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BULLETIN 102, 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 * 1 of the petroleum consumed 
in the United States goes into the production of power. Of this 
amount, one-quarter 1 is employed in the form of gasoline as a motor 
fuel, 2 while three-quarters, 1 in the form of crude petroleum and fuel 
oil, is used as a convenient substitute for coal chiefly in firing steam 
boilers. 3 While the efficiency of the internal-combustion engine is 
much greater than the steam engine, now commonly referred to as 
u wasteful ” in comparison with more modern 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.” 4 
This high-compression oil engine, as it may be termed, gains its en- 
erg}^ 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 . 5 
Efficiency. 
Diesel type of oil engine 4 
Oil-fired steam engine (triple expansion type) 1.6 
Coal-fired steam engine 6 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.” — E. W. Dean, 
Fuel for automotive apparatus, Journal of the Society of Automotive Engineers, January, 
1918, p. 53. 
1 Rough approximation. 
2 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 conlinuously used, the importance of the gasoline engine in power generating 
is strikingly great. 
3 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. 
4 O. P. Hood in Technical Paper 37, Bureau of Mines, 1913, p. 8. 
5 Figures generalized from data presented in Technical Paper 37, Bureau of Mines, 
1913, pp. 12-15. 
6 For marine use the advantages of the Diesel engine over the coal-fired steam engine 
includes the factors of speedier bunkering, greater fuel storage, etc. 
