Chapter 22. -DIESEL AND GASOLINE ENGINES 



UPPER 



CONNECTING 



ROD 



UPPER 

 CRANKSHAFT 



VERTICAL- 

 GEAR DRIVE 



UPPER 

 PISTON 



SCAVENGING 

 , AIR PORTS 



INJECTOR 



LOV^ER 

 PISTON 



LOWER 

 CONNEOTNG? 

 ROD 



OMBUSTION 

 CHAMBER 



EXHAUST 

 PORTS 



LOV^ER 



CRANKSHAFT 



75.8 

 Figure 22-8.— Cylinder and related parts- 

 opposed-piston engine. 



Movement of the opposed pistons is such that 

 the crowns are closest together near the center 

 of the cylinder. When at this position, the pistons 

 are not at the true piston dead centers. This is 

 because the lower crankshaft operates a few 

 degrees in advance of the upper shaft. The 

 number of degrees that a crank on the lower 

 shaft travels in advance of a corresponding 

 crank on the upper shaft is called lower crank 

 lead. This is illustrated in figure 22-9. 



Opposed-piston engines used by the Navy 

 operate on the 2-stroke cycle. In engines of the 

 opposed-piston type, as in 2-stroke cycle single- 

 acting engines, there is anoverlapof the various 

 events occurring during a cycle of operation. In- 

 jection and theburningof the fuel start during the 

 latter part of the compression event and extend 

 into the power phase. There is also an overlap of 

 the exhaust and scavenging periods. The events 

 in the cycle of operation of an opposed-piston, 

 2-stroke cycle diesel engine are shown in figure 

 22-10. 



Modern engines of the opposed-piston design 

 have a number of advantages over single-acting 

 engines of comparable rating. Some of these 

 advantages are: less weight per horsepower 

 developed; lack of cylinder heads and valve 

 mechanisms (and the cooling and lubricating 

 problems connected with them); and fewer 

 moving parts. 



Functions of Reciprocating 

 Engine Components 



The design of most internal combustion en- 

 gines of the reciprocating type follows much the 

 same general pattern. Though engines are not 

 all exactly alike, there are certain features com- 

 mon to all, and the principal components of most 

 engines are similarly arranged. Since the gener- 

 al structure of gasoline engines is basically the 

 same as that of diesel engines, the following 

 discussion of the engine components applies 

 generally to both types of engines. However, dif- 

 ferences do exist and these will be pointed out 

 whereever applicable. 



The principal components of an internal 

 combustion engine may be divided into two 

 principal groups— parts and systems. The main 

 parts of an internal combustion engine may be 

 further divided into structural parts and moving 

 parts. Structural parts, for the purpose of this 

 discussion, include those which, with respect 

 to engine operation, do not involve motion; 

 namely, the structural frame and its components 

 and related parts. The other group of engine 

 parts includes those which involve motion. Many 

 of the principal parts which are mounted within 

 the main structure of an engine are moving parts. 

 Moving parts are considered as those which con- 

 vert the power developed by combustion in the 

 cylinder to the mechanical energy that is avail- 

 able for useful work at the output shaft. 



The systems commonly associated with the 

 engine proper are those necessary to make 



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