单项选择题
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
单项选择题 On a medium-speed main propulsion diesel engine, the crank-pin or crank journal bearings receive lubricating oil from （）.
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 （）
单项选择题 The crankcases of many diesel engines are kept under a slight vacuum to （）