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单选题
A piston is said to be at top dead center when it is （）
A
opening the exhaust ports
B
placed on top of the engine along its centerline
C
farthest from the cylinder head
D
nearest to the cylinder head
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更多 “单选题A piston is said to be at top dead center when it is （）A opening the exhaust portsB placed on top of the engine along its centerlineC farthest from the cylinder headD nearest to the cylinder head” 相关考题
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If the diesel engine fuel injection timing is changed to delay the start of injection until the pistons are at top dead center, the engine will_________.A.backfire through the air intakesB.develop less power under loadC.have high firing pressuresD.lift its cylinder relief valves
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When fuel is injected late into a diesel engine cylinder_______.A.the exhaust will be clearB.fuel consumption will be lowC.all the fuel will be burned at top dead centerD.fuel consumption will be high
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Molded depth is measured from the ______.A.inside of the shellB.outside of the shellC.top of the center vertical keelD.top of the garboard stake
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共用题干
第二篇Night of the Living AntsWhen an ant dies,other ants move the dead insect out of the nest.This behavior is interesting to scien-tists,who wonder how ants know for sure一and so soon一that another ant is dead.Dong-Hwan Choe,a scientist at the University of California,found that Argentine ants have a chemical on the outside of their bodies that signals to other ants,"I'm dead一take me away."But there's a twist to Choe's discovery. These ants behave a little bit like zombies（僵尸）.Choe says that the living ants一not just the dead ones一have this death chemicals. In other words,while an ant crawls around,perhaps in a picnic or home,it's telling other ants that it's dead.What keeps ants from hauling away the living dead? Choe found that Argentine ants have two additional chemicals on their bodies,and these tell nearby ants something like,"Wait一I'm not dead yet."So Choe's research turned up two sets of chemical signals in ants:one says,"I'm dead,"the other set says,"I'm not dead yet."Other scientists have tried to figure out how ants know when another ant is dead.If an ant is knockedunconscious,other ants leave it alone until it wakes up.That means ants know that unmoving ants can still be alive.Choe suspects that when an Argentine ant dies,the chemical that says"Wait一I'm not dead yet"quickly goes away. Once that chemical is gone,only the one that says"I'm dead"is left."It's because the dead ant no longer smells like a living ant that it gets carried to the graveyard（墓地）,not because its body releases new,unique chemicals after death,"said Choe.When other ants detect the"dead"chemical without the"not dead yet" chemical,they haul away the body. This was Choe's hypothesis（假设）.To test his hypothesis,Choe and his team put different chemicals on Argentine ant pupae（蛹）.When the scientists used the"I'm dead"chemical,other ants quickly hauled the treated pupae away.When the sci-entists used the"Wait一I'm not dead yet"chemical,other ants left the treated pupae alone.Choe believes this behavior shows that the" not dead yet" chemical overrides（优先于）the" dead" chemical when picked up by adult ants.And that when an ant dies,the"not dead yet"chemical fades away.Other nearby ants then de-tect the remaining"dead"chemical and remove the body from the nest.According to Choe's hypothesis,_______________.A:an ant still smells like a living one when it diesB:the"I am dead"chemical leaves the ant's body when it diesC:the"I am not dead yet"chemical is left when an ant diesD:the"I am not dead yet"chemical quickly goes away when it dies
考题
共用题干
第二篇Night of the Living AntsWhen an ant dies,other ants move the dead insect out of the nest.This behavior is interesting to scien-tists,who wonder how ants know for sure一and so soon一that another ant is dead.Dong-Hwan Choe,a scientist at the University of California,found that Argentine ants have a chemical on the outside of their bodies that signals to other ants,"I'm dead一take me away."But there's a twist to Choe's discovery. These ants behave a little bit like zombies（僵尸）.Choe says that the living ants一not just the dead ones一have this death chemicals. In other words,while an ant crawls around,perhaps in a picnic or home,it's telling other ants that it's dead.What keeps ants from hauling away the living dead? Choe found that Argentine ants have two additional chemicals on their bodies,and these tell nearby ants something like,"Wait一I'm not dead yet."So Choe's research turned up two sets of chemical signals in ants:one says,"I'm dead,"the other set says,"I'm not dead yet."Other scientists have tried to figure out how ants know when another ant is dead.If an ant is knockedunconscious,other ants leave it alone until it wakes up.That means ants know that unmoving ants can still be alive.Choe suspects that when an Argentine ant dies,the chemical that says"Wait一I'm not dead yet"quickly goes away. Once that chemical is gone,only the one that says"I'm dead"is left."It's because the dead ant no longer smells like a living ant that it gets carried to the graveyard（墓地）,not because its body releases new,unique chemicals after death,"said Choe.When other ants detect the"dead"chemical without the"not dead yet" chemical,they haul away the body. This was Choe's hypothesis（假设）.To test his hypothesis,Choe and his team put different chemicals on Argentine ant pupae（蛹）.When the scientists used the"I'm dead"chemical,other ants quickly hauled the treated pupae away.When the sci-entists used the"Wait一I'm not dead yet"chemical,other ants left the treated pupae alone.Choe believes this behavior shows that the" not dead yet" chemical overrides（优先于）the" dead" chemical when picked up by adult ants.And that when an ant dies,the"not dead yet"chemical fades away.Other nearby ants then de-tect the remaining"dead"chemical and remove the body from the nest.Which of the following statements is NOT true of ants?A:Ants know very soon that?another ant is dead.B:When an ant is dead,others move its body out of the nest.C:If an ant is unconscious,it is moved out of the nest.D:Living ants have the"I'm dead"chemical on their bodies.
考题
我们想要将表格中的文字放在靠上居中的位置，应该怎么办？（）A、align="middle" align="top"B、align="center" align="top"C、valign="middle" align="top"D、valign="top" align="center"
考题
单选题At bottom dead center, the centerline of the connecting rod usually coincides with the（）A
angularity of the piston motionB
inertia moment from the pistonC
centerline of the cylinderD
centerline of the king pin
考题
单选题Cross scavenging requires the fitting of （） to prevent air or exhaust gas escape when the piston is at the top of the stroke.A
a exhaust valveB
a piston skirtC
a piston crownD
an air suction valve
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单选题Insufficient end clearance on newly fitted piston rings in a diesel enginewill cause the rings to（）A
jam in the most worn part of the cylinder when the rings expandB
break in the most worn part of the cylinder when the rings expandC
wear eccentrically on the side opposite the end gapD
overheat and jam at the top center on the combustion stroke
考题
单选题A connecting rod in a four-stroke/cycle diesel engine is subject to（）A
tension load twice each crankshaft revolutionB
compression load during power and compression strokesC
inertia load once every four crankshaft revolutionsD
bending loads at bottom and top dead center
考题
单选题A diesel engine will lose power if fuel injection occurs too early because the （）A
fuel will not be properly atomized in the cylinderB
ignition will be delayed due to low ignition temperatureC
maximum fuel expansion will occur on the compression strokeD
fuel will ignite before top dead center
考题
单选题A piston is at bottom dead center when it is（）A
opening the exhaust portsB
closing the fuel portsC
farthest from the cylinder headD
nearest to the cylinder head
考题
单选题Because the top of the connecting rod swings about the pin and changes direction each time the piston reaches mid-stroke, the relative speed between bearing and pin at mid-stroke is zero, （）to a maximum as the piston approaches top or bottom dead center and then （） back to zero again as the piston approaches mid-stroke and the connecting rod changes direction.A
accelerates；deceleratesB
accelerates；acceleratesC
decelerates；deceleratesD
decelerates；accelerates
考题
单选题When fuel is injected late into a diesel engine cylinder,（）.A
the exhaust will be clearB
fuel consumption will be lowC
all the fuel will be burned at top dead centerD
fuel consumption will be high
考题
单选题The clearance volume for a single stage compressor is defined as the space created between the （）.A
top of the piston and bottom side of head, with the piston at BDCB
piston and head, including the space around the piston to the top of the upper ring and under the valves, with the piston at TDCC
bottom of the piston and bottom side of the head at TDC, regardless of upper ring location and valve placementD
top of the piston and bottom side of the head at TDC as compared to that which exists between the top of the piston and bottom side of head at BDC
考题
单选题A disadvantage of a four-stroke/cycle diesel engine is （）A
higher working temperature of piston and cylinderB
the use of scavenge portsC
fewer power strokes per revolution of the crankshaftD
part of the fuel is burned as the piston is moving away from top dead center
考题
单选题In a diesel engine, when the fuel is injected into the cylinder,（）A
the piston is just coming upward from the bottom dead centerB
the piston has moved about one-fifth of the way upC
the piston has moved most of the way up and almost reached the TDCD
the piston has just past the TDC
考题
单选题When applying thermal compound to the top of a CPU, apply a:（）A
thick layer, making sure to cover the sides of the CPU.B
very thin layer, making sure to cover the CPU.C
little bit on the tip of a brush, making sure to cover the top and sides of the CPU.D
small amount in the center of the CPU.
考题
单选题If the diesel engine fuel injection timing is changed to delay the start of injection until the pistons are at top dead center, the engine will（）A
backfire through the air intakesB
develop less power under loadC
have high firing pressuresD
lift its cylinder relief valves
考题
单选题An individual injection pump is designed for variable beginning and constant ending of injectionFor diesel engines operating at constant speeds, the start of injection will（）A
advance as the load increasesB
retard as the load increaseC
remain unchanged regardlessD
always occur at top dead center
考题
单选题The scavenging air ports are located at （） that they are just exposed by the upper edge of the piston when the piston is in the bottom dead center position.A
so a heightB
such a heightC
so highD
such high
考题
单选题The pressure in an operating diesel engine cylinder continues to rise for a short period after the piston passes top dead center as a result of the （）A
expansion of the combustion gasesB
exhaust and intake valves just closingC
maximum compression is just being attainedD
fuel injection occurring at that point and combustion begins
考题
单选题In a refrigeration system, which of the following statements describes the actions occurring when a solenoid valves, used in conjunction with an unloader head is energized?（）A
The solenoid valves directs high pressure gas to the valve lifting device raising the suction valve off its seat and causing one specific cylinder to become unloadedB
The solenoid valves directs high pressure gas to the underside of the unloading piston, causing it to rise and allowing the recirculating ports to be openedC
When the solenoid valve becomes energized, the valve ports become closed, allowing discharge pressure to build up above the piston, shifting it and causing it to unloadD
The solenoid valve allows the refrigerant to pass from the suction chamber to the top of the unloader piston, causing the piston to lift and unload the cylinder
考题
单选题Fuel oil injected into the cylinder of a diesel engine just after the piston passes top dead center, will（）A
increase engine powerB
increase engine loadC
decrease engine powerD
improve fuel economy
考题
单选题If the engine is naturally aspirated, or is a small high-speed type with a centrifugal turbocharger, the period of valve overlap（）,ie when both valves are（）, will be and the exhaust valve will close some 10°top dead canter（）.A
open；short；afterB
closed；short；afterC
open；long；beforeD
closed；long；before
考题
单选题In a turbocharged four-stroke/cycle diesel engine, the exhaust valve remains open until after top dead center and the intake valve opens before top dead center to（）.A
produce a scavenging effect in the combustion spaceB
equalize cylinder and exhaust manifold pressuresC
alleviate the difference in valve size between the intake and exhaustD
flush out condensate that collects after each compression stroke
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