Home Wood Gasification: An Intriguing Emergency Fuel Source

Wood Gasification: An Intriguing Emergency Fuel Source

The User's Profile Dutch John May 25, 2011
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A personal note

As a daily visitor of, I first want to thank Dr. Chris, his staff and all members for the excellent job achieved in this community. I value the high quality articles backed by data and the informative member comments that are pleasant to read. All of you keep me on track. Up until I found Chris, his Crash Course and articles three years ago, I often was very unsure about my feelings, thoughts and fears about the future. Of course I still expect a different future, but knowing I’m not alone in making preparations and gathering knowledge and skills increases my personal resilience.

Like many members of the “Martenson Brigade” I am becoming less dependent on fossil fuel, high living standards and money. I gave up a very nice income ten years ago to move towards greater self-sufficiency. Investing in home gardening, livestock, solar, wind and biomass energy has made my life more simple, slow and sweet. Yes, I am a big fan of John Seymour. No rat race for me and my wife anymore. Unfortunately, community building is still tough since the local farmers here in the Netherlands have no idea what the world is turning into and I do not live in a city where contrarian thinkers are easier to find. Likewise thinkers are scattered all over the country.

After these three years of absorbing knowledge, I feel payback time has come. As it happens I know a little more about wood gasification compared to the average person. Since wood is the most accessible, free and ever-regenerating storage medium of solar energy, it would be a shame not to use it. This article will not deal with the direct burning of wood, nor with gasifiers meant for heating purposes. Instead, we’ll talk about wood gas generators connected to internal combustion engines and vehicle engines in particular. Wood gasification for transportation purposes will not save the world. But it has and will continue to have an important role as a viable emergency method.

My first language is Dutch, so I apologize in advance for my plain-school English.

What is wood gasification?

Wood gasification is a thermo-chemic way to extract flammable gases from wood, leaving nothing but a few small char particles -known as bio-char- and some condensate. We distinguish two major stages in the process. The first step is heating up the wood to temperatures near 1,300 degrees centigrade. This is done by burning about 15% of the wood by means of injecting a restricted flow of air, but at high velocity. Wood consists of carbon (C) and chemically bound water (H and O). By burning it with oxygen (O), the end products are carbon dioxide (CO2) and water vapor (H2O), both superheated to the previously-mentioned high temperatures. During this oxidizing stage, the remaining wood becomes char and the escaping tars are cracked by the heat into much smaller hydrocarbons. We call this first stage an exothermic reaction or heat-producing reaction. We need this heat for the second stage.

This second step concerns the remaining 85% wood, now white-glowing char. The char reacts  with the superheated water vapor and carbon dioxide into flammable carbon monoxide (CO) and hydrogen (H2). Also formed is a minor quantity of methane (CH4). This reaction is also called reduction and is endothermic, so uses up heat in order to occur. In a few sentences this is what wood gasification is about. Actually it’s more complicated than I’ve described, but I will not bore you with that. 

Unfortunately, the ready wood gas is substantially diluted with useless nitrogen (N2) which came in with the incoming air. Other inflammable byproducts are minor quantities carbon dioxide and water vapor. These make the gas low from a calorific standpoint and reduce engine power to about 60 % of the original power vs petrol. This is one of the reasons why driving on wood gas never became very popular.

Wood gasification is an on-demand process. The gasifier and engine are connected, so the draw of the engine determines how much gas is being produced. It is also self-controlling. When the throttle is opened, it allows the engine intake vacuum to pull harder on the gasifier:  more air is drawn into the gasifier and, as a result, more wood is gasified. Of course, first the gasifier has to be fired up with the help of a fan, creating and artificial draw.

Almost any wood can be used, except woods that contain a lot of oil. Although oil has potential to bring more energy, it adds to the tars that distillate out of the wood. As I mentioned earlier, these tars have to be cracked into smaller hydrocarbons in the hot part of the gasifier. It’s a tricky process, taking place in a very short time, and is therefore sometimes not completely done. A tarry gas can result, which can ruin a good engine in minutes. Tarry gas is the worst enemy of a woodgasser (guys who drive on wood) and the most difficult one to fight.

Soft woods, like coppice willow, are fast and easy to grow and will gasify excellently in a well-dimensioned gasifier. Hardwoods, like beech, are better; because these contain more energy per volume and allow a stable char bed. It is not possible to fill up your fuel bin with any-size wood. The wood has to be uniform in size and shape, appropriate to the gasifier. It’s best if it’s as dry as possible, although the fuel bin can be adapted to catch water vapor from the wet wood bits. Green wood cannot be gasified.

The combination of an engine that delivers less power, a fuel that often is not ideal, and a driver/operator who needs certain skills makes a wood-powered engine unattractive to many. But the most pleasant advantage of wood as an engine fuel is the fact that it is accessible to almost everyone. Imagine driving around the world with nothing else but an axe and a hand saw to harvest your fuel.

What are the components of a wood gasifier system?


Above you see a typical WW2 gasifier system for cars. It is light-weight and simple. At left, we see the gasifier, also called a gas generator. It has a fuel bin on top, with the primary combustion air nozzles (that create the intense heat) just below. Between the restriction plate (fat black drawn) and the grate, the actual reduction to carbon monoxide and hydrogen takes place. The grate supports the char bed.

After the generator comes an extensive cleaning train, since the gas is dusty with carbon particles and is water-saturated. We do not want either to mess up the engine, so in this setup the coarse particles are taken by a cyclone filter. Meanwhile the temperature of the gas is lowered towards the dew point, so after the cyclone comes a cooler to remove the condensed water. Next is a fine particle filter as well as the startup blower, powered by the car battery. Finally, in the carburetor, the gas is mixed with secondary air at a rate of about 1:1. Today many components are designed differently, because of better materials. I refer to my website below this article for those interested in reading more information on this process.

What are the applications for wood gassification?

We distinguish two popular applications.

The most widely-used is co-generation of heat and power. Bulky gasifier systems feed an electric power generator while most of the heat is recaptured and used to dry the wood and heat buildings. Size matters in the wood gasification world. Stationary systems are often much bigger compared to vehicle gasifiers, less compromised and therefore more reliable, easier-to-control, and produce cleaner gas. Many medium to large-sized installations can be found in forested areas. Short transportation distances and abundant fast-growing wood allow wood gasification for “co-gen” applications to be an interesting method for regional power and heat supply. After all, wood is bundled solar energy, allowing for a continuous power supply (which cannot be said of PV panels or wind turbines). Decent wood-fueled cogeneration is more than just an emergency method. Should the wood only be used for electric power generation and the heat being wasted, then I consider it again as a crisis fuel.

The second application is the earlier-mentioned transportation purpose. It was much-used in Europe in WW2, but quickly abandoned after petroleum fuels became available again. Nothing beats a liquid fuel when it comes to reliability, power and range. But, boy, what a thrill it is to drive on wood gas! Now, almost three years after I finished my refinery-equipped car, I am still driving with a big grin on my face…

Of course you can think of more applications. Every petrol-fueled engine can be adapted to wood gas. Even diesel engines can run on wood gas, but come with some complications.

How sustainable is wood gasification when used for transportation?

How sustainable is a car? Let’s be honest. We only replaced the fuel. We cannot make cars from wood; they still need inputs of fossil energy and other commodities. On the scale of personal transportation, a wood-powered car is somewhere in the middle if the scale has a petroleum fueled car on one end and a horse on the other. A wood-powered car is slightly more sustainable than a biodiesel-fueled car, because preparing the basic fuel (wood blocks versus vegetable oil) asks for less – or even no – fossil input. But both need a refinery and both use a vehicle.

Wood is virtually free, because trees can thrive on land that is not suitable to grow crops. It does not compete with food. Of course there are limits. If everyone would drive on wood, we would run out of trees very fast.

A gasifier unit made of decent materials can survive several cars. One made of junk will not, but hey, it was already disposed and you gave it new life.

If the car wood is made and transported by petroleum-fueled machines, the fossil CO2 output is only about 10 grams per driven kilometer. If you make the wood fuel all by hand and don’t eat much meat, the fossil CO2 output is minus 10 grams per kilometer. Minus? Yes, my car produces about 3 grams of bio-char per kilometer. That is carbon forever taken from the atmosphere and corresponds to about 10 grams of CO2/kilometer. Still, a horse does much better…

One can harvest 1,000 km worth of car wood –that is about 1 m3 of loosely filled wood blocks – in 8 hours. From standing tree to chopped wood. It can be manually done, with an electric chainsaw and a small axe as tools.

The EROEI number. While the basic wood block fuel can produce excellent numbers, we still have to take the refinery into account. I cannot calculate the amount of energy put into the materials and the construction. The number also depends on how sophisticated the gasifier unit is. But does it really matter? It is a not-for-everybody emergency transportation fuel. If this method would have to become the standard, then we are in serious trouble and have bigger problems to worry about.

What are the (dis-)advantages?

Now we are entering a tricky area. I will try to be honest and objective. For cogen applications with short fuel transportation distances, a big advantage is the energy source being an ever-regrowing solar battery. A disadvantage is the fact that a lot of machinery is involved for harvesting, processing and transportation of the fuel. The gasifier system itself is also complex. It all depends on the lifespan of the total system.

First: the disadvantages of a vehicle gasifier system.:

  • As I told you before: nothing beats a high calorific, easy to handle liquid fuel. It provides long range, a lot of power and doesn’t require a skillful operatorating expertise. It is possible to refine wood gas to a liquid using the so-called Fischer-Tropsch process, but not on a small personal scale. Wood gas cannot be stored by compressing it, since carbon monoxide is an unstable gas and will fall apart under pressure.
  • Having less engine power while carrying a heavy refinery all the time can be cumbersome. For instance. the top speed of my Volvo has been reduced to 120 km/h. Less cargo can be carried.
  • The driver needs to be a skilled operator. Gasification combines science with black art. Often literally black. Mind that it’s not uncommon for the tars to get on you.
  • It CAN be dangerous. Carbon monoxide is a poisonous gas and can kill a person swiftly. A well-designed gasifier in combination with an experienced operator will minimize this danger.
  • Refilling a hot fuel bin will release dirty pyrolysis gas. The condensate from the cooler has some phenols dissolved in it. However there are easy and clean ways to deal with this condensate.
  • It can be unreliable. The gasifier, wood and operator all have to work in a successful trinity, otherwise it will not work.

Fortunately there are also a few advantages:

  • The fuel is renewable, therefore sustainable. Exhaust emissions beat many modern cars.
  • The fuel, as well as the technology, is very accessible. Every handyman with an angle cutter and a welder can build a gasifier.
  • Independency of Big-oil.
  • A woodgas-powered car will not allow you to get somewhere fast, but it will allow you to get there. And fairly comfortably.
  • Driving a woodgas car brings back some of the romance of early automobile driving, combined with modern clean emissions.                                                                                                              -For me personally, building a wood gasifier brought me a mind turn. Making car wood by hand is hard on the muscles, but sweet to the mind. It allows you time to think about how to work on a better world.                      
An intriguing crisis method?

Yes, woodgas for transportation purposes is an emergency method. The disadvantages show you that. It can be very cumbersome. It’s not a method for everyone. Besides that, it cannot be scaled up to present mileages, simply because there is not enough wood. Or must I say: there is enough wood, but an excess of driving Homo Sapiens?

On the other hand, the advantages make it intriguing. A very accessible fuel, combined with a refinery that relatively easy can be built, allows one to be independent. Even the unpredictable character of a gasifier, always playing hard to get, attracts us stubborn types…

Where do I start?

Ouch. When you want to build a wood gasification system yourself, a couple of hundred hours studying cannot be avoided. Gasification (as well as simply building a gasifier) is a combination of thermodynamics, math, material knowledge and manual crafts. Don’t let the required study discourage you, but don’t skip it, either. You need the science to build a well-dimensioned gasifier setup. Once ready, the black art starts… Yet, a very simple gasifier can be made in only one day. It is exciting and stimulating to obtain a perfect purple flame from a black box filled with chopped wood.

A gasifier unit can be build with new and fancy materials. New materials do not compromise dimensions or performance, but come with a price. Well-working gasifiers can also be built with materials from the local scrap yard. Whatever you use: work tidy and neat. Leaks are not allowed.

When you want to build yourself, always start with a well-proven, existing design. Don’t fall into the trap of adding own “improvements” to your first gasifier. Perhaps you want to start with the simple WW2 designs. Mind you that these designs are very clever. In those times it was a full-time job for teams of engineers. Compared to them, I and even some of the present commercial manufacturers are laymen. Yes, we have the old documents and drawings. But the masters who could explain all the multifunctional details are all gone.

Building a gasifier should be the last item on your “What Should I Do” wish list. It is both very time-consuming and addictive. You better have the other items done before becoming a woodgasser.

Since a few years back, commercial manufacturers of small gasification systems has become active in many countries, including the US. Google them,;I only know some of them so do not want to recommend anyone particular. They are an excellent choice if you want a gasifier and have more money than manual skills. Just remember the black art part. A sharp brain, patience and perseverance are needed regardless Buying a gasifier and immediately storing it for crisis times is not the way to go. You are the student, while the gasifier is your teacher.

I thank you for your attention. It is an honor to me having my experiences shared with this community.

Best regards,                                                                                                                                           

Dutch John, Netherlands

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