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單項選擇題In slow speed two-stroke engines,（）the fresh air entering begins when and stops as（）

A.the inlet port is opened by the up coming piston； the port is closed by the down going
B.the inlet valve is opened by the down going piston；the inlet valve is closed
C.the inlet port is opened by the down going piston；the port is closed by the up coming
D.the inlet valve is opened

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1.單項選擇題Usually we take the cooling effect of the air flown through the cylinder during the overlap period as（）

A.inevitable
B.harmful
C.helpful
D.unacceptable

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2.單項選擇題When the air charge contacts with the cylinders and pistons and mixes with the residual gases, it will（）

A.increase in temperature
B.lose its energy partly
C.expand and do work
D.begin to be compressed

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3.單項選擇題“This increase in charge air density is accomplished on most modern diesel engine types by use of exhaust gas turbo-charging, in which a turbine wheel driven by exhaust from the engine is rigidly coupled to a centrifugal type air compressor” According to this sentence, we can know that increases density（）, drives the compressor directly（）

A.a modern diesel engine；a turbine wheel
B.a modem diesel engine；exhaust gases
C.a compressor；an exhaust gas turbocharger
D.a compressor；a turbine wheel

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4.單項選擇題Gas exchange, which is a basic part of the cycle of an internal combustion engine, is（）

A.the supply of normal air and removal of compressed air
B.the supply of fuel oil and combustion of the atomized oil
C.the supply of fresh air and removal of exhaust gases
D.the supply of fresh air and removal of the extra heat

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5.單項選擇題“The use of a poor quality oil can lead to rapid deterioration of its properties with the resultant formation of deposits in the piston crown which in turn results in a considerable reduction in heat transfer with subsequent overheating and thermal cracking” According to this sentence, we can know that the principle reason of the overheating and thermal cracking is（）

A.the use of a poor quality oil
B.the deterioration of its properties
C.the formation of deposits
D.the reduction in heat transfer ability

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