單項(xiàng)選擇題The crankcases of many diesel engines are kept under a slight vacuum to （）

A.improve fuel economy
B.increase the air charge velocity
C.reduce the risk of explosion
D.all of the above


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1.單項(xiàng)選擇題Which of the following conditions could cause the feed pump for an auxiliary boiler to lose suction?（）

A.Increased suction head pressure
B.Decreased feedwater temperature
C.Pump recirculating line being open too much
D.Excessive feedwater temperature

2.單項(xiàng)選擇題In readying an auxiliary water-tube boiler for a routine hydrostatic test, which of the following procedures should be undertaken prior to filling the boiler with fresh water?（）

A.The safety valve escape piping should be disconnected from the valve body and a blank inserted
B.The boiler vent valves should be opened
C.All handhole/manhole covers should be tightened up as much as possible to preclude any leaks
D.All of the above

3.單項(xiàng)選擇題The fuel supply system to an automatic auxiliary boiler, will be automatically shutdown if the boiler （）

A.salinity is abnormally high
B.steam demand is too high
C.water level is abnormally low
D.feedwater flow is low

4.單項(xiàng)選擇題Lubricating oil is supplied to the crank-pin bearings in a marine diesel engine by （）.

A.internal crankshaft passages
B.immersion in oil
C.splash lubrication
D.injection lubrication

5.單項(xiàng)選擇題What function is provided by the crankcase ventilation system on some diesel engines?（）

A.Increases the sludge forming tendency of lube oil
B.Prevents the accumulation of combustible gases
C.Improves lube oil cooling
D.Improves cold weather starting