WOOD-GAS UPDATE
(Page 3 of 4)
September/October 1981
By the Mother Earth News editors
In practice, the new piece of equipment performs three separate functions. First, like a cyclone filter, it centrifugally forces the heavier ash particles in the wood gas to strike the walls of the outer tank and drop to a collection chamber near its base. Second, as the whirlwind of gaseous fuel spirals around the water fill ed coils, it [a] cools rapidly and [b] loses, to condensation, any moisture not disposed of in the gasifier. Finally, the dry-relatively clean-gas goes through the woven filter medium, where it is stripped of any remaining dust, ash, and soot before entering the engine.
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FACTS AND FIGURES
While working out these modifications, we were also able to come up with several sizing criteria for the design of the gasification unit. In general, the dimensions used in certain parts of the wood "cooker" are dependent upon the size and/or operating . speed of the engine 10 be fueled. For example, our homestead utility system's 195-cubic-inch engine turns at a continuous 1,800 RPM. Given that displacement and speed, the total nozzle area is 0.627 square inches (each of the eight horizontal jets is 0.26" in diameter, and the remaining eight vertical jets are 0.18" across), the distance between the nozzles and hearth restriction is 5", and the hearth diameter is 4-1/4". On the other hand, the 250-cubic-inch powerplant used in our Chevrolet truck (which turns at about 2,800 revolutions per minute at 55 MPH, the speed at which most of its mileage is logged) requires an overall nozzle area of 1.237" (horizontals 0.36", and verticals 0.26" in diameter) ...a nozzle-to-hearth separation of 5-1/2" ...and a hearth restriction width of about 5-1/4". (Generally, the total nozzle area should be 5 to 10% of the overall hearth area.)
To size the openings in the nozzles, we simply drilled holes of the proper diameter through 16 pipe caps, and threaded them over the feed-tube outlets. Likewise, the orifice at the base of the hearth (that platform, by the way, is fashioned from a No. 5 cast-iron frying pan) was made by boring a series of adjacent holes in a circular pattern and then knocking out the resulting "plug". In any case, the dimensions given are merely guidelines, and—should you wish to construct a unit of your own—you can likely extrapolate from these figures according to your engine's displacement and working speed, and still come out in the ballpark.
