:
The other side of the coin is the total carbon going to the secondary [combustion should be used when] determining the efficiency of that energy being used for the task.
I think Frank is saying that the “energy efficiency” of a TLUD stove should be measured in relation to the energy in the pyrolytic gases. And that means leaving aside the charcoal for separate discussion.
Paul