The Development of the Octane Number Tests and their Impact on Automotive Fuels and American Society

Abstract

Modern automobiles and fuels were shaped heavily by the development of the octane number tests. These tests were developed between 1929 and 1932 to quantify a fuel’s anti-knock performance in spark-ignition engines. Since knock imposes limits on the maximum engine compression ratio, which correlates to engine performance, the anti-knock property of a fuel is a crucial design constraint. Prior to the development of the octane number tests, engines were designed to run at very low compression ratios to avoid knock, significantly limiting their performance. The octane number tests created standards that allowed for better engine development and advancements in fuel technology. Engines could now be designed to handle a specific octane number of fuel allowing for increased performance. The demand for better performing engines resulted in an increase in the average fuel octane number from 50 to 75 during this period, with the Great Depression and World War II setting the stage for this advancement. These advancements in fuel technology played a crucial role in the survival of the American automobile industry during the Great Depression, the Allied success in World War II, in addition to creating the ‘American obsession’ with powerful automobiles. This paper provides an overview of knock, a historical summary on the development of the octane number tests, the corresponding advancements in fuel technology, and the implications of these advancements on American society.