The Effects of Fuel Structure on the Autoignition of Fuel-Air Mixtures

This paper contains the results of studies of self-ignition of differently-structured hydrocarbons, as well as of different gasolines, under varying rates of compression. Two oxygen-containing compounds, methanol and ether, were also examined. The air-fuel equivalence ratio was held at 1.2 for all tests. The experimental conditions simulate the end-gas state in an engine where compression takes place at different rates when engine speed is changed. Using the modern concept of the gas-phase oxidation of hydrocarbons, and drawing on the experimental data, a new scheme of hydrocarbon oxidation was developed. The activation energy for five individual hydrocarbons was calculated according to this scheme. The experiments with different gasolines have shown that the presence of more than 30% aromatic or olefinic hydrocarbons in gasoline leads to independence of fuel-knock resistance from engine speed. This last fact can promote high-speed knock.