Molecular Structure and Component Blending Effects on Knock Related Chemistry

Atmospheric pressure flow reactor experiments were conducted on the oxidation and pyrolysis of n-octane and iso-octane and the oxidation of blends of iso-octane and n-heptane have led to the conclusions that a) the difference in knocking tendency of fuels may result primarily from the comparative oxidation rates of the intermediates rather than the rate of attack on the initial fuel molecule, b) certain small unsaturated hydrocarbons interfere with the oxidation of other intermediates and serve as model compounds for the development of octane number enhancers, c) high temperature homogeneous oxidation chemistry of n-heptane/iso-octane mixtures and single component paraffin fuels can be correlated with the global phenomena of octane number measurement in a test engine, d) the contribution of thermal and oxidative processes to the rapid decay of the initial fuel can be evaluated from rate parameters from pyrolysis studies of pure hydrocarbon fuels.