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Wood based fuels
In a gas generating process with wood based fuels the efficiency depends on the moisture content of the fuel. There are no major differences between the various kinds of wood. The wood must be dry. The drier the wood is the better it suits the gas generating process. If the wood is dried to 20% moisture content with natural methods it must be peeled in stripes when limbed and stored outside in an airy storage.

The size of the wood particles affects the gas generating process. The suitable size is defined by the dimensions of the generator. The generator can be made to be able to use either wood chips or chopped wood. A generator designed to use chopped wood can not be used with wood chips. A generator designed to use wood chips can be used with wood chips.

The best wood chips can be made from unpeeled limbed wood. The wood can be either leaf wood or coniferous wood. For reliable operation of the generator big chips are better than little ones even if the amount of gas generated is not the greatest possible. The smaller the chips are the more gas is generated but also more malfunctions occur. So for example cuttings are not suitable fuel if not pelleted. The best size of the wood chips is 10x20x30 mm and the size of all chips should be as equal as possible. This kind of fuel produces an airy glowing charcoal layer on the hearth. The amount of gas generated is constant and no malfunctions occur.

The best possible fuel for gas generating is charcoal which produces very pure gas with a high heating power. To produce one cubic meter of charcoal 2,5 cubic meters of wood is needed and a great part of the total heating power of the wood is lost in the process. One cubic meter of wood is equal to 200 liters of gasoline. One cubic meter of charcoal is equal to only 80 liters of gasoline.
Sod is not proper fuel for a gas generator. It produces much ash which melts on the hearth and clogs it after a while.
Pelleted straw can be used as a fuel in a gas generator. The properties of straw vary from crops to crop. The most suitable straw for gas generating is one that produces ash with a high melting temperature. For example turnip rape produces this kind of straw.

When generating gas from solid fuel the combustion is incomplete. The gas contains carbon monoxide and several organic compounds: ethylic acid, formaldehyde, etc. The gas contains substances that are harmful to personal health. Therefore the gas generator may not be started or used in a closed space. In addition to this the user must not inhale the gasses released from the generator and the condensed liquids must be treated properly.

Fuel recommendations: The most recommended fuels for a forward flow gas generator are wood-based fuels:

The wood based fuel must meet the following requirements:

Translated by Olli.