|Webbed by Markus Almroth|
3. OPERATING AND MAINTAINGING YOUR WOOD GAS GENERATOR
3.1 USING WOOD AS A FUELBecause,wood was used extensively as generator fuel during World War II, and since it is plentiful in most parts of the populated United States, it merits particular attention for use as an emergeney source of energy. When used in gas generators, about 20 lb of wood have the energy equivalence of one gallon of gasoline.
Wood consists of carbon, oxygen, hydrogen, and a small amount of nitrogen. As a gas generator fuel, wood bas several advantages. The ash content is quite low, only 0.5 to 2% (by weight), depending on the species and upon the presence of bark. Wood is free of sulphur, a contaminant that easily forms sulfuric acid which can cause corrosion damage to both the engine and the gas generator. Wood is easily ignited a definite virtue for the operation of any gas generator unit.
The main disadvantages for wood as a fuel are its bulkiness and its moisture content. As it is a relatively light material, one cubic yard of wood produces only 500 to 600 lb of gas generator fuel. Moisture content is notoriously high in wood fuels, and it must be brought below 20% (by weight) before it can be used in a gas generator unit. By weight, the moisture in green wood runs from 25 to 60%, in air-dried wood from 12 to 15%, and in kiln-dried wood about 8%. Moisture content can be measured quite easily by carefully weighing a specimen of the wood, placing it in an oven at 220o F for thirty minutes, reweighing the specimen, and reheating it until its weight decreases to a constant value. The original moisture content is equivalent to the weight lost.
The prototype unit in this manual (with an 6-in.-diam firetube) operated well
on both wood chips (minimum size: 3/4 by 3/4 by 1/4 in.) and blocks
(up to 2-in. cubes); see Fig. 3-1 (all figures and
tables mentioned in Sect. 3 are presented at the end of Sect. 3).
Larger sizes could be used, if the firetube diameter is increased to prevent
bridging of the individual pieces of wood; of course, a throat restriktion
would then have to be added to the bottom of the firetube so as to satisfy
the dimensions in Table 2-2 in Sect. 2.
When the wood gas leaves the gasifier unit, all the oxygen pulled down with the air through the firetube has been chemically converted and is contained in carbon monoxide (CO) and water (H20). The wood gas is unable to burn without being mixed with the proper amount of additional oxygen. If an air leak develops below the grate area, the hot gas will burn while consuming the available oxygen and will create heat; this will almost certainly destroy the gasifier unit if it is not detected soon. If an air leak develops in the filter unit or in the connecting piping, the gas will become saturated with improper amounts of oxygen and will become too dilute to power the engine. Therefore airtightness from the gasifier unit to the engine is absolutely essential.
Ideally, as the wood gas enters the engine manifold
it should be mixed with air in a ratio of 1:1 or 1.1:1 (air to gas) by volume.
The carburetion system described in this report will provide this mixture
with a minimum of friction losses in the piping.
The throttle control valve and the air control valve must be operable
from the driver's seat of the vehicle. The engine's spark plug gaps
should be adjusted to between 0.012 and 0.015 in.; the ignition timing
should be adjusted to 'early.'
Fill the firetube with charcoal to a level 4 in. above the grate. Fill the hopper with air-dried wood; then, proceed with the routine start-up directions below.
Charcoal produced for outdoor barbecue grills is not well suited for gas generator
use. To produce a better grade of charcoal, place a rag soaked in alcohol on
the grate, or place 3 to 5 pages of newspaper on the grate, then fill the fire
tube to a beight of 10 to 12 in. with well-dried wood. Have all the valves
closed and let the Fire tuhe act as a chimney until the wood is converted
3.5 DRIVING AND NORMAL OPERATIONShift gears so as to keep the engine speed (rpm) high at all times. Remember that it is the vacuum created by the pistons that provides the force which moves the gas from the gasifier unit into the engine.
Refill the hopper with wood (as shown in Fig. 3-4) before it is completely empty, but avoid refilling just before the end of engine operation. Periodically shake down the ashes from the grate. If your system is equipped with a gas cooler, drain water from the cooler from time to time.
Under operation in dry weather, the gasifier can be operated without the
lid on the fuel hopper. However, when the gasifier unit is shut down the
hopper must be covered to prevent air from continuing to burn the wood
in the hopper. Under wet-weather operation, the cover must be placed
on the fuel hopper, and then lifted up and rotated about 2 in. until
the triangular pieces line up with the holes in the support bars.
The tension of the screen door springs will then hold the lid closed.
See Fig. 3-5 for clarification.
In case of carbon monoxide poisoning, first aid should consist of the following procedures:
3.9.2 Technical Aspects of 'Generator Gas Poisoning'Generator gas poisoning is often caused by technical defects in the functioning of the gas generator unit. When the engine is running, independent of the starting blower, the entire system is under negative pressure created by the engine's pistons; the risk of poisoning through leakage is therefore minimal. However, when the engine is shut off, formation of wood gas continues, causing an increase of pressure inside the generator unit. This pressure increase lasts for approximately 20 minutes after the engine is shut off. For this reason, it is not advisable to stay in the vehicle during this period. Also, the gas generator unit should be allowed to cool for at least 20 minutes before the vehicle is placed in an enclosed garage connected with living quarters. It should be emphasized that the gas formed during the shutdown period has a carbon monoxide cdntent of 23 to 27% and is thus very toxic.
3.9.3 Fire HazardThe outside of a gas generator housing drum may reach the same temperature as a catalytic converter on today's automobiles. Care should be taken when operating in areas where dry grass or combustible material can come into contact with the housing drum of the gas generator unit. If a gas generator unit is mounted on a personal car, bus, van or truck, a minimum 6-in. clearance must be maintained around the unit. Disposal of ashes must only be attempted after the unit has cooled down (to below 150oF). Such residue must be placed away from any combustible material and preferably be hosed down with water for absolute safety.