28 THE DESIGN OF AN OIL ENGINE. 
without loss from back pressure. This would result in an additional saving of a 
very considerable amount. On the proposed cycle this is accomplished. Let us 
assume that the admission valve is closed at two-thirds of the suction stroke. Then 
when two-thirds of the expansion stroke is completed a normal cycle is closed. On 
the low-power cycle the expansion is continued 50 per cent further before the 
charge is exhausted. In this way the efficiency of the low-power cycle is greatly in- 
creased. 
Besides this condition of economical low speed there comes the condition of 
extreme low speed which is only occasionally needed. Here economy is not a factor. 
The engine must run slow regardless of economy. The limit in low speed comes 
from the loss of ignition temperature due to radiation. This can be overcome to a 
degree by controlling the circulation of the cooling water. As the engine slows 
down the work done per stroke is reduced and consequently the heat which must be 
carried off is reduced. So far as is known the author is the first student of the in- 
ternal-combustion engine to suggest attaining a lower speed through a regulation 
of the temperature of the cooling water. This seems, however, to be important. 
There will never be a call for a prolonged operation at extreme low speed. In such 
cases as picking up a disabled ship at sea, or in similar emergencies, it is most im- 
portant to be able to regulate the amount of cooling water fed to the jackets in order 
that the excessive radiation losses may be avoided. The means for accomplishing 
this result seem to be practical and to follow the commonly accepted laws of ther- 
modynamics, which apply to the oil engine as well as to the steam plant. 
FUELS. 
This is a subject of utmost importance. The oil engine has come to stay, and as 
the number of engines increases the inevitable result will be a rise in the price of 
the available fuel. The oil-producing interests have so far met the oil engine 
rather more than half way. There are fuels on the market known as “Diesel en- 
gine oils.” These fuels are, if the author is not misinformed, distillates, that is, the 
refuse from the production of lighter oils is heated to a temperature above that at 
which the kerosene is evaporated and the resulting vapor is condensed. This gives 
a fuel which is fairly fluid, and which in a way is a by-product. Gasoline was origi- 
nally a by-product and, like gasoline a few years ago, this fuel is at present very 
reasonable in price. It is not safe or wise to depend upon this condition continuing. 
The oil engine is doomed to be extremely limited in its application if this fuel is de- 
pended upon. 
The fact that this fuel is a volatile product like gasoline, although vaporizing at 
a much higher temperature, is of no importance to the oil engine. All that is 
needed for the oil engine is a free flowing fuel. Even the presence of a considerable 
amount of non-volatile matter like the asphaltum residue seems to be of no disad- 
vantage in this type of engine. The one essential is that the fuel must be free flow- 
ing. In this one great point Dr. Diesel stood out pre-eminently ahead of his time. 
