网友您好， 请在下方输入框内输入要搜索的题目：
题目内容
（请给出正确答案）
单选题
A piston is at bottom dead center when it is（）
A
opening the exhaust ports
B
closing the fuel ports
C
farthest from the cylinder head
D
nearest to the cylinder head
参考答案
参考解析
解析：
暂无解析
更多 “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” 相关考题
考题
When the________is large, the ship is stiff;and when it is small,she is tender.A.GMB.Free surfaceC.Longitudinal center of gravityD.transverse center of gravity
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.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
Which of the following provides the BEST security and accountability for a Data Center?（）A、Entry loggingB、Combination locksC、Card keysD、Dead bolts
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
考题
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In order to keep excess oil from the intake ports in two-stroke/cycle diesel engines, （）A
wide compression rings are usedB
oil rings are located above the pistonC
chromium plating is used on all piston ringsD
oil rings are located near the bottom of the piston skirt
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The two-stroke cycle begins with the piston coming up from the bottom of its stroke, with scavenge ports in the sides of the cylinder being （）.A
shutB
closingC
openedD
closed
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The exhaust valve opens before bottom dead center in a four stroke engine to（） Ⅰ.allow for blow down Ⅱ.Reduce pumping lossesA
Ⅰ onlyB
Ⅱ onlyC
both Ⅰ and ⅡD
neither Ⅰ nor Ⅱ
考题
单选题Starting air valves are held firmly on their seats by（）A
cam rollers on the camshaftB
spring forceC
air pressure on top of the valve differential pistonD
air pressure on the bottom of the valve differential piston
考题
单选题When the（）is large, the ship is stiff; and when it is small, she is tender.A
GMB
free surfaceC
longitudinal center of gravityD
transverse center of gravity
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To prevent loss of stability from free communication flooding you should（）.A
close the cross-connection valve between the off-center tanksB
completely flood high center tanksC
ballast double bottom wing tanksD
close any opening to the sea in an off-center tank
考题
单选题The abbreviation BDC means （）.A
Boston Diesel CompanyB
base circle diameterC
switch board caseD
bottom dead center
考题
单选题The sealing function of the piston ring is brought about by the gas pressure above and behind the piston ring, which forces it （） against the bottom of the ring groove, and （） against the cylinder wall.A
upwards；inwardsB
upwards；outwardsC
downwards；inwardsD
downwards；outwards
考题
单选题In order to keep the oil film on the cylinder liner during the running-in period, the piston rings are slightly rounded（）A
on both the external and internal top edgesB
on both the external top and bottom edgesC
on both the external and internal bottom edgesD
on all the four edges
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
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
热门标签
最新试卷
