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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 cooling
B
constant pressure from the turbochargers
C
cooler operation of the exhaust system
D
effective constant pressure for turbocharger operation
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High cylinder firing pressure, accompanied by low exhaust temperature, can result from ___.A.improper fuel rack positingB.lengthy exhaust valve durationC.extend operation at light loadD.excessively early injection timing
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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
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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
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单选题During working, thermostatic expansion valve should be （）.A
either all the way open or all the way closedB
normally fully openC
throttled depending on loadD
controlled by liquefied pressure
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Late fuel injection timing is indicated by （）A
lower than normal cylinder pressure and low exhaust temperatureB
lower than normal cylinder pressure and high exhaust temperatureC
higher than normal cylinder pressure and low exhaust temperatureD
higher than normal cylinder pressure and high exhaust temperature
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The loss of the diesel engine cylinder air charge through leaky valves, piston rings, worn or scored liners, would be indicated by which of the following sets of conditions?（）A
Low compression pressure and high exhaust temperatureB
Low firing pressure and high exhaust temperatureC
Low compression pressure and low exhaust temperatureD
Low firing pressure and low exhaust temperature
考题
单选题During the fuel injection period, fuel pressure must exceed cylinder gas pressure to （）.A
ensure penetration and distribution of the fuel in the combustion chamberB
ensure the needle valve is flushed clean during each injectionC
prevent combustion gas blowback into the open needle valveD
prevent reflected pressure waves when the needle valve closes
考题
单选题Leaky exhaust valve will result in which of the following?（） (1) high exhaust temperature; (2) low compression pressure; (3) low firing pressure.A
(1) and (2)B
(1) onlyC
(2) onlyD
(1),(2) and (3)
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Aburned exhaust valve may be detected by a higher than normal （）A
firing pressureB
exhaust temperature from a particular cylinderC
cooling water temperatureD
compression pressure
考题
单选题The arrangement and shape of the cams on a diesel engine camshaft directly control which of the listed groups of operating conditions?（）A
speed, torque, and horsepower productionB
firing order, valve timing, and valve liftC
fuel consumption, efficiency, and cylinder pressureD
scavenge pressure, compression ratio, and exhaust pressure
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A fuel injection valve opening at pressure lower than normal will result in（）.A
late fuel injectionB
early fuel injectionC
high exhaust temperature from that cylinderD
decreased effective stroke from that injector
考题
单选题Which of the following statements is correct regarding a turbocharged four-stroke/cycle diesel generator?（）A
At zero load the intake manifold pressure is greater than the exhaust manifold pressureB
At full load the intake manifold pressure and exhaust manifold pressure are equalC
At full load the intake manifold pressure is less than the exhaust manifold pressureD
At full load the intake manifold pressure is greater than the exhaust manifold pressure
考题
单选题High cylinder firing pressure, accompanied by low exhaust temperature, can result from （）A
improper fuel rack positingB
lengthy exhaust valve durationC
extend operation at light loadD
excessively early injection timing
考题
单选题An indication of a diesel engine air intake being partially clogged, is （）.A
low firing pressure and low exhaust temperaturesB
low firing pressure and normal exhaust temperaturesC
high firing pressure and low exhaust temperaturesD
high firing pressure and high exhaust temperatures
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Increasing the valve clearance between a valve stem and rocker arm, will result in the valve （）A
closing laterB
opening soonerC
staying open for a shorter period of timeD
staying open for a longer period of time
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The rate of pressure rise during the period following fuel ignition in a diesel will result in （）A
valve overlapB
volumetric efficiencyC
turbulence of the air changeD
fuel efficiency
考题
单选题Usually we take the cooling effect of the air flown through the cylinder during the overlap period as（）A
inevitableB
harmfulC
helpfulD
unacceptable
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