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Measurement of the volatility of motor fuels by batch distillation is regarded by the author as unsatisfactory, because the carbureted fuel is vaporized in an internal-combustion engine by continuous distillation, hence there is great difficulty in correlating the temperatures of test with those of actual use. Whereas formerly gasoline was produced by batch distillation in the refinery, it is produced now by removing the gasoline from crude oil by continuous distillation or is produced by cracking and continuous fractionation. Therefore the temperatures of production also bear no rational relation to those of test by batch distillation. Similarly, in an engine, fresh gasoline is supplied continuously by the carbureter and is vaporized continuously in the manifold and cylinder, all of the constituents being present at any time in any cross-section of the manifold.

The paper analyzes and states the factors affecting the power requirements of cars as rubber-tired vehicles of transportation over roads and the factors affecting the amount of power supplied the car as fuel to produce at the road the power required for transportation. Quantitative values are given wherever possible to indicate the present knowledge of the relation between the factors involved, and the text is interspersed with numerous references, tables, charts and diagrams. Among other important factors specifically discussed are mixing and vaporization, charge quantity control, the heat of combustion, gas-pressure, transformation loss and power transmission efficiency. Six appendices contributed by other associates of the Bureau of Standards are included.

Supplementing a “more miles per gallon” movement in 1919, a series of experiments outlined by the S. A. E. Committee on Utilization of Present Fuels was undertaken by the Bureau of Standards, in May, 1920, which included measurements of engine performance under conditions of both steady running and rapid acceleration with different temperatures of the intake charge secured by supplying heated air to the carbureter from a hot-air stove, by maintaining a uniformly heated intake manifold and by using a hot-spot manifold, fuel economy being determined for both part and full-throttle operation. A typical six-cylinder engine was used, having a two-port intake manifold with a minimum length of passage within the cylinder block, an exhaust manifold conveniently located for installing special exhaust openings, rather high peak-load speed and conventional general design.