Charcoal autos: still not most efficient

I remember seeing automobiles in Spain after World War II which used charcoal gas generators for power. I'm not sure how they ran out wonder if such devices are available in the US. Will you comment? Charles M. Blair Buena Park, Calif.

The gasification of solid fuels -- wood and/or coal -- produces a gas that can be used to fuel internal-combustion en gines and was widely used during World War II in Germany, France, the Soviet Union, Sweden, and Australia, among other countries.

Gasifiers were first developed in the mid-19th century in Germany. Most of these producers were of the updraft type with air forced into the bottom of the reactor and gas discharged at the top, according to William Agnew of the General Motors Technical Center in Warren, Mich.

"The producer gas was either directly combusted in a furnace or boiler, or cleaned and cooled to operate an internal-combustion engine," says Mr. Agnew.

The most successful portable gasifiers were the downdraft versions which had lower tar production.

After World War II, howerver, automotive gasifiers were abandoned due to the plentiful supply of more convenient and less-costly fuels, such as natural gas and oil.

Now, with fuel prices hitting the roof, some motorists are remembering the gas-producing cars they saw either during or directly after the war. I remember seeing charcoal-burning cars in Western Australian in 1944, for example.

Major advantages for automotive gas producers, according to Dr. Agnew, are:

* Availability of fuel supplies.

* Low fuel cost.

* Retrofit adaptability.

* Good overall energy efficiency.

The overall energy efficiency of converting coal to liquid transportation fuels is about 50 percent. In an automotive gas producer, the conversion of coal or wood to producer gas could be as high as 60 to 70 percent efficient.

Anthracite, coke, charcoal, and wood were among the solid fuels widely used in the 1940s. Of these, the most successful was charcoal which has low ash content (less than 2 1/2 percent), is relatively easy to gasify (due to high porosity), and results in less tar in the gasified products. By contrast, the abundant US coals have high concentrations of sulfur and nitrogen and generally have an ash content greater than 10 percent.

If coal is not pretreated, more complex cleaning equipment is required for the gas-producer system than would be required for wood- and charcoal-fueled systems.

For deisn calculations, the energy requirement for a small GM car -- a 1978 Pontiac Sunbird -- cruising at 64 kilometers per hour was chosen, sayd Dr. Agnew.

"The estimated volume of a gas-producer system -- fueled with bituminous coal -- is 500 liters and the estimated mass is 260 kilograms," he reports. "A similar system fueled with wood (spruce) chips woudl require more than twice as much space and would be about 20 percent heavier for comparable range.

"These results should be compared with a volume of 75 liters and a mass of 55 kilograms for a gasoline fuel system."

Thus, the size and weight would make its future use unlikely.