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Figure  1-10.Four-stroke  cycle  diesel  engine.
Figure  1-12.-Spherical  chamber.

Equipment Operator Basic - Beginning construction equipment operators manual
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DIESEL  ENGINE  COMPRESSION  STROKE.— The piston is at bottom dead center at the beginning of the  compression  stroke,  and,  as  the  piston  moves upward, the air compresses. As the piston reaches top dead center, the compression stroke ends (fig. 1-10, view  B). DIESEL  ENGINE  POWER  STROKE.—  The piston begins the power stroke at top dead center. The air  is  compressed  to  as  much  as  500  psi  and  at  a compressed  temperature  of  approximately  1000°F.  At this point, fuel is injected into the combustion chamber and is ignited by the heat of the compression. This begins the power stroke. The expanding force of the burning  gases  pushes  the  piston  downward,  providing power to the crankshaft. The diesel fuel will continue to bum through the entire power stroke (a more complete burning of the fuel) (fig. 1-10, view C). The gasoline engine has a power stroke with rapid combustion in the beginning, but little to no combustion at the end. DIESEL ENGINE EXHAUST STROKE.—  As the piston reaches bottom dead center on the power stroke,  the  power  stroke  ends  and  the  exhaust  stroke begins (fig. 1-10, view D). The exhaust valve opens, and, as the piston rises towards top dead center, the burnt gases are pushed out through the exhaust port. As the piston reaches top dead center, the exhaust valve closes and the intake valve opens. The engine is now ready to begin  another  operating  cycle. Multifuel  Engine The  multifuel  engine  (fig.  1-11)  is  basically  a four-stroke cycle diesel engine with the capability of operating  on  a  wide  variety  of  fuel  oils  without adjustment or modification. The fuel injection system is equipped  with  a  device  called  a  fuel  density compensator  that  varies  the  amount  of  fuel  to  keep  the power  output  constant  regardless  of  the  type  fuel  being used. The multifuel engine uses a spherical combustion chamber (fig. 1-12) that aids in thorough fuel and air mixing, complete combustion, and minimizes knocks. NOTE:   Because  of  environmental  pollution controls  and  the  development  of  more  efficient  diesel engines, the multifuel engine is being phased out. Figure  1-11.—Multifuel  engine. 1-8







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