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单选题
Surface irregularities, such as erosion and pitting on injection pump plungers, will（）
A
increase ignition delay
B
affect fuel oil metering
C
affect engine performance at low speed
D
only disappear due to fuel oil abrasion
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材料：Spark erosion is caused by a voltage discharge between the main bearing and journal surface. The cause of the potential is the development of a galvanic element between the ship’s hull, sea water, and the propeller shaft/crankshaft.The oil film acts as a dielectric. The puncture voltage in the bearing depends on the thickness of the oil film. With increasing engine ratings, the specific load in the main bearing is increased. his will reduce the oil film thickness, and enable the discharge to take place at a lower voltage level.Since the hydrodynamic oil film thickness varies through a rotation cycle, the discharge will take place at roughly the same instant during each rotation cycle, i.e. when the film thickness is at its minimum. The roughening will accordingly be concentrated in certain areas on the journal surface. In the early stages, the roughened areas can resemble pitting erosion. but later, as the roughness increases, the small craters will scrape off and pick up white metal-hence the silvery white appearance.Therefore, to ensure protection against spark erosion, the potential level must be kept at maximum 80 mV, which is feasible today with a high efficiency earthing device. If an earthing device is installed, its effectiveness must be checked regularly. Spark erosion is only observed in main bearings and main bearing journals.问题：According to the paragraph one, a voltage between the main bearing and journal surface is produced by______.A.propeller rotationB.leakage from M/E electric control unitC.a galvanic elementD.friction between the main bearing and journal surface______engine ratings increase, the hydrodynamic oil film between the main bearing and journal surface is______.A.The lower/thinnerB.The higher/the thickerC.The lower/thickerD.The higher/thinnerWhen will the spark erosion take place on the journal surface during each rotation cycle?A.when the film thickness is at its minimumB.when the film thickness is at its maximumC.when the engine is on its compression strokeD.when the engine is on its exhaust strokeDuring the engine room watch keeping, which equipment must be noted to ensure protection against spark erosion?A.the antifouling plantB.the earthing deviceC.the main engine electric heating coilsD.the shaft generator请帮忙给出每个问题的正确答案和分析，谢谢！
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单选题To calculate the free surface correction，it is necessary to divide the free-surface moments by the（）.A
total weight of liquid loadsB
total displacementC
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单选题The correction to KG for longitudinal free surface effects for a vessel can be found by dividing the vessel’s displacement into the（）.A
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填空题The quick-growing exotic tree species are replanted in the deforested land because they can help prevent soil erosion.____
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单选题Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.A
cavitationB
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单选题As the propeller turns，voids are formed on the trailing and leading edges of the propeller blades causing a loss of propulsive efficiency，pitting of the blades，and vibration. These voids are known as（）.A
advanceB
cavitationC
edgingD
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单选题Many vessels are provided with flume tanks，which also have a dump tank located under the flume tanks. In the event the ship is damaged，you could dump the flume tanks into the dump tank which would（）.A
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单选题Pitting in the area close to the pitch line and on the same end of each gear tooth of a reduction gear unit would be caused by （）A
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dirt in the oilD
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考题
单选题When fuel enters the crankcase of a diesel engine, it （）A
dilutes the lube oil and reduces its viscosityB
forms sulfuric acid in the lube oilC
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