PETROLEUM — FIELD 243 



external pressure, rather than letting the engine draw it in by the 

 vacuum created on the suction stroke. This development, started 

 mildly by the automobile designer and adapted mainly for racing-car 

 engines, really went ahead at a tremendous pace when the aviation- 

 engine designers started to use it. While the superchargers built for 

 racing-car engines operated with only a few inches of water "boost 

 pressure," the aviation-engine designer moved ahead to the point 

 where, during World War II, combat aircraft equipped with exhaust- 

 driven turbo superchargers actually delivered a boost pressure in the 

 range of 60" of mercury or about 2 atmospheres increase. This de- 

 velopment threw a tremendous burden on the petroleum industry 

 for high antiknock fuel and, as will be mentioned later, the industry 

 responded by adapting their newer processes and developing other 

 specialized processes in order to produce the required volumes of 

 aviation gasoline having performance characteristics well in excess of 

 100 octane. 



Another type of engine was becoming important and giving the 

 petroleum research laboratories critical problems to solve. This was 

 the Diesel engine initially developed for propelling ships, later for 

 long-distance truck hauling, and now becoming very important as 

 a source of power for railway locomotives. The Diesel engine, unlike 

 the gasoline engine, does not depend on a spark for ignition but de- 

 pends on autoignition induced by the heat and pressure created by 

 the compression stroke of the piston. It is a fact that an operating 

 cycle of this type necessitates a chemical composition of the fuel dis- 

 tinctly different from the type of compounds which are included in 

 motor gasoline and to a greater extent in aviation gasoline to improve 

 antiknock characteristics. The latter have a decidedly deleterious 

 effect on the starting and ignition qualities of the Diesel fuel, par- 

 ticularly for high-speed truck and railway Diesel engines. Thus a 

 technical contrast is presented in which the best Diesel fuel was found 

 to be a carefully refined fraction obtained directly from high-grade 

 crude oil, whereas high-grade motor and aviation gasolines consist 

 of a blend of various fractions of crude oil molecularly rearranged by 

 severe thermal and catalytic cracking together with synthetic prod- 

 ucts of complicated structure obtained from alkylation, polymeriza- 

 tion, etc. 



Most of the comments made with respect to automobile-engine lubri- 

 cating oil hold for lubricating the Diesel engine, except that whatever 

 is done to the oil to improve its inherent characteristics must be 

 greatly emphasized for the Diesel. Most high-speed Diesels run under 

 much more severe conditions of loading, combustion roughness, and 

 high-temperature operation than most automobile engines. 



In industrial fields a new tempo of development has been evident. 



