The use of
energy applications is hot. Numerous fermentation and gasification
projects have been started recently, mostly stationary units to produce
heat and power. For mobile applications the world has been already
indulged with alternative fuels such as ethanol and biodiesel.
Indulged, because we are talking about liquid alternative fuels that
are as easy and convenient to use as petroleum products are.
No fuel can be stored or transported as easy and contains so much
energy as a liquid fuel. This, until now, wide and cheap availability
of fossil fuels and the dictatorship of big-oil, conspiring with the
car manufacturers, have led to an enormous mobility and economic
development in the world. An increase which can, and probably already
is, turning against us.
After this short, cynical and philosophical sidetrack (I will annoy you
again on several occasions), back to the business at hand.
Methane, or biogas as it is also called, is produced and compressed in
a central fermentation or digester factory. Or made and used
individually in a rural setting. Fermentation is a slow
and can not be regulated for “on demand” use. For
reason it is difficult to use in mobile applications. Gasification of
biomass, or wood, can be produced on demand on the vehicle. The
internal combustion engine itself regulates the quantity of produced
gas and the installation is relatively compact, at least compared to
However, compared to modern gasoline cars, driving on woodgas is not
very user-friendly. Start-up demands time. Driving requires the
necessary knowledge and skills, because the engine power on woodgas is
considerably lower and the gas quality never constant. It often needs
refueling and the fuel size must fit the design of the gasifier. After
the second world war, wood gasifiers disappeared in a short
because petroleum fuels once again became widely available and were
much more convenient to use.
In the current era, mobile gasification will not be widely used. Not
only because there is less wood available for drastic up-scaling, but
the modern consumer does not want to give up his luxury and comfort. He
will like the fact of cheap woodgas, but leaving his bed ten minutes
earlier to fill up the tank, remove ash and condensate and start the
generator will be too much to ask. Rather, the motorist pays
considerably more for the convenience of fossil fuel, than give up his
current lifestyle and status.
Status and the social rat race, fed by the mass bombardment of the
media, paralyze the mental ability of the individual. Only when this
individual can shake off status and excessive consumption, can he open
his eyes for alternatives. Then he is ready for something like wood
gasification. In a certain way real woodgassers are individualists and
little anarchists. Like artists, at the same time admired and
Now you will start to understand why I have gone into this project.
Also several personal items came together: idealism, interest,
background and skills. What me and those few fellow-gassers find
interesting, is the fact that a raw, but very accessible fuel can be
used directly, without an extensive refinery. Dream about a journey
around the world with only a hacksaw and an axe to produce the fuel
This is also a not unimportant aspect of wood as a fuel:
self-sufficiency. The accessibility makes the user independent of
Pictures of modern Finnish installations made of stainless steel,
professionally built by amateurs, were enough to push me over. These
units are more efficient and user-friendly than the installations from
the second world war and manage chipped and relatively wet wood.
Despite the fact that most woodgassers are loners, it is not possible
to manufacture everything by yourself. Motivation of other people, to
successfully finish the project with their aid, without a financial
catastrophe, appeared to be surprisingly simple. Driving on wood
interests many people. When their eyes start to shine, it is clear that
another soul is won…
Mobile gasification will not save the world. The installation is too
complex, too large and because of that too expensive. Driving demands a
mind-turn, knowledge and skill of the driver. Moreover most countries
have insufficient wood to provide a national fleet with fuel.
It has always been, is now and will remain a method for crisis times
and for idealists.
What is gasification?
Gasification is a
process, where heat converts solid biomass into flammable gas. Thereby
the gas can be burned immediately by adding secondary air, like in
heating applications. The gas can also be fed to an IC (internal
combustion) engine, when first cleaned and dewatered.
Gasification consists of four processes:
1. Drying. By using heat, water evaporates from the wood. This is good,
because a surplus of water reduces the oxidation temperature, which
doesn’t provide clean gas.
2. Pyrolis. Above 270 degrees Celsius the wood structure falls apart.
Long molecules are made smaller. Charcoal and tarry gases appear.
3. Oxidation. Under supply of a measured quantity of air, a part of
carbon oxidizes (burns) to carbon dioxide and hydrogen oxidizes to
water. A lot of heat is released. This heat is necessary for:
4. Reduction. In the reduction area the most important conversions take
place. Most of these reactions however ask energy. This energy has just
been released in the oxidation zone, which reaches a temperature of
1400 degrees Celsius. Carbon reacts with carbon dioxide and converts it
to carbon monoxide. Carbon also reacts with water, stealing an oxygen
atom to convert it to carbon monoxide and hydrogen. These are the most
important reactions. Furthermore carbon binds with hydrogen to create
methane and carbon monoxide reacts with hydrogen to methane and water.
Oxidation, produces energy:
C + O2 <==> CO2
H2 + 0.5 O2 <==> H2O
Reduction, takes away energy:
C + CO2 <==> 2CO
C + H2O <==> CO + H2
CO2 + H2 <==> CO + H2O
C + 2H2 <==> CH4
CO + 3H2 <==> CH4 + H2O
Roughly woodgas consists of:
20% carbon monoxide CO
18% hydrogen H2
4% methane CH4
8% carbon dioxide CO2
50% nitrogen N2
The carbon dioxide and the nitrogen do not contribute to the combustion
of the gas. The nitrogen is as a superfluous component led in by
primary air for the oxidation. Large stationary installations partly
use superheated steam in the process. This also brings in hydrogen,
while useless nitrogen does not dilute the gas. For mobile
installations steam is no realistic option, because the construction is
complicated and therefore too heavy.
and internal combustion engines
Woodgas is a low
gas, with little energy content The nitrogen from the air
not contribute to combustion, and carbon monoxide is a slow burning
gas. For combustion engines that means several disadvantages. Because
the high proportion of nitrogen the engine gets an insufficient fuel.
The fact that the fuel is present before the intake manifold as a gas
and engine vacuum is necessary to create this gas, reduces the filling
degree of the cylinders. All woodgas engines are asthma suffering
patients with lung cancer.
These facts cost approximately 40% engine power. Moreover high engine
speed is not possible, because the gas burns slowly. Ignition advance
is necessary to allow time for complete combustion because woodgas has
a slow flame front. At too high rpm’s, combustion has not yet
finished, when the exhaust valve is already opening. The effective
engine speed for car engines is limited to 3,000 rpm, despite of the
fact that the rpm can go up higher on low loads.
Literature often shows a power decline of 40%. This would mean that an
engine which provides 100 hp on petrol, should have a remaining 60 on
woodgas. This is not correct. The engine has 60% left at 3000 rpm and
therefore perhaps only 40 hp!
Ignition advance on modern engines with ECU’s is not easy for
layman. The engine control management can get confused and go into limp
mode or stop entirely. It’s not just in society that managers
more harm that good…
Big, slow running engines with an old-fashioned, but electronic
distributor, are best for woodgas.
and cons of the different types of gas generators
four types of gasifiers:
1. The fixed bed gasifier; simple for small applications such as
camp-site burners. Some power plants work according to this principle.
2. The fluidized bed gasifier; generally very large installations.
Mostly applied in electricity power plants.
3. The updraft and crossdraft gasifier; generally used to gasify
charcoal or coals. Not applicable for IC engines, because of the high
tar output. Frequently applied in central heating systems.
4. The downdraft gasifier. Very suitable for IC engines, because they
are both compact and produce little tar. Tar has to pass the hot
oxidation and reduction area and is cracked into useful gas. Tar is
undesirable in woodgas, because it plugs filters, pollutes piping and
sticks valves in the engine. Tar is cumbersome to remove and can cause
damage, therefore prevention is preferred above healing.
We distinguish two types of downdraft gasifiers. The old
Imbert, such as used in the second world war. And the Stratified
Downdraft, a development from the eighties. The stratified is a very
simple construction. It can consume different fuel sizes and
compositions. One would be tempted to choose the stratified. However,
an important disadvantage sticks to this gasifier. There are, as it
happens, no nozzles for supply of primary air. By lacking a nozzle
position, the oxidation and reduction area are not fixed, like in the
Imbert. Too dry fuel can lead to burning up the bunker stock. Too wet
fuel slows down the process, the result being that the reduction area
ceases to exist and the production of flammable gas is interrupted.
With water injection the process can be controlled. The tar production
is high, unless charcoal is used as fuel. But the stratified can be
made very simply. FEMA has plans on the internet, how to manufacture a
gasifier with scrap materials such as oil drums, trashcans and simple
tools. Nevertheless serious builders leave the stratified principle
after time and embrace the Imbert.
I show a picture of a statified downdraft, but will spend no further
time on it. The stratified downdraft is for me the proof that it is
simple to make woodgas, but very difficult to produce tar free woodgas.
The Imbert gas
A bit of history:
The Imbert is an invention of Georges Imbert. He developed this
principle in the 1920’s. During the second world war more
one million woodgas generators there were driving the European roads,
practically all according to the Imbert principle. After the war petrol
became widely and cheaply available again and motorists said farewell
to the woodgasifiers. Knowledge and experience are mainly lost since
During the cold war the Swedes developed the Imbert further, but
besides documentation, little has been done with it. Sweden has
virtually no fossil fuels, but sufficient wood, so wood gasification
could solve their shipping problems in crisis times.
The energy crises in the seventies had again contributed to a small
bounce, which sank as rapidly as it came.
Only in Finland has mobile wood gasification never
However not on a large scale, or subsidized by the government, but kept
alive by a group devotees. They refined the improvements of the Swedes.
The drawing shows how a World War 2 Imbert works.
The gasfier unit is filled with wood blocks. The nozzles meter the
primary air. Engine vacuum ensures flow in the complete system. The
engine speed regulates the quantity of produced gas and with that the
quantity of primary air. At the shown generator, the gas is taken high
out of the generator to allow dust to fall down. From there the gas
passes through a cooler for dewatering and reducing the gas volume. By
volume reducing and disposal of water, the energy content of the gas
increases. After the filter train the gas is mixed with secondary air
and fed to the engine. A blower is necessary to start up the
Modern Imbert units work somehow different.
The generator has a condensing mantel around the fuel bunker in order
to dry the fuel stock and remove redundant water. A cyclone removes the
coarse ash and char particles. Glass-fiber socks or envelopes filter
the fine dust out. The cooler drains the water from the gas. During
start up, the fan blows the gas out before the filter train to prevent
constriction of the filter by tar and water mist from the still cold
Compared to the original Imbert principle, many details are changed.
Much attention has been given on preheating primary air, to raise the
oxidation temperature. This however, creates new problems, because not
all materials can resist the high temperatures. All in all rather more
complex than in former days, but it results in tar free, clean gas.