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.
3.2 SPECIAL CONSIDERATIONS AND ENGINE MODIFICAITONS
To 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 nccessary to install two such blowers and run them
simultancously 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 PROCEDURE
Initially, 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 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
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 clarification.
3.6 SHUTTING DOWN THE GASIFIER UNIT
When 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 MAINTENANCE
Periodically 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 Maintenance
Open 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 necessary.
3.8 OPERATING PROBLEMS AND TROUBLE-SHOOTING
A 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 OPERATION
Unfortunately, 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: