William Kovarik
Radford University
and
Matthew E. Hermes
Kennesaw State University

Fuels and Society: 10. Knocking

Back to: 5. High Compression Engines

Back to: 7. Poor Quality Gasoline

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In the early years of the auto industry, no one knew exactly what caused engine knock. Some kinds of crude oil produced gasoline that would knock less. (As we know now they had more branched chain compounds in the C5 – C9 range). And some fuels would allow high compression ratios without engine knock. These included benzene and alcohol which were widely used in high performace racing engines of the era.

The era's leading automotive engineer was Charles F. Kettering, then president of the Society of Automotive Engineers and vice president of the newly formed research division at General Motors. Even if oil was running out, Kettering maintained that engineers should refuse to compromise the design of the engine. In his1919 SAE address, he insisted that the route to conservation of oil was through better quality fuel to be used in more efficient engines.

This must have seemed contradictory at the time, since declining fuel quality was the original problem. But Kettering urged the SAE members to take a longer view. He argued that low quality fuels would also run out and low compression engines would use them up even faster. If, on the other hand, the fuel could be improved, engines could be developed with higher compression ratios, which would give better mileage, which in turn would extend fuel supplies.

In the short term, two "classes" of solutions to fuel improvement were available, Kettering said: the "high percentage class" and the "low percentage class." The former involved adding large amounts of another liquid fuel to gasoline, such as 40 percent benzene, which "makes an engine operate entirely satisfactorily," Kettering said. Alcohol was another fuel in this class. The "low percentage class" of solution was represented in 1919 by a single impractical discovery -- one percent iodine solution in gasoline -- which cut engine knock and would allow higher compression ratios were it not far too expensive and corrosive, Kettering said.

In the long run, if oil were no longer available, Detroit would need something to run automotive engines. Kettering and most engineers were convinced that if oil were to run out, alcohol would be the fuel of the future.