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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 losses
A
Ⅰ only
B
Ⅱ only
C
both Ⅰ and Ⅱ
D
neither Ⅰ nor Ⅱ
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更多 “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” 相关考题
考题
A two stroke diesel engine exhaust temperature will be lower than a four stroke diesel engine of the same displacement because the _____. ① MEP is lower and the scavenging air is cooling the exhaust gases ② valve overlap in a four strokeA.①B.②C.① and ②D.Neither ① nor ② is correct
考题
During the valve overlap period, the exhaust pressure of a turbocharged four-stroke/cycle diesel engine must be less than the intake manifold pressure to ensure ______.A.effective cylinder scavenging and coolingB.constant pressure from the turbochargersC.cooler operation of the exhaust systemD.effective constant pressure for turbocharger operation
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The period of valve overlap is when （）.A
the inlet valve is openB
the exhaust valve is openC
both valves are closeD
both valves are open
考题
单选题Valve overlap is the period during which （）.A
the inlet valve is openB
the exhaust valve is openC
both valves are closedD
both valves are open
考题
单选题Which of the following problems represent one possible cause of high lube oil consumption in a four stroke diesel engine?（）A
Worn intake valve guidesB
Pitted pre-combustion chambersC
Loose valve tappetsD
High exhaust back pressure
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 two-stroke diesel engine exhaust temperature will be lower than a four-stroke diesel engine of the same displacement because the （） (1) MEP is lower and the scavenging air is cooling the exhaust gases (2) valve overlap in a four-strokeA
(1) only is correctB
(2) only is correctC
both (1) and (2) are correctD
Neither (1) or (2) are correct
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The size of the exhaust valve opening is （）A
most critical in a four-stroke cycle diesel engineB
most critical in a two-stroke/cycle diesel engineC
most critical in a four-stroke/cycle diesel engine if it is turbochargedD
of equal importance in a two-stroke/cycle diesel engine as in a four-stroke/cycle diesel engine
考题
单选题Excessively worn, or polished ends on a diesel engine valve spring, indicate（）A
burned exhaust valvesB
excessive spring compressionC
spring surgeD
worn valve seats
考题
单选题Icreasing the exhaust valve tappet clearance of a diesel engine will result in the exhaust valve opening （）A
later and closing earlierB
later and closing laterC
earlier and closing earlierD
earlier and closing later
考题
单选题During the valve overlap period, the exhaust pressure of a turbochargers, four-stroke/cycle diesel engine must be less than the intake manifold pressure to ensure （）A
effective cylinder scavenging and coolingB
constant pressure from the turbochargersC
cooler operation of the exhaust systemD
effective constant pressure for turbocharger operation
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Exhaust valve openings in a diesel engine cylinder head are made as large as practical to （）A
increase back pressure during the exhaust processB
facilitate periodic replacement of the valvesC
reduce the pumping loss associated with scavengingD
reduce tension on valve springs
考题
单选题Clearance volume scavenging in a turbocharged, four-stroke/cycle diesel engine is accomplished （）.A
during the valve overlap periodB
with only the exhaust valve openC
at a pressure below atmosphericD
without cooling the cylinders or pistons
考题
单选题Why is it important for fuel oil tanks not to be topped off at the inner bottom level when loading on a cold day?（）A
Increased viscosity of the product needs higher loading pressure, which increases the chances of a spillB
Air pockets may cause the fuel to bubble out of the ullage holeC
The temperature rise of the fuel will cause an overflowD
Fueling valve may become stuck closed and cause the fuel oil to spill before the valve can be opened
考题
单选题In an engine with air inlet valve and exhaust valve on its cylinder heads the fresh air will enter into the cylinder （） and the gases exhaust （）, there being an adequate overlap between the inlet opening and the exhaust closing.A
downwards；upwardsB
upwards；downwardsC
downwards；downwardsD
upwards；upwards
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Which of the listed design features is found in an exhaust valve and NOT in an intake valve?（）A
Hard alloy steel constructionB
Beveled edges on the valve headC
Low alloy steel constructionD
Poppet type design
考题
单选题A turbocharged, four-stroke/cycle diesel engine has a larger valve overlap than a naturally aspirated four-stroke/cycle diesel engine, in order to in crease the （）.A
temperature of the exhaust gasesB
energy supplied to the turbochargerC
air pressure to the intake manifoldD
purge of exhausted gases from the cylinders
考题
单选题Scavenging in a turbocharged, four-stroke/cycle diesel engine is accomplished（）A
during the valve overlap periodB
with only the exhaust valve openC
at a pressure below atmosphericD
without cooling the cylinders or pistons
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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