轮机英语（二三管轮）Lesson 2 Working Principle of Marine Diesel Engine.ppt

Unit1MainPropulsionPlantLesson2WorkingPrincipleofMarineDieselEngine2.1Four-strokedieselengine2.2Two-strokedieselengine2.3Comparisonbetweentwo-strokedieselengineandfour-strokedieselengine

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2.1Four-strokedieselengineInfour-strokecycleenginestherearefourstrokescompletingtworevolutionsofthecrankshaft.Thesearerespectively,thesuction(inductionorintake),compression,power(expansion)andexhauststrokes.ThewholeworkingcycleisdemonstratedinFig.2-1.Fig.2-1WorkingCycleoffour-strokeengine

2.1Four-strokedieselengineThesuctionstrokeisshowninFig.2-1(I).Thepistongoesdownfromtopdeadcenter(TDC)andtheintakevalve(a)opens,whereas,theexhaustvalve(b)isclosed.Asthevolumeofthecylinderincreasesandthepressureinthecylinderdecreases,achargeoffreshairisdrawnintothecylinderthroughtheintakevalvedependingonthepressuredifferencebetweenthecylinderandtheatmosphere(一定量的新鲜空气依靠气缸与大气之间的压差从进气阀吸入到气缸).Generally,theintakevalveopens(point1)beforethepistonreachesthetopdeadcenter,andcloses(point2)afterthebottomdeadcenter(BDC).Thecrankshaftangleφ12(angleofshadowinFig.2-1(I))indicatingtheintakedurationangleis220-250°.

2.1Four-strokedieselengineThenextstrokeisthecompressionstroke(II).Thepistonmovesupwardfromthebottomdeadcenter,andstartstocompressuntiltheairinletvalveisclosed.Thepressureattheendofthecompressionstroke(point3)rangesfrom30