Detonation Characteristics of Petroleum Motor-Fuels 270005
AN examination for detonating qualities of 18 petroleum gasolines was made by the authors, the methods used being those of direct engine-tests and of chemical analysis. A single-cylinder lighting-plant engine, suitably modified, and a direct-reading detonation-indicator were utilized and they are described. The method of Morrell and Egloff was followed in the chemical analysis. This consists in determining the proportions of paraffins, naphthenes, unsaturated and aromatic hydrocarbons and calculating the aromatic equivalence of the hydrocarbons so found by the use of data compiled by Ricardo on the relative knock-reducing tendency of unsaturated hydrocarbons, naphthenes and aromatic hydrocarbons. These data indicate an equivalence expressed by the ratio 5 to 4 to 1.
Experiments were made in which a constant proportion of one hydrocarbon of each class was added to a gasoline, and the detonating tendency of the resulting mixture was determined by engine test. Use of two gasolines as base fuels and a system of inter-comparisons gave results indicating, for the particular experimental conditions and for the hydrocarbons used an equivalence indicated by the ratio 2 to 2 to 1. The examination by engine test involved comparing each gasoline with mixtures of a standard gasoline and benzene or kerosene. The mixture equivalent to each gasoline gave the so-called benzol equivalent. The equivalent was determined for each gasoline against two standard fuels, one a straight-run Mid-Continent gasoline and the other a good average motor-gasoline. It is pointed out that the degree of correlation between results by engine test and results by chemical analysis will vary with the quality of the standard fuel employed. In general, the benzol equivalents calculated from chemical analysis did not agree satisfactorily with those found by engine test. In the absence of published data on the influence of volatility of gasoline fractions on detonating tendency, a straight-run Mid-Continent gasoline was fractionated into 18-deg. fahr. fractions, and succeeding fractions were then added to the original gasoline in fixed proportions. The distillation data and detonating tendencies of the mixtures are given. The work confirms the general belief that detonating tendency increases with rise in boiling-point. The indications of the work are that petroleum gasolines of satisfactory antiknock value are available, and that the detonating tendency of gasolines is best determined by direct engine-test.
Important written contributions on the relation of volatility to detonation, on comparison of detonation, characteristics and on combustion experiments, appear in the discussion.