PRINCIPLES OF NAVAL ENGINEERING 



il==: 



TOTAL VOLUME 

 AT TOO. 



TOTAL VOLUME 

 AT B DC. 



A -START OF UPSTROKE 

 (COMPRESSION OR EXHAUST) 



B-START OF OOWNSTROKE 

 (POWER OR INTAKE) 



14.7 



-ONE-HALF CRANKSHAFT REVOLUTION - 

 — TOTAL VOLUME (BDC) 



C-CYCLE DIAGRAM 



Figure 22-6.— Pressure-volume diagram, Otto 4-stroke cycle. 



54.19B 



the line represent compression. The bottom 

 horizontal line provides a means of represent- 

 ing cylinder volume and piston movement. The 

 volume line has been divided into six parts 

 which correspond to the divisions of volume 

 shown in illustration A. Since piston movement 

 and volume are proportional, the distance be- 

 tween O and 6 indicated the volume when the 

 piston is at BDC, and the distance from O to 1 

 the volume with the piston at TDC. Thus, the 



distance from 1 to 6 corresponds to total piston 

 travel and units of the distance may be used to 

 identify changes in volume resulting from the 

 reciprocating motion of the piston. 



The curved lines of illustration C represent 

 the changes of both pressure and volume which 

 take place during the four piston strokes of 

 the cycle. To conform to the discussion on the 

 relationship of strokes and events (see fig. 

 22-1), the cycle of operation starts with intake. 



552 



