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The Basic Concepts Behind Wood Gas Generators

Fuel gas produced in a gasifier unit, or a wood gas generator, was often used for heating homes between 1840 and 1940. Wood gas generators weren’t extensively used, but folks were still pretty familiar with them.

In World War II thanks to oil shortages the folks in Western Europe started using them for transportation. Charcoal burning taxis were pretty common … even as late as 1970 as far away as Korea. Since the United States never had the kind of oil shortage that Europe suffered from, we never really adopted wood gas generators.

But if we ever run into any problems here, well, we might need to know how to use wood gas gasifiers. While it isn’t necessarily the top of the line power generation contraption, it’s something worth considering.

You can build a basic gasifier like they used during World War II with a few easy pieces … a garbage can, a small drum, a few plumbing fittings, and a couple other odds and ends. It’s got enough gas generation capability to operate a simple four cycle gas engine up to about 150 horsepower.

All internal combustion engines actually run on vapor, not liquid. The liquid fuels used in gasoline engines are vaporized before they enter the combustion chamber above the pistons. In diesel engines the fuel is sprayed into the combustion chamber as fine droplets which burn as they vaporize.

The purpose of a gasifier is to transform solid fuels into gaseous ones and to keep the gas free of harmful constituents. A gas generator unit is simultaneously an energy converter and a filter.

If you light a wooden match; hold it in a horizontal position; and notice that while the wood becomes charcoal, it is not actually burning but is releasing a gas that begins to burn brightly a short distance away from the matchstick.

Notice the gap between the matchstick and the flame.  This gap contains the wood gas which only starts burning when properly mixed with air (which contains oxygen). By weight, this gas (wood gas) from the charring wood contains approximately 20% hydrogen (H2), 20% carbon monoxide (CO), and small amounts of methane, all of which are combustible, plus 50 to 60% nitrogen (N2).

The nitrogen is not combustible.  But it does occupy volume and dilutes the wood gas as it enters and burns in an engine. As the wood gas burns, the products of combustion are carbon dioxide (CO2) and water vapor (H20).

The same chemical laws which govern combustion processes also apply to gasification. Solid fuels suitable for gasification cover a wide range, from wood and paper to peat, lignite, and coal, including coke derived from coal.

All of these solid fuels are composed primarily of carbon with varying amounts of hydrogen, oxygen, and impurities, such as sulphur, ash, and moisture. The aim of gasification is the almost complete transformation of these constituents into gaseous form so that only the ashes and inert materials remain.

In a sense, gasification is a form of incomplete combustion; heat from the burning solid fuel creates gases which are unable to burn completely, due to insufficient amounts of oxygen from the available supply of air. In the matchstick example above, wood gas was created as the wood was burned and pyrolyzed into charcoal, but the gas was also consumed by combustion since there was an enormous supply of air in the room.

All over Europe, Asia, and Australia, millions of gas generators were in operation between 1940 and 1946. Because of the wood gasifier’s somewhat low efficiency, the inconvenience of operation, and the potential health risks from toxic fumes, most of such units were abandoned when oil again became available in 1945.

Except for the technology of producing alternate fuels, such as methane or alcohol, the only solution for operating existing internal combustion engines when oil and other petroleum products are not available has been these simple, inexpensive gasifier units.

I’ll probably have more to say about wood gas generators over the next few weeks.  It’s a fascinating topic for me.  If you have any specific questions about them, do let me know in the comments!

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4 Responses to The Basic Concepts Behind Wood Gas Generators

  1. I think getting to know how the older technology works is a good idea. I am very interested in how to build and operate one of these units. Never know when you might need it.

  2. After evaluating my rural homestead for non-grid power generation, the wood gasifier seems to be the best choice. I do not have natgas/coal under my property, it is windy but from what I read windmills don’t produce much electricity, and it is in Wisconsin so sunlight isn’t very intense. To me it seems like the wood gas generator would be perfect for me to get off the grid, since I have 17.5 acres of large trees at the property. I do have electric there but want to be self-sufficient. It is strange though how little information is out there on wood gasification.

    I am hoping to build a wood gasifier and test it however I have not had time to research it yet. Just wondering how ‘low efficiency’ it would be… would I have to cut down an acre of tall trees per year to power a small cabin?

    • I honestly don’t know what they are efficiency wise. I’m investigating them further now, so I may come up with some good info on that. Or maybe not… We’ll see!

      • So if you build a gasifier for heat only, it is over 90% efficient. If you build it to power an engine, it will give you from 50 to 70% of the rated horsepower depending on the quality of construction.