Principles of naval engineering - Historic Naval Ships Association

PRINCIPLE OF NAVAL ENGINEERINGdeveloped within an engine. Since the temperatureof combustion alone is about twice that atwhich iron melts, it is apparent that, withoutsome means of dissipating heat, an engine wouldoperate for only a very limited time. Withoutproper temperature control, the lubricating-oilfilm between moving parts would be destroyed,proper clearance between parts could not bemaintained, and metals would tend to fail.Of the total heat supplied to the cylinder ofan engine by the burning fuel, only one-third,approximately, is transformed into useful work:an equal amount is lost to the exhaust gases.This leaves approximately 30 to 35 percent ofthe heat of combustion which must be removedin order to prevent damage to engine parts. Thegreater portion of the heat which may produceharmful results is transferred from the enginethrough the medium of water; lubricating oil, air,and fuel are also utilized to aid in the cooling ofan engine. All methods of heat transfer are utilizedin keeping engine parts and fluids (air,water, fuel, and lubricating oil) at safe operatingtemperatures.In a marine engine, the cooling system maybe of the open or closed type. In the open system,the engine is cooled directly by saltwater.In the closed system, fresh water (or an antifreezesolution) is circulated through the engine.The fresh water is then cooled by salt water.In marine installations, the closed system isthe type commonly used; however, some oldermarine installations use a system of the opentype. The cooling systems of diesel and gasolineengines are similar mechanically and in functionperformed.The cooling system of an engine may includesuch parts as pumps, coolers, engine passages,water manifolds, valves, expansion tank, piping,strainers, connections, and instruments. Theschematic diagrams in figure 22-27 and 22-28show the parts and the path of water flow in thefresh- and sea-water circuits of one arrangementof a closed cooling system.Even though there are many types and modelsof engines used by the Navy, the cooling systemsof most of these engines include the same basicparts. Design and location of parts, however,may differ considerably from one engine toanother.ENGINE LUBRICATING SYSTEMS. -It isessential to the operation of an engine that thecontacting surfaces of all moving parts of anFRESH WATER PUMPEXHAUST MANIFOLD EXTENSIONATMOSPHERIC VENTDUPLEX PRESSUREGAGE^EXPANSION TANKSUPERCHARGERCONNECTIONLUBE OIL HEATEXCHANGERADAPTERTHERMOMETERFRESH WATER HEATEXCHANGERRESTRICTIONNOZZLEBOXFRESH WATER PUMP-TEMPERATURE INDICATOR-^MhERMOSTATCOUPLINGFigure 22-27.— Fresh water circuit of a closed cooling system.75.208X576