單項選擇題

The crankcase of many diesel engines are kept under a slight vacuum by the （）.

A.scavenging action of the piston
B.piston type vacuum pump taking suction off a differential manometer
C.gland exhausting manometer
D.crankcase exhaust fan

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單項選擇題

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

單項選擇題

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