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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 sulfur, 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 restriction
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.
3.2 SPECIAL CONSIDERATIONS AND ENGINE MODIFICATIONSTo start
the fire in the gasifier, the blower must be used to create a suction
airflow through the wood in the hopper and downward in the firetube. If an
especially high horse power engine is to be fueled by the gasifier unit,
then it might be necessary to install two such blowers and run them
simultaneously during start-up.
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.'
3.3 INITIAL START-UP PROCEDUREInitially, you will need to add
charcoal to the grate below the firetube. Subsequent operation will
already have the grate full of charcoal which has been left over from the
previous operating period.
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 height of 10 to 12 in. with well-dried
wood. Have all the valves closed and let the Fire tube act as a chimney
until the wood is converted to charcoal.
3.4 ROUTINE START-UP PROCEDURE
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
3.6 SHUTTING DOWN THE GASIFIER UNITWhen shutting down the
gasifier unit, turn off the ignition switch and open the carburetor's air
control valve for ten seconds to relieve any pressure from within the
system. Then, completely close the air control valve, and place the cover
tightly on the fuel hopper. When restarting after a short stopover, let
the engine warm up briefly. After longer stops (up to one hour), tamp down
the wood lightly and try to use the blower for restarting without
relighting the wood fuel. After very long stops (over two hours) the
charcoal must be ignited again.
3.7 ROUTINE MAINTENANCEPeriodically check all nuts on the
gasifier unit, the fuel hopper, the filter unit, and the carburetor for
snugness; check all penetrations and fittings for airtightness. In
addition, perform the following maintenance activities as scheduled:
3.7.1 Daily MaintenanceOpen the ash cleanout port of the
gasifier housing drum and remove the ashes after shaking the grate for at
least thirty seconds. Replace the cover of the port after coating the
threads with high-temperature silicone to ensure airtightness. Open the
drain tube, at the bottom of the filter container and allow any liquid
condensate to drain out; remember to close the drain tube when finished.
3.7.2 Weekly Maintenance (or every 15 hours of operation)
Clean out the gasifier housing drum, the fuel hopper, and the
filter. Rinse out the piping and connections to and from the filter.
Replace the wood chips inside the filter, (The used wood chips from the
filter can be dumped into the fuel hopper and burned to produce wood gas.)
Use high-temperature silicone on all pipe connections and on the filter
lid to ensure airtightness.
3.7.3 Biweekly Maintenance (or every 30 hours of operation)
Make sure that all pipe connections are secure and airtight.
Check and tighten all mounting connections to the vehicle chassis. Check
for rust on the outside of the gas generator housing drum, especially on
the lower region. Coat with high-temperature protective paint as
3.8 OPERATING PROBLEMS AND TROUBLE-SHOOTINGA discussion of
problems and their related causes and cures is contained in the
trouble-shooting guide of Table 3-1. Many
operational problems can be traced to failure to maintain the airtightness
of all piping connections and fittings; the piping should be routinely
checked to prevent such problems.
3.9 HAZARDS ASSOCIATED WITH GASIFIER OPERATIONUnfortunately,
gas generator operation involves certain problems, such as toxic hazards
and fire hazards. These hazards should not be treated lightly; their
inclusion here, at the end of this report, does not mean that these
hazards are unimportant. The reader should not underestimate the dangerous
nature of these hazards.
3.9.1 Toxic Hazards
Many deaths in Europe during World War II were attributed to poisoning from wood gas generators. The danger of 'generator gas poisoning' was one of the reasons that such gasifiers were readily abandoned at the end of World War II. It is important to emphasize that generator gas poisoning' is carbon monoxide (CO) poisoning. Acute 'generator gas poisoning' is identical with the symptoms that may develop if a heating stove damper is closed too early, or if a gasoline vehicle is allowed to idle in a poorly ventilated garage.;Table 3-2 shows how poisoning symptoms develop according to
the concentration of carbon monoxide in breathable air. It is important to
note that rather brief exposures to very small concentrations of carbon
monoxide result in undesirable physiological effects.
In case of carbon monoxide poisoning, first aid should consist of the following procedures:
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