单项选择题
A.Because the piston is exposed to very high temperature, it must be cooled
B.The lower the piston cooling temperature is, the better it is
C.Both water and lube oil can be used as coolant
D.One of the piston cooling methods is vibration cooling, with better effect
单项选择题 The essential part of the diesel engine, whose function is to convert the heat energy into the mechanical power, is the （）.
单项选择题 Among the main propulsion units on board the ship with the same capacity, the lightest one is（）.
单项选择题 The rotating range of the low speed diesel engine is usually lower than （）.