220 THE SUBMARINE OF TO-DAY AND TO-MORROW. 



the charging of the batteries to be accomplished in a much shorter time where the charging 

 was of supreme importance to enable the submarine to again operate electrically below the 

 surface. 



Thermo-dynamically it should be pointed out that it is not primarily the fuel but the 

 amount of oxygen in a cylinder charge of air which limits the power of the engine. This raises 

 the question of the possibility of increasing the oxygen contained in a given amount of air. 

 The pre-compression of the air and the reduction of its heat content before its introduction 

 into the working cylinder would make it possible to add a considerably greater amount of heat 

 without increasing the initial temperature above that found to be the limit in the present prac- 

 tice. The amount of this heat is that represented by the mechanical energy used to compress 

 the air, and is of very considerable amount. 



Another matter which should receive careful consideration from a thermo-dynamic point 

 of view is that of running the compression to a sufficiently high degree to start combustion. 

 This from a mechanical engineering point of view is an absurdity. It is so easy to obtain an 

 initial temperature by electricity, and its control is so positive, that the matter of initial com- 

 pression to combustion temperatures should be eliminated from the Diesel engine problem. 



The matter of injecting other material into the cylinder after the heat has been gener- 

 ated to carry out and increase the mean effective pressure is another point which should be 

 investigated, and it should be pointed out that past investigation has been altogether too much 

 controlled by the desire for very high thermal efficiency. Thermal efficiency is of very 

 great importance, but is relatively of small importance in a submarine, the power problem of 

 which we now have under discussion. 



I am very confident that there are possibilities in the Diesel engine far beyond the pres- 

 ent developments, and they will be discovered and developed by working along special lines 

 such as the application to the submarine, where the demands are quite different to an engine 

 used in industrial purposes working perhaps twenty-four hours a day, and therefore consum- 

 ing a very large amount of fuel, the cost of which becomes the most important item in the 

 problem. 



Beyond question, the most important consideration in the Diesel engine as applied to 

 the submarine is that of increasing its output per unit of weight, and one of the first things 

 to be sacrificed in attaining this end is its very high efficiency. From the fact that the 

 cost of fuel for operating the engine of a submarine is probably the very smallest item to be 

 considered and of relatively small importance, I would ask the mechanical and thermo- 

 dynamic engineers for the time being to disregard thermal efficiency and concentrate their 

 attention on the purely mechanical efficiency which we find so exceedingly low in the Diesel 

 engine. 



Mr. John F. Wentworth, Member: — The problem of the submarine is out of my 

 line. The heart of the submarine, the internal-combustion engine, is, however, my specialty. 

 I came as an interested listener to get information upon the subject of submarines. The 

 queries of Mr. Sperry relative to the possibility or desirability of reducing the present stresses 

 in the oil engine, and of Mr. Donnelly relative to the desirability of searching out some 

 method for increasing the mean effective pressure of the oil engine are particularly interest- 

 ing subjects to me, inasmuch as I have spent a good deal of time in the hopes of solving 

 these two problems. 



First I would like to take up the question of stresses in the engine which make the pres- 



