單項選擇題A mixture of 45%cetane and 55% alpha-methyl-naphthalene is found to have the same ignition delay as a sample of diesel oil √The sample can be described as having a/an（）

A.cetane number of 55
B.cetane number of 45
C.octane number of 55
D.octane number of 45


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1.單項選擇題Worn main bearing will cause the compression ratio of an auxiliary diesel engine to（）

A.increase
B.decrease
C.remain the same
D.increase on compression decrease on expansion

2.單項選擇題With respect to diesel fuel, the ease with which a cold engine will start is dependent upon the（）

A.ignition quality of the fuel
B.high heating value of the fuel
C.amount of carbon residue after combustion
D.internal flow resistance in the injectors

3.單項選擇題A two-stroke/cycle diesel engine requires less starting air than a four-stroke/cycle diesel engine, of equal displacement, because the two-stroke/cycle diesel engine（）

A.has little or no internal friction
B.has a lower effective compression ratio
C.operates with scavenge air under a positive pressure
D.operates without energy absorbing intake and exhaust strokes

4.單項選擇題Which of the following operating conditions can occur when shims are removed from the joint between the foot of a marine type diesel engine connecting rod and the bearing box?（）

A.Decreased connecting rod bearing clearance
B.Increased connecting rod bearing clearance
C.Decreased compression ratio
D.Increased compression ratio

5.單項選擇題The longer the ignition delay period resulting from improper use of low cetane fuel, the （）

A.less fuel will enter the cylinder
B.higher the cylinder combustion temperature
C.more complete the fuel combustion
D.more rapid the rise in combustion pressure