Can We Use Wood to Beat the Gasoline Shortage?

Enlarge Image Image Gallery ABOVE: Herman Reese adds wood to hopper of first truck he converted. RIGHT: Diagram of gas producer. OPPOSITE PAGE: Before it enters the engine of a vehicle, producer gas is mixed with air by the perforated valve on the pipe. OPPOSITE PAGE, RIGHT: Chunks of charcoal-like ash are removed from the generator daily.

Under ordinary driving conditions, wood is added to the gas producer every 50 to 60 miles. Hardwood, cut into chips less than 4" in length to prevent arching or pocketing in the generator, is used in preference to softwood such as pine because it leaves fewer tars and gummy residues. Even so, the cooling tanks and filters on the vehicle must be cleaned every 900 miles, and motor overhauls are in order every 5,000 to 8,000 miles.

Technical studies indicate that about 1.76 lb. of wood are required per horsepower hour. Gas producers fueled by coal or coke are more efficient, but they are much larger and more complicated. With wood, if no major changes are made in converting the engine, the maximum horsepower is about 70 percent of that on gasoline, provided that the spark is advanced and the fire is properly managed. But if the compression ratio of the motor is increased (producer gas knocks less readily than gasoline), horsepower can be pushed up to 85 or 90 percent of the gasoline rating. In general, tests show that substantially more gear-shifting is needed with producer gas.

When a cold start is to be made, wood is added from the top of the hopper and an electric fan is attached to the gas offtake pipe so as to suck a current of air through the producer. Ten minutes after the wood is lighted, the generator manufactures enough gas to run the truck. Starting the engine on gasoline will create sufficient suction to build up the fire, but this takes much longer.

As shown in the schematic drawing, the gas producer is a downdraft type. Air is supplied to the fire — within the conical walls of the refractory, or gas-generating area — by five air nozzles which run through the firebrick from the outer air jacket. The gas, produced by partial combustion of the fuel, flows out the offtake pipe to four cleaning and cooling tanks, fitted with baffles and connected in series. As it is cooled the gas becomes denser (under Boyle's law) and hence more Btu's are supplied to the motor at each intake stroke.