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IMPROVEMENT in the control of smoke in the automotive diesel engine can be brought about by the use of lighter fuels of suitable ignition quality in cases where either design, maintenance, or adjustment fail to accomplish the degree of smoke control desired, the authors conclude. But this control is accomplished by some reduction in power and a loss in fuel economy. They suggest taking the power loss required for smoke control by means of resetting the smoke stop adjustment while retaining the advantage from an economy standpoint of the higher Btu per gal of the heavier fuel. The satisfactory performance of the heavier fuels in European bus operation clearly shows that smoke control can be effected by other means than resorting to fuels approaching kerosene in volatility.

OF the many characteristics of diesel fuels, heating value, ignition quality, and possibly fuel viscosity are the only important ones affecting engine power and economy, the authors disclose. In their paper they present data obtained from an extended fuel research program concerning the power and fuel economy obtained when using fuels differing in their physical and chemical characteristics. The points which seem to the authors to be of greatest practical significance are summarized as follows: 1. Assuming complete combustion, fuel volatility affects the pints per brake horsepower-hour only indirectly as it is related to heating value and ignition quality. 2. Most present-day engines have fixed injection timing and, on such engines, ignition quality is a major factor in determining volumetric fuel economy in the upper speed ranges. At the lower engine speeds, heating value in terms of Btu per gal, or as estimated from API gravity, is the most important consideration. 3.

PRESENT-DAY cars are not capitalizing on the continued efforts of the petroleum industry to provide better fuels, the authors believe. The wide differences found in the octane-number requirements of individual cylinders, plus the failure to obtain uniform mixture distribution from cylinder to cylinder without resorting to fuels of aviation-grade volatility have led them to reach this conclusion, they explain. The probability that significant reduction in the average antiknock requirements of cars might be effected without making any major changes in the engine is indicated by a survey of the technical literature, they point out. The extensive studies of ignition-system characteristics and gasoline-mixture distribution as affecting detonation reported in their paper bring out the following pertinent points: 1. Variations actually occurring in the spark advance from cylinder to cylinder may vary the octane-number requirement of individual cylinders by about 10 points. 2.

STARTING, oil pumping, sludging and wear are the subjects considered specifically in connection with low operating temperatures. Tabular data and curves relating to starting are presented. Sludge is more dangerous in cold-weather operation, and the importance of selecting a quality non-sludging oil is emphasized. Tests to determine the causes of sludging are described, and the five conclusions reached are stated. The indications that wear is due to corrosion, rather than to removal of lubricant from cylinder walls, are analyzed. With regard to kerosene and Diesel engines, the author states that it seems reasonable to believe that the effect of operating temperatures, as such, with resultant moisture condensation, will result in at least equal relative wear to that which obtains in the gasoline engine. In conclusion, seven general rules are stated whereby the utmost satisfaction may be obtained during operation at low temperatures.