No coin nor oath required. For personal study only.
In a paper presented at the winter meeting of the Society of Automotive Engineers in Detroit on January ~ I, I946, Donald B. Brooks, chief of the Bureau's Automotive Section, reviewed the development of knock rating scales and described a new reference fuel made up from various proportions of triptane and normal heptane. He pointed out that today the antiknock quality of motor fuels is the outstanding characteristic by which they are graded. The average motorist realizes that when he pays more for a premium motor fuel, he is buying higher antiknock quality than is available in regular gasoline. Many even have at least a practical understanding of the term "octane number" by which this quality is now expressed.
A quarter of a century ago, the first yardstick for measuring the antiknock quality of fuels was brought forth in England by H. L. Ricardo. He designed an engine, the compression ratio of which could be varied so as to cause knocking with any fuel then available. The point at which this occurred was called the highest useful compression ratio, abbreviated HUCR, and was used as a measure of the antiknock quality of the fuel, As interest in knock rating spread, many laboratories used engines conveniently at hand in making their determinations. These varied fron 2 small engines designed to power farm-lighting plants to complete automobile and truck engines, and single cylinders of airplane engines. .\ variety of test procedures were used, and the results frequently were expressed in terms of the blend of high and low reference fuels equalling the test fuel in knock. As there was no uniformity either of test engine, test procedure, or reference fuels used, the results were meaningless except to the laboratory of their origin.
An urgent demand, therefore, arose for standardizing the essential details of knock rating. Under the direction of the Cooperative Fuel Research (CFR) Committee, a test engine was developed and standardized. After considerable study and discussion, the present octanenumber scale was adopted. Isooctane, produced at the rate of millions of barrels a month as a large constituent of the aviation fuel that powered the recent war, was unknown 2o years ago. First prepared in r926, it was found to be of much higher knock rating than any fuel of that time. Blended with normal heptane, a hydrocarbon poorer in
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