From the article:
Gasification of coal and biomass can be considered to be a century old technology. Besides gasoline and diesel oil, producer gas has been used to· drive internal combustion engines almost since their invention. The generation of producer gas from wood and coal has been reliable and inexpensive compared to the use of gasoline and diesel oil for a long time but was generally only accepted during emergencies and war times. Although more than one reason accounts for this phenomena, the most significant factor has been the inconvenience and the required skill necessary to operate a gas producer-engine system.
The recent interest in gas producers has somehow diverted the attention away from the real problem of gasification. A gas producer itself is of little use. Gasification must be clearly seen as a whole system consisting of the gasification unit, the purification system and the final energy converter such as burner or internal combustion engine. The real difficulties are not so much to obtain a combustible gas, but to generate it in a physical and chemical state necessary for long-term internal combustion engine operation. Gasoline and diesel engines draw their fuel from a tank by natural suction or forced injection. These fuels are homogenous and do not change composition or physical properties over many months. It is therefore sufficient just to turn a key and start the engine. A gas producer driven power unit requires much more care and understanding. The gas producer generates the combustible gases as demanded by the engine with no storage container between the engine and the gas producing plant. Physical and chemical properties of the gas such as energy content, gas composition and impurities will vary widely, even within a few minutes or seconds. Their control is limited by the very nature of gasification, a complex sequence of partial combustion, distillation and reduction of lignocelluosic material under high temperatures and close to atmospheric pressure. The gas generated needs to be highly purified before it is used in an engine. The commercially available filter, condensing, and cooling components are not specifically designed to adequately handling the wide range of requirement for the many biomass fuels. In summary, a gas producer engine system, whether it is used for generating electricity, pumping water or driving an automobile must be custom tailored and the operator trained in the peculiarities of the system. No ·one would ever try to run a gasoline engine on diesel or vice versa. The same restriction applies to the gasifying unit of the system. It needs to be designed for a specific class of fuels. Variations in the physical and chemical composition of the fuel are tolerable within limits. For instance, a fixed bed gas producer designed to gasify wood blocks of a specific size and moisture content will not run as well on the same wood blocks with a much higher moisture content and will cease operation all together if fueled with straw. The claims sometimes found in papers and manufacturers' brochures of gasifiers operating on almost every type of waste product containing combustible carbon must be taken with extreme caution.