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Early in the war, Axis submarine packs were able to roam the Atlantic almost at will, preying on United Nations' tankers to such an extent that it appeared probable that shipment of gasoline for nonmilitary use from the United States to neutral or friendly non-belligerent countries might have to be seriously curtailed or discontinued altogether. Foreseeing the effects of such a move on the countries affected, the Foreign Economic Administration (then the Board of Economic Warfare, later the Office of Economic Warfare) charged the Bureau with the problem of investigating the characteristics of materials that might be used as substitute fuels for internal combustion engines (Technical News Bulletins 339 and 34I (July and September I945) ).
One of the first steps in the survey of the properties and effects of the use of available substitutes was a study of their antiknock qualities. This study, the results of which will be published as RPI673 by Alton D. Puckett in the October number of the Journal of Research, included the determination of octane numbers of both liquid and gaseous fuels by current standard test procedures. Carbon monoxide, one of the chief constituents of automotive producer gas, was found to rate well above IOO octane number. The paraffinic gases, from methane through the butanes, were also found to be high in antiknock value, ranging from well above IOO for methane down to 90 ASTM motor octane number for normal butane. All the olefinic gases through C4 were found to be equal to, or better than, present premium grade motor fuels.
The liquid substitute fuels investigated, listed in order of descending octane number, were acetone, ethyl alcohol, normal butyl alcohol, and diethyl ether. Ether was included in the study, in spite of its known knocking tendency, because of the possibility of using it to improve the volatility of other substitutes. Blends containing varying percentages of ether in ethyl alcohol were found to have somewhat peculiar characteristics, but octane numbers indicated that blends containing ether in amounts less than 45 volume per cent. should give knock-free performance in most present automotive equipment.
Because of the necessity for conserving tetraethyl lead as well as extending gasoline supplies, the amount of ethyl alcohol necessary to raise the knock rating of a 68 motor octane number straight run gasoline to 70 and to 75 motor octane number was determined. With this particular gasoline, 5 volume per cent. and I6.3 volume per cent. respectively of alcohol accomplished these increases in knock rating, as did 0.25 and I.I milliliters of tetraethyl lead per gallon. Knock ratings were determined on blends of acetone and ethyl and normal butyl alcohols in a straight run naphtha as well as in gasoline. Although the octane number of acetone exceeds that of ethyl alcohol, it is less effective in blends. Both acetone and ethyl alcohol exhibited lower blending values in a shale-oil motor fuel than in straight run gasolines and naphthas.
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