THE THERMODYNAMICS OF THE MARINE OIL ENGINE. 17 



temperature volume diagrams shown on Plate 2 1 were drawn in. The results from 

 the Diesel engine are well known. It is of interest to us to know how these results 

 are obtained. The first thing to note is that the temperature rises almost vertically 

 during injection. This not alone proves the absurdity of the contention of the 

 Bureau of Mines and their quoted authority, but comparing the 1898 and the 19 13 

 Diesel cards also shows that the trend of the Diesel engine is to approach the con- 

 ditions of the normal gas engine. 



Owing to the fact that the scale of the spring used to indicate this type of 

 engine is so high, there is some difficulty in drawing in the temperature volume 

 line for compression. Since this is the most important part in our present consider- 

 ation, one way is shown by which this trouble can to a degree be overcome as indi- 

 cated in Fig. I and Table I of Plate 21. The pressures are scaled from actual cards 

 and the temperatures then calculated. Since the pressures are low, a small error in 

 reading will make a large error in the temperature figure. We know that the tem- 

 perature rise must be gradual. Consequently, if we plot these first temperatures 

 and draw a smooth curve through the points and then figure back from these tem- 

 peratures, we can get accurate pressure and temperature lines. Table I is calculated 

 from one of my own cards. 



On Plate 22 the temperature curves for several conditions have been figured 

 out and plotted. One fact stands out pre-eminent, namely, that the Diesel engine 

 cycle shows no essential difference in operation from the so-called explosion cycle. 



In this connection attention is called to work done by Mr. Dugald Clerk. In 

 an attempt to arrive at some figures on the temperatures at different points of the 

 stroke, Mr. Clerk concluded that in a gas engine the temperature of the charge at 

 the end of the suction stroke would be around 260° F. Mr. Clerk arrived at this 

 conclusion as a result of experimenting with a pyromotor on a special testing or ex- 

 perimental engine. This temperature was the result of mixing with the incoming 

 air some of the products of combustion left in the cylinder at the end of the ex- 

 haust stroke, and also of drawing the incoming air into the cylinder over the sur- 

 faces of the passages of the heated cylinder head. By assuming a like condition 

 in the Diesel engine and by referring to the temperature volume diagrams on either 

 Plate 21 or Plate 22 the following conclusion can be positively drawn: If the Diesel 

 engine can start with a compression pressure of 500 pounds, the charge igniting at 

 a temperature of around 920° F. (glass reading), then after the engine has been 

 running awhile the temperature at the end of compression must be around 1450° F. 

 (glass reading). If this be so the charge will ignite in any Diesel engine at any 

 time after the pressure has exceeded 120 pounds, provided that the engine has run 

 long enough to become normally warm. 



In addition to this proof, more interesting are the cards taken by the 

 writer on his experimental engine. These cards are shown on Plate 25. In this 

 engine it was not possible to vary the amount of air compressed per stroke as much 

 as was desirable. Also the timing of the fuel valve caused slight trouble. As a 

 result the fuel valve was arranged so that the timing of the injection during a run 



