Spectroscopic investigation of the mechanism of the combustion of alcohol

While lead compounds reduced knocking for gasoline they tended to increase knocking in alcohol fuels. Spectroscopic analyses were made to help clarify the cause of this phenomenon. To ethanol and iso-octane was added 0.2 vol.% tetramethyl-lead and the mixtures burned at different air ratios. Spectroscopic photographs were taken of the inner flame. With leaded alcohol, the greater the air ratio, the more intense was the lead oxide band (lambda5678) in the flame spectrum. Leaded iso-octane gave much weaker emissions with a maximum point of 88% air ratio, where the air ratio is the % of the amount of air needed for complete combustion. In alcohol the intensities of the Pb0 band relative to that of Pb line spectrum was 1.1, 1.4, 4.1, and 11.2 for air ratios 62%, 75%, 88%, and 105% respectively. For iso-octane the intensities were 0.7, 1.7, 1.5, and 1.0 for air ratios 71%, 82%, 93% and 95% respectively.