Puukaasu - Wood-Gas Powered Vehicles

By Lasse O. Hiltunen, FHM Webmaster

During WWII, Finns faced an overwhelming energy crisis. All available petrol
was rationed to support the war effort. A critical choice was required. Normal
life could either stop or an alternative method to continue needed to be found.
Could it be done? Yes. Had it been done? Another yes. Was it ever crucial for
essential transportation in some other countries? Another astounding yes.

Being able to take energy from a cord of wood is easy. It's done every
day when we burn it. However, taking the energy out of a cord of wood, and powering
an automobile from point A to point B is much more complicated, but worth it.

A 1946 Finnish puukaasu booklet estimates that 90% of the energy contained in
wood can be harnessed. The trick is to take wood, agricultural residue, switchgrass,
urban wood waste, and leftovers from timber harvesting and feed this "biomass" into
a gasification unit, produce a gas, and then use that in an internal combustion engine. 

So, imagine being in a situation where it was critical for you to get from
one place to the next and actually transport goods to and from those places
every day. For example, children needed to be transported on school busses,
farmers relied on their tractors, and people needed to get to work. Normally
this was no problem, if there were vehicles and power for them. But what if
you did not have gasoline for your vehicle and there was no reason to expect
more petrol.

In Finland, a dilemma arose. Would the country stop dead, or would sisu
kick in? Finns decided to take proactive measures. That is when sisu
kicked in as well as a visit from the mother of invention, "Necessity."
Many countries had used wood gasification propulsion, but wartime Finland was
a particularly good and logical example of its use. After all, they had plenty
of wood to burn and an extreme shortage of petrol.

To accomplish this, Finland relied on theories and designs established as early
as 1839 when a German named Bischof recognized that gas was produced from burning
wood. The first "car" came later in 1901 when J.W. Parker harnessed
that gas to power the first gas producer vehicle. Those designs were certainly
crude, cumbersome and heavy, leaning heavily on the materials and expertise
available at the time.

Just heating wood will not power a vehicle; it simply provides the component
fuel. It takes this process connected to a modified internal combustion reciprocating
engine to provide the mechanics for the wheels to turn and propel the automobile.
Many resourceful Finns simply converted their car or truck (which might have
sat unused during WWII because of lack of fuel) and "hooked" it
up to a "puukasuutin" (wood gas machine).

The actual process works by subjecting a biomass (wood) to a high temperature
(above 800 degrees Fahrenheit), which affects a release of an aromatic hydrocarbon,
or arene. This hydrocarbon, similar to a benzene ring in structure provides
the necessary energy when further burned. It is flammable because of the methane,
hydrogen, carbon monoxide and tar contained in the original wood. The so-called
"gasifier" thus takes wood chips, charcoal, or sawdust and burns
them. Ashes, dirty soot and wood gas are produced. Those are periodically cleaned
from the gasifier, like cleaning the old coal burner in the basement making
the operators dirty as well! Also, the gas had to go through another step before
it was delivered to the internal combustion engine. The tars and other impurities
had to be filtered out to deliver clean "gas" to be burned. Without
this step, the motor would easily become "gummed up" after a period
of use.

It is interesting to note that the World War II gasifier models were essentially
single stage, with the combustion, pyrolysis (basically incineration without
oxygen), and gasification occurring in the same chamber. This produced impure
gas with larger volumes of tar and resultant gum. This gas had to be cleaned
in another stage to remove or convert those impurities. The older models were
not terribly efficient.

The newer "staged" gasifiers dealt with the impurities, which are
found in any wood or biomass source naturally, in a more engineered process.
Pyrolysis and gasification were separated and thus tar-free gas was produced.
Of course there is a trade off. One is more efficient but heavier and bulkier,
but the other is more compact, lighter, and less efficient. Some estimates suggested
that one to one and a half pounds of charcoal were used per mile traveled in
these gasifier cars. They were awkward almost comical "Rube Goldberg-esque"
looking machines, actually cars or trucks with a huge backpack contraption either
fixed to the back of the car or pulled along as a trailer. Or, the front-pack
gasifier package decorated the front of the truck or car. They all worked and
Finland persevered.

Finns successfully used the wood powered cars, trucks, busses and tractors
extensively during WWII. An estimate of over 80 per cent of the vehicle
traffic during the war in Finland and Sweden relied on puukaasu, or
wood-gas power. Denmark had even a higher percentage. Unfortunately, there are
only about 20 of these unusual vehicles still in use in Finland.










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