74 BULLETIN 102, VOL. 1, UNITED STATES NATIONAL MUSEUM. 



entirety — a bent as yet only dawningly perceptible. Whether radical 

 changes in motor principle are in prospect is a question that need not 

 affect the present argument. 



In point of bulk nearly three-fourths ^ of the petroleum consumed 

 in the United States goes into the production of power. Of this 

 amount, one-quarter ^ is employed in the form of gasoline as a motor 

 fuel,2 while three-quarters,^ in the form of crude petroleum and fuel 

 oil, is used as a convenient substitute for coal chiefly in firing steam 

 boilers.^ While the efficiency of the internal-combustion engine is 

 much greater than the steam engine, now commonly referred to as 

 " wasteful " in comparison with more modem types of power genera- 

 tion, the use of the superior principle has thus far been confined in 

 this country almost exclusively to an explosion motor using gaso- 

 line — the ordinary automobile engine familiar to all. The fact has 

 generally been ignored in this country that a type of engine, com- 

 parable in efficiency to the gasoline motor, but making use of heavy 

 oils (as fuel oil and even crude petroleum) and suitable for power 

 generation on a large as well as a small scale, has for many years 

 been in successful use abroad. This is the so-called Diesel type of 

 engine, which has its conception as far back as 1893 and " has proved 

 to be, from a thermal standpoint, the most economical heat engine so 

 far devised, and the one that most nearly approaches theoretical 

 maximum efficiency." * 



This high-compression oil engine, as it may be termed, gains its en- 

 ergy from the expansion that results when oil is sprayed into a cyl- 

 inder filled with compressed air and ignites under the influence of the 

 heat of compression. The relative efficiency of this type of engine 

 may be shown in the accompanying tabular comparison : 



The efficiency of the Diesel type of engine.^ 



Efficiency. 



Diesel type of oil engine 4 



Oil-fired steam engine (triple expansion type) 1.6 



Coal-fired steam engine ' 1 



the gasoline produced with it In the refining of crude oil. In other words, attention 

 should not be given to the utilization of kerosene, but to the utilization of petroleum 

 distillates containing both the gasoline and kerosene fractions of crude oil." — B. W. Dean, 

 Fuel for automotive apparatus. Journal of the Society of Automotive Engineers, January^ 

 1918, p. 53. 



^ Kough approximation. 



• It has been estimated for the United States that the horsepower of gasoline internal- 

 combustion engines is over twice that of all engines driven by steam. While the latter 

 are more continuously used, the importance of the gasoline engine in power generating 

 Is strikingly great. 



* The relatively small quantity of kerosene used in power generation need not enter 

 the present consideration. A small portion of fuel oil is used for gas making and for 

 other purposes than steam raising, but for most of this work coal Is likewise effective. 



* O. P. Hood in Technical Paper 37, Bureau of Mines. 1913, p. 8. 



s Figures generalized from data presented in Technical Paper 37, Bureau of Mines, 

 1913, pp. 12-15. 



• For marine ^se the advantages of the Diesel engine over the coal-fired steam engine 

 Includes the factors of speedier bunkering, greater fuel storage, etc. 



