Principles of naval engineering - Historic Naval Ships Association

Chapter 22. -DIESEL AND GASOLINE ENGINES2- STARTINJECTION3-ENDINJECTION4-EXPANSION 5-SCAVENGING 6-SUPERCHARGEFigure 22-10.— Events in operating cycle of an opposed-piston engine.75.10combustion possible, and those which minimizeand dissipate heat created by combustion andfriction. Since combustion requires air, fuel,and heat (ignition), systems providing each maybe found on some engines. However, since adiesel engine generates its own heat for combustionwithin the cylinders, no separate ignitionsystem is required for engines of this type. Theproblem of heat, created as a result of combustionand friction, is taken care of by two separatesystems— cooling and lubrication. The functionsof the parts and systems of engines which operateon the principles already described are discussedbriefly in the following paragraphs.MAIN STR UCTURAL PAR TS. -The main purposeof the structural parts of an engine is tomaintain the moving parts in their proper relativeposition. This is necessary if the gas pressureproduced by combustion is to fulfill itsfunction.The term frame is sometimes used to identifya single part of an engine; in other cases, itidentifies several stationary parts fastened togetherto support most of the moving engineparts and engine accessories. For the purposeof this discussion, the latter meaning will beused. As the load-carrying part of the engine,the frame of the modern engine may includesuch parts as the cylinder block, crankcase,bedplate or base, sump or oil pan, and endplates.The part of the engine frame which supportsthe engine's cylinder liners and heador heads is generally referred to as the cylinderblock. The blocks for most large enginesare of the welded-steel type construction. Blocksof small high-speed engines may be of the enbloc construction. In this type construction, theblock is cast in one piece. Two types of cylinderblocks coming to Navy service are shown infigures 22-11 and 22-12. The block shown infigure 22-11 is representative of blocks designedfor some large engines with in-line cylinder arrangement.The block illustrated infigure 22-12is representative of blocks constructed forsome engines with V-type cylinder arrangement.The engine frame part which serves as ahousing for the crankshaft is commonly calledthe crankcase. In some engines, the crankcaseis an integral part of the cylinder block (seefig. 22-11), requiring an oil pan, sump, or base557