In slow speed two-stroke engines,（）the...

单项选择题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.单项选择题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.单项选择题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.单项选择题“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.单项选择题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.单项选择题“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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6.单项选择题Large crosshead type engine generally has two lubrication systems, a function performed only by crankcase oil system is（）

A.lubricating
B.cooling
C.cleaning
D.neutralizing

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7.单项选择题Large crosshead type engine generally has two lubrication systems, a function performed only by cylinder oil system is（）

A.lubricating
B.cooling
C.sealing
D.cleaning

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8.单项选择题In some diesel engine designs,（）the injection of cylinder oil is timed to impinge when the piston and only impinge on（）

A.is coming upward；cylinder ring belt
B.is going downward；piston ring belt
C.is coming upward；piston ring belt
D.is going downward；cylinder ring belt

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9.单项选择题（）diesel engines generally have two systems of lubrication:（）a total loss system feeding and a circulating system lubricating the running gear and cooling the pistons.

A.Large crosshead type；crossheads
B.High speed；the cylinders
C.Large crosshead type；the cylinders
D.Four-stroke；pistons and cylinders

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10.单项选择题The following options are all the functions of lubricating oil except（）

A.removing heat and deposits
B.neutralizing acidic products
C.lubricating
D.improving combustion efficiency

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