78 THE THERMODYNAMICS OF THE MARINE OIL ENGINE. 



of the engine could be changed, and these cards are the result. So far as the writer 

 knows, this is the first time that a timing arrangement has been used on the fuel 

 valve of the engine. The ignition of the fuel was obtained under conditions which 

 undoubtedly were only possible in an engine which had been run long enough to get 

 warmed up. It certainly seems a fair assumption that, if the fuel ignited as shown 

 in these cards, it would have ignited if the clearance had been so increased that these 

 low pressures were obtained at the end of compression. In these cards the fuel is 

 shown as igniting from 70 pounds up to full compression of about 475 pounds. Card 

 II, where the igniting point or injection point was 130 pounds by the volume of the 

 cylinder contents at 130 pounds pressure on the compression line as compared to 

 the same pressure on the expansion line, makes it apparent that much energy is lost 

 by radiation during the time of high pressure and high temperature. This loss at 

 the end of compression should be somewhat reduced in the low-pressure type owing 

 to the fact that, whereas the cylinder volume at the end of compression might be 

 doubled, the radiating surface would be but slightly increased. 



In order to get a better grasp of what was happening in the cylinder under 

 different conditions the writer made a model for showing up the events of the 

 stroke. The figures on Plate 22 for pressure and temperature were mounted on the 

 edges of discs. The model showed the section of an engine with a movable piston. 

 As the piston made two complete strokes these discs made one complete revolution. 

 A disc for any desired condition could be attached to the mechanism of the model, 

 and by moving the piston up and down the temperature and pressure for each posi- 

 tion of the piston are shown. This emphasizes, even more clearly than the dia- 

 grams, the sudden changes in the cylinder. 



Let us next consider the proposition that the ratio of air to fuel should be kept 

 constant. 



This has been done on the best gas engines as a means of governing. It has 

 not as yet been done on the Diesel engine because apparently the full amount of 

 air must be compressed per stroke in order that the igniting temperature may be 

 obtained. The writer in March, 19 13, brought this out in Power, where Figs. 

 I to 3 of Plate 25 were published. In Fig. i referred to is a Diesel full load and 

 Diesel two-thirds load card, and what was proposed at that time as a means for im- 

 proving the present form of governing; that is, if only two-thirds of the fuel was 

 used then only two-thirds of the regular amount of air should be compressed. A 

 pressure curve was plotted in each case having crank angles for abscissae. If the 

 friction loss is a function of the pressure per square inch of the piston then the 

 friction of the Diesel two-thirds load condition would be 50 per cent greater than 

 in the proposed form of governing. This can be stated in another way. The fric- 

 tion is not a percentage of the net load but is a percentage of the work done in the 

 cylinder regardless of whether the effect is plus or minus on the brake. 



Figure 3, Plate 25, shows the way the efficiency varies with engines having dif- 

 ferent clearances. Fig. 4, Plate 25, is a set of curves constructed from tests made 

 by Professor Denton in 1898 on a small Diesel engine. Improvements have been 



