Because the well known knock engine method of measuring fuel octane or other measure of knock avoidance is not continuous, requires an internal combustion engine under load, and involves spark hazard and substantial maintenance; a continuous method for measurement of octane number, etc. has long been sought.
Kelly, Barlow, Jinguji and Callis of the University of Washington, Seattle, (Analytical Chem. 61, 313-320,) found gasoline octane numbers could be predicted from near infrared absorbance in the range 660-1215 nanometers (nm). They found best correlation between absorbance and octane number to occur at 896, 932 and 1164 nm for research octane number, 930, 940 and 1012 nm for motor octane number, and 896, 932 and 1032 nm for pump octane number.
A search in Lexpat (U.S. patents from 1975 forward) under infrared, octane, and (gasoline or fuel) within 25 words of each other showed only four patents: U.S. Pat. Nos. 4,277,326; 4,264,336; 3,496,053; and 903,020, none of which relate to new techniques for the measurement of octane.
The present invention, by measurement of absorbance in a range close to but above the Kelly et al. wavelengths, shows dramatically improved correlation as compared to measurements made in the wavelengths described by Kelly et al.