September 19, 1887 – What do the numbers on the gas pump mean?

On this day in 1887 Dr. Graham Edgar, developer of the octane rating system, was born in Fayetteville, Arkansas. During the pioneering era of the early automobile it was impossible to tell if a gasoline would cause engine knocking due to irregular combustion caused by a nonstandard refining processes and the use of numerous types of fuels within gas engines. The only real way to find out if a particular fuel would work in a certain car was to fill it up and crank it and just see what happens. In 1926, while working for a division of General Motors

, Edgar solved this issue by developing the octane rating system. He found that the chemical isooctane would not knock in any engine, under any operating conditions, while n-heptane would always knock in any engine. By mixing isooctane and n-heptane in different amounts, he was able to create fuels of all qualities, suitable for different types of engines. The percentage of isooctane in the mixture is the octane number read on the fuel pump today.