32 THE DESIGN OF AN OIL ENGINE. 
The steam engine starts with an expansion stroke and has steam available for 
this stroke, so the starting feature is not a factor. In the internal-combustion en- 
gine the starting problem is a most difficult one. Not alone does the engine have to 
be accelerated but the acceleration has to impart sufficient energy to overcome in- 
ertia, do the work of the engine and at the same time produce the compression 
stroke. 
Up to the present compressed air has been universally used for this purpose. 
The oil engine is still in its swaddling clothes and many developments must be worked 
out before the engine can take its place in the world’s work as a tried and reliable 
element. For the generation of heat on shipboard the use of steam is practically 
essential. Then it is recognized that air starting is not absolutely reliable, for air 
must be generated. This may be done by a small oil engine. The auxiliary plant 
in turn must be started by air. This condition has brought about the use of a small 
steam-driven air compressor, or an electric air compressor, supplied with current from 
a turbo-generator set driven by steam. This is mentioned to show that even now it 
is realized that steam, either directly or indirectly, is the only reliable means for 
starting the oil engine. This being the case, why not abandon the use of air al- 
together and start directly from steam? This feature was taken up in the previous 
paper on the oil engine, but not in detail. The data on Plate 18 are presented to 
show the advantage in the use of steam. The effective energy in one cubic foot 
of water at a steam pressure of 200 pounds and of air at a pressure of 500 pounds 
are compared, as well as the cost of producing this energy. This cost is a matter 
of small importance. However, bulk and first cost of apparatus are great factors. 
Energy for starting can be stored in the form of water in a tank or boiler having 
large volume. In storing high-pressure air it is not practical to store the 
energy in such bulk. It is rather necessary to store the air in individual bottles of 
relatively small capacity and great weight. For this reason it becomes very evident 
that more energy can be stored in the boiler than in the bottles for the same weight 
and space occupied. 
As to cost, the air for starting is used for starting alone and so there is a di- 
rect expense chargeable to starting alone. On the other hand, the water container 
can be used as an auxiliary boiler for steam-operated auxiliaries. Hence this ele- 
ment cannot be properly charged to the cost of starting the engine. 
As to reliability, there is no argument. Steam has proven its reliability, and the 
only advantage of the oil engine is its economy. The disadvantage of the oil en- 
gine is its lack of reliability and a certain feeling of doubt which exists with all new 
elements. The matter of unreliability can be done away with by the use of steam 
as outlined. There is a limit to the slowness with which the oil engine can run. 
Suppose it necessary to run below this limit, can air be depended upon? Appar- 
ently not. When the engine is running slow no great amount of power is generated, 
and this condition will not be needed for any length of time.. The chief need of this 
extreme slow speed would seem to be in picking up a tow at sea or in making dock. 
In maneuvering to make dock there have been several instances where the air has 
