27. of October 2016
Probably based on GENGAS, Vesa Mikkonen has published a few curves covering the effect of preheating on product gas' heating value ~as translated into motorpower. ~200 --- 600*Celcius. (if remembering right ~15 -- 20%)
In the same bunch curves of wood humidity affecting motorpower.
Some time ago I attempted to clarify the grounds of exchanging heat back to the primary air. (among messages)
If I remember right, it would be hard to come over 40%.
And this is because of the volume difference in/out (measured cold).
With max to no preheat the gasquality goes steadily down.
The air consumption will increase with less preheat.
As less than half of the exiting gas heat can be used for preheating the primary air, the rest goes to the crows, if not using it for "baking" the wood.
This will benefit already on short trips, as it dries the wood for a comfortable start up next time.
It's not the normal heat leakage to the silo i am talking about, that is not enough, but by Imbert mantel (excluding condensation out).
Even that is questionable "halfways", as the condense remains in the wood, so both active silo-center heating and periphery condensation is needed to have all benefits.
To get the best gas cleaning effect at the last end of purification, after cooling-condensing, the gas has to be reheated = dried before going through a large paperfilter which is also kept warm to be functional.
That is on the warm surface of the cyclone (same envelope for the cyclone and the paperfilter).
Fast warming, works on short trips.
Never place a paper filter for woodgas in the motor compartment! It will never be dry at start-up!
In the cyclone envelope it is guaranteed!