單項選擇題When comparing different fuels for different engines, the ignition quality of diesel fuel oils becomes a less critical consideration as （）

A.the amount of lube oil additives increase
B.piston speeds increase
C.injection pressure decrease
D.engine speeds decrease


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1.單項選擇題To reduce the weight of the reciprocating parts, pistons of high-speed engines are made considerably shorterThis results in （）

A.less piston slap and quieter running
B.increased crankshaft bearing wear
C.slightly greater piston wear
D.decreased side pressures

2.單項選擇題Which of the following statements concerning cylinder liner wear is true?（）

A.Liner wear is distributed equally between the upper and lower portions of the cylinder
B.Excessive liner wear causes wear between piston ring and groove
C.Excessive, but uniform liner wear will not cause wear between piston ring and groove
D.Liner wear is normally greatest in the middle of the cylinder

3.單項選擇題If clearance between a piston and the cylinder wall is excessive, piston slap will occurThe slap itself is caused by （）

A.alternation of side thrust
B.a breakdown of the lube oil film on the cylinder wall
C.worn piston boss piston pin bearings
D.fluctuating gas pressure in the combustion space

4.單項選擇題Poor quality fuel being used in a turbocharged medium-speed, diesel engine could result in （）

A.hard starting
B.excessive fuel consumption
C.loss of power
D.all of the above

5.單項選擇題Many diesel engine exhaust valves are being constructed with hollow stems filled with sodium in order to （）

A.provide added wear protection against today’s corrosive quality of fuel
B.increase overall valve strength due to the high gas pressures
C.assist in dissipating heat due to the extreme operating temperatures
D.reduce the overall weight of the valve thus helping eliminate valve spring surge and hammering