单项选择题

Fins are installed on the generating tube surfaces in waste heat boilers to （）.

A.prevent soot fires in the exhaust system
B.prevent exhaust gas erosion of the tubes
C.increase the velocity of exhaust gas flow
D.increase the rate of heat transfer

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单项选择题

On a medium-speed main propulsion diesel engine, the crank-pin or crank journal bearings receive lubricating oil from （）.

A.a spindle lubricator
B.an oil jet
C.internal splashing
D.drilled passages in the crankshaft

单项选择题

The rate of cylinder lubricating oil metered to each cylinder of a large low-speed main propulsion diesel engine is （）

A.the same, whether at sea, or during maneuvering
B.adjusted during each hour of operation while at constant RPM
C.higher at sea than while maneuvering
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单项选择题

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